The principle of a Solar Collector for hot water
The principle of a Flat-Plate Collector for hot water
The principle of a Vacuum-Tube Collector for hot water
The principle of a Parabolic Reflector Collector for steam and cooking
The principle of a Photovoltaic Collector for electricity
The principle of a Solar Collector for hot water
If sunrays hit a flat-plate collector very few will be reflected, most of them will be absorbed and their energy is turned into heat. The heat is then transfered from the surface of the collector to water flowing in pipes. Even in January, in Ireland there can be enough sunshine to heat the water in those pipes to over 100°C. top 
The principle of a Flat-Plate Collector for hot water
The flat-plate collector is normally supplied in a flat box that is covered by sheets of special solar glass. The collector surface extents right below the glass which protects it from the elements, except sunlight. The glass creates a green-house effect which helps the collector to reach maximum temperature levels. Insulation on the back of the collector help to prevent heat losses. The water-filled pipes extract the heat from the collector panels and transport it to the hot cylinder or to the heating system. top
The principle of a Vacuum-Tube Collector for hot water
The Vacuum Collector works more efficient then the flat-plate collector, but they are more expensive and less robust.
The black absorber pipe is placed in the vacuum of a glass tube. On the inside back is a reflector, bundling sunlight from its surface to casts it to the tube. Several tubes are normally connected together in an array to form a collector field. top
The principle of a Parabolic Reflector Collector for steam and cooking
Parabolic Reflector Collectors are used in industry and to generate power with steam. They need to be mechanically turned to follow the sun path and focus its rays to an absorber. In form of a parabolic dish they can be used to cook food and may be a solution to environmental problems in some parts of the third world, where firewood is becoming scarce. Great care must be taken when handling parabolic mirrors with sunlight, as they can set off fires and cause severe burning. top
The principle of a Photovoltaic Collector for electricity
Sunlight is made up of tiny packets of energy, called photons. Every minute enough of this energy reaches the earth to meet the world's energy demand for one whole year. Photovoltaic panels consist of an array of cells. These are made of materials like silicon, one of the most common elements on earth. The individual cell is designed with a positive and negative layer, to create an electric field, just like in a battery. As photons are absorbed in the cell, their energy causes electrons to become free. The electrons move to the bottom of the cell and exit through the connecting wire. This flow of electrons is what we call electricity.
At present, one square foot of photovoltaic panel will generate about 10 Watt/peak. This means, that on a sunny day a panel that is directed to face the sun will generate 10 Watt per square foot (the amount to run one energy-saving light bulb). If a roof is covered by 100 square feet of panels, these will generate 1 Kilowatt if the sun shines on them perpendicular to their surface, enough energy to run a big drill or a strong hover. The amount is reduced if the sun does shine in an angle towards the panels or shading occurs. top
