The bitcoin network is run by miners, computers that maintain the shared transaction ledger called the blockchain. A new study estimates that this process consumes at least 2.6GW of power—almost as much energy as the nation of Ireland. This figure could rise to 7.7GW before the end of 2018—accounting for almost half a percent of the world’s electricity consumption. The study is an updated version of calculations performed late last year by analyst Alex de Vries.

In this new version, de Vries has gathered more detailed information about the economics of the mining business. But his new numbers are broadly consistent with the old ones. Last December, he estimated that the bitcoin network was consuming roughly 32TWh annually, or 3.65GW. His website, which is updated daily, now shows the network consuming 67TWh annually, just under that upper bound of 7.7 GW shown in his new study.

As de Vries makes clear in his new paper, these numbers are necessarily speculative. Bitcoin mining is a decentralized and secretive industry. We know how much computing power the bitcoin network has—right now it’s about 30 trillion SHA-256 hashes per second. But miners are making these calculations on a variety of different types of hardware with different levels of energy efficiency, so we can’t convert that figure directly to energy consumption.

If you assume that the entire network is using the most efficient known mining hardware—the Antminer S9 from Bitmain—that yields de Vries’s lower bound energy consumption of 2.6GW. However, we know that people are using other, less efficient hardware, so the true energy consumption is probably significantly higher.

To establish his upper bound of 7.7GW, de Vries uses some economic reasoning. Bitcoin’s rules allow the creator of a block to award itself 12.5 bitcoins—worth more than $100,000 at today’s prices. With a new block being created every 10 minutes, that works out to around $15 million per day in mining revenues.

A crucial point here is that the difficulty of the mining task automatically adjusts to maintain a 10 minute average block creation rate. So if more computing power joins the network, the result isn’t that more bitcoins get created. Instead, it takes more computing power to produce each bitcoin, making existing mining hardware less profitable than before—and driving up the energy consumed per bitcoin, according to arstehnica.com.

So de Vries calculated how much electricity bitcoin miners would have to consume for bitcoin mining to no longer be profitable. He assumed that electricity prices make up 60 percent of the cost of mining and that electricity costs an average of 5 cents per KWh.

That yielded energy consumption of 7.7GW, which serves as an upper bound of the bitcoin network’s energy consumption. If energy consumption rose above that figure (assuming that the average electricity cost really is at least 5¢) that would mean that some miners would be losing money and would have to shut down.