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The difference between the price of electricity sold by a generator and the price of the fuel used to generate it, adjusted for equivalent units. The spark spread can be expressed in dollars per megawatt hour ($/MWh) or dollars per million British thermal units ($/mmBtu) or other applicable units. To express it in $/MWh, the spread is calculated by multiplying the price of gas, for example (in $/mmBtu), by the heat rate (in Btu/kilowatt hour), dividing by 1,000 and then subtracting the electricity price (in $/MWh). Also called a spark arbitrage.