Undervolting
Undervolting means lowering the voltage, and often the frequency, of a miner's chips to use less energy per unit of hashrate.
Undervolting is the opposite of overclocking. Instead of pushing the chips beyond the factory setting, you lower their supply voltage, usually together with their frequency. The machine produces a little less hashrate, but it draws noticeably fewer watts and gives off less heat. On ASICs and graphics cards alike, it is one of the settings most used by miners who keep an eye on their electricity bill.
Why does it work? The power a chip consumes rises much faster than its voltage, so a small drop in voltage saves a lot of watts. Since hashrate falls more slowly than power consumption, energy efficiency, expressed in J/TH for a Bitcoin ASIC, improves. Each chip does, however, have its own minimum stable voltage: going too low causes hardware errors and work rejected by the pool.
In practice, undervolting is useful when electricity is expensive, when the room gets too hot or when the electrical installation is limited. On a product page, look at the stated efficiency in J/TH and the operating modes available: a recent machine often keeps good efficiency in eco mode. After changing a setting, monitor the error rate and temperature for several hours before confirming the profile.
The HappyMining firmware offers eco profiles and a power limit set as a percentage or in watts for the Antminer S19, S21, T19 and T21. We install it free of charge on machines bought from us.