RENEWABLE ENERGY

Introduced by Milan Miessler, Editor, `Wind Energy' (Czech Republic) on 24 September 1999

The speaker first explained why renewable energy sources were necessary. Most fossil fuels will be in low supply in the next century, although coal will last into the 22nd century, but they cause global warming and pollution. Nuclear power is not trusted by the population, so the renewable sources _ geothermal, tidal, solar, hydro, wind, waves and biothermal _ must be developed to replace fossil fuels. The problem with renewable sources is that they are unsteady and cyclic but predictable.

The annual world demand for energy is now about 75,000 TWh. (One TWh (Terrawatt-hours) = one million MWh; one MWh runs 1000 one-bar (1kW) electric fires for an hour). Of this, the UK demand is about 2,600 TWh.

Fossil fuels and uranium provide 68,300 TWh. Solar radiation provides annually 219 million TWh to the Earth's land surfaces; direct solar radiation supplies 0.1 kW/m2 of surface, but there are large areas available. If the south-facing facade of 3 million houses in Britain was covered with 10m2 of photocells and the roof with 10m2 of thermal collector this would provide 4 TWh of electricity and 16 TWh of heat per year.

Biothermal energy from growing selected crops _ eucalyptus, poplar, straw or reeds _ is a suitable method for local generation of 10 - 20 MW and could use the `set aside' agricultural land. These crops have to be harvested before they seed to prevent uncontrolled spreading. Agricultural waste, forest waste, sewage and refuse, including car tyres, might also be burnt, although there are problems with domestic and industrial refuse containing plastic packaging.

Hydro (water-power) provides 2.3% of world energy at present and is useful for supplying the peak demands of electricity using a pumped storage system. Tidal power requires a huge investment initially but then supplies a large amount of energy for many years in short bursts _ 3 hours, twice in 24 hours. Experiments on wave power have been discontinued and geothermal is only efficient in a few sites: Italy has had one 440 MW station working for 150 years and Southampton a 1MW source since 1980.

Wind power is thus the most viable renewable source at present. There are 250 new sources

installed each year world-wide. Typically, they each produce 700 kw for 1.2 GWh/yr, although some larger turbines are in operation. Denmark is the leading producer and user of wind turbines supplying 10% of the national demand. They are siting them off-shore and this could be done around Britain, off East Anglia and in the Irish Sea, to prevent noise pollution. The wide variation in the output over a short period is a problem and a storage facility is badly needed. Pumped storage of water or compressed air is used and manufacture and storage of hydrogen is under consideration.

The discussion revealed that it takes six years out of the 20 year life of a wind turbine to repay the manufacturing energy and capital cost but that the cost of power is now comparable with that of power from coal.

The demand for power world-wide will increase, especially in places like China and India, and it is to be hoped that they will `jump' to renewable sources instead of using fossil fuels. A final suggestion was that, by using a Stirling engine, it would be possible to generate power from ice instead of using heat.

Don Lovell