PoW coins that's relatively low in traffic, newly created with low amount of miners or PoS coins. elon's view regarding energy consumption feels so random though, he prefer coin that's green but choose doge instead even though there's other coins that are greener and better. however, Nano have been discussed a lot recently and people keep saying that it's greener than doge by a lot so maybe nano is the good option here if we're talking about low energy consumption.