Power supply system

1. A power supply system, comprising:

a cogeneration unit equipped with;

an internal combustion engine,

a generator driven by the engine to generate power to be supplied to a power destination,

a hot water tank for supplying hot water to a hot water destination by selectively using heat exhausted from the engine and an electric heater to heat the hot water, and

a cogeneration unit (CU) controller for controlling the operation of the cogeneration unit;

a natural energy generation unit that generates power with natural energy;

a power supply unit, including a power supply unit (PSU) controller, that receives the power generated by the generator and the natural energy generation unit to supply the received power to the power destination;

a connecting bus that electrically connects the cogeneration unit, the natural energy generation unit and the power supply unit;

a voltage detector that detects voltage of the power flowing through the connecting bus;

wherein the power supply unit controller controls operation of the electric heater based on the detected connecting bus power voltage.

2. The system according to claim 1 , further including:

a storage unit that is connected to the connecting bus and stores the power not supplied to the power destination;

and the power supply unit controller controls operation of the storage unit based on the detected connecting bus power voltage.

3. The system according to claim 2 , wherein the power supply unit controller controls the operation of the storage unit to discharge the stored power when the detected connecting bus power voltage is equal to or less than a predetermined voltage.

4. The system according to claim 1 , further including:

a storage unit that is connected to the connecting bus and stores the power not supplied to the power destination; and

a detector that detects voltage of the power stored in the storage unit,

and the power supply unit controller controls the operation of the electric heater based on the detected stored power voltage.

5. The system according to claim 4 , wherein the power supply unit controller controls the operation of the electric heater to on when the detected connecting bus power voltage exceeds a predetermined first voltage and the detected stored power voltage exceeds a predetermined second voltage.

6. The system according to claim 5 , wherein the power supply unit controller controls the operation of the electric heater to on when the detected connecting bus power voltage exceeds the predetermined first voltage, but is equal to or greater than a predetermined third voltage, and the detected stored power voltage exceeds the predetermined second voltage.

7. The system according to claim 4 , wherein the connecting bus is connected to a commercial power source and the power supply unit controller determines whether or not to receive power from the commercial power source based on the detected connecting bus voltage and the detected stored power voltage.

8. The system according to claim 7 , wherein the power supply unit controller determines to receive the power from the commercial power source when the detected connecting bus power voltage is equal to or less than a predetermined first voltage and the detected stored power voltage is equal to or less than a predetermined second voltage.

9. The system according to claim 1 , wherein the natural energy generation unit comprises a photovoltaic generator.

10. The system according to claim 1 , wherein the cogeneration unit has a solar heater that heats the water with solar heat.

11. The system according to claim 1 , wherein the PSU controller is communicatively coupled with the CU controller and interfaces with the CU controller to control the operation of the electric heater.