Distributed Energy Resources (DERs)

Learning objectives

By the end of this lesson you should be able to:

Understand what Distributed Energy Resources (DERs) are.
Recognise the different technologies that make up DERs.
Explain how DERs differ from traditional centralised electricity systems.
Understand the opportunities and challenges created by millions of distributed devices.
Appreciate why coordination is becoming more important than generation itself.
Recognise why DERs should be viewed as active system resources rather than simply small generators.

Introduction

For most of the twentieth century, electricity systems were relatively simple.

Large power stations generated electricity.

High-voltage transmission networks transported it across the country.

Distribution networks delivered it to consumers.

Power flowed almost entirely in one direction.

Today, this picture is rapidly changing.

Homes, businesses and communities are increasingly generating, storing and managing their own electricity.

Millions of small devices—including solar panels, batteries, electric vehicles and heat pumps—are becoming active participants in the electricity system.

Collectively, these technologies are known as Distributed Energy Resources (DERs).

Rather than replacing the electricity grid, DERs fundamentally change how it operates.

What are Distributed Energy Resources?

Distributed Energy Resources are relatively small electricity resources connected close to where electricity is consumed.

Examples include:

Rooftop solar panels.
Home battery systems.
Electric vehicles.
Heat pumps.
Smart appliances.
Small wind turbines.
Commercial battery systems.
Community energy projects.
Small combined heat and power (CHP) plants.

Unlike traditional power stations, DERs are distributed throughout towns, cities and communities.

Centralised versus distributed systems

Traditional electricity systems were largely centralised.

A relatively small number of large generators supplied millions of consumers.

The system looked something like this:

Large Power Station

↓

Transmission Network

↓

Distribution Network

↓

Consumer

Modern electricity systems are increasingly distributed.

Consumers may now:

Generate electricity.
Store electricity.
Export electricity.
Provide flexibility.
Respond to market signals.

Power increasingly flows in both directions.

Consumers become prosumers—both producers and consumers of electricity.

Bidirectional power flows

Historically, electricity almost always flowed from generators towards consumers.

Today this assumption is no longer valid.

Consider a sunny summer afternoon.

Many homes with rooftop solar generate more electricity than they consume.

Instead of importing electricity from the grid, they export surplus electricity back into the local network.

Later that evening the same homes may import electricity again.

Power flows therefore change direction throughout the day.

This fundamentally changes how distribution networks must be designed and operated.

Examples of DERs working together

Imagine a typical suburban neighbourhood.

Each home may contain:

Rooftop solar panels.
A home battery.
An electric vehicle.
A heat pump.
Smart appliances.

Individually, each device is relatively small.

Collectively, thousands of these devices represent a substantial electricity resource.

If coordinated effectively, they can support the wider electricity system while continuing to meet consumers' needs.

Virtual Power Plants (VPPs)

One way of coordinating DERs is through a Virtual Power Plant (VPP).

A Virtual Power Plant combines many small distributed resources so that they behave like a single large power station.

For example:

Instead of controlling:

100 MW gas turbine,

an operator may coordinate:

20,000 home batteries.
50,000 electric vehicles.
30,000 heat pumps.

Together they provide the same overall flexibility while remaining physically distributed.

The "power plant" exists in software rather than at a single physical location.

The advantages of DERs

Distributed Energy Resources offer several important benefits.

Renewable integration

Rooftop solar allows renewable electricity to be generated close to where it is consumed.

Reduced transmission requirements

Locally generated electricity may reduce the amount of power that must be transported over long distances.

Improved resilience

Many small resources can be more resilient than relying upon a few very large generators.

The failure of one rooftop solar system has little impact on the wider system.

Consumer participation

Consumers gain greater control over:

Electricity costs.
Energy use.
Environmental impact.

Flexibility

DERs provide valuable services including:

Demand response.
Energy storage.
Peak demand reduction.
Frequency response.

New challenges

The rapid growth of DERs also creates new engineering challenges.

Scale

Electricity systems were historically designed around hundreds of generators.

Future systems may involve tens of millions of controllable devices.

Coordinating them becomes a major challenge.

Visibility

System operators often have limited visibility of low-voltage distribution networks.

Without improved monitoring, understanding local network conditions becomes increasingly difficult.

Communication

Millions of devices require secure, reliable communication.

