BSC Insight: Reliant on the weather? A review of weather dependent generation in GB

The British have always felt a strong connection to the weather. A typical conversation in any part of the country will generally include a reference to either how: hot, cold, rainy, windy, sunny or grey the weather is! In the last 10 years, the weather has also begun to fuel our day-to-day lives as more weather dependent generation has been used in the fuel mix. This is making Britain greener and helping the nation reach its goal of NetZero by 2050. In this Insight Emma Tribe, our Analysis and Insight Delivery Lead, shows how Great Britain’s fuel mix is connected to the weather more than ever through an increase in weather dependent generation.

What is weather dependent generation?

The types of weather dependent generation considered in this article are:

• The electricity generators that are registered as Wind Balancing Mechanism Units,
• Embedded wind turbines that are not registered as Balancing Mechanism Units, and
• Embedded solar panels that are not registered as Balancing Mechanism Units.

A Balancing Mechanism Unit is a collection of electricity meters aggregated together for the purposes of Balancing and Settlement. The Balancing Mechanism Units that are registered as wind contain only electricity meters for wind turbines, an example of this would be an offshore wind farm. Some solar panels and wind turbines are not part of large generation farms, instead they are aggregated with homes or businesses to form part of a larger Balancing Mechanism Unit.

The volumes of electricity from Wind Balancing Mechanism Units are provided by operational electricity metering. The volumes of electricity from embedded wind and solar are estimates provided by National Grid ESO.

Why is hydropower not weather dependent?

There is no doubt that GB has an abundance of rain; however, hydropower is not included in our consideration of weather dependent generation. This is because we already have a way to store and regulate the volume of electricity that is generated by rain in our lakes and rivers. Whereas the energy from wind and solar need to be converted to electricity immediately. This means that we can use electricity created by hydropower at anytime meaning it isn’t weather dependent, but if the wind isn’t blowing or the sun isn’t shining GB is currently unable to be powered by solar or wind energy.

Ten years of weather dependent generation

In 10 years weather dependent generation has seen a dramatic increase. In 2010, 2.97% of the fuel mix came from weather dependent generation. In 2020, we saw the fuel mix proportion from weather dependent sources increase ten times to 29.87%. The increase has been made possible by the installation of more solar panels and wind turbines. Schemes such as the feed in tariff and contracts for difference have made these technologies a more attractive investment. In 2021 so far (up to 15 March 2021) it has been 26.48%. 

The gap between fossil fuel and weather dependent generation is closing. In 2020, fossil fuels were still the main form of electricity generation at 35.79% of the fuel mix, or a total of 99TWh generated. The total volume of electricity generated by weather dependent generation was 83TWh in 2020, making it the second biggest source of electricity generation. If we compare that to 2019, there was 120TWh of electricity generated from gas and 70TWh from wind and solar. We see that in only one year, the difference between the generation output of gas compared to wind and solar dropped from 44TWh to 12TWh.

If current trends continue, it is likely that within 2021 or 2022, the volume of electricity generated in Great Britain by wind and solar power will overtake the volume generated by gas.

As unpredictable as the weather

What makes the weather so interesting is that it is always changing, often unpredictably. Many of us will have planned a barbeque, only to cancel it after a sudden downpour of rain, or gone for a stroll on a cloudy day and gotten burnt because the sun came out. This unpredictability also affects the electricity grid. Because solar and wind generation are difficult to predict and cannot be stored, the fuel mix has extreme highs and lows for weather dependent generation.

Unpredictably high

In 2020, the maximum output from weather dependent generation in a half hour was 12,224MWh on 12 March 2020 in Settlement Period 24 (between 11:30 and 12:00). During this period, registered wind Balancing Mechanism Units generated 6,284MWh, embedded solar generated 3,440MWh and embedded wind generated 2,500MWh. Overall weather dependent generation contributed to 56.57% of the fuel mix.

Unpredictably low

The minimum output was 212MWh on 17 June 2020 during Settlement Period 4 (between 01:30 and 02:00 in the morning), this represented 1.95% of the fuel mix. Wind Balancing Mechanism Units generated 93MWh, embedded wind generated 119MWh and since it was the middle of the night, embedded solar generated no energy.

In 2020 there were 1,750 Settlement Periods (9.96% of the year) where less than 10% of the electricity fuel mix was from wind and solar. There was also 1,837 Settlement Periods (10.46% of the year) where more than 50% of the electricity fuel mix was from wind and solar.

The consequences of unpredictability

Because the contribution of weather dependent generation to the fuel mix can vary, the rest of the fuel mix also needs to be flexible. Electricity generation from gas, biomass and coal power stations in Great Britain are able to change by increasing or decreasing their output. Electricity can be imported or exported over the interconnectors. Pumped Storage and battery storage can charge and discharge when required.

The future of weather dependent generation

Great Britain is transitioning towards net zero emissions by 2050. A net zero electricity fuel mix enables other sectors of the British economy, such as transport, to reduce emissions by electrifying.

Electricity generation from wind and solar generation supports a lower carbon fuel mix while the sun is shining and the wind is blowing. Excess wind and solar generation in Great Britain can also be exported to our European neighbors through interconnectors and likewise we can import excess wind and solar.

To have a net zero fuel mix all of the time, flexible, net zero alternatives to weather dependent electricity still need to be developed and scaled-up. Elexon are supporting this transition by progressing modifications to the electricity balancing and settlement arrangements that will facilitate net zero and encourage innovation.

Note on data sources:

We have combined two datasets for the analysis given in this article. The latest generation by fuel type data can be downloaded from BMRS. We also publish historical generation by fuel type data going back to 2008 on the Elexon Portal.

National Grid ESO’s data portal provides the estimates for embedded solar and embedded wind generation.