Direct study link (with associated diagrams): https://www.science.org/doi/10.1126/sciadv.adq5660

The study compares a percentage increase of solar power against an absolute decrease of CO2 emissions.

This seems like questionable reasoning to me. If California has 100 MW of solar power for every 10 MW in Indiana, a 10% increase in solar will show up as 10x more CO2 savings for California just because it has a larger installed base.

To me the relevant question is the relative dirtiness of the nonrenewables being replaced, and the relative cost and effectiveness of solar. IMHO the data ought to be normalized to a per-MW-installed-rating basis.

I wish the study went like this (all the following numbers are completely made up, based on nothing more than the fertile imagination of an HN commentator mildly annoyed by the study's questionable numeracy):

- In California, clouds / latitude / etc. mean a panel's only usable 10/24 hours on average per day

- In Indiana, the geography's less ideal, so clouds / latitude / etc. make it usable 8/24 hours on an average day

- In California, it would be replacing a super-clean natural gas plant installed in 2008 that has expensive high-tech emissions control devices required by the super-strict California environmental regulations and emits 0.4 tons of CO2 per MWH.

- In Indiana, there was no money or political will for modern power plants or strict environmental regulations, so the solar panel would be replacing a smoke belching coal plant from the previous millenium that emits 1.2 tons of CO2 per MWH.

- In California, labor for >1 MW solar installations costs $0.20 / W, costs are inflated by high CoL / taxes and business unfriendly regulations but there are lots of firms with experience who can install quickly.

- In Indiana, labor for >1 MW solar installations is $0.15 / W, they pay a lot less and don't have as much red tape, which slightly outweighs the fact installers don't have much experience and bumble around being slow and making expensive mistakes.

- Your per-watt cost is $0.20 / (10/24) = $0.48 in California but $0.15 / (8/24) = $0.45 in Indiana (which is also your per-MW cost in millions).

- Your daily emissions reduction is 0.4 x 10 = 4.0 tons for California and 1.2 x 8 = 9.6 tons emissions reduction for Indiana.

- Therefore every $1M spent in California buys 4.0 / $0.48 = 8.3 tons / day of emissions reduction and every $1M spent in Indiana buys 9.6 / .45 = 21.3 tons / day of emissions reduction.

If you care about efficiently spending money to reduce emissions, in this example (using made-up numbers) Indiana is the low-hanging fruit, investments there are better by a factor of 21.3 / 8.3 ~ 2.6.

But the way the study's written, if we assume solar is currently 2000 MW for California and 200 MW for Indiana, its calculations would suggest a 10% increase in California (200 MW) would save 200 x 4.0 = 800 tons and a 10% increase in Indiana would save 20 x 9.6 = 192 tons.

This is very misleading.

If you don't think about the units and just look at the numbers, you might be tempted to conclude the study's telling you that California's emissions reduction rating is 800 and Indiana's rating is 192, so if you care about CO2 reduction every dollar of investment is a factor of 4 as effective in California -- when in reality, with these numbers every dollar is actually a factor of 2.6 more effective in Indiana.

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malfist 5 days ago | parent | next [-]

There is no "super clean natural gas plant" you're still burning a nonrenewable hydrocarbon and letting its carbon go into the atmosphere

	▲	csense 4 days ago \| parent [-]
		I think you missed the point of the example. The question I'm asking (and that I think the study was trying to ask) is "If we have limited resources to apply, how should we try to minimize CO2 emissions?" The point I was trying to make (and that I think the study was trying to make) is that replacing the plants that emit the most tons of CO2 per MWH is a decent place to start, especially when you know you don't have the money and political will to replace them all. (But you probably ought to put other factors into the math, like that you need X MW of solar to replace 1 MW of fossil fuels, to account for the fact the sun doesn't shine at night -- and the exact value of X differs due to local conditions like latitude and weather.) Saying "I wish we had the money and political will to replace all fossil fuel plants" or "We have a moral imperative to replace all fossil fuel plants" is...not productive. Your wishes or moral views don't change the fact that we don't actually have that much money and political will. There will be some bureaucrat or politician or somebody somewhere who at some point says "Okay, we know how much money and political will we have for this CO2 emissions reduction thing. Where should we spend it? Let's see if anyone's made a study." And when that decision maker goes off searching the literature, we really want them to find a study that gives an honest, non-misleading analysis -- with the example numbers I gave, that would mean closing the coal plant in Indiana is the optimal play, even though that state's climate and weather is less ideal than south or west. If the study uses misleading math and the resources get applied in a sub-optimal place -- if we could have gotten rid of X tons of emissions with the money and political will available, but because of the bad math we applied it in the wrong place and got rid of Y tons instead, for some Y < X -- that just seems like unnecessary societal inefficiency and stupidity.

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spwa4 5 days ago | parent | prev | next [-]

> The study compares a percentage increase of solar power against an absolute decrease of CO2 emissions.

local CO2 emissions. This has not affected pumping of oil, and since we aren't even able to store much oil, that means it's getting burned. That makes it clear the global effect must be very close to zero. And for CO2, only global matters.

	▲	two_handfuls 5 days ago \| parent [-]
		You're essentially arguing that reducing demand won't reduce supply. It may not do so immediately, but certainly over time it will. For example, there are oil fields that are unexploited because they would not be profitable. If demand rose, prices would rise and new wells would be opened. The reverse is also true.

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5 days ago | parent | prev [-]

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