Good morning again Luke,


> [my personal favourite is a focus on power-efficiency: battery-operated 
> hand-held devices at or below 3.5 watts (thus not requiring thermal pipes or 
> fans - which tend to break). i have to admit i am a little alarmed at the 
> world-wide energy consumption of bitcoin: personally i would very much prefer 
> to be involved in eco-conscious blockchain and crypto-currency products].

If you mean miner power usage, then power efficiency will not reduce energy 
consumption.

Suppose you are a miner.
Suppose you have access to 1 watt of energy at a particular fixed cost of 1 BTC 
per watt, and you have a current hardware that gives 1 Exahash for 1 watt of 
energy usage.
Suppose this 1 Exahash earns 2 BTC (and that is why you mine, you earn 1 BTC).

Now suppose there is a new technology where a hardware can give 1 Exohash for 
only 0.5 watt of energy usage.
Your choices are:

* Buy only one unit, get 1 Exohash for 0.5 watt, thus getting 2.0 BTC while 
only paying 0.5 BTC in electricity fees for a net of 1.5 BTC.
* Buy two units, get 2 Exohash for 1.0 watt, thus getting 4.0 BTC while only 
paying 1.0 BTC in electricity fees for a net of 3.0 BTC.

What do you think your better choice is?

That assumes that difficulty adjustments do not occur.
If difficulty adjustments are put into consideration, then if everyone *else* 
does the second choice, global mining hashrate doubles and the difficulty 
adjustment matches, and if you took the first choice, you would end up earning 
far less than 2.0 BTC after the difficulty adjustment.

Thus, any rational miner will just pack more miners in the same number of watts 
rather than reduce their watt consumption.
There may be physical limits involved (only so many miners you can put in an 
amount of space, or whatever other limits) but absent those, a rational miner 
will not reduce their energy expenditure with higher-efficiency units, they 
will buy more units.

Thus, increasing power efficiency for mining does not reduce the amount of 
actual energy that will be consumed by Bitcoin mining.

If you are not referring to mining energy, then I think a computer running 
BitTorrent software 24/7 would consume about the same amount of energy as a 
fullnode running Bitcoin software 24/7, and I do not think the energy consumed 
thus is actually particularly high relative to a lot of other things.

Regards,
ZmnSCPxj
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