When you add a marginal kWh of electricity usage, how is that extra 1 kWh generated?
If France runs its nuclear power at nearly 100% utilisation, then if you add 1 kWh usage then that power comes from another source, which could be a high CO2 emitter.
The same goes for hydroelectricity: if all the hydroelectric power is already being utilised (no spillway), then you cannot claim that your electric car is being charged by hydro even if your country has a large percentage of it. There are complications when lakes are involved because whether your power usage is green or not often depends upon future inflows (lots of future rain = green; no future rain = dirty generation in future when lakes get low).
This is an interesting topic - I agree with your interpretation, but to add another wrinkle, I live in the UK which has a decent but not amazing proportion of renewable energy now. I pay a little extra to my supplier to provide me with "100% renewable electricity" - meaning that for every customer on that tariff, they total up the power usage and buy at least that much renewable energy from the grid. I assume that this puts some upwards price pressure on renewable energy compared to non renewable, but how much? Presumably every extra watt I use doesn't result in a whole extra watt of renewable capacity being added, but what's the conversion - 5%? 50%? I don't even know where to start answering that question.
I always figured those programs just would lead to people not on the green plans buying less green energy. Though I guess if you got enough of a critical mass of users on the plan it could have that upward pressure. I wonder if any studies have been done? It seems that green energy is often used as much as it can, as solar/wind/geo all have low marginal costs once built, and gas/coal/oil are the ones manually turned on/off based on total demand. That would lead me to believe buying green power would have no effect, but this is all conjecture.
"100% renewable electricity" obviously doesn't change where the electricity you actually use comes from. We certainly don't want the lights to go out and our oven to stop working just because it's a cold still night and all the hydro was used up. You would need to check the supplier's fine print very carefully if you actually decide you care what this means. The consumer magazine "Which" have attempted that for you if you subscribe, but basically buy from "Ecotricity" or maybe "Good Energy".
The most cynical thing your supplier could do in the UK is buy REGOs (Renewable Energy Guarantee of Origin). At that point the 100% Renewable claim would be legal, without any other effort. If that's all your supplier does it isn't worth a penny, we'll get to why below, but if they charge extra for the tariff based on REGOs it's pure profit for them I assure you.
A better thing they could do is arrange to buy in bulk from a renewable generator or (more practical for larger outfits) just own the renewable generator. This means their interests would at least somewhat line up with yours - if their renewable energy generators are cheaper they get to keep more of your money while offering attractive prices.
But back to REGOs. So, when you make renewable electricity in the UK you get REGOs, and you're allowed to sell them. You could sell your electricity with the REGOs, here you go, 100% renewable electricity. Or, you could snip the REGOs off, sell those to anybody who wants them, and sell the electricity as just electricity, which people wanted anyway.
If "100% renewable" was in very high demand this wouldn't be a problem, a handful of more expensive suppliers would bid for the REGOs, and this would create pressure to deploy more renewable power.
But in the UK the vast majority of households use the incumbent supplier. What does "incumbent" mean here? Well, historically the UK had regional monopoly suppliers who both billed consumers and handled the last mile distribution infrastructure that actually means electricity works in your house. But the Conservative party believes strongly in Free Market principles, even where there's no evidence they would help. So, it privatised the industry, giving away national infrastructure for a song and creating dozens of private companies that notionally can compete to supply electricity. Except of course your actual supply is the same as ever, there is still a monopoly last mile supplier, it just doesn't deal with consumers. What had been the regional suppliers were now private companies that had "grandfathered in" millions of residential customers in their region, but were free to compete to "supply" customers anywhere.
All these companies immediately offered somewhat lower prices to anybody who'd switch, and began raising the prices for those who didn't switch. Switching is annoying (despite efforts to make it simpler it cannot be entirely painless) and so most people never switch. Sounds like you have, so immediately you're not the usual case. They also began aggressive (indeed sometimes outright illegal) campaigns to keep "their" customers and prevent defection to rivals.
