The main element of active heat supply systems is a solar collector (SC) In modern low-temperature heat supply systems (up to 100 ° C), which are used to convert solar energy into low-grade heat for hot water supply, heating and other thermal processes, a so-called flat collector is used, which is a solar collector. an absorber through which the coolant circulates; the structure is thermally insulated from the back and glazed from the front.

In high-temperature heating systems (above 100 ° C), high-temperature solar collectors are used. Currently, the Luza concentrating solar collector is considered the most effective of them, which is a parabolic trough with a black tube in the center, on which solar radiation is concentrated. Such collectors are very effective in cases where it is necessary to create temperature conditions above 100 ° C for industry or steam generation in the power industry. They are used in some solar thermal plants in California; for northern Europe, they are not effective enough, since they cannot use scattered solar radiation.

World experience... In Australia, wearing non-fluids to temperatures below 100 ° C consumes about 20% of the total energy consumed. It has been established that to provide warm water to 80% of rural residential buildings for 1 person, 2 ... 3 m2 of solar collector surface and a water tank with a capacity of 100 ... 150 liters are required. Installations with an area of ​​25 m2 and a water boiler for 1000 ... 1500 liters, providing warm water to 12 people, are in great demand.

In Great Britain, residents of rural areas meet 40 ... 50% of their thermal energy needs through the use of solar radiation.

In Germany, at a research station near Dusseldorf, an active solar water heating installation (collector area of ​​65 m2) has been tested, which allows to receive on average 60% of the required heat per year, and 80 ... 90% in summer. In Germany, a family of 4 people can fully provide themselves with heat in the presence of an energy roof with an area of ​​6 ... 9 m2.

The solar thermal energy is most widely used for heating greenhouses and creating an artificial climate in them; several ways to use solar energy in this direction have been tested in Switzerland.

In Germany (Hannover), the Institute of Technology, Horticulture and Agriculture is investigating the possibility of using solar collectors located next to the greenhouse or built into its structure, as well as the greenhouses themselves as a solar collector using a colored liquid that is passed through the double greenhouse cover and heated solar radiation Research has shown that, in Germany's climatic conditions, heating using only solar energy throughout the year does not fully meet the heat demand. Modern solar collectors in Germany can meet the needs of agriculture in warm water in summer by 90%, in winter by 29 ... 30% and in the transition period - by 55 ... 60%.

Active solar heating systems are most common in Israel, Spain, Taiwan, Mexico and Canada. In Australia alone, more than 400,000 homes have solar water heaters. In Israel, more than 70% of all single-family houses (about 900,000) are equipped with solar water heaters with solar collectors with a total area of ​​2.5 million m2, which provides an opportunity for annual fuel savings of about 0.5 million toe.

Constructive improvement of flat ICs occurs in two directions:

• search for new non-metallic structural materials;
• improvement of the optical-thermal characteristics of the most critical unit of the absorber-translucent element.

MINISTRY ENERGY AND ELECTRIFICATION USSR

MAIN SCIENTIFIC AND TECHNICAL DEPARTMENT
ENERGY AND ELECTRIFICATION

INSTRUCTIONS
CALCULATION AND DESIGN
SOLAR HEAT SUPPLY SYSTEMS

RD 34.20.115-89

SOYUZTEKHENERGO BEST EXPERIENCE SERVICE

Moscow 1990

DEVELOPED State Order of the Red Banner of Labor Research Power Engineering Institute. G.M. Krzhizhanovsky

CONTRACTORS M.N. EGAY, O. M. A. S. Korshunov LEONOVICH, V.V. NUSHTAIKIN, V.K. RYBALKO, B.V. TARNIZHEVSKY, V.G. BULYCHEV

APPROVED BY Main Scientific and Technical Directorate of Energy and Electrification 07.12.89

Chief V.I. GORI

The validity period is set

from 01.01.90

until 01/01/92

These Guidelines establish the procedure for performing the calculation and contain recommendations for the design of solar heat supply systems for residential, public and industrial buildings and structures.

The guidelines are intended for designers and engineers involved in the development of solar heat supply and hot water supply systems.

... GENERAL PROVISIONS

where f - the share of the total average annual heat load provided by solar energy;

where F - surface area of ​​the SC, m 2.

where H is the average annual total solar radiation on a horizontal surface, kWh / m 2 ; located from the application;

a, b - parameters determined from the equation () and ()

where r - characteristic of the thermal insulation properties of the building envelope at a fixed value of the DHW load, is the ratio of the daily heating load at an outside air temperature of 0 ° C to the daily DHW load. The more r , the greater is the share of the heating load in comparison with the share of the DHW load and the less perfect the building structure is in terms of heat losses; r = 0 is assumed when calculating only the DHW system. The characteristic is determined by the formula

where λ is the specific heat loss of the building, W / (m 3 ° С);

m - the number of hours in a day;

k - rate of ventilation air exchange, 1 / day;

ρ in - air density at 0 ° С, kg / m 3;

f - the replacement rate, roughly taken from 0.2 to 0.4.

The values ​​λ, k, V, t in, s are laid down in the design of the FTS.

Coefficient α values ​​for solar collectors II and III types

	Coefficient values
	α 1	α 2	α 3	α 4	α 5	α 6	α 7	α 8	α 9
	607,0	80,0		1340,0	437,5	22,5	1900,0	1125,0	25,0
	298,0	148,5	61,5	150,0	1112,0	337,5	700,0	1725,0	775,0

Β values ​​for solar collectors II and III types

	Coefficient values
	β 1	β 2	β 3	β 4	β 5	β 6	β 7	β 8	β 9
	1,177	0,496	0,140			0,995	3,350	5,05	1,400
	1,062	0,434	0,158	2,465	2,958	1,088	3,550	4,475	1,775

Values ​​of coefficients a and bare from table. ...

The values ​​of the coefficients a and b depending on the type of solar collector

	Coefficient values
		0,75
		0,80

where q i - specific annual heating capacity of SGWS at values f other than 0.5;

Δq - change in the annual specific heat output of DHWS,%.

Change in the value of the specific annual heating capacityΔq from the annual input of solar radiation on a horizontal surface H and coefficient f

... SOLAR DESIGN RECOMMENDATIONS where З с - specific reduced costs per unit of generated heat energy SST, rubles / GJ; Зb - specific reduced costs per unit of generated heat energy by the base unit, rubles / GJ. where C c - reduced costs for FTS and backup, rubles / year; where k s - capital expenditures for FTS, rubles; к в - capital costs of the backup, rubles; E n - standard coefficient of comparative efficiency of capital investments (0.1); E s - the share of operating costs from the capital costs of the FTS; E in - the share of operating costs from the capital costs of the backup; C is the cost of a unit of thermal energy generated by the backup, RUB / GJ; N d - the amount of thermal energy generated by the backup during the year, GJ; k e - the effect of reducing environmental pollution, rubles; k p is the social effect of saving the salaries of the personnel serving the backup, rubles. Specific reduced costs are determined by the formula where C b - reduced costs for the basic installation, rubles / year;	Definition of the term
	solar collector	A device for capturing solar radiation and converting it into thermal and other types of energy
Hourly (daily, monthly, etc.) heating capacity	The amount of heat energy removed from the collector per hour (day, month, etc.) of work
Flat solar collector	Non-focusing solar collector with a flat configuration absorbing element (tube-in-sheet type, only made of tubes, etc.) and flat transparent insulation
Heat-absorbing surface area	The surface area of ​​the absorbing element illuminated by the sun under normal incidence conditions
Heat loss coefficient through transparent insulation (bottom, side walls of the collector)	Heat flux into the environment through transparent insulation (bottom, side walls of the collector), per unit area of ​​the heat-absorbing surface, with a difference in the average temperatures of the absorbing element and the outside air of 1 ° C
Specific coolant consumption in a flat solar collector	Coolant flow rate in the collector per unit area of ​​the heat-absorbing surface
Efficiency ratio	A value characterizing the efficiency of heat transfer from the surface of the absorbing element to the coolant and equal to the ratio of the actual heating capacity to the heating capacity, provided that all thermal resistances of heat transfer from the surface of the absorbing element to the coolant are equal to zero
Surface blackness	The ratio of the surface radiation intensity to the black body radiation intensity at the same temperature
Glazing transmission capacity	The fraction of solar (infrared, visible) radiation transmitted by transparent insulation incident on the surface of transparent insulation
Understudy	Traditional source of thermal energy, providing partial or full coverage of the heat load and working in conjunction with a solar heating system
Solar heating system	Solar system to cover heating and hot water loads

Appendix 2

Thermal characteristics of solar collectors

	Collector type
Total heat loss factor U L, W / (m 2 ° С)
The absorption capacity of the heat-receiving surface α	0,95	0,90	0,95
The emissivity of the absorbing surface in the collector operating temperature range ε	0,95	0,10	0,95
Glazing throughput τ p	0,87	0,87	0,72
Efficiency ratio F R	0,91	0,93	0,95
Maximum coolant temperature, ° С
Notes I - one-glass non-selective collector; II - one-glass selective collector; III - two-glass non-selective collector.

