I would simply assume that the value of a Sol Credit would be proportional to how much power you have and are generating. I'm not sure how it works right now with the American Dollar backed by Oil but I can dream.
Basically as more power is available, the value of a Sol Credit lowers and less power means the value of a Sol Credit is higher. The reason I say this is because power is a critical component of any developed city. It powers literally everything you have and its going to keep you alive (depending on your atmosphere). So if power is rare, people are willing to trade more things for it and its value goes up and when there is plenty of power, its value drops because people know there is a surplus and traders will want to move power off their grids/storage and generate income, rather than holding it back (well atleast some money savy person will drop their price, and once they do it everyone will).
Another way to look at it would be to compare it to the fallout series and the value of bottlecaps. The value of a bottle cap was decided to be 1, because the people who could generate clean water decided they wanted to. They backed the price using an essential need, so suddenly everyone had to use it because it was required if you wanted to live.
In terms of actual processing, people will always be trying to expand how much power they can generate. A solar panel is basically free power right? But as more and more people generate power, the value of a single Sol Credit or 1MWh drops. This means everything is basically going to cost more and more money. Eventually the value of a single Sol Credit is too low to be profitable unless you have already invested a large sum of money into it and are able to generate and store a considerable amount of volume.
You could kind of see this sort of investment and money generation happen with bitcoin and ethereium. There was an initial investment into equipment by many people when it was profitable. As more and more was generated and more was available, the value dropped because people wanted to move their bitcoins that they mined rather than hold onto it. People undercut other people, people sold all their bitcoins they stored, etc etc and the price comes down. Now if you want to invest into it, you realise you need a lot of capitol to make a profit. The value of bitcoin has dropped so much that you only make returns on initial investments after several months. People who have already invested and have paid off the inital cost still find it profitable. They can increase their farms because their profit covers the setup cost and do so at a steady pace. They make enough to factor into maintenance and large corporations who farm the coin can do this so efficiently that no normal person can keep up. Eventually the value will settle down, with only minor fluctuations due to changes in production, demand, security, etc, etc.
I'm ignoring a large section of the reason crypto increased so fast, but basically if you say 1MWh is worth 1 Sol Credit, the value of a Sol Credit will fluctuate until it reaches a steady state. It will be profitable for big organizations but not small ones or individuals because the startup cost to make a profit would be incredibly high because people would undercut each other to shift the power they are making and get returns. So at the start 1 Sol Credit might be worth 1 piece of bread, but when it settles it could be 100 Sol Credits for 1 piece of bread or 1000 Sol Credits for 1 piece of bread due to it being necessary, a sudden surge as everyone tried, a large drop as competitive pricing drove the value down and then a increase when small players dropped out followed by a steady state where only the big players are left.