Solar driven micro-ORC system assessment for residential application

The purpose of this study is to estimate the electricity production obtainable by coupling an existing kWsize recuperated Organic Rankine Cycle (ORC) prototype with a commercial solar thermal collector to reduce the yearly electricity purchased by a single-family user. A detailed semi-empirical steady-state model, validated against experimental data, is employed for the power plant simulation. The optimal sizes of both the collector surface and the storage tanks were assessed considering that a solar collector surface larger than 32.25 m2 would lead the micro-ORC working in off-design conditions; while storage volumes higher than 6000 l become too large to be completely exploited. Then, different low global warming potential fluids and blends were simulated for comparison with HFC-134a, the reference fluid for low-temperature ORC. Results show that the integrated system working with R134a can cover approximately 39% of the yearly electricity demand, corresponding to more than 1150 kWh. The replacement of R134a with the alternative fluids results in a penalization in the output electric power, related to thermodynamic properties such as density, liquid viscosity, and latent heat. Indeed, with R1234yf barely 16% (466 kWh) of the yearly electricity demand is covered; whilst the blend R513A allows to reach only 17.5% (525 kWh).