A Tale of Two Suppliers

One of the biggest problems with the annualised system of accounting is that it's a very crude measure and therefore fails to capture significant differences between suppliers; even among suppliers who are '100% renewable' there can be big differences in the character and quality of electricity that consumers receive.

In this blog we dig into the differences in the electricity delivered by two of the UK's suppliers, both of whom are marketed as 100% renewable. Both are medium-sized suppliers, serving a few terawatt-hours per year (equivalent to powering several hundred thousand homes).

Seasonal stability

The charts below show the total electricity that each supplier sells to its customers (dark purple), and the total electricity they buy from wind, solar, and hydro (green, yellow, and blue).

Supplier A has a good match between consumption and supply across all seasons: although they have less renewable supply in the second half of the year, they manage to frequently match all consumption throughout the year.

Supplier B, by contrast, has much less seasonal stability: in the last four months of the year their consumption is elevated and their supply depressed, and renewables never once fully satisfy consumption.

Both suppliers are marketed as '100% renewable'. But the pictures changes when you look at the portfolios on an hourly basis. Customers of Supplier A get 80% of their electricity from renewables, whereas customers of Supplier B get 60% of their electricity from renewables.

Supplier A commonly matches all consumption to renewables throughout the year

Supplier B doesn't ever match consumption to renewables in the last four months of the year

Diversification across technologies

What causes this variance? In large part, it's down to the types of technologies.

Supplier A buys a lot of renewables from solar farms - a quarter of their total - and the peak of solar output each day nicely aligns with the peak in consumption. Having a portfolio that is diversified across technologies is partly how Supplier A satisfies so much consumption with renewables.

Supplier B relies almost entirely on wind - 95% of their total - and as a result they are more exposed at times of peak consumption, and more exposed to the inter-day variation in wind generation. Both factors make it harder for Supplier B to regularly match consumption with renewables.

Solar generators help Supplier A to regularly match their daily peak consumption

Supplier B has less support from solar and is more exposed to volatility in wind output

Diversification across generators

Another factor is the number of generators involved.

Both suppliers buy renewables from about 180 generators, and both rely on a small number of really big generators to provide a substantial chunk of their supply. However, in this regard too, Supplier A is more diversified.

Supplier A relies on its largest generator for less than 10% of its volume, while Supplier B depends on its largest generator for more than 60%. This makes Supplier B vulnerable to output fluctuations from this single generator, causing significant portfolio-level variations that make it harder to consistently match consumption with renewables.

Supplier A buys renewables from a diverse range of generators

Additionally, the five biggest generators at Supplier A represent two technologies—wind & hydro—whereas Supplier B relies exclusively on wind.

Supplier B is strongly dependent on the output from just one generator

Same branding, different reality

Despite both suppliers marketing themselves as "100% renewable," the reality is starkly different. Supplier A customers receive 20% of their electricity from non-renewable sources, while Supplier B customers receive 40%—double the amount. Current regulations allow this dramatic variation between identically branded suppliers.

We need more transparency

Consumers need more insights into their renewable energy supply to make informed choices. Discerning customers are increasingly questioning the substance of current annual claims. If, as seems likely, carbon accounting rules are updated to require temporal matching, customers of Supplier B would be severely disadvantaged.

Leading suppliers would also benefit from more transparency: a market that clearly recognised their efforts would incentivise providers like Supplier A to further develop their careful and committed procurement of renewables.

Follow Matched

Matched is helping improve transparency by using public data to build verifiable ratings of renewable energy suppliers. We'll be making our first public data release in the autumn.