The Solar Chimney - an alternative configuration
Summary
The solar chimney involves a tall cylindrical chimney at the centre of a large area solar collector with turbines at the base of the chimney to harness the kinetic energy of the air flow. The alternative configuration described in this paper involves horizontal axis turbines symmetrically sited around the circumference of the solar collector, each at the throat of a convergent nozzle in a sealed structure. The chimney proposed is an annulus (ring-shaped) involving two concentric walls built at around mid-radius of the collector. In this way a much larger area of cross-section of chimney is possible. If the chimney cross-sectional area is several times the total area of cross-section of the turbines, the venturi principle dictates that the velocity of air flow through the turbines is also several times its velocity through the chimney. Available kinetic energy for the turbines is increased by the square of this ratio.
A model configuration is outlined with collector diameter 1000 m and with 100 turbines of diameter 10 m sited symmetrically around the circumference. The chimney of height 300 m is an annulus of outer diameter 540 m and inner diameter 460 m. It is calculated that at insolation 750 wm-2 the air flow velocity through the turbines is 32.59 ms-1 providing available kinetic energy of 160.4 MW with an efficiency of 38.45%.