In theory this demand drives up prices for the certificates which then goes to renewable energy producers?

I would strongly assume that them claiming 100% RES means they have bought so-called Guarantees of Origin (GoOs) [1]. You can only sell GoOs to the extent that you actually produce energy, so while the actual energy that eons customers receive could come from any given source, it is matched by production from RES (which in turn goes to customers who may or may not have an energy provider that provides renewable energy).

[1] https://en.wikipedia.org/wiki/Guarantee_of_origin#Production...

You don't believe there is enough renewablably-produced electricity to meet the demand for certificates? I suspect you might be over-estimating the demand for certificates!

Not demand for certificates but demand for electricity overall.

My understanding is that if you're producing through natural gas and someone else is producing through wind you can buy a certificate from them and then claim that your electricity is renewable.

The UK's energy mix is still 50+% gas, and I believe nuclear is not considered renewable... So there is a serious limit to what suppliers can claim is really coming from renewable sources. Especially at night.

I'm not a big fan of certificates but there is already enough renewable to power all eon customers.

gas is 40%, wind 16.9% solar 4% biomass 6.3% [1]

E-ON is about 13% [2] of the market share, just wind is enough to cover that and more (and 13% is assuming the grid generates energy just for customers, not industries, which it isn't)

Point is, there is enough renewable energy on the grid, it's a matter of how energy suppliers are going to fight to package it to clients. If the fight becomes hard on their end, they will be incentivised to generate more renewable.

[1] http://www.mygridgb.co.uk/last-12-months/

[2] https://www.ofgem.gov.uk/data-portal/electricity-supply-mark...

I'm not sure about this logic though. I've been thinking about it recently as I'm on a similar renewable-only tarrif with a different energy company and was thinking of switching to an eletric car.

If the price is the same as the non-renewable suppliers and not all electricity is from renewable sources, then by switching to a renewable supplier all you're doing is bumping someone else onto a non-renewable supplier aren't you?

Presumably if everyone switched to a theoretical renewable-only supplier with no offset certificates now, they would have to stop making the renewable energy promise?

The question is whether there is enough renewable energy at any time, not just on average.

Eon are not the only ones coming up with such tariffs, most suppliers are jumping on the bandwagon.

But does it matter that this is just an average?

What I want is the big picture, moving the needle towards more renewable. I don't want all of my electrons to come from a wind turbine, just voting with my wallet such that renewable percentage goes up and up.

With all the challenges it implies in terms of peak management, storage, seasons etc.

Yes it does matter.

Advertising "100% renewable energy" means that there is enough renewable energy produced to meet demand at all times.

That's part of why I am dubious of these claims. It does not seem straightforward to guarantee this to millions of customers.