I hope Bitcoin is more than just a fad because it would provide a really convenient way of harnessing solar energy in space without having to beam it all back to Earth. But this can only happen if Moore's Law slows way down (which is happening) and if mining ASICs hit an efficiency plateau lasting for years (is this happening?).
Currently, it costs about 9MWh per BTC, or about $1000 in electricity per bitcoin to mine on a pretty efficient S9 antminer. S9s currently go for about $2/Watt and require about 100 J/TH and weigh, I don't know, maybe 1kg per kilowatt (or 1000W/kg).
Solar modules are about 30 cents per watt on the spot market, produce about 100W/kg (if weight optimized, i.e. not such a thick aluminum frame). Since all the heat must be dumped into space at the ASIC's operating temperature, radiators are about 100W/kg and probably cost as much as solar modules ($0.30/W) if mass produced.
So 1000W of mining capacity would weigh 21 kg and cost $2000+$300+$300= $2600. To launch 21kg at $100/kg to GSO (this is an incredibly low cost, but could be achieved with SpaceX's or Blue Origin's long-term ITS/BFR or New Armstrong rockets) would cost about $2100. So a total of about $4.7/W.
Assuming the lifetime of that whole thing is about 12 years (a reasonable time for a risk-free doubling of an investment), that's about 12 BTC, or about $47,000 at today's prices, or a factor of 10 return.
(Today's BTC returns ~40 cents per kWh invested, this scheme would break-even at about 4 cents per kWh generated.)
...but:
1) There's a whole bunch of glue, like a network link and spacecraft subsystems that must be included as well as spacecraft processing.
2) Moore's Law in the strict sense is over, but progress still continues.
3) ASIC improvement is possible.
4) We don't have Musk's or Bezos' huge reusable rockets quite yet.
5) If return was this well-proven, you'd likely have a bunch of competition from even cheaper sources of energy.
6) I still think Bitcoin is far too volatile and speculative to justify this kind of investment. Given the reduction in mining rate, if you knew Bitcoin would be able to justify this kind of investment over decades, then you'd probably be better off just buying a bunch of BTC right now and holding it.
But maybe the future of cryptocurrency will eventually enable a less volatile and more proven return, making stuff like this worth investing in. I hope so.