I've been looking into "green energy" tariffs recently. tl;dr: mostly, they're equivalent to voting Green in a safe Labour seat. A protest vote, with minimal immediate impact.
This was prompted by a friend expressing skepticism about them, words to the effect of "just rearranging slices in the pie chart, without changing any of the sizes".
You probably know that most electricity suppliers don't actually own power plants. Instead, they buy energy from power plants and then resell it to you, all via the National Grid. So how can they say they're supplying "green" energy, when all electricity basically goes into and comes out of the same bucket?
Two ways. One is for the reseller to have contracts directly with renewable energy generation companies. very few resellers actually do this, and the ones that do usually don't do it for 100% of the energy they sell.
The other way is to buy generic electricity on the wholesale market, and then also buy an equivalent number of "certificates" from renewable generation companies, which they can use to claim that their slice of the energy pie came from the renewable section.
The certificates are called "REGO certificates", you can read about them here https://www.which.co.uk/news/2019/09/how-green-is-your-energy-tariff/ as well as see which "green" suppliers use them, vs which ones buy directly from generators.
OK but is this all a bad thing though? -- That's what I asked myself. And it all depends on what the relative percentages are: if the % of consumers that want a green tariff is less than the % of energy generated that's green (about 30-40%), then you'd expect the demand for REGO certs to be less than the supply, and so the price would be zero.
Finding out what percentage of consumers (commercial and residential) are opting for green tariffs is very hard. But finding out the price of REGOs is easy, and sadly the answer is almost zero -- about 50p per MWH, so probably less than 1% of the cost of your electricity.
So that means far fewer REGO certs are bought than are issued, so there is effectively no market pressure being exerted as a result. When you opt for a green tariff, no extra money goes towards renewable energy companies, and none is diverted away from fossil-fuel plants.
So it is a protest vote.
But look, a protest vote doesn't have zero value, and if enough people do it, then eventually things can change.
Alternatively you can switch providers to one that actually does have a direct commercial link to renewable generation companies. But they do tend to be more expensive!
I'm certainly going to look into it.