Appendix 3

Technical characteristics of solar collectors

	Manufacturer
	Bratsk plant of heating equipment	Spetshelioteplomontazh GSSR	KievZNIIEP	Bukhara plant of solar equipment
Length, mm	1530	1000 - 3000	1624	1100
Width, mm			1008
Height, mm		70 - 100
Weight, kg	50,5	30 - 50
Heat-absorbing surface, m		0,6 - 1,5		0,62
Working pressure, MPa		0,2 - 0,6

Appendix 4

Technical characteristics of TT type flow-through heat exchangers

	Outer / inner diameter, mm		Flow area		Heating surface of one section, m 2	Section length, mm	Weight of one section, kg
			inner pipe, cm 2	annular channel, cm 2
	inner pipe	outer pipe
TT 1-25 / 38-10 / 10	25/20	38/32	3,14	1,13		1500
TT 2-25 / 38-10 / 10	25/20	38/32	6,28	6,26		1500

Appendix 5

Annual arrival of total solar radiation on a horizontal surface (N), kWh / m2

Azerbaijan SSR
Baku	1378
Kirovobad	1426
Mingachevir	1426
Armenian SSR
Yerevan	1701
Leninakan	1681
Sevan	1732
Nakhichevan	1783
Georgian SSR
Telavi	1498
Tbilisi	1396
Tskhakaya	1365
Kazakh SSR
Alma-Ata	1447
Guriev	1569
Fort Shevchenko	1437
Dzhezkazgan	1508
Ak-Kum	1773
Aral Sea	1630
Birsa-Kelmes	1569
Kostanay	1212
Semipalatinsk	1437
Dzhanybek	1304
Kolmykovo	1406
Kirghiz SSR
Frunze	1538
Tien Shan	1915
RSFSR
Altai region
Annunciation	1284
Astrakhan region
Astrakhan	1365
Volgograd region
Volgograd	1314
Voronezh region
Voronezh	1039
Stone steppe	1111
Krasnodar region
Sochi	1365
Kuibyshev region
Kuibyshev	1172
Kursk region
Kursk	1029
Moldavian SSR
Kishinev	1304
Orenburg region
Buzuluk	1162
Rostov region
Tsimlyansk	1284
Giant	1314
Saratov region
Ershov	1263
Saratov	1233
Stavropol region
Essentuki	1294
Uzbek SSR
Samarkand	1661
Tamdybulak	1752
Takhnatash	1681
Tashkent	1559
Termez	1844
Fergana	1671
Churuk	1610
Tajik SSR
Dushanbe	1752
Turkmen SSR
Ak-Molla	1834
Ashgabat	1722
Hasan-Kuli	1783
Kara-Bogaz-Gol	1671
Chardzhou	1885
Ukrainian SSR
Kherson region
Kherson	1335
Askania Nova	1335
Sumy region
Konotop	1080
Poltava region
Poltava	1100
Volyn region
Kovel	1070
Donetsk region
Donetsk	1233
Transcarpathian region
Beregovo	1202
Kiev region
Kiev	1141
Kirovograd region
Znamenka	1161
Crimean region
Evpatoria	1386
Karadag	1426
Odessa region
	30,8	39,2	49,8	61,7	70,8	75,3	73,6	66,2	55,1	43,6	33,6	28,7
	28,8	37,2	47,8	59,7	68,8	73,3	71,6	64,2	53,1	41,6	31,6	26,7
	26,8	35,2	45,8	57,7	66,8	71,3	69,6	62,2	51,1	39,6	29,6	24,7
	24,8	33,2	43,8	55,7	64,8	69,3	67,5	60,2	49,1	37,6	27,6	22,7
	22,8	31,2	41,8	53,7	62,8	67,3	65,6	58,2	47,1	35,6	25,6	20,7
	20,8	29,2	39,8	51,7	60,8	65,3	63,6	56,2	45,1	33,6	23,6	18,7
	18,8	27,2	37,8	49,7	58,8	63,3	61,6	54,2	43,1	31,6	21,6	16,7
	16,8	25,2	35,8	47,7	56,8	61,3
Boiling point, ° С	106,0	110,0	107,5	105,0	113,0
Viscosity, 10 -3 Pa · s:
at a temperature of 5 ° C		5,15		6,38
at a temperature of 20 ° C					7,65
at a temperature of -40 ° С	7,75	35,3		28,45
Density, kg / m 3				1077	1483 - 1490
Heat capacity kJ / (m 3 ° С):
at a temperature of 5 ° C	3900	3524
at a temperature of 20 ° C				3340	3486
Corrosion ability	Strong	Average	Weak	Weak	Strong
Toxicity	No	Average	No	Weak	No

Notes e. Heat transfer fluids based on potassium carbonate have the following compositions (mass fraction):

Recipe 1 Recipe 2

Potassium carbonate, 1.5-water 51.6 42.9

Sodium phosphate, 12-aqueous 4.3 3.57

Sodium silicate, 9-aqueous 2.6 2.16

Sodium tetraborate, 10-aqueous 2.0 1.66

Fluorescoin 0.01 0.01

Water Up to 100 Up to 100

27.09.2019

Classification and basic elements of solar systems

Solar heating systems are systems that use solar radiation as a source of thermal energy. Their characteristic difference from other low-temperature heating systems is the use of a special element - a solar receiver, designed to capture solar radiation and convert it into thermal energy.

According to the method of using solar radiation, solar low-temperature heating systems are divided into passive and active.

Passive solar heating systems are called, in which the building itself or its individual enclosures (collector building, collector wall, collector roof, Figure 1) serve as an element that perceives solar radiation and converts it into heat.

In passive solar systems, the use of solar energy is carried out exclusively through the architectural design of buildings.

In a passive system of solar low-temperature heating, a collector building, solar radiation, penetrating through the light openings into the room, falls into a heat trap, as it were. Short-wave solar radiation freely passes through the window glass and gets on the internal fences of the room, is converted into heat. All solar radiation entering the room is converted into heat and is able to partially or completely compensate for its heat losses.

To increase the efficiency of the collector-building system, large area light openings are placed on the southern facade, supplying them with blinds, which, when closed, should prevent losses with counter-radiation at night, and during a hot period, in combination with other sun protection devices, overheating of the room. The inner surfaces are painted in dark colors.

The task of the calculation with this heating method is to determine the required area of ​​the light openings for the passage of the solar radiation flux into the room, which is necessary, taking into account the accumulation to compensate for the heat losses. As a rule, the capacity of the passive building-collector system in the cold period is insufficient, and an additional heat source is installed in the building, turning the system into a combined one. In this case, the calculation determines the economically feasible areas of the light openings and the power of the additional heat source.

The passive solar system of low-temperature air heating "wall-collector" includes a massive outer wall, in front of which a radiant screen with shutters is installed at a short distance. At the floor and under the ceiling, slot-like holes with valves are arranged in the wall. The sun's rays, having passed through the translucent screen, are absorbed by the surface of the massive wall and converted into heat, which is transferred by convection to the air in the space between the screen and the wall. The air heats up and rises up, getting through the slot under the ceiling into the serviced room, and its place is taken by the cooled air from the room, penetrating into the space between the wall and the screen through the slot at the floor of the room. The supply of heated air to the room is controlled by opening the valve. If the valve is closed, heat accumulates in the wall mass. This heat can be removed by convective air flow, opening the valve at night or in cloudy weather.

