Worth mentioning the cryptocurrency that Bram Cohen (inventor of bittorrent) is creating that is explicitly designed to be low-energy usage and more distributed: https://www.chia.net/ It uses "Proof of Space" (proof that you're allocating a certain amount of storage space) instead of Proof of Work or Proof of Stake. Pretty interesting and they're coming out of beta into their mainnet in the next few weeks. Their on-c…
If that takes off, aren't we liable to see a rocketing demand for storage, doing to the storage market what PoW does for the graphics card market? And while it may be low energy to run, creating hard drives just to prove you have space seems a less than environmentally friendly activity. It looks just like another proof of waste
Storing the whole chain takes a bunch of space anyway, so you have a similar storage problem there too.
If you want to see how cheap persistent storage can get, look up the cost of Amazon Glacier. It's shockingly cheap - $0.005 per GB or even less.