A Proof-of-Work (PoW) is a piece of data which is costly to produce, so as to satisfy certain requirements, but is trivial to verify. Bitcoin uses the Hashcash PoW. Mining, the process of producing PoW, plays a central role in creating, distributing, and securing Bitcoin and many of its variants. The most common criticism of PoW mining is its massive waste of energy. At the time of writing, the total daily revenue of mining Bitcoin is around $1.8 milion USD. Depending on the aggregate profit margin and the fraction of overall cost that electricity accounts for, we estimate the daily total electricity cost between $200k and $500k USD. In addition to this wastefulness, there are several more reasons why mining remains a very controversial aspect of PoW cryptocurrencies.
Proof-of-Stake is an alternative to Pow, where based on connectivity to the network and random chance, you can receive new coins to assist in the decentralization of the network. One useful feature of Proof-of-Stake is the significant savings in energy consumption in that it requires no dedicated hardware and negligible amounts of electricity to reward miners, and in many cases is far more resilient to a 51% attack on the network. (Blackcoin Core Team 2016)