When calculating such a passive low-temperature solar air heating system, the required wall surface area is determined. This system is also duplicated with an additional source of heat.

Active solar low-temperature heating systems are called in which the solar collector is an independent separate device that does not belong to the building. Active solar systems can be subdivided:

• by purpose (hot water supply systems, heating systems, combined systems for heat and cold supply purposes);
• by the type of coolant used (liquid - water, antifreeze and air);
• by the duration of work (year-round, seasonal);
• according to the technical solution of the schemes (one-, two-, multi-circuit).

For active solar heating systems, two types of solar collectors are used: concentrating and flat.

Air is a widespread non-freezing coolant in the entire range of operating parameters. When using it as a heat carrier, it is possible to combine heating systems with a ventilation system. However, air is a low-heat heat carrier, which leads to an increase in metal consumption for the device of air heating systems in comparison with water systems. Water is a heat-retaining and widely available heat carrier. However, at temperatures below 0 ° C, it is necessary to add anti-freeze liquids to it. In addition, it must be borne in mind that water saturated with oxygen causes corrosion of pipelines and apparatus. But the consumption of metal in water solar systems is much lower, which greatly contributes to their wider application.

Seasonal solar hot water systems are usually single-circuit and operate in the summer and transitional months, during periods with a positive outside temperature. They can have an additional source of heat or do without it, depending on the purpose of the serviced facility and operating conditions.

The SVU solar water heating plant (Figure 2) consists of a solar collector and a heat exchanger-accumulator. A coolant (antifreeze) circulates through the solar collector. The heat carrier is heated in the solar collector by the energy of the Sun and then gives off thermal energy to the water through a heat exchanger built into the storage tank. Hot water is stored in the storage tank until it is used, so it must have good thermal insulation. In the primary circuit, where the solar collector is located, natural or forced circulation of the coolant can be used. An electric or any other automatic backup heater can be installed in the storage tank. If the temperature in the storage tank drops below the set one (prolonged cloudy weather or few hours of sunshine in winter), the backup heater automatically turns on and heats up the water to the set temperature.

Solar heating systems for buildings are usually double-circuit or, most often, multi-circuit, and different heat carriers can be used for different circuits (for example, in the solar circuit - aqueous solutions of non-freezing liquids, in the intermediate circuits - water, and in the consumer circuit - air). Combined year-round solar systems for heat and cold supply of buildings are multi-circuit and include an additional heat source in the form of a traditional fossil-fueled heat generator or heat transformer. A schematic diagram of a solar heat supply system is shown in Figure 3. It includes three circulation circuits:

• the first circuit, consisting of solar collectors 1, a circulation pump 8 and a liquid heat exchanger 3;
• a second circuit consisting of a storage tank 2, a circulation pump 8 and a heat exchanger 3;
• the third circuit, consisting of a storage tank 2, a circulation pump 8, a water-air heat exchanger (air heater) 5.

The solar heating system functions as follows. The heat carrier (antifreeze) of the heat-receiving circuit, being heated in the solar collectors 1, enters the heat exchanger 3, where the heat of the antifreeze is transferred to the water circulating in the annular space of the heat exchanger 3 under the action of the pump 8 of the secondary circuit. The heated water enters the storage tank 2. From the storage tank, water is taken by the hot water pump 8, is brought, if necessary, to the required temperature in the backup 7 and enters the building's hot water supply system. The accumulator tank is replenished from the water supply. For heating, water from the storage tank 2 is supplied by the pump of the third circuit 8 to the heater 5, through which air is passed with the help of the fan 9 and, when heated, enters the building 4. In the absence of solar radiation or lack of heat energy generated by solar collectors, into operation turn on the backup 6. The choice and arrangement of solar heat supply system elements in each specific case are determined by climatic factors, the purpose of the facility, heat consumption mode, economic indicators.

Figure 4 shows a diagram of a solar heating system for an energy efficient eco-friendly home.

The system uses as a heat carrier: water at positive temperatures and antifreeze during the heating season (solar circuit), water (second underfloor heating circuit) and air (third solar air heating circuit).

An electric boiler was used as a backup source, and a 5 m 3 battery with a pebble attachment was used to accumulate heat for one day. One cubic meter of pebbles accumulates on average 5 MJ of heat per day.

Low-temperature heat storage systems cover the temperature range from 30 to 100 ◦C and are used in air (30 ◦ C) and hot water (30–90 ◦ C) heating and hot water systems (45–60 ◦ C).

The heat storage system, as a rule, contains a reservoir, heat storage material, with the help of which heat energy is accumulated and stored, heat exchange devices for the supply and removal of heat during charging and discharging of the battery, and thermal insulation.

Batteries can be classified according to the nature of the physicochemical processes occurring in heat storage materials:

1. capacitive batteries, in which the heat capacity of the heated material is used (pebbles, water, aqueous solutions of salts, etc.);
2. phase transition accumulators of a substance, in which the heat of fusion (solidification) of a substance is used;
3. energy accumulators based on the release and absorption of heat during reversible chemical and photochemical reactions.

The most widely used heat accumulators are of the capacitive type.

The amount of heat Q (kJ) that can be accumulated in a capacitive-type heat accumulator is determined by the formula

The most effective heat storage material in liquid solar heat supply systems is water. For seasonal accumulation of heat, it is promising to use underground reservoirs, rock soil and other natural formations.

Concentrating solar collectors are spherical or parabolic mirrors (Figure 5.), made of polished metal, in the focus of which a heat-receiving element (solar boiler) is placed, through which the coolant circulates. Water or non-freezing liquids are used as a heat carrier. When using water as a heat carrier at night and during a cold period, the system must be emptied to prevent it from freezing.

To ensure high efficiency of the process of capturing and converting solar radiation, the concentrating solar receiver must be constantly pointed strictly at the Sun. For this purpose, the solar receiver is equipped with a tracking system that includes a sun direction sensor, an electronic signal conversion unit, an electric motor with a gearbox for rotating the solar receiver structure in two planes.

The advantage of systems with concentrating solar collectors is the ability to generate heat with a relatively high temperature (up to 100 ◦ C) and even steam. The disadvantages include the high cost of the structure; the need for constant cleaning of reflective surfaces from dust; work only during daylight hours, and therefore the need for large batteries; large energy consumption for the drive of the solar tracking system, commensurate with the generated energy. These disadvantages hinder the widespread use of active low-temperature solar heating systems with concentrating solar collectors. Recently, flat solar collectors are most often used for solar low-temperature heating systems.

Flat solar collectors

A flat plate solar collector is a heat exchanger designed to heat a liquid or gas using solar energy. The area of ​​application of flat solar collectors is heating systems for residential and industrial buildings, air conditioning systems, hot water supply systems, as well as power plants with a low-boiling working fluid, usually operating according to the Rankine cycle. Flat solar collectors (Figures 6 and 7) consist of a glass or plastic cover (single, double, triple), a heat-absorbing panel painted black on the sun-facing side, insulation on the back and a housing (metal, plastic, glass , wooden).

Any metal or plastic sheet with coolant channels can be used as a heat-absorbing panel. Heat-absorbing panels are made of aluminum or steel of two types: sheet-pipe and stamped panels (pipe in sheet). Plastic panels are not widely used due to their fragility and rapid aging under the influence of sunlight, as well as because of their low thermal conductivity. Under the influence of solar radiation, heat-sensing panels are heated to temperatures of 70–80 ◦ C, higher than the ambient temperature, which leads to an increase in the convective heat transfer of the panel to the environment and its own radiation to the sky. To achieve higher coolant temperatures, the surface of the plate is covered with spectrally selective layers that actively absorb short-wavelength radiation from the Sun and reduce its own thermal radiation in the long-wavelength part of the spectrum. Such designs based on "black nickel", "black chrome", copper oxide on aluminum, copper oxide on copper and others are expensive (their cost is often commensurate with the cost of the heat-absorbing panel itself). Another way to improve the performance of flat plate collectors is to create a vacuum between the heat absorbing panel and the transparent insulation to reduce heat loss (fourth generation solar collectors).

