Potassium Nitrate

Potassium Nitrate KNO₃ is a chemical compound that is both an ionic salt and an alkali metal nitrate. Like calcium nitrate, potassium nitrate is also a popular fertilizer material.

Solar power plants
Potassium nitrate (along with calcium nitrate and sodium nitrate) is a key component of of both binary and ternary solar power molten salt, which functions as a heat transfer fluid that allows the transfer and storage of solar thermal power. This molten salt can be tapped into at will to generate steam and steam-powered energy similar to how coal can be used to power steam-driven devices.

Additional Notes:
* Potassium nitrate and humans have a long history, and other applications include or have included: fireworks, gun powder, and even food preservative.
* Originally a material that nature recycled from waste back into a naturally occurring fertilizer and mineral, potassium nitrate was once primarily collected from bat guano, and it can also be collected from other forms of manure and urine. Such methods include the French method, the Swiss method, and this method detailed in the following article: http://www.todayifoundout.com/index.php/2013/04/urine-facts/ or click here.
* Like calcium nitrate, potassium nitrate salt (aka niter or salt peter) can also be found as in efflorescent growths in caves.