How cutting power to Bitcoin miners can actually burn more energy

Some Bitcoin mining vardiff (variable difficulty) controllers can keep demanding work calibrated for a machine's former speed after it cuts hashrate. The miner can keep hashing and consuming electricity while accepted shares become vanishingly rare.

Bitcoin Optech highlighted the failure mode on Sept. 18, drawing wider attention to an analysis that mining engineer Eric Price published in July. The finding concerns pool-assigned share difficulty, not Bitcoin's network difficulty, and it describes a testable controller weakness rather than evidence of widespread miner losses.

How Bitcoin mining vardiff gets stuck

Pools assign each connection a share difficulty that is easier than Bitcoin's block difficulty. A higher assigned difficulty corresponds to a harder share target. The submitted shares let the pool estimate hashrate and account for contributed work, while a variable-difficulty, or vardiff, controller adjusts the assignment to keep shares arriving at a useful rate.

Price's controller analysis describes a trap after a miner slows sharply. If the controller recalculates only when a share arrives, the old, harder assignment makes the next share less likely. With no fresh share to trigger an update, the controller can hold the wrong difficulty, which keeps the share stream sparse.