Evaluating alternatives for integrating distributed DC generation with AC power systems

Distributed generation generally means on site electric power generation devices such as photovoltaics or fuel cells that are installed at the customer end of the electric power system. One complication is that the photovoltaic panel and the fuel cell generate direct current (DC) while the electric power system and thus existing end use equipment has been designed for alternating current (AC). This paper suggests a method which converts all AC power from the electric utility to DC with rectifiers at the distribution substation or at the point of building entry and then interfaces the DC distributed generation from the photovoltaics or fuel cells directly with the rectified DC from the electric power system. Some of the equipment in the house such as light bulbs and electric heating in stoves and clothes dryers can operate indifferently on DC. Equipment such as induction motors in refrigerators and air conditioners can operate from small dedicated nonsynchronous chord mounted DC to AC inverters until replaced with DC compatible equipment. Electronics such as televisions and computers can also operate from chord mounted DC to AC inverters until replaced by DC compatible equipment. Ultimately, the entire electric utility system should be converted from a transformer based multiple voltage AC system to a more efficient solid state converter based multiple voltage DC system. This type of system would not only be fundamentally more efficient. It would also be directly compatible with distributed DC generation.