Specs: 300MWe, nominally $1B first-of-a-kind build cost and $675M next-of-a-kind build cost. Runtime between fuel changes is 18-24 months.

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On the battery side I was looking at the Tesla Megapack 2 XL, since our neighbouring province has a bit of capacity installed.

Specs: 979kW output per pack, 3.9MWh capacity. For 300MW output capacity we need 306 units => $425M. The total capacity from fully-charged to fully-discharged is 1193MWh. Total time from full-charge to full-discharge: 3.9h.

In the middle of winter we have 8h of daylight and 16h of night/twilight. To provide 300MW overnight on a calm day we need 4.02x the storage capacity (16h runtime/3.9h discharge). That gives us 1231 units for a total cost of $1.7B.

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Yes, the nuclear plant will be more expensive to run (trained staff, security, disposal, etc). On the other hand, the $1.7B cost doesn't include any of the devices that would actually be charging the battery packs either.

We do often get cloudy days and calm days here as well. Saturday, for example, we actually had pretty good wind performance but negligible solar performance: https://twitter.com/SkElectricity/status/1762085119576125812.... A week ago we had both dark and calm: https://twitter.com/SkElectricity/status/1760635567136452664.... These plots are summed across the entire grid in our province, so the commonly stated "well it's never calm everywhere" isn't really valid.