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Question:

Calculating how long it would take to use 20kW?

HelloI am doing a question on my homework and im being asked to determine how long a tank of gas on a diesel generator would last a family if one tank produced 20kW of electricity. This family uses 2.052kWh of electricity every day. The problem i have run into is that i don't know how to determine how long tha tank can last with only those values, i have a feeling im missing something very obvious here. Any help would be great.Thanks!

Answer:

You do seem to be missing some information here. 20kW of electricity is an amount of power, not an amount of energy. The other answerers assumed that you meant 20kWh, if that is what you meant than their answers are correct.
20/2.052 # of days. about 9 1/2.
Can you post the actual question as written? You have to be able to somehow get a kWh value out of the diesel generator. Otherwise, the answer to the question is 0 days. You can't put gas into a diesel generator and expect it to do anything.
You can't quite do this from first principals. The Gen-set manual may give a spec for fuel consumption, or for efficiency. More likely it does not. The solution is to fill the tank, run it on a dummy load or a real load, if you like, and see how long it takes to get to half way. Or some graduated point. I wouldn't run a diesel dry, as they tend to continue to run on their lubricant until they seize up. Much as I like to model and estimate things, I'm still an empiricist at heart. Jim Jarvis
Yup, you missed the obvious. It is not important how big the tank is, simply that when you have used the whole tank you have produced a total of 20kW/hours of electricity for consumption. So as shown by the first person to answer, the tank will last for around 9.5 days. (Assuming the family's consumption is consistent throughout the day.)

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