His findings are not completely accurate, but also not completely wrong either. My own formal well-documented estimate is that Bitcoin used 0.09% of the world's electricity as of January 11th, 2018 (http://blog.zorinaq.com/bitcoin-electricity-consumption/). After 4 months of growth I estimate we are around 0.15-0.20% today. Therefore reaching 0.50% by the end of 2018 is plausible; not likely but plausible. That said, overall I think Alex de Vries's figures are rather inflated because he makes two errors. Firstly, his model assumes that manufacturers sell at cost and make zero profits, which allows miners to spend more on electricity. In reality we've seen Bitmain, the largest manufacturer, make billions of dollars over the last few years. No one expects them to make zero profits by the end of 2018. Secondly, de Vries makes the mistake of assuming that all cryptocurrency mining chips produced by TSMC on behalf of Bitmain end up in Bitcoin mining machines. In reality many chips are fabricated for cryptocurrencies other than Bitcoin. This altcoin sector is rapidly growing. It wouldn't be unreasonable to assume that Bitcoin mining machines will represent less than half of Bitmain's sales by the end of 2018.
(This is a copy of my comment from yesterday's thread on the same topic https://news.ycombinator.com/item?id=17084253)