BOINC uses a lot of energy. Energy produced by fossil power plants produces not only CO2 but is also very expensive. When it is dark or there is no wind, the prices and CO2 emissions are high, while the opposite is the case when it is windy and the sun is shining.
The renowned German "Fraunhofer Institute" provides a "traffic light" for many European countries, which shows how high the share of renewable energies in the energy supply is and/or nhow high the price is. (these factors correlate)
red: price >80% of the average price
yellow: price 20-80%
green: price <20% or <0€/MWh

Wouldn't it be possible to link this data to BOINC so that CPU utilization is lower in times of high energy prices and higher CO2 emissions per kWh?
This could be integrated into the settings, only the information about the country is needed.

Some examples:
Denmark: https://www.energy-charts.info/charts/consumption_advice/chart.htm?l=en&c=DK
France: https://www.energy-charts.info/charts/consumption_advice/chart.htm?l=en&c=FR
Germany: https://www.energy-charts.info/charts/consumption_advice/chart.htm?l=en&c=DE
Spain: https://www.energy-charts.info/charts/consumption_advice/chart.htm?l=en&c=ES[/url]
Italy: https://www.energy-charts.info/charts/consumption_advice/chart.htm?l=en&c=IT[/url]
etc

Yes, I know that most people don't have an electricity contract that is billed by the hour. But managing energy demand (using more energy at times when energy is cheap) has a long-term impact on the individual price of the contract and on the planning of the electricity system.

Unfortunately, I'm not an IT expert, so I can't really assess the feasibility.
However, I would like to give an impulse for a - in my eyes - reasonable further development.

I'm not a programmer but don't doubt it is possible. My computer while near the top of the range performance wise,uses very little power on idle. The place to request such a feature would be over at git-hub. I would not hold my breath however.

There have been several post/question similar to yours over the years... The most recent one was created in the topic Controlling BOINC using IFTTT.

A possible solution was to use scripting to turn on/off BOINC but the original person never did reply if they managed to create/get a script to work or not.

Using the Boinccmd tool you possibly can write your own scripts/commands using information from a website to do what you mentioned.