So today the situation is that essentially every company advertising their prices to you offers 100% Renewable Energy, because they're buying REGOs for customers like you (and me). They can get REGOs very cheaply because they don't need very many because there are so few customers like us.
And the vast majority of households aren't on any of those supply contracts, they have a "legacy" contract that's more expensive. And so in practice when it's cold and dark the coal and gas power stations are cranked up exactly the same but on paper we can blame those millions of people not all of us with our cheaper 100% Renewable contracts...
Thanks for the in depth answer - pretty much what I suspected. I think this sort of thing only even starts to work when you have a critical mass of people on this kind of tarriff (and more than that, willing to pay more and/or switch supplier for it). I wonder what actual proportion of the UK market is currently on a "100% renewable" plan.
Your entire assumption is that France nuclear is at 100% utilization. While utilization%s aren't publicly available, from this graph on Wikipedia about TWh produced [1], you can see that Nuclear has upside capacity, and was probably never 100% utilized (it's the main baseload, thus the biggest buffer option).
So the assumption that any marginal utilization is non-nuclear is flawed.
What you'll see there is as you'd expect if you understand how fission power plants work and how economics works for electricity supply. The nuclear plants may not be running at what is notionally 100% nameplate power output but they are not in fact being used as a "buffer option" very much.
That big yellow-green splodge on the "Origin 24 hours" chart? That's nuclear power. Varying, maybe +/- 2GW , but nowhere close to enough to offset France's varying power requirements over the course of a day.
France's (much fewer) gas turbines are much more able to spin up and down quickly to benefit from transient utilization and so they, together with the interconnects possible due to France's relatively central location (the UK to the West, Germany to the East, Spain to the South) allow it to manage well on most days without tinkering with the power efficiency of the fission generators.
I am glad I will able to put to rest this common misconception about nuclear power ramping up speed. While it's a common rebuttal argument against nuclear, it's rather incorrect since nuclear power is actually able to ramp up fast enough. Moreover, French nuclear stations are typically older than they should and newer ones could move even faster. But better than Germany's
Anyway, enough empty talk and here is a real world use case from West Europe the 19th of march 2019, lots of wind a sunday. I should translate the whole thing for everyone one day.
All I see there is consumption %s. I think your thoughts about marginal power usage seem reductive.
Of course, immediately your marginal power will be by gas turbine. However if power increases overall, wouldn't sustained power usage force an increase nuclear baseload? The overall GW output of nuclear has varied YoY substantially.
The section you apparently didn't scroll down to, "Origin of electricity in the last 24 hours" shows you exactly what I described.
The chart you've offered is denominated in TWh, thus energy not power, because it is cumulative over an entire year rather than showing marginal power. So you end up concluding that if a nuclear power station is closed for two months for repairs, or a new one is brought online those somehow constitute energy "flexibility".
I thought it was obvious I was using 100% as an unrealistic example.
1. Have a quick quick look at https://www.electricitymap.org/zone/FR and scroll down to “Electricity production in the last 24 hours” on the left. Natural gas was used from about 7pm to 5am. If you heat your house in France using crypto during those hours, you are using up to 100% non-renewable peaker gas (ignoring hydro because it is even more complicated as per previous comment).
2. France exports a lot of electricity, so it is quite possible for your marginal increase in usage within France to cause a decrease in exported electricity, which leads to a marginal increase in non-renewables in another country... i.e. your extra load causes an increase in world CO2 production.
I think you are making the same mistake that I am trying to illustrate... understanding marginal usage is difficult and most people jump to conclusions that are not factual.
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When you add a marginal kWh of electricity usage, how is that extra 1 kWh generated?
If France runs its nuclear power at nearly 100% utilisation, then if you add 1 kWh usage then that power comes from another source, which could be a high CO2 emitter.
The same goes for hydroelectricity: if all the hydroelectric power is already being utilised (no spillway), then you cannot claim that your electric car is being charged by hydro even if your country has a large percentage of it. There are complications when lakes are involved because whether your power usage is green or not often depends upon future inflows (lots of future rain = green; no future rain = dirty generation in future when lakes get low).