Bitmain Antminer S21 Hydro — Crypto Mining

What does that actually mean?

At the world-average grid intensity of about 475 g CO₂e/kWh, Bitmain Antminer S21 Hydro running 24/7 for a year releases about 21,997 kg of carbon dioxide equivalent. Here's what that looks like in everyday terms:

Where you plug in matters

Electricity is not one thing. A kilowatt-hour from a coal plant carries roughly 820 g of CO₂; the same kilowatt-hour from a hydro reservoir carries about 24 g. That's a 34× difference — large enough that Bitmain Antminer S21 Hydro's annual footprint swings from roughly 37,975 kg on coal-heavy grids down to about 1,111 kg on hydro-dominated grids. The single biggest lever a miner has on their carbon footprint is choosing where to plug in.

Regions commonly used for low-carbon crypto mining include Quebec and British Columbia (hydro-dominated, typically <50 g CO₂/kWh), Iceland and Norway (geothermal + hydro, often <30 g), Paraguay (Itaipú hydro), and parts of the US Pacific Northwest. Coal-heavy grids — Kazakhstan, Inner Mongolia, Poland, parts of Australia — sit at the opposite end, often above 700 g CO₂/kWh.

Some operators also reduce their net impact by using otherwise-wasted energy: flare gas at oil wells (burning methane that would be vented anyway), curtailed renewables (wind or solar that the grid can't absorb), or behind-the-meter hydro during off-peak hours. These arrangements can drop effective emissions below the local grid average because the energy would have been wasted or flared without the mining load.

How to reduce this rig's footprint

• Pick a greener ASIC. The efficiency column above matters as much as the grid: a 15 J/TH rig emits roughly half the CO₂ of a 30 J/TH rig for the same hashrate.
• Choose a low-carbon host. Data centres advertising hydro, geothermal, or nuclear power typically sit at <100 g CO₂/kWh.
• Look for stranded or curtailed energy. Flare-gas miners, wind-curtailment co-location, and off-peak hydro arrangements use energy that would otherwise be wasted.
• Use heat recovery. Capturing the heat for greenhouse agriculture, pool heating, or district warmth offsets fossil-fuel heating that would have been burned anyway.
• Time-shift your uptime. In grids with high daytime solar, running more during the day and less at night lowers your effective intensity even if you don't switch providers.
• Purchase verifiable offsets. Treat this as a last resort, not a substitute — and favour additional, permanent, third-party-verified projects (Gold Standard, Verra VCS).

Frequently asked questions