Thermochemical energy transport costs for a distributed solar power plant

Abstract

Thermochemical energy transport costs are calculated for a solar thermal power plant based on a distributed network of para-boloidal collectors. The optimum pipe size distribution within the fluid transport network has been generated subject to requirements of minimum cost and pressure drop equality across parallel conduction paths. The optimization procedure includes the installed capital cost of pipework together with the effective cost of pumping power. An analytical expression for the overall thermochemical energy transport cost has been derived, based on a Black and Veatch pipe cost survey in which conventional pipelaying technology is assumed. Thermochemical energy transport costs are calculated for systems based on ammonia, methanol, water-methane and sulphur trioxide. The derived costs are dominated by the pipe installation component whereas other parameters such as choice of system, operating pressure, reaction enthalpy and degree of reaction are of secondary importance. Larger collectors favour a lower installed cost per unit energy while increases in network area and hence in plant output capacity lead to slow increases in unit cost. Typical thermochemical energy transport costs for a solar thermal power plant operating only during sunlight hours and based on large collectors are estimated at $20 kWt −1 (1974 U.S. dollars). It is suggested that there is a need for reduction of this estimate by developments in pipelaying technology tailored to the requirements of solar thermal power plants. Such developments would seem to be feasible for thermochemical energy transfer systems based on small diameter pipes and hence on high system pressures.