alt Hacker NewsThis 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.
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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.
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.)