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.

>EIA publishes hourly operational data across the United States electricity grid, including demand, net generation of electricity from various sources (such as coal, natural gas, solar), CO2 emissions, import/export to other regions, and many more. The complete details of the EIA-930 data is available here: https://www.eia.gov/electricity/gridmonitor/about. Furthermore, we obtained the solar capacities of each year and each region from EIA (https://www.eia.gov/electricity/data/state/) and had stored the information in the file solar_capacity_factor.csv. (2023-07-01)

€0.3943 / kWh

That's about US$0.46 or AU$0.71 per kWh

That largely explains the surge in popularity of patio solar in Germany.

The savings is minuscule. But important nonetheless. It just goes on to show how much more solar is required.