A system for power generation includes a boiler configured to receive heat from an external source and a liquid stream and to generate a vapor stream. The liquid stream comprises a mixture of at least two liquids. The system also includes an expander configured to receive the vapor stream and to generate power and an expanded stream. A condenser is configured to receive the expanded stream and to generate the liquid stream. The system further includes a supply system coupled to the boiler or the condenser and configured to control relative concentration of the two liquids in the liquid stream.