[cygx]

Countries which currently are replacing nuclear power do so with a combination of renewables and fossil fuels

Which countries? Germany for example isn't - yet. We're still in a place where we can reduce usage of both fossil fuels and nuclear, though that won't last unless we figure out effective means of energy storage.

[belorn]

As an example, Sweden. People will use fossil fueled energy when the choice is between people freezing in their home or burning fossil fuels. Sweden rely on a mix between hydro and nuclear, but it is not feasible to extend hydro beyond current capacity. The nuclear plants however is getting older, and politically people want to shut them down. Something has to produce the energy, and during the winter it is imported fossil fuels energy when the wind is not blowing.

Germany as an example illustrate the issue quite nice, as can be seen live at electricitymap.org. When the wind is blowing the country goes green with around 70% of energy being produced by wind. Very sunny days you get around 20% solar. Days like today that is a bit rainy and not very windy, and you have 60% fossil fuels. The constant is nuclear around 10%, so remove that and the above numbers will go up depending on weather conditions.

[renaudg]

German anti-nuclear activists like to tout the percentage figure of renewables in the country, but that's not the right metric to look at : the coal+gas baseline is so bad in terms of CO2 emissions, that even in ideal conditions when wind production is 70%, German electricity's carbon intensity is still way higher than in France, Sweden or Iceland (

Coal causes 35.000 premature deaths in Europe every year, and 7 of the 10 most polluting industry sites on the continent are German lignite power plants.

The hypocrisy and constant lecturing from Die Grüne needs to stop.

[cygx]

Sure. But that doesn't make Germany an example of replacing nuclear with fossil fuels. From 2002 to 2019, percentage wise, fossil fuels went down by 1/3 (from ~60% to ~40%) and nuclear by 1/2 (from ~30% to ~15%).

[belorn]

Since electricitymap gives current say 40% coal and 15% gas, to a total of 55%, I assume fossil fuels are not down to 40% all the time. What you are describing is the average.

Feel free to prove me wrong, but when the wind over Germany is still (<4ms) and its night, the amount of energy production using fossil fuels are higher than 70%, and thus at peak, fossil fueled energy production is higher now then before when nuclear stood for 30%.

[cygx]

and thus at peak, fossil fueled energy production is higher now then before when nuclear stood for 30%

But that's an irrelevant metric: What matters is the total CO2 released, ie the integrated value. So short-term, you replace coal plants by gas peakers, and transition to next-gen storage mechanisms long-term (better batteries, cryogenic storage, power-to-gas - the latter is especially interesting as Germany has pre-existing gas infrastructure than can store hundreds of TWh, and we use natural gas anyway for heating and industrial purposes).

[belorn]

What matters is to close down the fossil fuel plants for good. The output of wind is on average 45% of maximum capacity for offshore wind, meaning if you have 100% of wind during optimal conditions and 0% when the wind is still on average you get around 45%. For land based wind parks the numbers are low, around 25%.

So far there is very little investment to build out wind beyond having 100% wind in optimal conditions. Germany has almost hit that point, and if we look at neighbor Denmark then we can see what happens when it does reach 100%. Building wind beyond full capacity turns uneconomical quickly, as investors found out in Denmark.

The result is that the coal and natural gas plants will burn and continue polluting the world. The competitiveness of renewable is based on the cheap initial costs while it goes towards max capacity. The price tag does not include overcapacity, the batteries, cryogenic storage, power-to-gas and so on. It works fine as long as we don't think about the fossil fuels that get burned when the wind is still.

Nuclear plants have a linear cost. Going from 10% to 20% cost just as much as going from 90% to 100%. No overcapacity, no batteries, no conversion loss. You add 10% nuclear plants and you can demolish 10% fossil fueled plants. You build 10% additional wind farms and the same old fossil plants must remain. You demolish 10% of the nuclear plants, and you have to build the same amount of new fossil fueled plants in order to compensate when the wind is not blowing. New fossil fueled plants are going to get used, investments is going to be repaid, and political influence fill make sure that they continue to operate.

> What matters is the total CO2 released,

If people really thought so they would look at the electricitymap and look which countries does exactly that. Who has the lowest total CO2? The answer: those that can produce a constant base load without releasing CO2. Hydro or nuclear. Those that have invested most in renewable are not the ones with lowest total CO2.

[Reason077]

> "Nuclear plants have a linear cost. Going from 10% to 20% cost just as much as going from 90% to 100%. No overcapacity, no batteries, no conversion loss."

In your nuclear-only scenario, without storage you'd need enough capacity to cover peak demand. This can be 2X or even 3X higher than average demand, so there would indeed be significant overcapacity. Very expensive!

Typical nuclear plants are also not good at demand response: to operate efficiently, their output must remain constant most of the time. Over-capacity at off-peak times is potentially a big problem on grids with a large portion of nuclear.

Some combination of storage, peaker plants, and demand response is required regardless of whether nuclear or renewables are used. The most cost-effective future grids are likely to use a diverse mix of technologies.

[renaudg]

Germany absolutely is relying on coal and (Russian) gas to afford its ideological decision to prematurely sunset nuclear plants, at the worst possible time in history : just as climate change becomes an emergency.

The cold hard truth is that it's impossible to operate a grid with solar & wind energy alone, unless and until a hypothetical battery storage breakthrough lands in the next decades.

I've just checked the realtime figures and as I write this, German electricity is 5 times more carbon intensive than in France (72% nuclear) : https://www.electricitymap.org/