Solar Convection Engines
Summary
A new method is described for the conversion of solar
energy into electricity. It involves natural convection
using a solar air collector, a warm air store, a
convergent-divergent nozzle and an air turbine. The
collector has a large area and absorbs incident solar energy
with high efficiency. This produces a flow of warm air which
rises into and through a warm air store. This is of large
volume and considerable height creating a strong buoyancy
force which draws air into and through the solar collector
with significant velocity. Incoming air passes through a
convergent-divergent nozzle (venturi) before entering the
solar collector. As air flows from the mouth to the throat
of the nozzle the constriction demands a multiplication of
its velocity. If a turbine is now placed in the throat of
the nozzle it can harness the kinetic energy of the high
velocity air flow producing electricity.
The warm air store of large dimensions provides a strong buoyancy force which draws ambient air through the configuration with significant velocity. The venturi multiplies this air flow velocity. As the cross-sectional area of the throat of the nozzle is reduced, the available kinetic energy increases continually. It is the author’s belief that in the limiting case of a very narrow throat of nozzle, the kinetic energy of the air flow at this location can equal the total solar energy taken up by the absorber. A turbine can harness and export this energy – in this way solar energy can be converted into electricity with high efficiency.
Where does the kinetic energy of the incoming air come from? It is the warm air store that drives the system by providing a strong buoyancy force which draws incoming air through the nozzle and collector. As ambient air flows from the mouth to the throat of the nozzle, the constriction requires a multiplication of its linear velocity. The fast moving molecules that make up ambient air rearrange their motions to provide the flow kinetic energy but it is at the expense of their internal energy and so the temperature must fall. If there is no turbine, the temperature of ambient air is restored in the divergent section of the nozzle when the linear kinetic energy is dissipated. If a turbine is inserted it can export a large proportion of this flow kinetic energy as electricity. The temperature of the incoming air is then partly restored by the divergent section of the nozzle and then fully restored and raised by the solar absorber.
It is the author’s belief that the use of optimum dimensions in the above arrangement will allow the conversion of solar energy into electricity with exceptionally high efficiency. Various configurations have been devised that illustrate possible applications e.g. garden solar electricity for an individual household, large scale generation using modular units on desert or scrub land in sunny regions, a 1000 MW solar power station using a man made mountain hollow or a mountain slope in a sunny climate. There is some attempt at cost estimates. Valuing electricity at $0.10/kWh and assuming 50% overall efficiency, these indicate a capital cost repayment period of about 3 years in sunny regions. If the principles are correct, then a miniaturised configuration may also be possible to provide solar home systems for individual households in rural developing countries.
This paper is purely theoretical – no experimental work has been conducted to validate or inform the proposals. The author asks individuals and organisations involved in solar/ renewable energy research or more widely in climate change/world energy supply to consider carefully the principles outlined, to initiate detailed investigation and to develop solar convection engines. This is the answer to the world energy problem.