Well, I'm pretty sure that miners (even with subsidized electricity) are selling over 90% of what they mine just to make expenses. And it's not terribly unlikely that some are selling 100%.
Make no mistake, mining is mostly about making spendable money. And the way to make bitcoins spendable in the wider economy, is to trade them for fiat.
Proof of Work (Pow) is not a sustainable reward system for maintaining a cryptographic transaction system. It would be impossible for bitcoin to reach any sort of mainstream adoption with this severely flawed energy-gobbling incentivizing scheme.
If we look at nature, rainfall is not rewarded for nourishing plants. The sun is not rewarded for its life giving rays. I think the sustainable mining system will be one that more closely models nature.Unfortunately, a solution is nowhere in sight. This is evidenced by a consensus model that has resulted in a maximum block size issue which is crippling the network. The community itself is destroying bitcoin with its continued support for the current fork.
Fortunately, a second generation of cryptocurrencies is being born that is learning from these failures and adapting.
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