In this paper, we examine the electrical power-generation potential of a
domestic-scale solar combined heating and power (S-CHP) system featuring
an organic Rankine cycle (ORC) engine and a 15-m2
solar-thermal collector
array. The system is simulated with a range of organic working fluids and
its performance is optimised for operation in the UK climate. The findings
are applicable to similar geographical locations with significant cloud coverage,
a low solar resource and limited installation areas. A key feature of the
system’s design is the implementation of fixed fluid flow-rates during operation
in order to avoid penalties in the performance of components suffered at
part-load. Steady operation under varying solar irradiance conditions is provided
by way of a working-fluid buffer vessel at the evaporator outlet, which
is maintained at the evaporation temperature and pressure of the ORC. By
incorporating a two-stage solar collector/evaporator configuration, a maximum
net annual electrical work output of 1070 kWh yr−1
(continuous average
power of 122 W) and a solar-to-electrical efficiency of 6.3% is reported with
HFC-245ca as the working fluid at an optimal evaporation temperature of
126 ◦C (corresponding to an evaporation pressure of 16.2 bar). This is equivalent
to ∼ 32% of the electricity demand of a typical/average UK home, and
represents an improvement of more than 50% over a recent effort by the same
authors based on an earlier S-CHP system configuration and HFC-245fa as
the working fluid [1]. A performance and simple cost comparison with standalone,
side-by-side PV and solar-thermal heating systems is presented.