Harnessing renewable energy with demand flexibility

As the UK’s energy system moves towards a lower carbon future, the take up of renewable energy sources, such as wind and solar, is inevitable. In 2023, renewable generation met 33% of the UK’s total electricity demand1, and this is expected to increase to around 70% by 2030.2

When renewables make up a large share of electricity supply, a degree of intermittency is introduced into the energy system due to the weather dependent nature of renewable generation sources. Put simply, the sun isn’t always shining, and the wind isn’t always blowing, so the of amount of electricity supplied by wind or solar farms can vary. To make sure everything runs smoothly, it’s important that the supply of energy meets the demand from households, businesses, and industry at any given time, but this can become more challenging with intermittent renewable energy supply.

Centrica and British Gas are well positioned to play a key role in making this energy transition as an integrated energy company operating across the value chain. From creating renewable energy in wind and solar farms, providing green tech at home - like heat pumps and EV chargers, to offering services like PeakSave that help us and our customers to energise a greener, fairer future.

What does intermittency of renewable energy look like?

Solar generation data from the ESO data portal3 and system demand data from Elexon BMRS4

This chart shows the average solar generation and average electricity demand over weekdays in summer 2023. Clearly, the demand for electricity doesn’t line up with the supply of electricity from solar generation, but why is that? Unsurprisingly, the solar generation peaks in the middle of the day, when it’s the sunniest, and stops overnight, when the sun isn’t shining.

The electricity demand shape is a little bit more complicated, let’s break it down:

  • (00:00 – 06:00) Electricity demand is lowest in the early hours of the morning, when most people are in bed.
  • (06:00 – 09:00) Electricity demand increases in the morning as people get ready for work and businesses open.
  • (09:00 – 16:00) Electricity demand dips throughout the middle of the day whilst people are at work.
  • (16:00 – 20:00) Electricity demand peaks in the evening when people get in from work and switch on all their appliances.
  • (20:00 – 00:00) Electricity demand decreases later in the evening as people start switching-off.

How can we deal with intermittency of renewable energy?

The Electricity System Operator (ESO) are responsible for ensuring energy supply meets demand, and they do a really great job at this. The ESO have a wide range of tools that they can use to handle energy imbalance, ranging from physical energy storage to designated balancing markets and ancillary services, but this can all get complicated very quickly. Learn more about the ESO here.

Let’s simplify things and consider two specific scenarios:

  • Excess supply - In a scenario where energy supply exceeds demand, which might occur in the middle of the day when there’s lower demand but lots of supply from wind or solar farms, the ESO might ask the operators of these wind or solar farms to reduce their output. This is often referred to as curtailment and although it does rebalance supply and demand, it isn’t ideal because we don’t want to waste any of that cheap, green electricity.
  • Excess demand - In the opposite scenario where energy demand exceeds supply, which might occur throughout high stress periods during the peak evening hours when everyone arrives home from work and the sun isn’t really shining anymore, the ESO might source some additional energy from flexible generation assets, like Combined Cycle Gas Turbines (CCGTs), by instructing them to turn up their energy production. Although supply and demand are rebalanced, the electricity from CCGTs isn’t as green or cheap as that from renewable generation sources, like wind or solar, which can increase the cost and carbon intensity of electricity for customers.

So, is there something that households could do to help the ESO mitigate intermittency, handle stress on the system, whilst also better utilising electricity from renewable sources? That’s where demand flexibility and PeakSave Green Flex comes in. 

Demand Flexibility and PeakSave 

With PeakSave, our customers are rewarded for shifting their electricity use away from peak hours, when system stress and carbon intensity are typically higher, into the hours when there’s less demand.

So, with PeakSave Sundays, our PeakSavers are rewarded with half-price electricity between 11am and 4pm every Sunday.

And with PeakSave Green Flex, we’re taking another new step to encourage our PeakSavers to move their energy use to when there’s more renewable electricity available - so if it’s going to be sunny, windy or both. We invite PeakSavers to take part in advance of each event, and they can choose to take part or not. Each event will last one or two hours and, as with PeakSave Sundays, PeakSavers are rewarded with half-price electricity.

You may be wondering how we’re able to notify our PeakSavers of PeakSave Green Flex events ahead of time. Well, we’ve a team of energy experts who have developed algorithms that monitor forecasts from National Grid ESO combined with Centrica's own GB generation forecasts and carbon intensity reports to identify periods of high renewable generation in advance. The timings of PeakSave Green Flex events will be flexible, but by using generation forecasts, we’re able to let you know about events ahead of time so you can prepare. 

The concept behind PeakSave Sundays and PeakSave Green Flex, demand flexibility is becoming increasingly relevant as households adopt net-zero technologies, like heat pumps, smart heating, or electric vehicles. These technologies allow households to shift their consumption more dynamically and be rewarded for better energy use. You can find out more about our net-zero technologies here.

How to take part in PeakSave Green Flex

To earn money with PeakSave Green Flex you’ll need to:

  • Be a British Gas electricity customer
  • Have a smart electricity meter – your smart meter will tell us how much you used, and we’ll work out your credit
  • Join PeakSave

We expect there to be two or three Green Flex events per month and each event will last between one and two hours. We’ll let you know when an event is happening ahead of time. You’ll need to opt-in to each event to take part.  

Find out more about PeakSave Green Flex and how to take part here.  


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Additional information

  1. Global Electricity Review 2024 | Ember (ember-climate.org)

  2. Energy and emissions projections: 2021 to 2040 - GOV.UK (www.gov.uk)

  3. Historic generation mix and carbon intensity | ESO (nationalgrideso.com)

  4. Demand outturn | Insights Solution (elexon.co.uk)