Methods and systems are disclosed to convert low temperature thermal energy to electricity. An example apparatus disclosed herein includes an electrical generating unit to receive heat energy to produce electricity, a concentrator including a heat engine, a liquid piston operatively coupled to the heat engine, and a heat pump operatively coupled to the liquid piston, the heat engine adapted to collect thermal energy, and the heat pump operatively coupled to the electrical generating unit to provide heat to the electrical generating unit. The example apparatus disclosed herein also includes a heat engine floating piston disposed in the heat engine, a heat pump floating piston disposed in the heat pump, and wherein the heat engine floating piston and the heat pump floating piston oscillate.