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Costs per kWhby maaariiianne
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#1
May210, 03:30 PM

P: 8

Dear Physics friends!
I would be very grateful if you could help me. I am currently working on my master thesis and I have the following question: The overall annuitized capital costs of a distribution grid amount to: 900 USD per kw and year. How do I get the costs per kwh? Thanks a lot! Best, Marianne 


#2
May210, 03:34 PM

P: 648

Divide by the number of hours in a year.
That's 24 x 365 


#3
Jul910, 09:07 AM

P: 8

Thanks a lot for the answer. helped me a lot.



#4
Jul910, 09:58 AM

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P: 22,313

Costs per kWh
$.1/kWh? Seems high. Where'd the data come from?



#5
Jul910, 06:48 PM

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P: 12,074

I pay 0.17 $/kWh, and I'm in central NJ not too far from you Russ.



#6
Jul910, 06:50 PM

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P: 22,313

That said, now that I know the OP is in Africa, my frame of reference is gone! 


#8
Aug1510, 04:54 PM

P: 8

Great! thanks a lot for your help!



#9
Aug1510, 05:00 PM

P: 8

Hey,
If I have a diesel generator with a capacity of 300 Watts and households consume on average 50kWh of electricity per months (Kenya), how many households can be supplied with such a generaor? Could you please, please tell me how to calculate this. Thanks a lot. Best, Mari 


#10
Aug1510, 05:42 PM

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P: 22,313

Welcome to PF.
watts * hours = watthours So 300 watts for 1 month is 218 kWh. So you could perhaps serve 4 houses with a 300 W generator. But, whether you can really supply 4 houses depends more on the peak usage of each house than the total monthly usage. 300 W is not a lot of power (it won't even run a coffee/tea pot), so odds are that you can't even supply a single house unless the generator is charging a bank of batteries that can then provide a variable load to the houses. 


#11
Aug1610, 02:18 AM

P: 665

Another way to look at it is that your generator will run five or six small electric light bulbs at the same time. (5 of 60 watt bulbs).
A fridge takes about 30 to 40 watts so you could run maybe 8 of them together. (Not at the same time as the lights!) A computer takes about 150 to 200 watts  you might be able to power two if you turned off the lights and the fridge. A television is about the same or slightly less. So really, one or two houses might be supplied if they were careful to share the electricity. (One or two fridges, one television and a couple of lights all on at once would be the limit) 


#12
Aug1610, 03:43 AM

P: 8

Thanks a lot for your answers. Does is mean that with a 300 Watt generator I can produce 300 Watts every hour? So if the generator is mainly used for lighting between 7pm and 10pm, around 3 households could use around 2 electric bulbs. This means then that the households consumes 360Watthours per day, 10800 (10.8Kwh) Watthours per month.
The generator could then supply 27000 Watthours (27kWh) per month. Are these calculations correct? Thanks a lot! 


#13
Aug1610, 04:01 AM

P: 665

Watts is a measurement of continuous supply or consumption of power.
That doesn't mean 'over a period of time' it means 'all the time' A 60 watt bulb, uses 60 watts of power while it is on and it needs a 60 watt generator to supply it. It's proportional to the rate you are burning diesel. (pints or gallons per hour) The total amount of power supplied over a time period is measured in watthours (or kilowatt hours). That is proportional to the total amount of diesel you burn in that time. So, 3 households, using 2 bulbs each would use (assume 60 watt bulbs) 6*60 = 360 watts. That would overload your generator. Say we turn off one of the bulbs  that gives 300 watts  your generator could handle that. In which case, for 3 hours each day your generator is supplying 300 watts  so that's 300 * 3 = 900 watthours per day. Over 30 days that's 27 kilowatthours per month. (The kilowatt hours figure isn't useful for anything  what matters is that 300 watt limit on the generator) 


#14
Aug1610, 04:09 AM

P: 8

Great, thanks a lot, now I understand it. Do you maybe know approximately how much diesel a generator of that size needs per hour? Is it common to use a battery with diesel generators



#15
Aug1610, 05:12 AM

P: 665

Wikipedia says: a modern diesel plant will consume between 0.28 and 0.4 litres of fuel per kilowatt hour
So your 300 watt generator will use about 100ml (0.1 litres) in an hour in theory  I would guess it may be twice that figure in practice. It isn't easy to use batteries for a couple of reasons. First, the output voltage of the generator will probably be your local mains voltage (I think that's 240 volts in Kenya?). And it will be AC. (Alternating current) Batteries (car batteries) are usually 12 volts DC (Direct current). Although you can charge a battery from your generator, using an ordinary battery charger, the battery won't be able to power your house appliances. You could set up low voltage lighting using car headlight bulbs running on the batteries  but don't try to connect these type of bulbs directly to the generator  they will blow. The most efficient use of your generator would be as russwatters suggested  charge some batteries from your generator and supply those to people to take away and run their lights. You could keep the generator running all the time charging enough batteries for several households to take away and use, bringing them back when empty to change for a fresh one. Batteries won't let you run many things but they will be ok for lighting. 


#16
Aug1610, 05:38 AM

Mentor
P: 22,313

One little quibble:



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