If I invest $20k in a rig with $0.12/kWh... what could my daily earnings be?

...or monthly earnings. Not counting setup labor.

1 S19 Pro at 110 TH/s is $12.5k. That eats up 3250W, or 78 kWh per day ($9.36 power costs at 12c) For the next 2 weeks or so, the miner should produce around $40 of BTC per day or around $30 on top of electrical costs. Difficulty will probably increase in 2 weeks, so this number goes down as difficulty rises, on average 4% per 2 weeks. This also assumes you have the 220v power already run, have internet and ventilation and noise all taken care of.

Here's a good website that you can take in consideration to estimate roughly how much you can earn per day with your rig (once you've decided which one you'll get) - https://whattomine.com/coins/1-btc-sha-256

With that power rate you might be wise to explore hosting options with cheaper electricity to be competitive with other miners. Mining profitability can change quickly and significantly so it isn’t always best to look at current conditions when trying to determine investment potential. This is especially true now because of the recent actions in China.

An alternative tool for RickDeckard suggestion above you can use these two tools below to calculate how much you can earn daily. - https://www.asicminervalue.com/ Scroll down to the bottom and edit the electricity cost and apply you will see all daily earnings on the right side. Another tool with advanced feature - https://www.mycryptobuddy.com/BitcoinMiningCalculator

Your question does not belong in the BTC mining question area if you want the rig that earns the most  per watt and the most per dollar the answer is not any BTC rig. Since you asked it here in BTC the BTC answer is what is in stock Avalon 1246 87th at 5679 and 4 at 22716 usd do 348 th use say 14000 watts an hour s19 pro 110th at 11442  so 2 at 22884 usd  do  220 th. uses say 6500 watts an hour I would argue get the Avalon if you have cheap power it is better deal. A lot more hash 348 vs 220 and more power 336 kwatts a day vs 156   so 180 more k-watts or  $33.60 vs  $15.60 a day at 10 cent  $16.80 vs. $ 7.60 a day at 5 cent power. the earnings today are 348 th = 121 pre power 220 th =   76 pre power

Since you are the wisest you are, I think you can help me solve a dilemma ... The idea of using ASIC Avalon seems really reasonable, but I also figured out another option, since after a year of using these installations, the issue of energy efficiency becomes an edge. Let's say my electricity price is only $ 0.062 and the highlight is that this is a fixed price, regardless of consumption. Still, the $ 620 monthly electricity bill still seems daunting to me. What if for this amount buy 3 Avalon and 1 solar station for 10 k-watts? The cost of 1 station is $ 5900, which is equivalent to the cost of the discussed Asic Miner, and the electricity consumption is within 10 k-watts, but on the other hand, the production is only $ 14 per day less than if you bought 4 Asics. [1] 4 Asics / 360th = Rev. $ 4000/Month - Cost $624 [14000W] = $3,400 [2] 3 Asics / 270th = Profit $ $2,569/Month + Cost $468 [Solar station 10500W] = $3,038 Both in the first and in the second case, the initial amount of costs is identical, but literally after 8 months or less, the cost of mining will tend to zero, (against the background of increasing complexity, etc). Anyway, I hope I hear a couple of thoughts from you ...

Could you explain why difficulty would increase after 2 weeks? Is that every two weeks that the difficulty would increase? Until when? Until I start making zero profit and go into negative?

well a 10k solar install is at best 7 x 10 = 70 kwatts. of power a day. that is in a desert on the equator. as the early and late sun lower the power. an avalon burns 3.4 x 24 = 81.6 or 81 kwatts. so your 10k watt install will not quite run 1 of the three units. this assumes a perfect location for solar. I am in NJ,USA we have a 100k install on 1+ acre it makes 5-5.5 hours a day due to morning and evening being weaker light and of course cloudy and rainy days. so it makes about 500-550 kwatts of power a day. It runs a home an office and 1 s19 pro 2 s17 pro 1 gpu rig. so do the math with 2x 10 k install for the solar. it would come close to running 2x avalon.

Yes, it will keep going up until you start paying more for the power bill than you earn. See, this rather simple math, your profit is decided mainly by two factors, price, and difficulty. You want higher prices and lower difficulty for more profit, the opposite = less profit and potentially a loss. The facts are, the price can go both ways, the difficulty only goes up, of course, it doesn't go up in a straight line, but if you google "bitcoin difficulty chart" you will understand that difficulty tends to go up a lot more often than the opposite direction, as a result, at one point into the future, your mining gear will become obsolete, that heavily depends on your power rate, someone who pays 5 cents can mine a lot longer with the same mining gear than someone who pays 10 cents, so with 12 cents kWh, you are going to be forced to shut down a lot faster than many other miners. The above doesn't mean you won't be able to ROI and make some profit on top of that before having to shut down your gears, it just means your chances are a lot lower than those who have free power or pay only 4 cents, and given that mining is essentially a competition between miners, you might want to avoid getting into a battle knowing that the other opponents have more chances than you do.