Wind

A rapidly expanding method of generating green electricity, wind turbines are becoming an increasingly familiar sight on European hillsides. EU wind farms have the capacity to supply 3.3 per cent of EU power needs, while globally £12bn worth of new equipment was installed. These turbines produce electricity without producing harmful emissions.

While it is fully renewable, there are problems with generating electricity in this fashion. The most obvious difficulty with wind farms is that the output of the turbines is proportional to wind speed. When there is no wind, there will be no power; therefore a back-up system would be required. Wind energy is also difficult to store and turbines have a relatively low power output.

Solar

Completely silent and emission free, solar panels which produce electricity from the sun's rays can operate entirely independently of any external power source and require very little maintenance. Installing solar panels is costly, however, and solar electricity can be up to four times more expensive than its fossil-based equivalent.

Cheaper and lighter plastic panels designed to absorb infrared rays and thus generate energy even on cloudy days are currently in development, though they are not expected to become a serious alternative to regular panels for several years.

Biofuel

Fuel derived from crops such as sugar cane could offer an environmentally sound alternative to petroleum fuels as it reduces greenhouse emissions and can be derived from a sustainable resource. Producing biofuels in sufficient quantities is expensive, however, and bound by standard agricultural considerations. Only certain crops can be grown in certain soils with the result that an increased reliance on biofuels may see food and energy crops forced to compete for space.

Tidal

The ocean's tides present a potentially inexhaustible supply of power. It has been estimated that the tides around Britain alone could supply over 60 TWh of power every year. Estimating the power of the tides is one thing, harnessing it is quite another.

Tidal stations are extremely expensive to build and there are a limited number of global sites where they could be made effective enough to justify the expenditure. Even then, they are only capable of operating for less than 12 hours a day; the predictability of the tides is both an advantage and a disadvantage. Once in place and in operation, however, costs would be low because the sea water which powers the turbines is, of course, free.

Geothermal

Geothermal power stations utilise the extreme heat of the earth's core to produce electricity by pumping hot water or steam from reservoirs beneath the earth's surface, which is then used to power turbines. The running costs of these plants are very low and they do not create any pollution. Geothermal electricity is slowly reaching the point where it can compete on cost with traditional forms of electricity production. Heat pumps can also be used to heat or cool buildings at a low cost, depending on the season. Suitable geothermal sites are difficult to find, however, as very specific conditions are required to support a plant effectively, and even sites which are initially suitable, may stop producing sufficient heat due to variations in the earth's core.

Hydrogen

One source of energy which could completely replace fossil fuels is hydrogen. When reacted with oxygen, hydrogen can produce large amounts of energy with only water as a by-product. Highly compatible with energy efficient fuel cells, hydrogen can also dramatically increase the efficiency of heat-burning engines.

There is unfortunately a fundamental problem. Hydrogen does not occur naturally as the fuel H2, it must first be extracted from chemical compounds, a process which currently involves the use of fossil fuels. While hydrogen fuel itself is emission free, obtaining it is environmentally costly. Serious advances in technology are required to produce and store large amounts of hydrogen before it can become a viable alternative to consuming fossil fuels.