Since 2001 the author has put forward a series of proposals on this website for harnessing solar energy using natural convection in large sealed ground level solar collectors. The convective energy conversion cycle involved requires no heat rejection and may allow the conversion of solar energy into electricity with very high efficiency. Consider the configuration depicted in Figure 1:
The outer dome and inner nozzle are made of glass or other transparent material. The dome contains air at atmospheric pressure and is sealed at ground level. The solar absorber is placed above ground level with substantial gaps to allow air flow. The ground is also covered with solar absorber material. A horizontal rotation wind turbine is placed in the centre of the dome with its vanes in the throat of the nozzle.
Solar energy is taken up with high efficiency by the absorber warming air in its vicinity which rises because of buoyancy. The raised temperature and pressure of the air drives flow through the nozzle. The constriction requires air to flow at higher velocity. The kinetic energy of the air flow is taken up by the turbine with accompanying cooling of the air. At the top of the dome the cooled air flows along the inside of the containment losing its residual excess energy through the glass of the dome. It then flows under the base of the nozzle and through the solar absorber to complete the cycle.
The author believes that this simple convection cycle allows conversion of the solar energy absorbed into electricity with high efficiency. Calculations indicate that with a nozzle mouth diameter double that of the throat and insolation 750 watts/m2 (maximum UK summer) air flow through the throat of the nozzle is 16.68 m/s (37mph). The fall in static pressure from the mouth to the throat of the nozzle is 180 Pascals (0.0018 atmospheres) and the rise in temperature as air flows through the absorber is 0.49°C. This energy gain is lost to the turbine and through the outer containment.
The author asks that theoretical and experimental work be carried out to test and develop the above model. It is suggested that laboratory experiments be conducted on models of about one metre dimensions. Simultaneously an outdoor prototype should be built with a dome of 10 metres diameter and turbine of 5 metres diameter. If such experiments were successful it is anticipated that a commercial module would be of 100 metres diameter with a turbine of 50 metres diameter housed in a sealed shallow dome of height 20 metres. This will generate an average output of over 1MW. Such units could be built on low value scrub or desert land at a density of up to 100 modules/km2.
The proposal outlined in this paper may allow solar energy to be converted into electricity much more efficiently and cheaply than for any other source of renewable energy using the mature technologies of the wind industry and solar collectors. Resource availability is far higher and more predictable than for wind and there would be minimal environmental impact.