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Comment by onlyrealcuzzo | Hacker News Reader

Contrary to popular belief, solar panels don't generate zero power on cloudy days.

They typically generate 10-25% of their maximum output on the cloudiest of days. Most cloudy days are not maximally cloudy.

We don't need solar panels everywhere to get even close to ~100% renewables (with nuclear, wind, new geothermal, and hydro). The areas where you put them are distributed enough that it would be exceptionally rare to ever encounter a meaningful need to ration.

So, storage is an issue, but not as big of an issue as most people think, and we do not generate anywhere near enough solar energy for it to be a reasonable concern yet...

There's also more solutions than just conventional batteries. There's pumped hydro, etc...

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> They typically generate 10-25% of their maximum output on the cloudiest of days. Most cloudy days are not maximally cloudy.

If you're at higher latitudes, this is notably less of a drop-off than you see between high/low season.

My friends with residential solar see <10% overall output in January vs July. (~60% drop from fewer sunshine hours, ~80% drop from decreased solar irradiance.)

This gets complex quickly, because temperature matters too: cells are more efficient when they are cold. These effects interact and the results are sometimes surprising.

Many pure-numbers theoretical comparisons also make the assumption that you can consume all the power that the cells generate, which is not always the case. In an off-grid installation with a battery, for example, you might not be able to consume everything, depending on the month of the year. Practical example: my installation gets some of peak usage numbers in March/April, because that's when it's still cold and I use the power for heating. The cells are cold, I need the power, and there is some sunshine, all this combines. It's not obvious.

Yeah, I mean these aren't entirely theoretical, like observationally, people I know locally are getting <10% January vs July generation - I'm working backwards to get the relative proportion of the drops due to solar hours vs irradiance.

They all have a relatively generous (I think - I'm not especially familiar with policies anywhere else) grid policy where they sell back any over-production in the summer. (They switch between summer/winter rates, so in the summer they buy/sell at ~35c/kWh and in the winter they buy/sell at ~8c/kWh. These rates are only effective as long as you don't have a net-surplus of generation in the year, so it doesn't make sense economically to oversize the system for more winter generation, as then you'll be generating more in the summer than you can use or sell back.)

Curtailment and dump loads are pretty straightforward, though, so using all the power isn't as critical as people might imagine either.

It's better to overbuild the dc-to-ac ratio moderately and just accept that on a summer noon you'll be dumping or curtailing, and still get useful percentages in the winter. I'm in the fortunate position of having an essentially infinite dump load (water pumping and heating) that would effectively turn most of my solar into real usage, but even most people can preheat a hot water tank and things like that. With electric cars it's even better.

One of Standard Thermal's use cases is excess DC power from existing solar farms that would otherwise be curtailed because of inverter/interconnect limits.

There's also the angle of the sun to consider, it changes quite a bit in higher latitudes between summer and winter so if you want maximum efficiency you need to tilt the cells accordingly. But I don't think most residential solar does that.

The way the math works for grid-connected residential here, if you're not adjusting the angle, between seasons, you'd be best off leaving it at the optimal winter angle all year, which would minimize the difference between peak/trough generation.

But they do generate zero power at night.

And people use less energy at night. Yes, they do need heating/cooling and a few other things at night, but the peak is during the day and in the evening.

This argument is almost closed at this point, with PV + batteries being quite price competitive. We're no longer in 2018.

Solution? Send large mirrors into space so it never stops shining.

https://www.reflectorbital.com/

That surely won't interfere with the ecosystem at all! /s

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