Regarding cryptocurrency and solar power, the argument has some gaping holes in it. The premise is that solar (and wind) does not have the constant generation rate that fossil fuels or nuclear plants provide, so by having miners going online when there is an energy surplus (and thus it is cheaper) can help pay for solar installations (which must be over-built to supply energy off-peak).

The most obvious problem with this line of reasoning is that miners make more money when they are constantly mining than when they only mine opportunistically. This has already been demonstrated in the real world, with miners generally clustering around energy that is cheap and always available. We have seen miners keep gas-burning plants that would have shut down online, bringing already shut-down coal plants back online, and clustering in countries and regions where coal/nuclear/etc. energy is cheap and abundant (China, a few former Soviet republics, etc.).

Moreover, anything that consumes power and that does not need to run round the clock would have the same effect on solar deployment. Why not create a smart washing machine that waits for energy prices to fall before starting a load? Why not a steel mill? A basic flaw in the argument is the assumption that there is no better use of energy than Bitcoin mining or that Bitcoin is unique in its "flexible" energy needs. Neither assumption is true. There are alternatives with the same "flexibility" that have a clearer benefit for humanity, like direct conversion of atmospheric CO2 and water into gasoline (still a research topic, but prototype facilities are being tested at small scales right now) or any other energy storage technology (which in theory could be operated separately from generation).

Finally, a basic economic point: energy spent on cryptocurrency mining is energy not available for anything else. Even if all Bitcoin mining was exclusively powered by solar, wind, and hydro power, Bitcoin would still be slowing the progress on phasing out fossil fuels by consuming so much energy. Electric cars need to be charged whether or not Bitcoin mining occurs, and if renewable sources are all being sunk into Bitcoin then cars will be charged using non-renewable sources.

I know you asked for the other side, but sometimes there is no other side and this is one of those times. The idea that Bitcoin is actually good for the environment because it could, possibly, subsidize solar production is just a desperate attempt to work around the criticism that Bitcoin wastes energy. Yet that criticism of Bitcoin is very easy to demonstrate: divide the number of transactions processed in one second by the power consumption of Bitcoin, and compare the same estimate for Visa or whatever. Even if the estimated power consumption of Bitcoin is off by a factor of 100 you would still be better off with Visa, since Bitcoin processes 7 transactions per second while Visa processes about 1700 (and Visa's annual reports on the topic always show much lower power consumption figures than even the most generous estimates for Bitcoin -- several orders of magnitude lower).

I'll give credit where it is due: people who reflexively shout "PoS" when these criticisms are raised are at least acknowledging that PoW is a problem that needs to be addressed. That is the only actual counterpoint to the complaints about energy consumption, a technical improvement that is ready for deployment (and is already partially used by Ethereum, with a full switch supposedly coming soon).

You raise some good points and you ultimately might be right, but from my perspective, you're recycling lazy arguments without much backing.

I live in New York state (USA) and we have restrictive policies about how much solar we can build and push back into the grid. In some cases, even doing an investigation to see if an area can support pushing a significant amount of solar back onto the grid can cost upwards of $10k (so I've heard). This steers solar production to only provide solar to the facility that it sits next to and disincentivizes pushing solar back onto the grid.

Let's say I wanted to build a solar system, at dirt cheap costs, that could meet 3x the energy needs of my house. What do I do with the excess that can't be pushed back into the grid? You're absolutely right, I could smelt aluminium, scrub C02, or open a "smart" laundry mat, but all those require a large up front capital expenditure.

Put another way, let's say you're producing an excess of cheap energy as an individual, so maybe 100kWh per day. What technology can you install that's cheap to set up, can use the energy in a linear fashion (can scale up) and be profitable? There's other benefits, like transportability and relatively sporadic use, that might come into play as well. I would genuinely like to know what other technology could fill this niche. Cryptocurrency is one and it seems well suited.

In terms of sporadic energy availability, I've heard this argument in a video that Elon Musk did as well and I'm not sure I believe it. If the energy availability is consistent enough, say in a block of 6-10 hours in a day, then I could imagine that could provide enough stability to mine intra-day. Regardless, battery technology is coming down in price and it wouldn't be hard to install a battery system to give consistent power by increasing the solar installation cost by a factor two to three times.

In terms of your basic economic point about Bitcoin using energy that isn't available for anything else, that's like saying energy invested in supporting the networking infrastructure can't be used for anything else. The energy invested in the system is so that the system can be used as intended. If you don't believe Bitcoin/cryptocurrency has any value, then just say that.

In terms of the Visa/scaling/energy/transaction limit, yes, Bitcoin can't use "layer 1" as the payment processor at scale, but maybe providing "layer 2" solutions, like Lightning or something similar can work out. This is what places like El Salvador are using and is why people are invested in Lightning development.

Again, you might ultimately be right, but my plea is for better discussion on this topic here. Especially for the "bitcoin mining needs consistent energy availability", I haven't seen any good resources to really refute or bolster this claim.