After the first 20 minutes, the water temperature seemed to increase at a fairly steady rate of 0.0006 degrees Celsius/second. This increase in temperature means there is an increase in thermal energy, which we can calculate as follows:
This I is the mass of the substance (in this case water) and C is the specific heat—the amount of heat energy required to raise the temperature of the substance by 1 degree Celsius. For water, C is 4.186 joules per gram per degree Celsius. So, with 1,000 mL of water and my rate of temperature change, I understand that the water requires 2.51 joules per second (or 2.51 watts) of power.
Oh, look. Even with this crude measurement system, it's pretty close to the power going into the Raspberry Pi. The difference is probably due to imperfect insulation. So you can see that the power of cryptocurrency is just heat energy. Honestly, I'm surprised it works as well as it does.
Show me the money!
While you might run a cryptocurrency miner as a way to heat your house, that's probably not why people do it. What is the bonus? Now, let's do some quick calculations. I ran my Raspberry Pi miner for 12 hours. How much money did that make? Wait… 0.00000006 XMR. Convert this amount to US dollars, it is 0.0012 cents (not dollars). Yes, this will be a slow way to accumulate wealth. If I ran it for 12,000 hours, I still wouldn't be able to buy a piece of gum. Probably don't even use gum.
And that's not even considering the cost. I mean, mining isn't free—you have to pay for electricity. Average electricity price in the city. US is 16.94 cents/kWh. If I ran my miner at 3 watts for 12 hours that would be 24 watt-hours or 0.024 KWh. Using electricity prices, this would cost 0.41 cents. Let me do some quick calculations here. That's right, 0.41 cents more than I generated. I'm no financial expert but this seems like a bad business model.
Of course, no one but a physicist will mine cryptocurrency on a Raspberry Pi. There are fancy mining machines (costing thousands of dollars) that allow you to mint coins faster and with less energy. The other thing to consider is the future price of the cryptocurrency. Even if the cost exceeds the reward today, it's possible that one day it could be worth much more. Finally, cryptocurrency miners can stay where electricity is cheaper. It is even possible to run a solar powered miner.
However, don't forget that for every joule of energy you put into the miner, you create 1 joule of thermal energy. You have to get rid of that heat, otherwise it will cause problems for your computer. But cooling systems use more energy, and that can make it difficult to generate a profit.
But it has to work because there is quite a bit of mining in the US. In 2024, it is estimated that 2.3% of electrical energy is transferred to cryptocurrency. That's a pretty big number, and I'm really not sure it's the best use of our energy supply—especially since cryptocurrency is a fabrication.