Bitcoin may be a useful way to send and receive money, but all this financial liberation doesn’t come for free. The community of miners who create bitcoins is using vast quantities of electrical power in the process. This had led some experts to suggest that bitcoin isn’t very environmentally friendly. So how much electricity does a bitcoin take to produce?

Bitcoins are mined by getting lots of computers around the world to try and solve the same mathematical puzzle.

Every ten minutes or so, someone solves the puzzle and is rewarded with some bitcoins. Then, a new puzzle is generated and the whole thing starts over again.

### Power to the People

As more people learn about bitcoin and get interested in mining, and as the bitcoin price increases, more people are using their computers to mine bitcoins. As more people join the network and try to solve these math puzzles, you’d expect each puzzle to be solved sooner, but that doesn’t happen.

The software that mines bitcoin is designed so that it will always take ten minutes for everyone on the network to solve the puzzle. It does that by varying the difficulty of the puzzle depending on how many people are trying to solve it.

What this means is that the time taken to produce a bitcoin doesn’t vary – only the computing power used to produce it does. As more people join the bitcoin network and try to mine bitcoins, they use more computing power, and therefore more electricity, for each bitcoin produced.

### Doing the Math

How do you calculate the electrical energy used to power the bitcoin network? One way to do it is to look at how many sums are conducted every second to solve bitcoin’s mathematical puzzles, and then to find out how much electrical energy it takes to do each sum.

These individual sums are called hashes, and there are vast numbers of them – so many, in fact, that we have to think of them in terms of millions of hashes (known as megahashes) or billions of hashes (gigahashes) to make any sense of them.

At the time of writing, the computers on the bitcoin network were doing 342,934,450 Gigahashes per second.

There are lots of different bitcoin mining computers out there, but in recent months, companies have focused on ASIC miners, which use less energy to conduct their calculations. Mining companies that run lots of ASIC miners as businesses have told me that they use one watt of power for every Gigahash per second of computing that they do when mining for bitcoins.

At this rate, the bitcoin network runs at 342934450 watts, which equates to around 343 megawatts. Calculations based on EIA data reveal that the average US household consumes about 1.2 kilowatts of power, meaning that 343 megawatts would be enough to power 285,833 US homes at the time of writing (May 2015).

That’s quite a lot of energy - about a third of the homes in San Jose. And our 1 watt per Gigahash/second figure is pretty efficient. There will be a large number of residential users who will be taking more power to run their miners.So it's likely that this is a conservative estimate.

Over the last few years, media outlets and blogs have produced various articles, with various estimates of its electrical energy use. Some decry bitcoin as the end of the world as we know it, while others thought the whole argument about bitcoin’s energy consumption was overblown.

It's really all relative because the bitcoin network itself has inherent value as a secure payment mechanism. What price you put on that in terms of energy consumption depends on how useful you think it's going to be to society.

The problem with estimating bitcoin’s energy consumption, and then judging it, is that it will change over time. The hash rate on the network – that is, the computing power that people are spending on it – has grown drastically over time, and tends to fluctuate with bitcoin’s price. If, as some suggest, bitcoin rises rapidly in price, how much more juice will it consume?