Cryptocurrency is a relatively new combination of cryptology and currency in financial areas and is increasingly frequently used worldwide. Blockchain applications are expected to reshape the renewable energy market. However, there is a lack of studies covering the power usage of digital currencies. Therefore, this study ran experiments on mining efficiency of nine kinds of cryptocurrencies and ten algorithms. A comparison of statistical analysis of data in a benchmark and experiment results of Monero mining was conducted. Thereafter, this study provided an estimation of global electricity consumption of the Monero mining activity. The results indicated that the hashing algorithm mainly determines the mining efficiency. Data analysis and experiments and estimated Monero mining electricity consumption in the world and its carbon emission in China as a case study. In 2018, Monero mining may consume 645.62 GWh of electricity in the world after its hard fork. The Monero mining in China may consume 30.34 GWh and contribute a carbon emission of 19.12–19.42 thousand tons from April to December in 2018. Although cryptocurrency mining and blockchain technology are promising, their influence on energy conversation and sustainable development should be further studied.