Renewable energy systems
Renewable energy is defined as "energy derived from resources that are regenerative or for all practical purposes can not be depleted." Renewable energy, also called alternative energy, is generally thought of as an alternative to conventional energy usually supplied by the combustion of fossil fuel such as oil, coal or natural gas. The prime source of renewable energy is solar radiation, i.e. sunlight. The Earth-Atmosphere system receives approximately 5.4 x 1024 joules per year in the solar radiation cycle (Sorensen, 2004). The solar irradiance at the top of the atmosphere is on average 1366 watts/meter-squared.
One of the main reasons for an interest in the development of renewable energy systems is a concern for the inevitable depletion of fossil reserves (See Hubbert peak theory) and the realization that it is the only viable means of achieving a truly sustainable society.
Required Knowledge 
It would be useful to have a basic knowledge of energy and sources of energy.
Learning Material 
Renewable energy systems may be powered by:
- solar energy (wiktionary | wikipedia | wikibooks)
- wind energy (wiktionary | wikipedia | wikibooks)
- biofuels (wiktionary | wikipedia | wikibooks)
- geothermal energy (wiktionary | wikipedia | wikibooks)
- hydroelectric power (wiktionary | wikipedia | wikibooks)
- wave power (wiktionary | wikipedia | wikibooks)
They also possess the characteristic of not being metered, in many cases, therefore can enable housholds and communities to exist "off-the-grid" thus enabling something that can be thought of as true independence.