The trick is in the mix. 100% clean energy (wind, solar, hydro) might be somewhat of a challenge. But it is rather easy to raise its share of the total energy production to about 80%. The rest would be provided mostly by gas, and perhaps a very few coal plants, which would run only in absolute emergency times. This would reduce our carbon footprint considerably. And for this, the additional cost is very small, if not already money can be saved. When we are at 80% renewable, we can then discuss the technical and financial requirements for the rest.
> it is rather easy to raise its share of the total energy production to about 80%
I know advocates claim this, but I am highly skeptical. The problem is capacity factor: yes, you might be able to build enough wind farms and solar panels (hydro is pretty much already built out--every site that is feasible for hydroelectric power in significant quantity already has a dam) so that their nominal capacity, if they were all running 24-7 at their rated output, exceeds 80% of total world energy usage. But they won't ever be running 24-7 at their rated output; not even close. Typical capacity factors, AFAIK, are less than 30% for these sources. Whereas nuclear plants (and fossil fuel plants, but we're assuming those are out of bounds since we're talking about clean energy) can run close to 24-7 at their rated output; typical capacity factors exceed 95%.
It is also quite possible and affordable to produce 80% taking the 30% capacity factor into account. Germany is already at 30% of all electricity being produced by renewables. The capacity factor only tells you how many you need to build.
That a nuclear power plant runs 24/7 causes also a lot of problems, because energy consumption heavily changes over the course of a day, especially at night there is little demand, and you cannot throttle a nuclear power plant quickly enough. That is why Belgium built illumination systems for all their highways, just to get rid of surplus nuclear power at night.
I doubt the 95% capacity factor for nuclear plants - perhaps for freshly built stations. Nuclear appears to be very reliable, but there are actually quite a lot of issues. One is, that for technical reasons, a nuclear power plant might have to be shut down entirely with no forewarning. This happens quite regular and has to be compensated for by the grid. Currently 50% of the German power plants are down for maintenance, and about 25% of the French, which caused electricity shortages in France last winter. And nuclear plants even are sensitive to the weather, because in hot summers or dry winters there might not be enough cooling water in the rivers that support their cooling needs.
"We have to get to 80%, then we can talk about cost"? Is this like the "we have to do it to find out if we can afford it" version of "we have to pass it to find out what's in it"?
No. Up to 80% the cost of renewables is, what you pay to set up the solar cells or wind generators. And these costs are known and quite competitive (if not cheaper already) to building a new coal plant, and definitely cheaper than building a nuclear plant. If there is enough controllable power generation in the other 20%, by todays technology that would be gas power plants mostly, this is about how far smart grids can deal with the varying nature of the renewables. Only going beyond 80% there are significant additional costs for storage. But as battery costs are significantly falling, it makes only sense to discuss the costs, when we really need them and then know the true numbers, as this is quite a few years in the future.
I think the idea of enormous batteries storing megawatts of power is potentially more dangerous than nuclear plants. At least reactors have control rods, but what do you do with a huge battery with an internal short? And compared to stores of coal, oil, or gas, at least they won't spontaneously combust like batteries have the potential to.
No, there is no comparison. Large battery storage are not a single large battery, but is split in small units. So, if there is a short, a few cells, at worst one rack of batteries burns down, the other batteries in the storage facility are physically separate.
Fukushima has shown us, how severely things can go wrong. The reactor was completely shut down, but that didn't help much. Even with the control rods deployed, these reactors had a thermal load of several megawatts, and when the cooling failed to keep up with this load, 2 of the reactor cores melted, and the landscape around was contaminated. Pure luck that it wasn't worse and most of the radioactivity went out to the ocean.
> Fukushima has shown us, how severely things can go wrong.
It should be emphasized, though, that this had nothing to do with the reactor; it was bad siting of the backup generators and switchgear for decay heat cooling. Other reactors in the same complex that did not suffer from this problem had no issues.
Also, newer reactor designs do not need a backup generator for decay heat cooling, so they are not vulnerable to this failure mode at all.
