Combined Cycle

A combined cycle is a power-generation arrangement that captures the hot exhaust of a gas (combustion) turbine and uses it to raise steam for a second, steam-turbine generating stage. By harvesting energy that a single turbine would otherwise dump to atmosphere, the configuration lifts electrical efficiency from the 33–43% range of a turbine alone to roughly 55–61% at full load. For every megawatt produced, a combined-cycle plant burns about a third less fuel than a simple-cycle unit, which directly lowers the cost per kilowatt-hour and the carbon intensity of that power.

How the two stages work together

The first stage is a Brayton-cycle gas turbine: compressed air and natural gas combust, the expanding gas spins the turbine, and a generator produces electricity. The exhaust leaving that turbine is still several hundred degrees Celsius — far too energetic to waste. It passes through a heat recovery steam generator (HRSG), essentially a large heat exchanger of tube banks, which boils water into high-pressure steam. That steam drives a Rankine-cycle steam turbine, the second stage, turning a second generator from the same original fuel feed. Some plants add supplementary duct firing in the HRSG for extra peak output, and many operate in cogeneration mode, exporting leftover steam or hot water to industry or a heat network. This layered heat harvesting is why combined-cycle gas turbines (CCGTs) dominate efficient grid-scale natural-gas generation worldwide.

Relevance to mining power economics

Bitcoin miners rarely run combined-cycle plants themselves, but the concept matters when evaluating behind-the-meter or stranded-gas deals. A simple-cycle peaker or a flare-gas genset converts perhaps a third of its fuel energy to electricity and wastes the rest as heat; combined-cycle hardware is reserved for baseload where its capital cost pays back over long running hours. Understanding that gap helps an operator judge what a power offer actually represents: efficient baseload generation priced accordingly, or cheap, otherwise-curtailed energy — flare gas, off-peak surplus, stranded capacity — that mining is uniquely able to monetize because an ASIC fleet can sit anywhere and consume any profile of power. Miners are frequently the buyer of last resort for exactly the megawatt-hours that efficient plants cannot economically serve.

The same logic, one level down

The philosophy of the combined cycle — never let usable heat escape without extracting value — is precisely the logic of mining heat reuse. A miner converts essentially all of its electrical input into low-grade heat while producing hashrate; capturing that heat for a workshop, greenhouse, water preheat, or a network connection turns a single energy purchase into two products, exactly as the HRSG turns one fuel feed into two generators' worth of output. A home miner heating a garage is running a personal combined cycle: hashes first, heat second, nothing vented that could have been used. That mindset — squeeze every joule twice — is the common thread from utility-scale CCGTs down to a single space-heater miner.

Compare the lower-efficiency, fast-dispatch sibling at Simple Cycle, see how recovered exhaust energy is captured in Waste Heat Recovery, and follow the heat to its community-scale destination in District Heating.

Reading a power contract with cycle literacy

Cycle literacy pays off in negotiation. If a counterparty offers "surplus" power from a combined-cycle plant, ask when the surplus occurs: CCGT baseload rarely produces genuinely stranded energy, so a deep discount usually signals curtailment windows, transmission constraints, or a plant running out of merit order — all of which shape how many hours per year your machines will actually run. Conversely, simple-cycle peakers and flare sites produce power that is cheap precisely because it is intermittent or remote, a profile mining tolerates better than almost any other load. Matching your fleet's flexibility to the generation profile on the other side of the meter — and pricing interruption honestly — is where the durable margins in mining power deals actually live.