Or recovery of waste energy.
In reality there is no such thing as free energy but there is ways to recover waste energy that you are normally throwing out.
One such method is to reclaim waste energy from your air conditioner. So far in Canada this energy is being wasted and is just dumped outside your home.
This waste energy is in the form of heat which could be recovered in your hot water tank and or swimming pool.
There is manufacturers that make heat recovery units that can be adapted to your air conditioning
One such manufacturer is Trevor-Martin Corporation, it produces HEAT RECOVERY UNIT FOR DOMESTIC HOT WATER FROM RESIDENTIAL HVAC SYSTEMS.
DESCRIPTION: The Aquefier Waste Heat Water Heater is connected to a water heater and an air conditioner, heat pump, or refrigeration compressor. A small pump circulates cool water from the bottom of the water heater tank through the heat exchanger. Hot refrigerant gas from the compressor is routed through the gas side of the heat exchanger. An optional adjustable heat activated valve that regulates the water flow rate to maintain the desired temperature at 120 or higher can be added; It is particularly useful in higher efficiency systems with lower hot gas temperatures. The heated water is returned to the water tank for domestic use. The AQUEFIER heat recovery unit also reduces the compressor load, which increases compressor efficiency and extends compressor life. Reclaiming waste heat from high compressor discharge temperatures is a proven principle of energy recycling that produces abundant hot water safely and economically.