Sun Energy - solar heat, water heating
Possibilities of utilization
Transformation of solar radiation into heat (photo-thermal transformation) can be passive (by passive solar elements of the buildings - glass facades, winter gardens) or active (by additional technical equipment - solar accumulators - collectors).
It is almost always possible to install active systems additionally to an existing building. They are used mainly to all-season preparation of warm supply water (WSW), swimming bath water heating and additional heating of the buildings by warm-water or warm-air heating.
Solar energy can be accumulated on a long term basis in the chambers (water, gravel etc.). The longer is the accumulation time, the as more expensive and less effective is the system. Therefore, mostly the short-term accumulation is used (several-day), together with flexible heating systems that decrease their output immediately, when there are solar gains by virtue of the glassing in the room.
Solar radiation impacting onto the Earth's surface consists of direct and distributed radiation. The direct radiation from the sun disc is formed by a beam of virtually parallel rays. The distributed (diffusive) solar radiation originates from distribution of direct solar rays at air molecules, water drops, ice crystals and at various aerosol particles. The distributed radiation appears as the sky light, if it wouldn't exist, the sky would appear black even during the day black with sharply blazing sun disc.
In the Czech Republic, there is an annual average of 1 081 kWh/m2 of energy shower on the surface.
The efficiency of the collectors depends mainly on the difference between the absorber temperature (or of the heat carrier liquid) and ambient air temperature. The higher temperature we require (e.g. 55 °C for preparation of WSW), the worse the efficiency will be. In case of vacuum collectors where the absorber is effectively isolated by vacuum, the efficiency changes just a little so these collectors work satisfactorily also in frosty days. On the contrary, in case of simple flat collectors, the efficiency collapses with the difference of temperatures very intensely, so during winter it is almost impossible to heat the water in them to the temperature higher than 80°C.