Consider the following: 1. Battery storage 2. Biomass generators 3. Fuel cells 4. Rooftop solar photovoltaic units. How many of the above are considered "Distributed Energy Resources"?

All four are considered Distributed Energy Resources (DERs). DERs are small-scale energy resources usually situated near sites of electricity use, such as rooftop solar panels and battery storage. The category includes battery storage systems, biomass generators, fuel cells, rooftop solar photovoltaic units, small wind turbines, combined heat and power systems, and electric vehicles with vehicle-to-grid capability. They contrast with centralized energy generation and can be connected to the local distribution grid.