Comparison of the performance-economics of thermochemical and sensible energy transport for distributed receiver solar thermal systems

ABSTRACT:
A major challenge facing the development of distributed receiver solar systems is the efficient transport of high-temperature thermal energy from the collectors to the point of use. As receiver temperatures increase, conventional sensible energy transport methods become less attractive

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because of increased heat losses and insulation costs. A promising alternative that is particularly attractive for the high temperatures characteristic of paraboloidal dishes and the extensive piping associated with large collector fields is the concept of thermochemical energy transport. Estimates of the performance and economics of four sensible and two thermochemical transport systems for a dish collector field are compared at four delivery temperatures ranging from 400 to 815°C. The sensible working fluids are Syltherm 800, NaK, Li-Na- K carbonate salt eutec tic, and steam. The thermochemical systems are carbon dioxide reforming of methane and dissociation of sulfur trioxide. On the basis of levelized energy cost, there is no clear choice between sensible and thermochemical energy transport at 400°C. At higher output temperatures, thermochemical transport is more cost-effective and is the only viable choice at temperatures above -700°C. The thermochemical system based on the carbon-dioxide reforming of methane has the best performance and lowest costs at temperatures >400°C and appears closest to meeting the DOE Solar Thermal Technology Program long-term IPH goal of 3 ¢/kWhth (9 $/MBtuth) LEC.

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