A sustainable energy source can be defined as one that:
- is not substantially depleted by continued use
- does not produce significant pollution or other environmental problems
- does not cause health hazards or social injustices.
In practice, few energy sources come close to these ideals, but renewable energy sources
are generally more sustainable than fossil or nuclear fuels: they are
essentially inexhaustible, and their use usually involves fewer health
hazards and much lower emissions of greenhouse gases and other
pollutants.
There are many forms of renewable energies:
Solar. This form of energy relies on the nuclear fusion power from the core of
the Sun. This energy can be collected and converted in a few different
ways. The range is from solar water heating with solar collectors to the complex
technologies of direct conversion of sunlight to electrical energy using photovoltaic cells.
Wind Power. Wind energy can be used to pump water or
generate electricity, but requires extensive areal coverage to produce
significant amounts of energy.
Hydroelectric energy. Water power is power derived from the energy of falling water or fast running water, which may be harnessed for useful purposes. It is not strictly speaking
renewable since all reservoirs eventually fill up and require very
expensive excavation to become useful again.
Biomass is organic matter
derived from living, or recently living organisms. Biomass can be used
as a source of energy and it most often refers to plants or plant-based
materials which are not used for food or feed, and are specifically
called lignocellulosic biomass .
As an energy source, biomass can either be used directly via combustion
to produce heat, or indirectly after converting it to various forms of biofuel. Conversion of biomass to biofuel can be achieved by different methods which are broadly classified into: thermal, chemical, and biochemical methods.
Geothermal power is Earth energy, a result of the heat storage in the
Earth's surface. Soil everywhere tends to stay at a relatively constant
temperature, the yearly average, and can be used with heat pumps to heat
a building in winter and cool a building in summer. This form of energy
can lessen the need for other power to maintain comfortable
temperatures in buildings, but cannot be used to produce electricity.
Other forms of energy.
Energy from tides, the oceans and hot hydrogen fusion are other forms
that can be used to generate electricity.
