In this news:
What about cryptocurrency? This is also made up by humans. You can “mine” crypto using a computer to do pointless, gnarly computations. These systems are usually set up so that it takes more computational power as more currency is mined, so the early coins are easily obtained and the later ones are more difficult. This also makes it like gold mining—after people find the easy stuff, you have to spend more to get more. But what happens when you use computers to solve massive problems? It's all about heat and energy. Real heat and energy.
A Raspberry Pi Monero Miner
To really understand crypto mining, you sort of need to mine some crypto. So that’s what I did, using a tiny, cheap, single-board computer called a Raspberry Pi to mint Monero cryptocurrency. Yeah, this tiny setup is like digging for gold with a teaspoon, but it’s fine for studying the physics involved.
Once I get this beast of a machine running, I can take some measurements. In particular, I can determine the power it uses as well as the thermal output. In physics, power is the rate of energy change in units of watts (1 watt = 1 joule per second). For an electrical device, power can be calculated as the product of the input electrical current (I) and the voltage (ΔV):
I know the Raspberry Pi runs at 5 volts, so I can just measure the electric current going into it to get the power. My meter registered a current of 0.62 amps, which gives a power of 3.1 watts. That’s 3.1 joules of energy used every second that it runs. But where does that energy go? Is there energy in cryptocurrency? No, it's all converted to thermal energy. Can we measure it? Yes we can.
To measure the thermal energy created, I put my Raspberry Pi in an insulated container with 1,000 milliliters of water. (Don't worry, the Pi was in a zip-lock bag so it wouldn't get wet.) Now I can measure the temperature of the water as crypto is mined. Here's the temperature as a function of time for a little over one hour of run time.
After the first 20 minutes, the water temperature seemed to increase at a fairly constant rate of 0.0006 degrees Celsius per second. This increase in temperature means there is an increase in thermal energy, which we can calculate as:
Here m is the mass of the stuff (in this case, water), and C is the specific heat capacity—the amount of heat energy needed to raise the temperature of that 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 get that the water requires a power of 2.51 joules every second (or 2.51 watts).
Oh, look at that. Even with this rudimentary measurement system, this is pretty close to the power going into the Raspberry Pi. The difference is probably due to imperfect insulation. So you can see that the cryptocurrency power is just thermal energy. Honestly, I'm surprised it worked so well.
Show Me the Money!
Although it's possible to run a crypto miner as a way to warm your house, that's probably not why people do it. What’s the payoff? Well, let's do some quick calculations. I ran my Raspberry Pi miner for 12 hours. How much money did that produce? Wait for it … 0.00000006 XMR. Converting this to US dollars, it's 0.0012 cents (not dollars). Yes, this would be a slow way to amass a fortune. If I ran it for 12,000 hours, I still couldn’t buy a piece of chewing gum. Probably not even used chewing gum.
And that’s not even accounting for the cost. I mean, mining isn't free—you have to pay for the electricity. The average cost of electricity in the US is 16.94 cents per kilowatt-hour. If I run my miner at 3 watts for 12 hours, that would be 24 watt-hours, or 0.024 KWh. Using the price of electricity, this would cost 0.41 cents. Let me just do some quick math here. Yup, 0.41 cents is more than the money I created. I'm no financial expert, but this seems like a bad business model.
Of course, no one but a physicist would mine crypto on a Raspberry Pi. There are fancy mining machines (costing thousands of dollars) that let you mint coins faster and with less energy. The other thing to consider is the future price of a cryptocurrency. Even if the cost exceeds the reward today, maybe one day it could be worth much more. Finally, a crypto miner could be in a location with cheaper electricity. It's even possible to run a miner on solar.
However, don't forget that for every joule of energy you put into a miner, you are going to produce 1 joule of thermal energy. You have to get rid of that heat, or it will cause problems for your computers. But cooling systems use more energy, and that can make it difficult to produce profitable currency.
But it must work, since there's quite a bit of mining in the US. In 2024, it was estimated that 2.3 percent of electrical energy went into cryptocurrency. That's quite a bit, and I'm really not sure it's the best use of our energy supply—especially since crypto is just a made-up thing.
