"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.
