Solar energy
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Description
Solar energy or radiation from the sun is a renewable energy that can be exploited to heat water or spaces or to generate electricity, commonly with the aid of photovoltaic panels.
Detailed description
It is recommended to read the article on solar radiation to understand how the radiation is converted into useful energy.
Thermal Energy
There are several ways of using solar energy for heating purposes. By proper design, it is possible to use it to heat a whole house for most of the year, even in the coldest climate.
The most popular way of using solar energy for heating is to provide hot water. In some Middle Eastern countries, such as Israel and Cyprus, most hot water is provided with the rooftop solar heating panels. In such climates, the direct method is mostly used. In this, solar panels are connected in a connection circuit with the hot water tank supplying the house. The panels themselves have an efficiency of up to about 85%. One design consists of copper pipes soldered onto a thick copper panel, the whole lot blackened, mounted behind double glazing (thumbnail shows a typical 3 kW household installation in Cyprus, with gravity fed cold-water tank on top)
In climates where there is a risk of frost in winter, the direct method is unsuitable. The indirect method uses similar panels connected to a heat exchanger mounted within the hot water tank, with an antifreeze solution in the circuit. Because the tank is often mounted some distance from the panels, it is often inconvenient to use a convection circuit and a small circulation pump becomes necessary. The efficiency of the indirect method is usually considerably lower, typically about 65%.
The orientation of the panels can be quite critical, depending on their design. Ideally, in the northern hemisphere, they should face directly south at an angle which places the panels normal to the winter sun. If the system has been designed correctly, this should give enough hot water throughout the year, at least in sunny weather!
Some panels are designed with parabolic reflectors. For ordinary household water heating, these offer little advantage, compared with a simpler design, and have the disadvantage of needing more maintenance, to ensure that the reflectors remain clean. Comparative experiments conducted by a company in Cyprus led them to abandon the commerce of reflector type panels.
