It is currently impossible to cover the total demand for thermal energy solely with solar energy in the climate of Poland on a massive scale. The efficiency of solar installations does not exceed 20%, and the problem of storing excess solar energy from the summer period is not satisfactorily solved yet. Currently operating installations of active solar heating systems must be supported by furnaces burning traditional energy carriers. These installations are able to cover over 50% total energy demand for heating and domestic hot water preparation. Solar installation systems used in single-family housing in Europe, or North America, for central heating, consist of two combined parts: solar and conventional. Such a system, presented ideologically, consists of a collector loop, domestic hot water preparation system. and central heating system. Such systems are associated with a traditional heat source (central heating stove. for solid fuels, liquid or gaseous). Heat pumps are becoming more and more common. Liquid solar systems are currently the most widespread, though in North America liquid-air or air-only systems are often used. Water has a better heat capacity (4,19 kJ/kgK) from the air (1,012 kJ/kgK), which is related to the size of the heat storage (water is much smaller than air).
For an average single-family house with a cubic capacity of 500 do 700 m3 and improved thermal insulation are needed to heat from 20 000 do 37 000 kWh of energy per year.
With an average amount of sunlight on 1 m2 of facing surface equal 1411,3 kWh/m2, taking into account differences in collector efficiencies, we will obtain the active surface area of the collectors from 30 do 90 m2. As it results from the analysis of the ratio of the collector area to the heated area, it is from 20 — 60% According to, and according to other authors, this ratio is as high as 100%.
The efficiency of the collectors is inversely proportional to the operating temperature of the working medium, therefore, it is advisable to use low-temperature surface or floor heating, where a medium temperature of 45°C is required.
The required capacity of the heat accumulators is very large. In a theoretical example, for a country house 720 m3 of volume and assuming, that the reservoir will hold approx. 40% annual demand, prof. J. Kozierski calculated, that he will have 200 m3 of volume. The use of such a warehouse in practice is absurd.
As can be seen from the analysis of completed objects and publications, the optimal capacity of the heat storage tank in relation to the collector surface is from 30 do 100 l na 1 m2 of collectors. Latent heat storage tanks are also increasingly used, whose volume is much smaller. These are short term warehouses, because after introducing the heat pump and traditional energy sources into the system, long-term water storage becomes redundant. After the introduction of the heat pump, the efficiency of the collectors is also increased (system), because it is inversely proportional to the operating temperature of the working medium.