Open Cycle Gas Turbine (OCGT / Peaker)

An Open Cycle Gas Turbine (OCGT), also called a simple-cycle gas turbine or peaker, is the most basic form of gas-fired generation: a single gas turbine — compressor, combustor, and power turbine on one shaft — that exhausts its hot gases straight to atmosphere without recovering any waste heat. That simplicity costs efficiency, with typical figures of roughly 33–43% at full load, but it buys speed and cheapness: an OCGT can start, synchronize, and reach full output in minutes, and its capital cost per kilowatt is among the lowest of any dispatchable plant. Grids worldwide keep fleets of them for exactly this reason — they are the fire extinguishers of the power system, idle most of the year and priceless during peaks.

The efficiency trade-off

A gas turbine's exhaust leaves at several hundred degrees Celsius, carrying away more than half the fuel's energy. A combined-cycle plant captures that exhaust in a heat-recovery boiler and runs a steam turbine on it, pushing plant efficiency toward 60%; an OCGT simply vents it, which is why its heat rate — fuel energy burned per kilowatt-hour produced — runs so much higher. Efficiency degrades further at partial load and on hot days (turbines breathe air, and hot air is thin), so an OCGT is happiest running near rated output in short bursts rather than throttled down for hours. The economics follow: cheap to build, expensive to run, ideal for machines that run rarely.

Where OCGTs fit mining

For a miner generating power on site, the OCGT's appeal is flexibility rather than fuel economy. Operators monetizing flared or intermittently available gas may favour a fast-starting turbine that can follow an unsteady fuel supply, and mining is the rare load that can absorb whatever the turbine produces and shut off just as fast — a natural pairing for flare-gas sites where the alternative is burning the gas for nothing. Turbines also bring practical advantages at remote sites: high power density, low vibration, modest maintenance per running hour, and tolerance for a range of gas qualities. But for sustained, fuel-cost-sensitive hashing, the arithmetic usually favours a reciprocating engine genset — modern lean-burn gas engines reach 45–50% electrical efficiency, hold that efficiency across a wide load band, and can be added in modular increments as the fleet grows.

Making the call

The decision hinges on run-hours and fuel price. Hashing is a near-constant 24/7 load, which stacks the deck toward efficiency: every point of heat-rate disadvantage is paid every hour, forever, and directly inflates cost per terahash. If the plant will hash around the clock on purchased gas, the engine or combined-cycle option almost always wins. If the fuel is free-but-fitful — flare gas that comes and goes with upstream operations — the OCGT's quick response, simple installation, and lower capital cost can justify the fuel penalty, since wasted potential fuel costs nothing. Weigh the unit's turndown ratio against how variable your gas supply really is, and be honest about which side of the baseload-versus-peaking line your operation actually lives on. A peaker asked to run baseload is the wrong tool wearing the right nameplate.

One more consideration deserves a line item: the exhaust itself. An OCGT's vented heat is a genuine resource — hundreds of degrees of clean, high-volume exhaust — and while grid peakers rarely run long enough to justify recovering it, a mining site with steady run-hours changes that calculus. Even partial heat recovery for buildings, greenhouses, or process heat claws back some of the simple cycle's efficiency penalty without the capital weight of a full combined cycle. The broader habit applies to every generation choice a miner makes: price the whole energy stream, not just the electrical output, because the machine you chose for its fast starts may be quietly venting your second-best product.