After its introduction in 2008, increasing Bitcoin prices and booming number of other cryptocurrencies lead a growing discussion of how much energy is consumed during the production of these currencies. Being the most expensive and the most popular cryptocurrency, both the business world and the research community have started to question the energy intensity of bitcoin mining. This paper only focuses on computational power demand during proof-of-work process rather than estimating the whole energy intensity of mining. We make use of 160 GB of bitcoin blockchain data to estimate the energy consumption and power demand of bitcoin mining. We considered the performance of 269 different hardware models (CPU, GPU, FPGA and ASIC). For estimations, we defined two metrics, namely; minimum consumption and maximum consumption. The targeted time span for the analysis is from 3 January 2009 to 5 June 2018. We show that the historical peak of power consumption of bitcoin mining took place during the bi-weekly period commencing on 18.12.2017 with a demand of between 1.3 - 14.8 GW. This maximum demand figure is between the installed capacities of Finland (~16 GW) and Denmark (~14 GW). We also show that, during June 2018, energy consumption of bitcoin mining between difficulty recalculation was between 15.47 – 50.24 TWh per year.