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"?

1. Battery storage — Yes. Distributed Energy Resources (DERs) include decentralized energy storage systems connected near the point of use.
2. Biomass generators — Yes. Small/local biomass-based generation units are a standard form of distributed generation, hence DER.
3. Fuel cells — Yes. Fuel cells can generate electricity at or near the consumer end and are recognized as DER technologies.
4. Rooftop solar photovoltaic units — Yes. Rooftop solar is a classic example of distributed generation installed close to load centres.

Therefore, all four are Distributed Energy Resources.