 those cryptocurrencies. In the case of Bitcoin, only the fastest miner who solves the mathematical problem gets the mining reward, and miners compete to be the one. As the price of Bitcoin has increased, more people have participated in mining. This phenomenon caused severe competition among the miners, and the problems miners have to solve became much more complicated. As a result, miners need high-performance mining equipment that requires more energy than before to win the competition. Moreover, an increased number of miners and difficulty of problems also provoke a large amount of electricity consumption. 