20–50 → 820 a solar panel emits about 20 to 50 grams of co2 for every kilowatt-hour it will ever make, almost all of it before it is switched on. coal makes the same kilowatt-hour for about 820, gas for about 490. the panel repays its own energy in one to two years and runs for thirty.
method lifecycle CO2 per kWh from IPCC AR5 harmonized medians (PV ~48, falling toward ~20 in recent studies; coal 820; gas 490); energy payback from Fraunhofer ISE.
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