Wind power has been around for centuries. Originally it was used to fill sails for vessels crossing the oceans, then by windmills grinding grain and pumping water. The best supplies of wind are in mountain passes and coastal areas such as Denmark, Holland, California, India, Argentina and China, all of which have significant existing wind farms. The beauty of wind is that once the wind farm is built and installed, there are only maintenance costs to worry about; everything else is free. However, the downside is that wind is a limited resource. The good news is that wind turbine technology is accelerating rapidly, generating more electricity from each turbine and allowing production a lower speeds when there is less wind and reduced risk to birdlife.

Solar power is an exciting renewable technology that dates back to the Greeks and Chinese using mirrors and glass to focus the sun to start fires. Homes have always been built to take advantage of the sun's warming effect, as well as rooftop collectors to heat home hot water and even swimming pools. The same principle is used in most solar-thermal electrical generation techniques in that electrical power is generated by heating water to turn a generator. Photovoltaic solar power was first discovered in 1839 by the French physicist Edmund Becquerel, however it wasn’t until the 1950's that the first solar electric cells were produced by Bell laboratories. The US space programme boosted things further, using solar cells to power satellites, boosting efficiencies to roughly 15%. Today, efficiencies of 30% and more are possible and the technology is now getting more attention than ever before. The downside is that the cells work best in highly sunny climates, which makes them ideally suited to desert location but with the complication of storing or transporting the resultant energy. Progress is being made with low-loss high voltage DC transmission lines which promise a future of desert-generated electricity piped to nearby urban conurbations.

Hydro-electricity is generated by the process of water flowing downhill under gravity and represents the world’s largest renewable source of energy. It is also a great way to store energy from other sources in that solar or wave power can be used to pump water uphill, for release at a later time as hydro energy when it's required. Most major hydroelectric dams were built during the 20th century, and currently accounts for 19% of the world's electricity generation. The limitations are that many of the west's ideal sites for hydro are already exploited and there are other environmental issues such as damage to streams, dried up waterfalls and harm to marine life. Hydro projects in less well developed parts of the world are attracting strong interest, as are micro-hydro projects from smaller rivers or streams.

Hydrogen is often quoted as the answer to all environmental ills as its a lightweight element, combines readily with oxygen, burns hot and produces only water as a by-product. However, hydrogen is not readily available for mining from underground reservoirs, and therefore has to be manufactured from hydrocarbon sources like coal or gas, which uses more energy than the resulting hydrogen will release. There's lot of research going on into producing hydrogen from algae and sewage wastes but it’s very early days for that.

Geothermal power occurs when underground steam can be harnessed for energy production. Electricity was first produced in this way near Rome in 1904, commercialised in New Zealand in 1954 and in 1960 a whole field of geothermal power plants was commissioned in northern California. Of course, geothermal power is very dependent on geography and tends to only occur around the edges of tectonic plates. This limits the technology to area like the west coast of America, Iceland, India, Kenya, the Philippines, Indonesia, Japan and Thailand. Overall less than 1% of the worlds energy comes from geothermal sources. It is also questionable as to whether geothermal really is a renewable source of energy, since as the steam is used for energy production it gradually depletes. There are ways to recharge the steam stores artificially but then the environmental credentials come into question and the economics also become less attractive.

Wave/tidal power uses the predictable rise and fall of waves and tides around sea coasts. Similarly, estuaries can be dammed to run turbines as the water rises and also as it falls. There are unfortunately only a small number of optimal sites in the world for wave/tidal power and they are in inhospitable areas like northwest Russia and Nova Scotia. The impact on fish stocks also needs to be taken into account. Smaller scale projects are being developed in area where the sea constantly laps the shore such as Japan, Norway, Britain, Belgium and India but the results are mixed with little sign of a reliable source of energy being available.

Bio-fuels comprise energy sources such as Biomass, Biodiesel and Ethanol. Biomass involves the burning on wood, animal waste, seaweed agricultural waste and rubbish, all of which generates lots of low-cost energy but with a high pollution cost. Biodiesel is chemically altered vegetable oil that can be used to run slightly modified diesel engines. Whilst biodiesel pollutes less than normal diesel, it also gives slightly less miles per gallon and its production process uses almost as much energy as it releases. Biodiesel produced from waste cooking oil is a good solution all round but only available to a limited number of consumers. Ethanol suffers from the same energy production issues as biodiesel, as it is a fuel grade form of alcohol produced from grain fermentation. As recently witnessed, all biofuels take land away from food production, which can then lead to unsustainable food price increases.

Fusion/cold fusion is something that scientists have been pondering for many centuries. How can 'free energy' be produced from a process or device that give out more energy than it consumes ? Cold fusion occurs when hydrogen and deuterium come together with metal such as palladium, titanium and lithium. The reaction releases massive amounts of energy, whilst giving off very little harmful radiation. The challenge is that this process is not possible with current technology and the only way to make fusion occur is at reactor temperatures of 200 million degrees Celsius, which is beyond the capabilities of existing materials. To date, no fusion reactor has been able to produce more energy than it consumes but there's no doubt that the research will continue.

Conservation is almost universally agreed to be the best way to cushion the impending energy shortfalls. Whilst significant improvements have been made in home insulation, car fuel consumption, and so on, there's still a long way to go before this path is exhausted. One of the few benefits of higher energy prices is that it stimulates more research into improved insulation materials, ultra-low consumption LED lighting solutions, advanced heat pump technology for heating and cooling buildings, solar panel advances, wave technology, wind turbine improvements, lightweight vehicles, hybrid vehicles, electric vehicles and so on.