Performance-Cost Analysis of Solar Combined Heat and Power Systems

Solar combined heat and power (CHP) systems can compete or exceed solar photovoltaics (PV) — which is often used as the benchmark in terms of efficiency, performance, and cost — in a range of distributed generation applications, and across a range of specific technology platforms. A common metric to evaluate the cost of photovoltaics is a cost per peak power output or “dollars per watt” metric. For the purpose of comparison, we develop a new analytic methodology to evaluate the cost of the electricity generated from a solar CHP system. The electricity generation and thermal subsystems of a solar CHP system are energetically intertwined, yet by comparing thermal and electrical outputs a sensible cost division can be determined. This method is then used to compare the cost of stationary PV and solar Rankine CHP systems with tracking and stationary collectors. The capacity factors of electricity generation for each system is found in simulation using NREL TMY3 climatic data for 1020 sites in the United States. The solar Rankine system with stationary collectors outperforms the PV system in warmer and sunnier climates relative to its rated “dollar per watt” output, while PV outperforms solar Rankine in cooler climates. With tracking concentrating collectors, the solar Rankine system outperforms PV systems in the vast majority of US sites at an estimated cost of $4/W and a collector high temperature of 250°C. In conclusion, a PV system and solar Rankine CHP system, sized equally in terms of peak power output, will produce comparable amounts of electricity (+/− 10% on average), however the solar Rankine CHP system will additionally provide 4 to 6 units of useful heat energy for every one unit of electricity generated.