Simple Cycle

A simple cycle (or open cycle) is the most basic gas-turbine power configuration: air is compressed, mixed with fuel and combusted, and the expanding gas spins a turbine coupled to a generator. The hot exhaust is then vented straight to atmosphere rather than recovered. This keeps thermal efficiency in roughly the 33–43% range at full load — falling further at partial load — but it makes the plant cheap to build, simple to operate, and very fast to start and stop. In grid parlance these units are the "peakers": machines that exist to be available, not to be efficient.

Why operators still choose it

Simple-cycle units survive because dispatch speed beats fuel efficiency in certain roles. A peaker can reach full output in minutes, making it ideal for covering demand spikes, backstopping intermittent wind and solar, or providing emergency capacity when baseload plants trip offline. The capital cost per megawatt is far lower than a combined-cycle plant, so for a unit that runs only a few hundred hours a year, burning extra fuel during those hours is cheaper than financing a heat-recovery train that sits idle. The thermodynamic price is steep: more than half of the fuel's energy leaves the stack as hot exhaust — exactly the energy a combined cycle plant would recapture with a steam bottoming stage.

Why miners care

Behind-the-meter Bitcoin mining frequently sits next to simple-cycle gensets, flare-gas units, or curtailed renewable capacity precisely because that energy is otherwise underused or wasted. A peaker that runs rarely represents stranded capital; a miner co-located with it can monetize the idle hours by consuming power the grid does not want, then curtail instantly when the grid calls. Because hashrate is the most interruptible industrial load ever invented — machines can drop to zero and return in seconds without damage — mining pairs naturally with generation assets whose whole identity is flexibility. A simple-cycle source signals cheap, opportunistic power rather than efficient baseload, and that shapes the economics of any co-location deal: the miner is buying the hours nobody else wants.

The heat-reuse angle

Reading the efficiency numbers

The plant-economics vocabulary is worth a minute, because it is the language every power-purchase conversation is conducted in. Generator efficiency is usually quoted as heat rate — fuel energy in per unit of electricity out — and a simple-cycle unit's heat rate is high precisely because the exhaust leaves unrecovered. That translates directly into a higher marginal cost per megawatt-hour than combined-cycle or baseload plants, which is why peakers only run when prices spike and sit idle otherwise. For a miner negotiating behind-the-meter power, this arithmetic is the deal: your offtake during idle hours turns a stranded asset into a utilized one, and your instant curtailment preserves the plant's core business of selling into price spikes. The same vocabulary flags the opportunity in the other direction — every point of efficiency the simple cycle gives up is recoverable heat, and a co-located load that can use warmth improves the site's total energy picture without touching the turbine.

The vented exhaust is also an opportunity hiding in plain sight. Every megawatt-hour a simple-cycle turbine wastes up the stack is heat that could serve greenhouses, grain drying, aquaculture, or district loads — and the same logic applies one layer down, to the miners themselves. An ASIC converts essentially all of its electrical input into low-grade heat, so a mining site attached to a peaker is a two-stage heat source: turbine exhaust at high temperature, miner exhaust at comfortable-space temperature. Capturing either stream turns a thermodynamic loss into a second revenue line, which is the core idea behind a Hashcenter — a facility designed from the start to sell computation and heat rather than throw half its product away. Contrast the efficiency-maximizing two-stage approach at combined cycle, see how exhaust energy is monetized in district heating, and for the miner-side version of the same philosophy see waste heat recovery.