correct, that statement should be BTUs convert to energy output of the engine/system depending on the efficiency of the engine/system.
BTUs convert to kWh by dividing the number of BTUs by 3413.
128,000 BTUs = 37.5 kWh
how much of the 37.5 is useable electricity depends on efficiency of the engine. Given that the diesel engine did not get hot while running on the biofuel, I would suspect that it was running more efficiently than it does on ordinary diesel fuel since less energy was lost as heat.
All of this banter won't matter when a contract is signed, unless you want to go the customer and argue that they'll be losing money from the arrangement. But my guess is that the customer will have done far more research than you have.
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