Communication failures must not compromise system reliability.

Cybersecurity

As electricity systems become increasingly digital, protecting them from cyber attacks becomes increasingly important.

Coordination

If millions of devices all respond to the same signal simultaneously, they may unintentionally create new problems.

Effective coordination therefore becomes essential.

From passive networks to active networks

Historically, distribution networks were largely passive.

Their role was simply to transport electricity from transmission networks to consumers.

Today distribution networks are becoming active systems.

Operators increasingly manage:

Local generation.
Flexible demand.
Batteries.
Electric vehicle charging.
Network congestion.
Voltage control.

The distribution network is no longer simply infrastructure.

It is becoming an active participant in electricity system operation.

The role of digital technology

DERs are made possible by advances in digital technology.

These include:

Smart meters.
Sensors.
Communications networks.
Cloud computing.
Artificial intelligence.
Advanced optimisation.
Real-time control systems.

Without these technologies, coordinating millions of distributed resources would be practically impossible.

The future electricity system is therefore not simply an electrical network.

It is increasingly a cyber-physical system, where digital information and physical electricity flows continuously interact.

Local versus global decisions

An important question arises.

Should every small device optimise only its own behaviour?

Or should it consider the wider electricity system?

For example:

Charging an electric vehicle may be inexpensive from a wholesale energy perspective.

However, if many neighbours begin charging simultaneously, the local distribution network may become congested.

This illustrates a recurring theme throughout this course.

Engineering decisions must consider both:

The physical network.
The wider electricity system.

Neither can be considered in isolation.

Why coordination matters

Imagine one million electric vehicles.

If every vehicle begins charging immediately after people arrive home, electricity demand increases sharply.

Now imagine those same vehicles coordinate intelligently.

Some charge immediately.

Others charge later.

Some wait until renewable generation increases.

The total amount of electricity consumed remains almost identical.

The impact on the electricity system is dramatically different.

The future challenge is therefore not simply connecting more devices.

It is coordinating them intelligently.

Why £/MWh is not enough

Suppose two neighbourhoods each generate:

10 GWh of rooftop solar electricity each year.

The first neighbourhood exports all surplus generation immediately.

The second neighbourhood combines:

Solar panels.
Batteries.
Flexible EV charging.
Smart heat pumps.

Although both generate the same amount of electricity, the second provides much greater value to the electricity system.

It:

Reduces peak demand.
Supports local voltage.
Relieves congestion.
Provides flexibility.
Increases renewable utilisation.

The additional value comes not from producing more energy, but from coordinating resources more effectively.

DERs as system resources

The most important change brought about by DERs is conceptual.

Historically, households were viewed as consumers.

Increasingly, households become providers of valuable system services.

Collectively, DERs can contribute:

Energy.
Capacity.
Flexibility.
Storage.
Frequency response.
Voltage support.
Congestion management.
Reserves.

The distinction between generators and consumers therefore becomes increasingly blurred.

Instead, every connected device becomes a potential participant in maintaining the electricity system.

A key insight

Distributed Energy Resources represent one of the most significant transformations in the history of electricity systems.

The challenge is no longer simply generating enough electricity.

It is coordinating millions of small, intelligent resources so that they operate as one reliable, efficient and secure system.

In the electricity system of the future, intelligence increasingly becomes as valuable as infrastructure.

Key takeaways

Distributed Energy Resources (DERs) are small electricity resources connected close to consumers.
Examples include rooftop solar, batteries, electric vehicles, heat pumps and smart appliances.
DERs transform consumers into active participants in the electricity system.
Virtual Power Plants coordinate many small resources so they behave like large power stations.
DERs improve flexibility, renewable integration and resilience but introduce new challenges in coordination, communication and cybersecurity.
Distribution networks are evolving from passive infrastructure into actively managed systems.
The value of DERs comes from the combination of technologies and their coordination, not simply the amount of electricity they generate.
Future electricity systems will increasingly depend on intelligent coordination of millions of distributed devices.

Looking ahead

Throughout this module we have explored the major technologies that make up modern electricity systems.

The final lesson brings these ideas together by comparing these technologies as system resources, demonstrating why technologies cannot be fairly compared using only their cost per megawatt-hour (£/MWh), but instead must be evaluated according to when, where and how reliably they contribute to the electricity system.