The principle of operation of the collector is based on the fact that it perceives solar radiation with a sufficiently high absorption coefficient of visible sunlight and has relatively low heat losses, including due to the low transmittance of a translucent glass coating for thermal radiation at operating temperature. It is clear that the temperature of the resulting coolant is determined by the heat balance of the collector. The incoming part of the balance represents the heat flux of solar radiation, taking into account the optical efficiency of the collector; the consumable part is determined by the recoverable useful heat, the total heat loss coefficient and the difference between the operating temperature and the environment. The perfection of a collector is determined by its optical and thermal efficiency.

The optical efficiency η o shows how much of the solar radiation that reaches the collector's glazing surface is absorbed by the absorbing black surface, and takes into account the energy losses associated with absorption in the glass, reflection and the difference in the coefficient of thermal emissivity of the absorbing surface from unity.

The simplest solar collector with a single-glass translucent coating, polyurethane foam insulation of the remaining surfaces and an absorber covered with black paint has an optical efficiency of about 85%, and the heat loss coefficient is about 5-6 W / (m 2 · K) (Fig. 7). The set of a flat radiation-absorbing surface and pipes (channels) for the coolant forms a single structural element - an absorber. Such a collector in the summer in mid-latitudes can heat water up to 55–60 ◦ C and has an average daily productivity of 70–80 liters of water from 1 m 2 of the heater surface.

To obtain higher temperatures, collectors from evacuated pipes with a selective coating are used (Figure 8).

In a vacuum collector, the volume in which the black surface absorbing solar radiation is located is separated from the environment by an evacuated space (each element of the absorber is placed in a separate glass tube, inside which a vacuum is created), which makes it possible to almost completely eliminate heat losses to the environment due to thermal conductivity and convection. Radiation losses are largely suppressed by the use of selective coating. In a vacuum manifold, the coolant can be heated to 120–150 ◦C. The efficiency of a vacuum collector is significantly higher than that of a flat collector, but it also costs much more.

The efficiency of solar energy installations largely depends on the optical properties of the surface that absorbs solar radiation. To minimize energy losses, it is necessary that in the visible and near infrared regions of the solar spectrum, the absorption coefficient of this surface should be as close to unity as possible, and in the wavelength region of the surface's own thermal radiation, the reflection coefficient should tend to unity. Thus, the surface must have selective properties - it is good to absorb short-wave radiation and well to reflect long-wave radiation.

By the type of mechanism responsible for the selectivity of optical properties, four groups of selective coatings are distinguished:

1. own;
2. two-layer, in which the upper layer has a high absorption coefficient in the visible region of the spectrum and a small one in the infrared region, and the lower layer has a high reflectivity in the infrared region;
3. with micro-relief, providing the required effect;
4. interference.

A small number of known materials have intrinsic selectivity of optical properties, for example, W, Cu 2 S, HfC.

The most widespread are two-layer selective coatings. A layer with a high reflectance in the long-wavelength region of the spectrum, for example, copper, nickel, molybdenum, silver, aluminum, is applied to the surface, which must be given selective properties. On top of this layer, a layer is applied that is transparent in the long wavelength region, but has a high absorption coefficient in the visible and near infrared regions of the spectrum. Many oxides have these properties.

The selectivity of the surface can be ensured by purely geometric factors: the surface irregularities should be greater than the wavelength of light in the visible and near infrared regions of the spectrum and less than the wavelength corresponding to the intrinsic thermal radiation of the surface. Such a surface for the first of the indicated regions of the spectrum will be black, and for the second - specular.

Selective properties are exhibited by surfaces with a dendritic or porous structure with appropriate sizes of dendritic needles or pores.

Selective interference surfaces are formed by several alternating layers of metal and dielectric, in which short-wavelength radiation is extinguished due to interference, and long-wavelength radiation is freely reflected.

The scale of the use of solar heating systems

According to the IEA, by the end of 2001, the total area of ​​installed collectors in 26 countries, the most active in this regard, amounted to about 100 million m2, of which 27.7 million m2 falls on the share of non-glazed collectors, mainly used for heating water in swimming pools. The rest - flat glazed collectors and collectors with evacuated pipes - were used in hot water supply systems or for space heating. In terms of the area of ​​installed collectors per 1000 inhabitants, the leaders are Israel (608 m 2), Greece (298) and Austria (220). They are followed by Turkey, Japan, Australia, Denmark and Germany with a specific area of ​​installed collectors of 118–45 m 2/1000 inhabitants.

The total area of ​​solar collectors installed by the end of 2004 in the EU countries reached 13.96 million m2, and in the world it has already exceeded 150 million m2. The annual increase in the area of ​​solar collectors in Europe is on average 12%, and in some countries it is at the level of 28-30% or more. The world leader in the number of collectors per thousand inhabitants is Cyprus, where 90% of houses are equipped with solar installations (there are 615.7 m 2 solar collectors per thousand inhabitants), followed by Israel, Greece and Austria. The absolute leader in terms of the area of ​​installed collectors in Europe is Germany - 47%, followed by Greece - 14%, Austria - 12%, Spain - 6%, Italy - 4%, France - 3%. European countries are the undisputed leaders in the development of new technologies for solar heating systems, but they are far behind China in terms of commissioning new solar installations.

Of the total area of ​​solar collectors installed in the world in 2004, 78% were installed in China. The IED market in China has recently been growing at a rate of 28% per year.

In 2007, the total area of ​​solar collectors installed in the world was already 200 million m2, including more than 20 million m2 in Europe.

Today, on the world market, the cost of an IED (Figure 9), including a collector with an area of ​​5–6 m 2, a storage tank with a capacity of about 300 liters and the necessary fittings, is US $ 300–400 per 1 m 2 of a collector. Such systems are predominantly installed in single- and double-family houses and have a backup heater (electric or gas). When installing the storage tank above the collector, the system can operate on natural circulation (thermosyphon principle); when installing a storage tank in the basement - on a forced one.

In world practice, the most widespread are small solar heating systems. As a rule, such systems include solar collectors with a total area of ​​2–8 m 2, a storage tank, the capacity of which is determined by the area of ​​installed collectors, a circulation pump (depending on the type of heat circuit) and other auxiliary equipment.

Large active systems, in which the storage tank is located below the collectors and the circulation of the coolant is carried out using a pump, are used for the needs of hot water supply and heating. As a rule, in active systems participating in covering part of the heating load, a back-up heat source is provided, operating on electricity or gas.

A relatively new phenomenon in the practice of using solar heat supply is large systems capable of meeting the needs of hot water supply and heating of apartment buildings or entire residential areas. Such systems provide for either daily or seasonal heat storage. Daily accumulation assumes the possibility of operating the system with the consumption of heat accumulated over several days, seasonal - over several months. For seasonal heat storage, large underground reservoirs filled with water are used, into which all excess heat received from the collectors during the summer is discharged. Another option for seasonal accumulation is soil heating with the help of wells with pipes through which hot water circulates from collectors.

Table 1 shows the main parameters of large solar systems with daily and seasonal heat storage in comparison with a small solar system for a single-family home.

Table 1. - Basic parameters of solar heat supply systems

Currently in Europe there are 10 solar heating systems with collector areas ranging from 2400 to 8040 m2, 22 systems with collector areas from 1000 to 1250 m2 and 25 systems with collector areas from 500 to 1000 m2. Below are the specifications for some of the larger systems.

Hamburg (Germany). The area of ​​the heated premises is 14800 m 2. Solar collectors area - 3000 m 2. The volume of the water heat accumulator is 4500 m 3.

Fridrichshafen (Germany). The area of ​​the heated premises is 33,000 m 2. The area of ​​solar collectors is 4050 m 2. The volume of the water heat accumulator is 12000 m 3.

