All solar - powered products are useless in the absence of sunlight (for example, during the evening) and therefore can be used only in the day. The Spanish "Gemasolar", however, is breaking these rules by operating during the night as well.
The operating procedure is simple, really. As you can see from the image, the design consists of a central beacon, that is surrounded by large curved mirrors called "Heliostats". These mirrors (more than 2500 in number) direct sunlight to this beacon, which gets heated up. This energy is then conducted to a storage device. This device is a tank, filled with potassium and sodium nitrate salts. The salts get heated up to temperatures as high as 500 degrees Celcius, and are always in liquid form. Thanks to the high enthalpies of melting of these ionic salts, the tank can store enormous amounts of energy (this may be almost nine times the energy stored by oils, which are conventionally used storage media). This plant is now able to generate almost 20MW of electricity, and can function even when there is no sunlight using the energy stored in the molten salts.
Gemasolar, which cost nearly 320 million USD to construct, is a joint venture of Spanish construction company Sener, and Masdar - an Energy company from Abu Dhabi.
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