Solar Power extracts the energy of sunlight. This may be done directly, with photovoltaic cells, or it may be done by using fields of mirrors to concentrate sunlight on a target, which then becomes extremely hot.

This heat can then be dumped to the surrounding air, providing electricity. In either case, a large expanse of land receiving steady sunlight is needed.

Deserts are the usual choices. Manufacture of solar cells results in environmental releases of pollutants and the emissions associated with the energy input to make and install the cells.

Once a large solar collector is built, its environmental impact is not very severe. It occupies a great deal of land, denying its use to the fragile desert ecosystems, and the heated air may lead to slight changes in local weather systems.

The mirrors or cells must also be kept clean, and this probably requires a certain amount of water. Where possible, solar power is generally quite environmentally friendly.

Some projects have been established to take advantage of relatively small solar cells by putting solar collectors on the roofs of individual houses.

Generally, the electrical power generated is not sufficient to pay back the cost at current electricity prices, so when government subsidies are not present, this method is rarely used.

It is generally more practical to use small solar collectors to heat water directly, satisfying household hot water needs.

Wind Power extracts electricity from the flow of air over the surface of the earth. Wind power stations generally consist of large "wind farms", fields of large windmills in locations with relatively high winds.

These farms are generally considered unattractive. In addition the windmills disrupt local low-level winds, and they can be very noisy. Both facts create problems for local bird populations, specifically the death of many birds.

The windmills also need constant maintenance, as they have many moving parts exposed to the elements. A lot of effort is now being directed into having off-shore wind-farms that will be situated several kilometres out to sea.

Supporters hope this will reduce the amenity concerns many opponents have. Many homeowners in areas with high winds and expensive electricity set up small windmills to reduce their electric bills.

A potentially more significant issue, is that of the 'spinning backup' that is required to compensate for the unpredictable and intermittent nature of wind generation in a national grid.

In order to maintain a reliable supply of electricity to consumers, it is necessary to control the energy generated, increasing and decreasing it according to demand. Wind energy however, cannot be controlled as such meaning that either other power stations (Preferably those with short 'spin-up' times such as gas fired power stations) must be left on stand-by to takeover supply generation when output from wind farms falls.

This however may reintroduce environmental issues with conventional electricity generation methods, somewhat curtailing the effectiveness of wind power as an environmentally friendly means of producing electricity. An alternative to compensating for the lulls in wind generation, is to effectively store the energy generated during high winds and then utilise it as required.

However this requires expensive grid energy storage schemes, such as pumped storage or (At a smaller scale) Battery storage, each of which introduce further environmental concerns.