Off-design analysis of ORC and CO2 power production cycles for low-temperature surplus heat recovery

Electricity production with an organic Rankine cycle and a transcritical Rankine cycle is investigated in this paper with R-123 and CO2 as working fluids, respectively. The analysis focuses on the off-design behavior with different control strategies to show some of the occurring difficulties. It was found that both cycles need an advanced control strategy to avoid non-feasible operation (R-123) or significant losses in work output (CO2). A challenge for the advanced control is the required large change in expander speed, which can lead to compatibility problems with the grid.