Preface: if you’re a bitcoin expert, gird your loins because I’m probably going to be making a LOT of technical errors in this post.
So: space based solar power, but instead of beaming the power to Earth, we mine bitcoin with it.
OK. I’m indifferent to Bitcoin. I generally think it’s a dumb idea but that has some interesting technology. But it’s useful conceptually for imagining a straightforward way to turn computing power into money. Or, once progress on mining hardware slows down to the now-slow Moore’s law of 4 year doublings, a way to turn electricity directly into money while only having to transmit a relatively short amount of data.
What it is, very briefly, is a kind of “cryptocurrency” designed to do away with a central ledger, instead using a sort of consensus of many distributed computers as a ledger. Money is added to the money supply by “mining,” which in this case just means doing some pointless but hard and verifiable calculation until you randomly free up a “block” which is a bunch of bitcoins (each bitcoin is like $750 right now… easily subdivided, by the way). Mining difficulty is adjusted to keep the pace of adding to the money supply at a steady but very slowly decreasing rate.
I googled “bitcoin mining hardware,” and this popped up: https://www.bitcoinmining.com/bitcoin-mining-hardware/
The best hardware listed uses about 1200 Watts of electricity (all turned into heat) and produces roughly $4 of BTC per day and costs $400-something (…while consuming about $400 of electricity at 14 cents per kWh…). And weighs about 4 kg, so 300W/kg. So a dollar gets you 3 Watts of useful bitcoin mining, and it takes about 100 days for it to pay for its own hardware cost assuming mining difficulty doesn’t change. (Which is a terrible assumption, as more and more mining hardware comes online, the actual yield of bitcoin mining reduces to compensate.)
But only 33 cents per watt-used is great! That means we can replace that super expensive laser or microwave transmitter and receiver with cheap computer chips and radiators. And double or quadruple the power is available, too, because we don’t have all those transmission losses. But we do need to radiate all that heat away, so we’ll need a few more radiators, but in principle that’s not too bad. Radiators in this temperature range are like 100W/kg, so if we assume about 200W/kg for the solar power and a little extra for comms and pointing, we’re looking at about 50Wbitcoin/kg launched to orbit.
So at $100/kg to orbit (same price as the mining hardware, by the way!), and another $100/kg for hardware for a total cost of $200/kg, We have about $4/Watt-bitcoin. At 4 year replacement cycles (probably the power and thermal system would last a lot longer, but hardware would need to be updated), that’s about 11 cents per kWh of bitcoin processing, which is competitive (since it includes the mining hardware as well as the power). At longer intervals, even better.
But of course, this assumes bitcoin remains popular WHILE bitcoin mining hardware stagnates. The latter is not a terrible assumption, given that we’ve essentially reached the end of Moore’s Law (we’ll still see large improvements, but over longer timeframes, like 4 years instead of 2 years): http://arstechnica.com/information-technology/2016/02/moores-law-really-is-dead-this-time/