Wind energy

This is, on the face of it, a poor proposition because its a secondary source: solar input creates wind at fairly low efficiency and that in turn drives wind turbines. Fortunately these are fairly cheap to erect and have high efficiencies. However, they only work when the wind blows, which still leaves the unsolved problem of bulk electricity storage as a disadvantage.

Smaller, domestic size, turbines cannot match the efficiency of large, bulk generation machines, but they are very cheap to build and operate. A 250-350 watt, 2 metre turbine backed by a lead-acid battery bank driving high efficiency lamps and an inverter is capable of meeting the lighting and entertainment, i.e. TV and radio, power requirements of a single household while still being cheap enough to be afforded by Nepali hill villagers.

Now (late 2007) it is being suggested that many of these disadvantages can be overcome by mounting the generators on tethered flexwings (parasails: kites without frames) and flying them on long tethers at, say, 1000 m altitude where winds are stronger and more constant. These would be big kites, generating anything up to 100 MW each. The idea is that the flexwing climbs vertically using its generators and turbines as motors driving propellers until its in strong enough wind to remain airborne while generating electricity and supplying current via its tether. This idea seems to have originated in 2003 with Pete Lynn[9]. He says that these should be more efficient than conventional wind turbines because they are operating in a faster, cleaner airflow, that they can gain efficency by circling or flying in a figure eight to increase their airspeed to considerably more than the wind speed and that, because there is far less material in them, they should be much cheaper to build too. As a result he thinks that they should be able to generate power at a fifth to a tenth of the cost of current systems. However, he has now concluded that handling difficulties, the limited range of usable wind speeds and the low efficiency make them impractical.

Wave energy

This is even more dilute than wind energy because its a tertiary source: solar input makes wind, which uses part of its kinetic energy to make waves. As a result the generators tend to be very large and are operated in a corrosive environment: sea water. Their sheer size gives them a large environmental impact too. Like solar and wind, it also requires that a solution is found for bulk electricity storage.