Ulm-am-Neckar (Germany). The area of ​​the heated premises is 25000 m 2. Solar collectors area - 5300 m 2. The volume of the ground heat accumulator is 63400 m 3.

Rostock (Germany). The area of ​​the heated premises is 7000 m 2. Solar collectors area - 1000 m 2. The volume of the ground heat accumulator is 20,000 m 3.

Hemnitz (Germany). The area of ​​the heated premises is 4680 m 2. The area of ​​vacuum solar collectors is 540 m 2. The volume of the gravel-water heat accumulator is 8000 m 3.

Attenkirchen (Germany). The area of ​​the heated premises is 4500 m 2. The area of ​​vacuum solar collectors is 800 m 2. The volume of the ground heat accumulator is 9850 m 3.

Saro (Sweden). The system consists of 10 small houses with 48 apartments. Solar collectors area - 740 m 2. The volume of the water heat accumulator is 640 m 3. The solar system covers 35% of the total heat load of the heating system.

Currently, there are several companies in Russia that produce solar collectors suitable for reliable operation. The main ones are the Kovrov Mechanical Plant, NPO Mashinostroenie and ZAO ALTEN.

Collectors of the Kovrov Mechanical Plant (Figure 10), which do not have a selective coating, are cheap and simple in design, are mainly focused on the domestic market. More than 1,500 collectors of this type are currently installed in the Krasnodar Territory.

The NPO Mashinostroyenia collector is close to European standards in terms of characteristics. The absorber of the collector is made of an aluminum alloy with a selective coating and is designed mainly for operation in two-circuit heat supply circuits, since direct contact of water with aluminum alloys can lead to pitting corrosion of the channels through which the coolant passes.

Collector ALTEN-1 has a completely new design and meets European standards, it can be used both in single-circuit and double-circuit heat supply schemes. The collector features high thermal performance, a wide range of possible applications, low weight and attractive design.

The experience of operating installations based on solar collectors has revealed a number of disadvantages of such systems. First of all, this is the high cost of collectors associated with selective coatings, increased transparency of glazing, evacuation, etc. A significant disadvantage is the need for frequent cleaning of glasses from dust, which practically excludes the use of the collector in industrial areas. During long-term operation of solar collectors, especially in winter conditions, their frequent failure is observed due to uneven expansion of illuminated and darkened areas of glass due to violation of the integrity of the glazing. There is also a high percentage of collector failure during transportation and installation. A significant disadvantage of the systems with collectors is also the uneven loading during the year and day. The experience of operating collectors in Europe and the European part of Russia with a high proportion of diffuse radiation (up to 50%) has shown the impossibility of creating a year-round autonomous hot water supply and heating system. All solar systems with solar collectors in mid-latitudes require the installation of large-volume storage tanks and the inclusion of an additional source of energy in the system, which reduces the economic effect of their use. In this regard, it is most advisable to use them in areas with a high intensity of solar radiation (not less than 300 W / m 2).

Efficient use of solar energy

In residential and office buildings, solar energy is mainly used in the form of heat to meet the needs for hot water supply, heating, cooling, ventilation, drying, etc.

From an economic point of view, the use of solar heat is most beneficial when creating hot water supply systems and in installations for heating water close to them in technical implementation (in pools, industrial devices). Hot water supply is necessary in every residential building, and since hot water needs change relatively little during the year, the efficiency of such installations is high and they quickly pay off.

As for solar heating systems, the period of their use during the year is short, during the heating season, the intensity of solar radiation is low and, accordingly, the area of ​​the collectors is much larger than in hot water supply systems, and the economic efficiency is lower. Usually, when designing, a solar heating system and hot water supply are combined.

In solar cooling systems, the operating period is even lower (three summer months), which leads to long equipment downtime and very low utilization rates. Considering the high cost of cooling equipment, the economic efficiency of the systems becomes minimal.

The annual equipment utilization rate in combined heating and cooling systems (hot water supply, heating and cooling) is the highest, and these systems, at first glance, are more profitable than combined heating and hot water supply systems. However, when the cost of the required solar collectors and cooling system mechanisms is taken into account, it turns out that such solar installations will be very expensive and hardly economically viable.

When creating solar heating systems, passive schemes should be used that provide for an increase in the thermal insulation of the building and the effective use of solar radiation coming through the window openings. The problem of thermal insulation must be solved on the basis of architectural and structural elements, using low-thermal-conductivity materials and structures. The missing heat is recommended to be replenished with the help of active solar systems.

Economic characteristics of solar collectors

The main problem of the widespread use of solar installations is associated with their insufficient economic efficiency in comparison with traditional heat supply systems. The cost of heat energy in installations with solar collectors is higher than in installations with traditional fuels. The payback period of a solar thermal installation T approx can be determined by the formula:

The economic effect of installing solar collectors in the areas of centralized energy supply E can be defined as income from the sale of energy during the entire service life of the installation minus operating costs:

Table 2 shows the cost of solar heating systems (in 1995 prices). The data show that domestic developments are 2.5–3 times cheaper than foreign ones.

The low price of domestic systems is explained by the fact that they are made of cheap materials, simple in design, and focused on the domestic market.

Table 2. - Cost of solar heating systems

The specific economic effect (E / S) in the district heating zone, depending on the service life of the collectors, ranges from 200 to 800 rubles / m 2.

Heat supply installations with solar collectors in regions remote from centralized power grids, which in Russia make up over 70% of its territory with a population of about 22 million people, have a much greater economic effect. These installations are designed to operate in an autonomous mode for individual consumers, where the demand for thermal energy is very significant. At the same time, the cost of traditional fuels is much higher than their cost in the areas of centralized heating due to transport costs and fuel losses during transportation, i.e., the regional factor r r is included in the cost of fuel in the Central heating region:

where r p> 1 and for different regions can change its value. At the same time, the unit cost of the C plant remains almost unchanged in comparison with the C tr. Therefore, when replacing Ts t with Ts tr in the formulas

the calculated payback period of autonomous installations in areas remote from centralized networks decreases by r p times, and the economic effect increases in proportion to r p.

In today's conditions in Russia, when energy prices are constantly growing and are uneven across regions due to transportation conditions, the decision on the economic feasibility of using solar collectors strongly depends on local socio-economic, geographic and climatic conditions.

Solar-geothermal heating system

From the point of view of uninterrupted supply of energy to the consumer, the most effective are combined technological systems that use two or more types of renewable energy sources.

Solar thermal energy can fully meet the needs for hot water in the house in the summer. In the autumn-spring period, up to 30% of the required energy for heating and up to 60% of the demand for hot water supply can be obtained from the Sun.

In recent years, geothermal heat supply systems based on heat pumps have been actively developing. In such systems, as noted above, low-potential (20–40 ◦ C) thermal water or petrothermal energy of the upper layers of the earth's crust is used as the primary heat source. When using the heat of the ground, ground heat exchangers are used, placed either in vertical wells with a depth of 100–300 m, or at a certain depth horizontally.

To effectively provide heat and hot water to decentralized low-power consumers, a combined solar-geothermal system has been developed at the IPG DSC RAS ​​(Figure 11).

Such a system consists of a solar collector 1, a heat exchanger 2, a storage tank 3, a heat pump 7 and a heat exchanger well 8. A coolant (antifreeze) circulates through the solar collector. The heat carrier is heated in the solar collector by the energy of the Sun and then gives off thermal energy to the water through the heat exchanger 2, mounted in the storage tank 3. Hot water is stored in the storage tank until it is used, so it must have good thermal insulation. In the primary circuit, where the solar collector is located, natural or forced circulation of the coolant can be used. An electric heater 6 is also mounted in the storage tank. If the temperature in the storage tank drops below the set temperature (prolonged cloudy weather or few hours of sunshine in winter), the electric heater automatically turns on and heats up the water to the set temperature.

The solar collector unit is operated year-round and provides the consumer with hot water, while the low-temperature underfloor heating unit with a heat pump (HP) and a heat exchanger well with a depth of 100–200 m is put into operation only during the heating season.

