The Design and Heat Pipe Tests for a Line Focus Solar Stirling Domestic Generation system

This paper outlines the methodology used in the design of a line focus solar Stirling power generation system for remote locations. Tests of potential working fluids for the heat pipes, used to transport energy from the solar concentrator focus to the Stirling engine heater heads, are also described. At the optimum achievable solar absorber temperature, very few heat pipe working fluids are available. Those tested were a sulphur iodine system, the organic fluid dioctyl phthalate and mercury These were designed to deliver energy to an already developed compact hermetically sealed Stirling engine battery charger of 200 W electrical power output. The only fluid to show promising performance was mercury, but safety considerations may rule mercury out for application in numerous dispersed small domestic systems.

The line focus system efficiency tends to be low because of the low Stirling engine heater head temperature at optimum system conditions and the greater losses associated with a larger focal area than that used in a point focus system of similar power output. Predicted system efficiency was 4.9 per cent for the prototype 200 W generator and 12.5 per cent for a 3 kW full-scale system on which better insulation of the heat pipe is possible. The size and cost of the 200 W unit in relation to output are likely to be too high to be economically attractive, but development of the 3 kW system may still be viable if alternator efficiency can be maximized and heat pipe thermal losses kept to a minimum.