It depends on a lot of factors, like depreciation of the mining hardware. If you're only mining during peak solar hours (the middle of the day), you're gonna get less out of your miners than a rig in kazakhstan that's running them 24/7.

Also, how does the pricing of power work during excess hours? You could set up some sort of script to fetch the rates from your supplier and start/stop mining based on the price. You might need to do some talking with your supplier or local power company to figure this stuff out.

You can also run the numbers to see if it's worth it to GPU or CPU mine another coin, but that probably won't be more profitable.

What does "connecting to solar farms" mean? Are you using "connecting" referring to dialog with them or are you referring to the actual physical wiring / connecting to their supply of power aspect?

I'm not an expert on utility scale solar generation, but I don't think there are many solar farms that have battery storage.

As far as the opportunity ... until S9s are back to being $25-ish (i.e., essentially being scrapped), the capex spend on rigs is still so high that there simply isn't an economically viable path that doesn't have them hashing somewhat approaching 24/7, 365 days a year. You won't have that with solar. Depending on various factors, PV solar produces less than 10 hours per day, ... and as little as only 6 hours per day. Clouds and other conditions will have an impact as well.

Now if there was also some baseload source that is in excess during off peak, you might be able to make the case where if the price on solar is good (e.g., $0.05) but only consumed from 8am - 4pm, and then the off-peak baseload (e.g., hydroelectric, or whatever) from 9pm to 6am ... also available at or near that $0.05 price, then you might be able to justify operating even if the rigs are powered on only for those 17 hours per day. I don't know anywhere today that such a tactic is performed, commercially, but it likely will happen, at some point.

You didn't mention your intent. Are you looking for this as a possible mining venture yourself, ... or are you simply hoping to see this unused solar be put to good use, and advise the solar operator on methods bitcoin could help?

Either way, firstly, try to learn to what extent there really is installed solar capacity that is in excess of demand. Sure, there may be days that the grid only wanted half the solar output capacity or something like that but I doubt it is something that occurs every day. Every scenario is going to be unique.