In the HP cycle, cold water with a temperature of 5 ◦ C descends into the annular space of the heat exchanger well and withdraws low-grade heat from the surrounding rock. Then the water heated, depending on the depth of the well, to a temperature of 10–15 ◦ C, rises along the central pipe string to the surface. To prevent heat backflow, the central column is thermally insulated from the outside. On the surface, water from the well enters the HP evaporator, where the low-boiling working agent is heated and evaporated. After the evaporator, the cooled water is again directed into the well. During the heating period, with constant circulation of water in the well, there is a gradual cooling of the rock around the well.

Calculated studies show that the radius of the cooling front during the heating period can reach 5–7 m. During the inter-heating period, when the heating system is turned off, a partial (up to 70%) recovery of the temperature field around the well occurs due to heat inflow from rocks outside the cooling zone; it is not possible to achieve full recovery of the temperature field around the well during its downtime.

Solar collectors are installed based on the winter period of system operation, when the sunshine is minimal. In the summer, part of the hot water from the storage tank is directed into the well to fully restore the temperature in the rock around the well.

During the interheating period, valves 13 and 14 are closed, and with valves 15 and 16 open, hot water from the accumulator tank is pumped into the annular space of the well by a circulation pump, where heat exchange with the rock surrounding the well occurs as it descends. Then the chilled water is directed back to the storage tank through the central insulated column. In the heating season, on the contrary, valves 13 and 14 are open, and valves 15 and 16 are closed.

In the proposed technological system, the potential of solar energy is used to heat water in the hot water supply system and rocks around the well in the low-temperature heating system. Heat recovery in the rock makes it possible to operate the heat supply system in an economically optimal mode.

Solar thermal power plants

The sun is a significant source of energy on planet Earth. Solar energy is very often the subject of a wide variety of discussions. As soon as a project for a new solar power plant appears, questions arise about efficiency, capacity, investment volumes and payback periods.

There are scientists who see solar thermal power plants as a threat to the environment. Mirrors used in thermal solar power plants heat the air very strongly, which leads to climate change and the death of birds flying by. Despite this, in recent years, solar thermal power plants have become more widespread. In 1984, the first solar power plant went into operation near the Californian city of Cramer Junction in the Mohabe Desert (Figure 6.1). The station was named Solar Energy Generating System, or SEGS for short.

Rice. 6.1. Solar power plant in the Mohabe desert

This power plant uses solar radiation to generate steam, which turns a turbine and generates electricity. The production of solar thermal power on a large scale is quite competitive. Currently, US power companies have built solar thermal power plants with a total installed capacity of more than 400 MW, which provide electricity to 350,000 people and replace 2.3 million barrels of oil per year. Nine power plants located in the Mohabe Desert have 354 MW of installed capacity. In other regions of the world, projects to use solar heat to generate electricity are also due to start soon. India, Egypt, Morocco and Mexico are developing related programs. Grants for their financing are provided by the Global Environment Protection Program (GEF). In Greece, Spain and the United States, new projects are being developed by independent power producers.

According to the method of heat production, solar thermal power plants are divided into solar concentrators (mirrors) and solar ponds.

Solar concentrators

Thermal solar power plants concentrate solar energy using lenses and reflectors. Since this heat can be stored, such stations can generate electricity as needed, day and night, in any weather. Large mirrors - either point or line focus - concentrate the sun's rays to the point that water turns into steam, while releasing enough energy to turn the turbine. These systems can convert solar energy into electricity with an efficiency of about 15%. All thermal power plants, except for solar ponds, use concentrators to achieve high temperatures, which reflect the sun's light from a larger surface onto a smaller receiver surface. Typically, such a system consists of a concentrator, receiver, heat carrier, storage system and power transmission system. Modern technologies include parabolic concentrators, solar parabolic mirrors and solar towers. They can be combined with fossil fuel plants and, in some cases, adapted for heat storage. The main advantage of such hybridization and heat storage is that such technology can provide dispatching of electricity production, that is, electricity generation can be produced during periods when there is a need for it. Hybridization and heat storage can increase the economic value of the electricity produced and lower its average cost.

Solar installations with a parabolic concentrator

Some thermal solar power plants use parabolic mirrors that concentrate sunlight on receiving tubes containing a heat transfer fluid. This liquid is heated to almost 400 ºC and is pumped through a series of heat exchangers; this generates superheated steam that drives a conventional turbine generator to generate electricity. To reduce heat loss, the receiving tube can be surrounded by a transparent glass tube placed along the focal line of the cylinder. Typically, such installations include uniaxial or biaxial solar tracking systems. In rare cases, they are stationary (Figure 6.2).

Rice. 6.2. Solar plant with parabolic concentrator

Estimates of this technology show a higher cost of generated electricity than other solar thermal power plants. This is due to the low concentration of solar radiation, lower temperatures. However, with operational experience, improved technology and lower operating costs, parabolic concentrators may be the least expensive and most reliable technology in the near future.

Disc type solar power plant

A dish-type solar array is a battery of parabolic dish mirrors similar in shape to a satellite dish, which focus solar energy onto receivers located at the focal point of each dish (Figure 6.3). The liquid in the receiver is heated to 1000 ° C and is directly used to generate electricity in a small engine and generator connected to the receiver.

Rice. 6.3. Disc type solar plant

High optical efficiency and low initial cost make mirror / motor systems the most efficient solar technology of all. The Stirling engine and parabolic mirror system holds the world record for the efficiency of converting solar energy into electricity. In 1984, Rancho Mirage in California achieved a practical efficiency of 29%. Due to their modular design, such systems are the best option for meeting the electricity demand for both autonomous consumers and for hybrid ones operating on a common network.

Tower solar power plants

Tower-type solar power plants with a central receiver The tower-type solar power plants with a central receiver use a rotating field of heliostat reflectors. They focus sunlight onto a central receiver at the top of the tower, which absorbs heat energy and drives a turbine generator (Figure 6.4, Figure 6.5).

Rice. 6.4. Solar power plant of a tower type with a central receiver

A computer-controlled biaxial tracking system sets the heliostats so that the reflected sunlight is stationary and always strikes the receiver. The liquid circulating in the receiver transfers heat to the heat accumulator in the form of vapor. The steam turns a turbine to generate electricity, or is directly used in industrial processes. Receiver temperatures range from 500 to 1500 ºC. By storing heat, the tower power plants have become a unique solar technology that generates electricity on a predetermined schedule.

Rice. 6.5. Solar power plant "Solar Two" in California

Solar ponds

Neither focusing mirrors nor solar cells can generate energy at night. For this purpose, solar energy accumulated during the day must be stored in heat storage tanks. This process naturally occurs in the so-called solar ponds (Fig. 6.6).

Rice. 6.6. Diagram of the solar pond device
1. High concentration of salt. 2. Middle layer. 3. Low salt concentration. 4. Cold water "in" and hot water "from"

Solar ponds have a high salt concentration in the bottom water layers, a non-convective middle water layer in which the salt concentration increases with depth and a convection layer with a low salt concentration on the surface. Sunlight falls on the surface of the pond and heat is trapped in the lower layers of the water due to the high concentration of salt. High salinity water heated by solar energy absorbed by the pond bottom cannot rise due to its high density. It remains at the bottom of the pond, gradually warming up until it almost boils. The hot bottom "brine" is used day or night as a heat source, thanks to which a special turbine with an organic heat carrier can generate electricity. The middle layer of the sun pond acts as thermal insulation, preventing convection and heat loss from the bottom to the surface. The temperature difference between the bottom and the surface of the pond water is sufficient to power the generator. The coolant, passed through pipes through the lower layer of water, is fed further into a closed Rankine system, in which a turbine rotates to generate electricity.

Advantages and disadvantages of solar thermal power plants

Solar power plants of a tower type with a central receiver and solar power plants with parabolic concentrators work optimally as part of large, grid-connected power plants with a capacity of 30-200 MW, while disk-type solar power plants consist of modules and can be used both in stand-alone installations and in groups of general with a capacity of several megawatts.

