Solar energy produces hot air which will rise – this can drive a convector generator producing electricity. At its simplest:
The apparatus is a modified solar panel. The base is covered with solar absorbing paint and the upper surface is glass. Warm air rises to drive the generator and will draw in cold air. The lower surface need not be air tight.
A more sophisticated version could involve heat recovery from the warm air to pre-heat incoming air.
The solar absorption surface could be of dimensions 10-1000 metres square. The structure must be air tight so that all rising warm air drives the generator. All cold air entering passes through the heat exchanger and is supplied at ground level via fresh air inlets. All of the materials above would be cheap and easy to construct. The convector generator is the only expensive equipment and could be one of many designs described earlier – its function is to efficiently convert the current of warm air into electricity.
The use of a Wells turbine may allow simultaneous extraction of energy from the current of warm air rising and incoming colder air:
Dimensions above for the generation unit could be one metre diameter and the heat exchanger 5 metres height. The solar absorption surface could be 100 metres x 100 metres with the sloping glass one metre high at the perimeter and 5 metres high at the centre. The mouth of the warm air exit pipe would need to be 1-5 metres above the cold air entry level to drive the system.
The geometry of the solar generator as drawn may appear inconvenient but it could be sited on a South facing hillside with the generator at the highest point. The only major energy loss above is through the glass of the solar collector – certainly double glazing or perhaps triple glazing with glass of low thermal conductivity will be needed to reduce such energy loss. For the absorption of solar energy the Solar One Power Plant in California has achieved an efficiency of 96% absorption using a special type of paint. The Wells turbine can capture as much as 90% of the energy of air flow. If heat losses through the glass can be minimised conversion of solar energy into electricity with over 80% efficiency should be possible.
Solar electricity is considered wildly uneconomic in the UK – but even in Britain, in Aberporth solar energy influx is 600 kWh/sq metre/year. At a value of 2 pence/kWh, an area of solar absorbers of 100 metres x 100 metres with 80% conversion efficiency into electricity would provide annually about £100,000 electricity per hectare of land. The capital cost of the equipment described would be repaid in a year. In California, most of Southern Europe and large areas of the developing world solar influx is 3-4 times as great.
If solar energy could be converted into electricity efficiently and cheaply that solves the energy problem and global warming. There is however a seasonal mismatch, a day/night mismatch and a geographical supply/demand mismatch. The advanced countries have highest energy demand whilst the potential for solar energy is greatest between the tropics. The best solution is to use solar electricity to generate hydrogen. This could become the fuel for transport using the fuel cell, for industrial and home heating as natural gas supplies diminish and of course could regenerate electricity. A new world trade could develop in the supply of hydrogen.