The two types of electric power used for hot water heaters are AC and DC. AC current from the mains permanently heats water to a preset temperature, which is 45degC. Further heating water is possible with the DC current generated by photovoltaic cell. Both currents heat water quickly and efficiently. Water heaters that use DC power have a thermostat for controlling the water temperature. To ensure that the water temperatures remain safe, however, AC power must be shut off once the temperature preset has been achieved.