Well here in the UK we are about to get a big price rise in energy costs. One of the things that can be switched off is the 1,2 or sometimes 3 computers that run the various projects. There is always one running and a second one for maybe 1 week a month + others on a whim.
Most other project w/u's are short(ish). Cpdn w/u usually last 20 odd days for me anyway. So once the w/u has started its best to let it finish uninterrupted.
So, once upon a time, doing this distributed processing was cheap and interesting. The cheap part is disappearing.
Years ago, back when electricity was cheap I used to have 30+ old machines running. Back in the early days of seti.
I will have to see how expensive having a 4 core 8 thread machine running is. It is only a hobby after all.

The newer machines are an awful lot cheaper to run than older ones in terms of compute per watt - but, also, don't have the "idle at nearly full power" behavior that a range of older systems had in which doing distributed compute was basically free. Back in the Windows 98 days, it didn't HLT the processor in idle loops (though there were some very useful utilities that could do that - CPURain, perhaps?), so "running compute" and "doing nothing" were almost exactly the same power.

Modern hardware will run over a range of power settings and corresponding performance points, though if you still want to do some, you can look into underclocking your CPU - or, at least, disabling turbo and setting lower power limits. The last 10% of compute takes a lot more than 10% the power, so running at a more efficient power setting is optimal for something like this.

I use mine mostly for heat, though. My office (standalone solar/battery system, off grid, comically overpaneled) has a lot of use-it-or-lose-it power - if the battery bank is full and I'm not using the full output of the panels, the energy just isn't collected. So, in that kind of system, the compute is quite literally free on an incremental power basis. If I don't have compute running and use 5kWh in a day, or have compute burning and run 10kWh in a day (including air conditioner loads), it's literally the same cost to me. Everything is already paid for, and the only real limit is that I'm inverter limited if I need to run the air conditioner.

The house has a few compute boxes too, though those generally only run in the winter. It's also on solar, though a big grid tied array. While heating with electrons directly (via compute) takes more energy than running the heat pump, I have no way of being paid out for surplus energy and generate quite a bit of it, so I'll crank up the compute boxes in the winter when I'm heating, and let them idle back down in the summer when I'd have to spend energy to remove the heat they generate. After this batch of MacOS tasks is done (doing OSX VMs on Linux, because... sure, why not?), I'll let the house systems go back to idle for the summer - temperatures are climbing enough that I don't need to have them assisting.

If you're on resistive heat in the winter, though (not sure where all this is common, but I know some areas of Canada use this because they have so much hydro in the winter that almost everywhere has resistive heat), using compute or using your strip heaters is literally the same end result, except that you get something else useful out of the computers. For that sort of use, some older, used systems you can get for free or nearly so work - my office has a 4th, 5th, and 6th gen Intel that I paid very little for, and while it's not running right now, I've also got an older dual Xeon that's a power hungry beastie I got literally for free. Given my power situation out there, it does turn in a bunch of useful compute, so it's still worth tossing into a compute pile.

The newer machines are an awful lot cheaper to run than older ones in terms of compute per watt

For sure. My old machine had two hyperthreaded 32-bit Xeon cores. They took about 90 watts each. It also had six 10,000rpm Ultra/320 LVD SCSI hard drives. That machine ran about 900 watts, IIRC.

My new machine is way way faster in terms or work units completed per day, has an 8-core hyperthreaded 64-bit Xeon processor that has about the same clock speed of the old machine. I let the boinc client run 8 cores, leaving the other 8 free. That machine turns out much more work than the old one ever did. and when running 4 N216 jobs, 3 WCG jobs and a rosetta job, all at once, it use about 250 watts. Right now it is running four universe@home jobs and my Firefox browser and is using 175 watts. It takes even less if I turn off my LCD monitor.

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I second optimizing your machines' power consumption via power settings but especially via undervolting and maybe some underclocking. I have an old i7-4790 that I used Intel XTU to undervolt everything that XTU allowed and now run the machine with much less energy than stock settings and no performance hit. Similarly with my new Ryzen9 5900X with NVIDIA 3060Ti. Using RyzenMaster and MSI Afterburner I undervolted the CPU and GPU and eventually underclocked them because it didn't seem like faster speeds produced noticeably faster results. Both of those PCs are HP prebuilts and stock cooling has been sufficient running them 24/7 full load with BOINC projects. It seems like even new (and old) machines can be made to run much more energy efficient without any noticeable performance hit.

Now we are getting light earlier in the day, from 7.00a.m. I can run my computer completely off solar. I have been using suspend to RAM at night but, for this to work with only 32GB of the stuff, I need to use the command elsewhere in these forums to clear the RAM first otherwise, it seems to start up OK and run but video doesn't work. When I upgrade to 64GB, it will be interesting to see how that changes. I will hopefully be getting battery storage later this year giving 24 hour free computing during the lighter months. But I am guessing cost of energy is going to be an issue for many for quite a while to come. Unfortunately panels with f0% more efficiency that have a film that absorbs blue and yellow wavelength light and gives out photons at lower frequency red wavelengths and increases the efficiency of panels by 50% to 30% are not being estimated to be on the general market till 2025.

The newer machines are an awful lot cheaper to run than older ones in terms of compute per watt

Retiring two quadcore PCs with hard drives for second-user i7 PCs with solid state drives has cut our annual 'leccy use by 1,200 kWh. The lower power cpus are 85% of the savings and hard drives are circa 15%. That's enough 'leccy for 4,000 miles in the EV.

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I will have to see how expensive having a 4 core 8 thread machine running is. It is only a hobby after all.

My Ryzen based machines (12 core, 24 thread) are drawing a steady 135 watts so the April tariff increase from 20.5p / unit to 27.6p / unit will take it up to £325 / year / machine, an increase of just over £80 / year.

up to £325 / year / machine, an increase of just over £80 / year.

Well it is a "hobby" so to speak and hobbies cost money. But the fun for me was building old machines out of scrap and getting a version of linux on it and crunching away with cheap elecy. A 24 thread machine is a wonderful bit of kit but at £325+ quid each to run is painful. It is a years worth of contributions tho. My I7 setup will be about £260 ish I think but easily more than £330 if I startup another 1 or 2 for a week at a time.

My energy supplier is going to almost double the standing charge also. Another sneaky rise.

It would be interesting to know how much of the contribution to the project are from dedicated crunching machines. I wonder if there will be a noticeable drop off in work returned (for all projects). Or maybe just from a few countries.

Hm. Good question.

I have three dedicated compute nodes online during daylight hours (4440S, 5775C, 6600K), plus the home server and house desktop contribute in the winter months.

It would be interesting to know how much of the contribution to the project are from dedicated crunching machines. I wonder if there will be a noticeable drop off in work returned (for all projects). Or maybe just from a few countries.

It started out as my daily user that had Boinc loaded and then got left on overnight and then upgraded from an FX4 to an FX8 to a Ryzen. Then I found an old case and put the old motherboard into it so I had two machines running then …