Table 6.1 Characteristics of solar thermal power plants

Solar parabolic concentrators are by far the most advanced solar energy technology and are likely to be used in the near term. Tower-type power plants with a central receiver, due to their efficient heat storage capacity, can also become solar power plants in the near future. The modularity of the poppet type plants allows them to be used in smaller plants. Solar power plants of a tower type with a central receiver and installations of a disk type allow achieving higher values ​​of the efficiency of converting solar energy into electricity at a lower cost than power plants with solar parabolic concentrators. Table 6.1 shows the main characteristics of three options for solar thermal power generation.

Building solar heating for a private house with your own hands is not such a difficult task as it seems to an uninformed layman. This will require the skills of a welder and materials available at any hardware store.

The relevance of creating solar heating for a private house with your own hands

Full autonomy is the dream of every owner starting a private construction. But is solar energy really capable of heating an apartment building, especially if the device for its accumulation is assembled in a garage?

Depending on the region, the solar flux can produce from 50 W / m2 on a cloudy day to 1400 W / m2 with a clear summer sky. With such indicators, even a primitive collector with low efficiency (45-50%) and an area of ​​15 sq. M. can produce about 7000-10000 kWh per year. And this is the saved 3 tons of firewood for a solid fuel boiler!

• on average, 900 watts per square meter of the device;
• to increase the water temperature, you need to spend 1.16 W;
• taking into account also the heat loss of the collector, 1 square meter will be able to heat about 10 liters of water per hour to a temperature of 70 degrees;
• to provide 50 liters of hot water needed by one person, you will need to spend 3.48 kW;
• after checking the data of the hydrometeorological center on the power of solar radiation (W / m2) in the region, it is necessary to divide 3480 W by the resulting power of solar radiation - this will be the required area of ​​the solar collector to heat 50 liters of water.

As it becomes clear, efficient autonomous heating exclusively using solar energy is quite problematic to implement. Indeed, in a gloomy winter season, solar radiation is extremely small, and place a collector with an area of ​​120 sq.m. on the site. will not always work.

So are solar collectors non-functional? Don't discount them in advance. So, with the help of such a storage device, you can do without a boiler in the summer - there will be enough power to provide a family with hot water. In winter, it will be possible to reduce energy costs by supplying already heated water from the solar collector to an electric boiler.
In addition, the solar collector will be an excellent helper for a heat pump in a house with low-temperature heating (underfloor heating).

So, in winter, the heated coolant will be used in warm floors, and in summer, excess heat can be sent to the geothermal circuit. This will reduce the power of the heat pump.
After all, geothermal heat is not renewed, so over time, an ever-increasing "cold bag" forms in the soil. For example, in a conventional geothermal circuit, at the beginning of the heating season, the temperature is +5 degrees, and at the end of -2C. When heated, the initial temperature rises to +15 C, and by the end of the heating season does not fall below + 2C.

Homemade solar collector device

For a self-confident master, it will not be difficult to assemble a heat collector. You can start with a small device for providing hot water in the country, and in case of a successful experiment, move on to creating a full-fledged solar station.

Flat solar collector made of metal pipes

The simplest collector is flat. For his device you will need:

• welding machine;
• pipes made of stainless steel or copper;
• steel sheet;
• tempered glass or polycarbonate;
• wooden boards for the frame;
• non-combustible insulation that can withstand metal heated to 200 degrees;
• matt black paint, resistant to high temperatures.

Assembling a solar collector is pretty simple:

1. The pipes are welded to the steel sheet - it acts as an adsorber of solar energy, so the fit of the pipes should be as tight as possible. Everything is painted in matte black.



2. A frame is placed on a sheet with pipes so that the pipes are on the inside. Holes are drilled for the entry and exit of pipes. Insulation is laid. If a hygroscopic material is used, you need to take care of waterproofing - after all, when wet, the insulation will no longer protect the pipes from cooling.





3. The insulation is fixed with an OSB sheet, all joints are filled with sealant.
4. Transparent glass or polycarbonate with a small air gap is placed on the side of the adsorber. It serves to prevent cooling of the steel sheet.
5. The glass can be fixed using wooden window glazing beads, after laying a sealant. It will prevent cold air from entering and protect the glass from squeezing the frame during heating and cooling.

For the full functioning of the collector, you will need a storage tank. It can be made from a plastic barrel, insulated from the outside, in which a heat exchanger connected to a solar collector is laid in a spiral. The heated water inlet should be at the top and the cold water outlet at the bottom.

It is important to correctly position the tank and manifold. To ensure the natural circulation of water, the tank must be above the collector, and the pipes must have a constant slope.

Solar heater made from scrap materials

If it was not possible to make friends with the welding machine, you can make a simple solar heater from what is at hand. For example, from cans. For this, holes are made in the bottom, the cans themselves are fastened to each other with a sealant, and they sit on it at the junctions with PVC pipes. They are painted black and fit into the frame under the glass in the same way as ordinary pipes.

Solar house facade

Why not decorate your home with something useful instead of regular siding? For example, by making a solar heater on the south side of the entire wall.

This solution will allow to optimize heating costs in two directions at once - to reduce energy costs and significantly reduce heat loss due to additional insulation of the facade.

The device is simply outrageous and does not require special tools:

• a painted galvanized sheet is laid on the insulation;
• a corrugated stainless steel pipe is laid on top, also painted black;
• everything is covered with polycarbonate sheets and fixed with aluminum corners.

If this method also seems complicated, the video shows an option made of tin, polypropylene pipes and film. Much easier!

Almost half of all energy produced is used to heat the air. The sun also shines in winter, but its radiation is usually underestimated.

On a December day near Zurich, physicist A. Fischer was generating steam; this was when the sun was at its lowest point and the air temperature was 3 ° C. A day later, a solar collector with an area of ​​0.7 m2 heated 30 liters of cold water from the garden water supply to + 60 ° C.

Solar energy can easily be used to heat indoor air in winter. In spring and autumn, when it is often sunny, but cold, solar heating of the premises will allow you not to turn on the main heating. This makes it possible to save part of the energy, and therefore money. For houses that are rarely used, or for seasonal housing (summer cottages, bungalows), solar heating is especially useful in winter, because eliminates excessive cooling of the walls, preventing destruction from moisture condensation and mold. Thus, the annual operating costs are mainly reduced.

When heating houses with the help of solar heat, it is necessary to solve the problem of thermal insulation of premises on the basis of architectural and structural elements, i.e. when creating an effective solar heating system, houses should be erected that have good thermal insulation properties.

Heat cost
Auxiliary heating

Solar contribution to home heating
Unfortunately, the period of heat input from the Sun does not always coincide in phase with the period of occurrence of heat loads.

Most of the energy that we have at our disposal during the summer period is lost due to the lack of constant demand for it (in fact, the collector system is to some extent a self-regulating system: when the temperature of the carrier reaches an equilibrium value, heat perception stops, since heat losses from solar collector become equal to the perceived heat).

The amount of useful heat absorbed by the solar collector depends on 7 parameters:

1. the amount of incoming solar energy;
2. optical loss in transparent isolation;
3. absorbing properties of the heat-absorbing surface of the solar collector;
4. the efficiency of heat transfer from the heat sink (from the heat-absorbing surface of the solar collector to the liquid, i.e. from the value of the efficiency of the heat sink);
5. the transmission capacity of transparent thermal insulation, which determines the level of heat loss;
6. the temperature of the heat-receiving surface of the solar collector, which in turn depends on the speed of the coolant and the temperature of the coolant at the entrance to the solar collector;
7. outdoor temperature.

The efficiency of the solar collector, i.e. the ratio of the used energy and the incident energy will be determined by all these parameters. Under favorable conditions, it can reach 70%, and under unfavorable conditions, it can drop to 30%. The exact value of efficiency can be obtained from a preliminary calculation only by fully modeling the behavior of the system, taking into account all the factors listed above. Obviously, such a task can only be solved with the use of a computer.

Since the density of the solar radiation flux is constantly changing, it is possible to use the total amounts of radiation per day or even per month for calculation estimates.

Table 1 as an example are given:

average monthly amounts of solar radiation, measured on a horizontal surface;

amounts calculated for vertical walls facing south;

sums for surfaces with an optimal slope angle of 34 ° (for Kew, near London).

