Power/energy: Connecting renewable power sources into the system: Windmills, fuel cells, and photovoltaics may serve existing grids, but first many technical, legal, and economic issues must be addressed

These alternative power sources, known as distributed storage and generation sources (DSG) consist of an energy converter to transform sun, wind, or chemical energy into electricity, a power conditioner to convert DC to AC, relays, breakers and fuses for equipment protection and personnel safety, and appropriate load-metering equipment for billing customers. Some of the technological problems of interconnecting many DSGs to a power grid are addressed together with the trend in using digital techniques for advanced protective devices.