DER (Distributed Energy Resources)

Definition

DER (Distributed Energy Resources) are small electricity generators and storage systems that work together with the traditional Electric Power System (EPS). They produce or store electricity close to where it is needed, while still staying connected to the main power grid. Examples include rooftop solar panels, small wind turbines, and batteries. In the overall power system, DER is the next evolution of EPS—it adds local energy resources without replacing the central grid.

The Problem That Led to It

EPS solved the problem of thousands of separate generators by centralising electricity generation into large power plants. However, as electricity demand grew and renewable energy became popular, relying only on distant power plants became less efficient. Long transmission lines caused energy losses, and a failure at a major power plant could affect many users. Instead of abandoning EPS, engineers brought back one useful idea from the old system—local electricity generation—but connected it to the central grid. This became DER.

What Problem It Solves

DER spreads electricity generation across many smaller locations. This:

• Reduces dependence on large power plants.
• Makes better use of renewable energy.
• Improves reliability because power can still be available locally if part of the grid has a problem.

What Happens If Not Used

The grid relies heavily on a few large power plants, increasing transmission losses and making large outages more likely if a major generator fails.

Easy Wording

DER means generating or storing electricity close to where people actually use it.

Layman Example

Imagine a city getting food from one huge supermarket. If it closes, everyone is affected. Now imagine many small grocery stores spread around the city. Even if one closes, people can still buy food nearby. DER works the same way for electricity.

Technical Example

Before DER

• Large power plant generates electricity.
• High-voltage transmission lines carry it long distances.
• Distribution lines deliver it to homes.

After DER

• Large power plant still supplies the grid.
• Rooftop solar panels generate electricity locally.
• A neighbourhood battery stores extra solar energy.
• Homes use nearby electricity first.
• The main grid supplies only the remaining demand.

Limitation

DER is a broad term—it tells us that power is generated or stored locally, but not what type of resource it is.

Solution

The next concept is DG (Distributed Generation) and DS (Distributed Storage). They divide DER into its two main categories:

• DG: Small systems that generate electricity (e.g., solar panels, wind turbines).
• DS: Small systems that store electricity (e.g., batteries).