Fig nbsp xA Theoretical efficiency as function of
5.3. Solar thermal system
The work on cost-effective, medium temperature flat plate solar thermal collectors described in Ref.  indicates that Pyridone 6 for larger collectors (e.g. 3 × 3 m area) are more efficient. For operating temperatures of 130 °C (G = 800 W/m2), efficiencies of 60% are possible. The overall mechanical efficiency (sun to shaft) of a collector combined with an atmospheric steam engine (operating temperature TEv = 100 °C) can then be estimated as 9–9.5%. This would probably give a sun-to-wire efficiency of approximately 8%. It should be noted chloroplasts the ORC engine reported in Ref.  had an engine-only efficiency of 7.98% for an operating temperature of 120 °C.
Overall efficiencies of the solar thermal system would be lower than those of e.g. PV systems. The atmospheric engine is however a simple machine, so that the overall cost-effectiveness needs to be considered in the next development step.