Evaluating Energy Sources: Six Criteria and Why No Source Wins Them All

The six criteria. An energy source is judged on carbon emitted per kilowatt-hour over its whole life cycle (building, fuelling, decommissioning); its capacity factor — the fraction of installed capacity actually delivered on average; cost per kilowatt-hour including capital; land taken; whether it is dispatchable, meaning output can be raised on demand; and its characteristic risk. Coal: about 820 g CO₂/kWh, capacity 0.6–0.8, cheap to moderate, large mines, dispatchable, and responsible for sulfur dioxide, particulates and mining deaths. Gas: about 490 g, 0.5–0.6, cheap, small footprint, dispatchable and fast to ramp, but methane leaks in extraction erode its climate advantage and many countries must import it. Nuclear: about 12 g, capacity 0.9, very little land, but huge capital cost, slow to change output, waste that must be isolated for millennia and rare but severe accidents. Hydro: about 24 g, 0.4–0.5, cheap once built, the best dispatchable source, but large reservoirs with displacement, sediment loss and drought risk. Solar: about 40 g, capacity only 0.15–0.25, cheap and falling, land-hungry at farm scale, not dispatchable. Wind: about 11 g, 0.25–0.45, cheap, land shared with farming, not dispatchable; birds, landscape and grid integration are the issues.

Two traps in reading the numbers. A capacity factor of 0.25 means 100 MW of installed solar delivers 25 MW on average, so comparing sources by installed capacity flatters intermittent ones four-fold; multiply by the capacity factor first. Life-cycle carbon counts the concrete and steel of building, which is why nuclear and wind score low despite heavy construction, and why gas scores worse than its combustion alone would suggest once leaks are included.

Why a mix. No source wins every column. Wind and solar are cheapest and cleanest but cannot be called on at will; hydro, gas or batteries provide the dispatchable balance; nuclear or hydro supply steady baseload. The right mix depends on geography — hydro needs mountains and rivers, solar needs sun, wind needs coasts or plains, gas needs pipelines — and on what is being optimised: cost, carbon, reliability, independence from imports, or local jobs. A country choosing energy is choosing which criterion matters most, and an evaluation should say so.

Beyond electricity. Electricity is only about a fifth of final energy; transport, heating and industry burn fuel directly. Decarbonising them means electrifying (electric vehicles, heat pumps) — which multiplies electricity demand — or switching to hydrogen and biofuels, each with its own land and efficiency costs. Efficiency — using less — is cheaper than any source and belongs in every answer.