Solar chemical

Solar chemical


Solar chemical processes convert solar energy into chemical energy. These processes use both light (photochemical) and heat (endothermic) to drive chemical, thermochemical or thermoelectric reactions. Solar chemical reactions can be used to store solar energy or replace energy that would otherwise be required from an alternate source.

Electrochemical cells, commonly known as batteries, convert electrical energy into chemical energy. Solar energy can indirectly be converted into chemical energy in a system involving a photovoltaic to electrochemical cell exchange. A more direct approach involves the use of photoelectrochemical cells which use light to produce hydrogen in a process similar to the electrolysis of water. A third approach involves the use of thermoelectic devices which convert a temperature difference between dissimilar metals into an electric current between those metals. This current can be use to produce hydrogen and oxygen through the electrolysis of water. The solar pioneer Mochout envisioned using the thermoelectric effect to store solar energy for later use during darkness; however, his experiments toward this end never progressed beyond primitive devices.

Concentrating solar thermal technologies can be used to drive high temperature chemical processes.
Ammonia can be decomposed into nitrogen and hydrogen at high temperatures (650-700°C). The stored gases can be subsequently recombined to generate heat or electricity via a fuel cell. A prototype system was constructed at the Australian National University.

Zinc Oxide (ZnO) can be decomposed at high temperatures (1200-1750°C). The resulting pure zinc can be marketed directly. Alternatively, the zinc can be reacted with water at (350°C) to produce ZnO and hydrogen.

Water can be directly dissociated at high temperatures (2300-2600°C). These process have so far been limited due to their high level of complexity and low solar to hydrogen efficiency (1-2%).An alternate path of research is investigating solar thermochemical cycles that can be used to dissociate water at lower temperatures. Thermochemical cycles are currently at the prototype stage.

Concentrating solar thermal has also been investigated as a direct thermal method of producing aluminum.

While not a technology, photosynthesis is arguably the most important photochemical interaction. A diverse biology has developed capable of photosynthesizing light in the visible, ultraviolet, near infrared and far infrared regions of the electromagnetic spectrum.

Salt evaporation ponds are shallow man-made ponds designed to extract salt from sea water. The seawater is fed into large ponds and water is drawn out through natural evaporation. After the sun and winds have evaporated the water the salt is harvested.