Table 1. Monthly amounts of solar radiation arrival for Kew (near London)

The table shows that the surface with the optimal angle of inclination receives (on average during 8 winter months) about 1.5 times more energy than the horizontal surface. If the sums of the arrival of solar radiation on a horizontal surface are known, then to recalculate on an inclined surface, they can be multiplied by the product of this coefficient (1.5) and the accepted value of the solar collector efficiency equal to 40%, i.e.

1,5*0,4=0,6

This will give the amount of useful energy absorbed by the inclined heat-sensing surface during this period.

In order to determine the effective contribution of solar energy to the heat supply of a building, even by manual calculation, it is necessary to draw up at least monthly balances of needs and usable heat from the Sun. For clarity, consider an example.

Using the above data and considering a house with a heat loss rate of 250 W / ° C, the location has an annual number of degree-days of 2,800 (67,200 ° C * h). and the area of ​​solar collectors is, for example, 40 m2, then the following distribution by months is obtained (see Table 2).

Table 2. Calculation of the effective contribution of solar energy

Month	° C * h / month	The amount of radiation on a horizontal surface, kW * h / m2	Useful heat per unit area of ​​the collector (D * 0.6), kW * h / m2	Total useful heat (E * 40 m2), kW * h	Solar contribution, kW * h / m2
A	B	C	D	E	F	G
January	10560	2640	18,3	11	440	440
February	9600	2400	30,9	18,5	740	740
March	9120	2280	60,6	36,4	1456	1456
April	6840	1710	111	67,2	2688	1710
May	4728	1182	123,2	73,9	2956	1182
June	-	-	150,4	90,2	3608	-
July	-	-	140,4	84,2	3368	-
August	-	-	125,7	75,4	3016	-
September	3096	774	85,9	51,6	2064	774
October	5352	1388	47,6	28,6	1144	1144
November	8064	2016	23,7	14,2	568	568
December	9840	2410	14,4	8,6	344	344
Sum	67200	16800	933	559,8	22392	8358

Heat cost
Having calculated the amount of heat provided by the Sun, it is necessary to present it in monetary terms.

The cost of the generated heat depends on:

fuel cost;

calorific value of fuel;

overall system efficiency.

The operating costs thus obtained can then be compared with the capital costs of a solar heating system.

In accordance with this, if we assume that in the above example, a solar heating system is used instead of a traditional heating system that consumes, for example, gas fuel and generates heat at a cost of 1.67 rubles / kW * h, then in order to determine the resulting annual savings, it is necessary 8358 kWh, provided by solar energy (according to the calculations of Table 2 for a collector area of ​​40 m2), multiplied by 1.67 rubles / kWh, which gives

8358 * 1.67 = 13957.86 rubles.

Auxiliary heating
One of the questions most frequently asked by people who want to understand the use of solar energy for heating (or other purpose) is, "What to do when the sun is not shining?" Having understood the concept of energy storage, they ask the following question: "What to do when there is no more thermal energy left in the battery?" The question is logical, and the need for a redundant, often traditional system is a major stumbling block for the widespread adoption of solar energy as an alternative to existing energy sources.

If the capacity of the solar heating system is not enough to keep the building during a period of cold, cloudy weather, then the consequences, even once a winter, can be serious enough, forcing to provide as a backup to the usual full-scale heating system. Most solar-powered buildings require a full back-up system. Today, in most areas, solar energy should be seen as a means of reducing the consumption of traditional forms of energy, and not as a complete substitute for them.

Conventional heaters are suitable alternatives, but there are many other alternatives, for example:

Fireplaces;
- wood stoves;
- wood-burning heaters.

Suppose, however, that we wanted to make the solar heating system large enough to provide heat in the most unfavorable conditions. Since a combination of very cold days and long periods of cloudy weather is rare, the extra solar power plant (collector and battery) required for these cases would be prohibitively expensive with relatively little fuel savings. In addition, the system will operate below rated power most of the time.

A solar heating system designed to provide 50% of the heating load can only provide enough heat for 1 day of very cold weather. When doubling the size of the solar system, the house will be provided with warmth for 2 cold, cloudy days. For periods longer than 2 days, the subsequent increase in size will be as unjustified as the previous one. In addition, there will be periods of mild weather when a second increase is not required.

Now, if we increase the area of ​​the heating system collectors by another 1.5 times in order to hold out for 3 cold and cloudy days, then theoretically it will be sufficient to cover 1/2 of the entire house's demand during the winter. But, of course, in practice this may not be the case, since sometimes 4 (or more) days in a row of cold cloudy weather happen. To account for this 4th day, we need a solar heating system that can theoretically collect 2 times more heat than the building needs during the heating season. It is clear that cold and cloudy periods can be longer than anticipated in the solar heating system design. The larger the collector, the less intensively each additional increment in its size is used, the less energy is saved per unit area of ​​the collector, and the lower the return on investment for each additional unit of area.

However, bold attempts have been made to accumulate enough thermal energy from solar radiation to cover all heating needs and to eliminate the auxiliary heating system. With the rare exception of systems such as H. Hay's solar home, long-term heat storage is perhaps the only alternative to the booster system. Mr. Thomason came close to 100% solar heating in his first home in Washington; only 5% of the heating load was covered by the standard oil heater.

If the auxiliary system covers only a small percentage of the total load, then it makes sense to use electric heating, despite the fact that it requires the production of a significant amount of energy at the power plant, which is then converted into heat for heating (a power plant uses 10500 ... 13700 kJ to produce 1 kWh of thermal energy in the building). In most cases, an electric heater will be cheaper than an oil or gas oven, and the relatively small amount of electricity required to heat a building may justify its use. In addition, an electric heater is a less material-intensive device due to the relatively small amount of material (compared to a heater) used to manufacture electric spirals.

Since the efficiency of the solar collector increases significantly if it is operated at low temperatures, the heating system must be designed to use the lowest possible temperatures - even at a level of 24 ... 27 ° C. One of the benefits of the Thomason warm air system is that it continues to extract usable heat from the battery at temperatures close to room temperature.

In new construction, heating systems can be counted on to use lower temperatures, for example, by lengthening the hot water finned radiators, increasing the size of the radiant panels or increasing the air volume at a lower temperature. Designers most often opt for space heating with warm air or the use of enlarged radiation panels. An air heating system makes the best use of low-temperature stored heat. Radiant heating panels have a long delay (between switching on the system and heating the air space) and usually require higher operating temperatures of the heating medium than systems with hot air. Therefore, the heat from the storage device is not fully utilized at lower temperatures, which are acceptable for systems with warm air, and the overall efficiency of such a system is lower. Oversizing a radiant panel system to achieve similar results with air can incur significant additional costs.

To improve the overall system efficiency (solar heating and auxiliary backup system) and at the same time reduce overall costs by eliminating component downtime, many designers have chosen to integrate the solar collector and battery with the auxiliary system. Common are such building blocks as:

Fans;
- pumps;
- heat exchangers;
- governing bodies;
- pipes;
- air ducts.

The figures in the System Engineering article show various schemes of such systems.

A trap in the design of butt joints between systems is the increase in controls and moving parts, which increases the likelihood of mechanical failure. The temptation to increase efficiency by 1 ... 2% by adding another device at the junction of systems is almost irresistible and can be the most common cause of solar heating system failure. Normally, the booster heater should not heat the solar heat accumulator compartment. If this happens, the solar heat harvesting phase will be less efficient, as this process will almost always take place at higher temperatures. In other systems, lowering the battery temperature through the use of heat by the building increases the overall efficiency of the system.

The reasons for other disadvantages of this circuit are explained by the large heat loss from the battery due to its constantly high temperatures. In systems in which the battery is not heated by ancillary equipment, the battery will lose significantly less heat if there is no sun for several days. Even in systems designed in this way, the heat loss from the container is 5 ... 20% of the total heat absorbed by the solar heating system. With a battery heated by ancillary equipment, the heat loss will be significantly higher and can only be justified if the battery container is inside the heated room of the building