Distributed Energy Resources (DERs) are small-scale units of power generation or storage that are situated closer to the end-users. Let's analyze each option:

• Battery storage: These store energy and can be deployed within the distribution network or at the consumer end, making them DERs.

• Biomass generators: These can be small-scale and located near the biomass source, making them suitable for distributed generation.

• Fuel cells: Similar to biomass generators, fuel cells can be deployed in a decentralized manner, qualifying as DERs.

• Rooftop solar photovoltaic units: These are a classic example of DERs, generating power at the point of consumption.

Therefore, all four options are considered Distributed Energy Resources.