Consider that the previous version of the S7, the S5, had an efficiency of just 0.
That means the S5 uses twice as much electricity per hash as the S7. Equipment Costs Miners generate heat, and also need to be supplied with electricity. Unless you already have the needed parts, you will likely need to purchase cooling fans and power supplies.
Electricity Costs Electricity costs can make or break any mining operation. A monthly electric bill means monthly costs on top of the upfront cost of the hardware. In the USA, for example, most mining hardware is run in Washington State, where there is cheap hydroelectricity. It can make or break your mining operation.
Extra Heat and Weather Creative miners in cold areas can use the heat generated by miners to heat their houses in the winter. If the heat generated by miners will partly replace your normal heating costs, it is one way to save money and improve your chances of profitability. Miners in cold areas also have an advantage because they may not need to use extra fans to cool the hardware. A higher difficulty is indicative of more hash power joining the network. As you would expect, more hash power on the network means that existing miners then control a lower percentage of the Bitcoin network hash power.
The image above shows the network hash power over the last 2 years. From September to Februarythe network hash rate tripled.
Hash rate and network difficulty are external factors that should be accounted for. However, pay attention to advances in mining technology and efficiency to get a better idea of how the hash rate and difficulty may look down the line.