I'm thinking of getting a propane-powered whole-house backup generator with the automatic switch on when the power fails. I went through the electric bills for the last twelve months and found that we used an average of 54.9 kilowatt hours per day or about 2.3 per hour. Quite a bit, but we have a we ll with pump and my wife keeps the greenhouse warm all winter with an elect ric heater.
I have a little gas-powered generator rated at 6,500 watts that I use to po wer the pump, boiler, refrigerators, etc., but it would be nice not to have to run out in the rain to start and fuel it during an outage.
I've read that an 11,000 watt unit should be enough to power a house, and w e wouldn't be using the electric oven or dryer during outages. That would b e almost 5 times the average usage, which should give coverage for start-up peaks.
Does anyone have any official formulas for this sort of thing?
There really isn't a formula that will convert your average or daily usage into a number for a genset. You really have to figure out your worst-case emergency usage and then scale that depending on what sorts of loads that you anticipate using. All loads are not equal. Motors need a lot of juice to start, for instance. The genset has to handle the *peak* not the average. You also have to scale the genset for the difference between kW and VA. The electrician doing the work should be able to give guidance, given your anticipated usage.
In your case the average would be like sticking your feet in boiling water and putting liquid nitrogen on yur head. The average would be 70 deg, but you would not like it.
Go here and add up all the wttages of everything you may have on at one time.
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This will give you a rough guide. If your 6,500 unit is powering everything you need now, the 11,000 gas will be plenty.
Just remember the larger the unit, the more it costs to run. Check out how much the unit will cost to run before you make the final decision.
Not me, but I would suggest that a smart transfer switch could reduce the size of generator needed - or compensate for an error in buying one that is too small to take everything the house is going to throw at it.
A smart switch will turn off specified circuits for a specified time in order to free up watts for other circuits' momentary demands.
The one I got didn't cost all that much more than a conventional transfer switch and it allows me to run a house sans AC on a 2KW (1.8 KW steady load) generator. So I'd think the same strategy could get quite a bit out of your "little" 6,500 watt generator. Might be worth getting the switch first and seeing if the current gennie can do what you need done.
As others have stated, it's about the peak, not the average. You already have a system that meets your needs.
If you don't wish to be inconvenienced by the outage, you need to add up the PEAK numbers for everything you want to run simultaneously. Then add some slack for motor starting peaks. Then add some more for future possibilities. That gives you the size generator you need.
The bottom line is that it's gonna be a BIG number.
Divide that by the number of outages you expect. That gives you the cost of being too lazy to go start the generator you have.
Then you imagine you can manage your usage during an outage to reduce the peak need. You'll find out that the inconvenience goes up faster than the generator cost goes down.
So, you decide that you'd get more bang for the buck by buying a boat or a motorcycle or taking a vacation... and a raincoat for those power outages. ;-)
no one has thought to ask where you live, what your climate is like, how much you are willing to spend and the cost of propane. it's possible, but you'd have to check, that in your area, you could run your proposed set-up during peak demand times and sell the excess to your utility, which might lower the over-all cost to you
If you can find a used propane/natural gas 15kw Onan air cooled 4 cylinder genset and transfer switch, you would have a genset that could power your home. I installed a number of used units that were salvaged from grocery stores and installed them in other grocery stores. The supplier was a company that salvaged the equipment from closed restaurants, grocery and retail stores. I installed a used 40kw Kohler genset at a fellow's home that was purchased from the salvage company. The genset had a 4cyl Ford liquid cooled engine and me and an electrical engineer I had worked with overseas installed it. I got my late friend GB to build a doghouse matching the exterior of the home to house the genset effectively disguising it. I really like the Onan air cooled gensets because even used, the darn things kept running year after year with very little trouble. All they needed was an oil/filter change, air filter service and spark plugs. ^_^
On Mon, 26 Aug 2013 19:47:22 -0400, snipped-for-privacy@attt.bizz wrote in Re Re: Generator Size Based On Average Kilowatts:
All good advice. To OP: is the 11Kw gen rating for gas or propane? If for gas, remember that when running on propane, you will get less than the 11Kw, so choose size accordingly.
You're on to something. During a power cut, it's wise to modify your power usage. Cook with gas, clothes line dry the laundry or delay the wash till the grid power comes back on. So, the backup generator can be smaller. And the family need to know the power hog devices, and not to use them on generator power.
In the long run, changing the greenhouse to vented wall heater may save a lot of money. Electric heat is very expensive.
It's really nice to be able to run refrigeration and AC, but they have a heavy start up current.
. Christ> >> I'm thinking of getting a propane-powered whole-house backup
I think anyone who tries to maintain all the comforts during a power cut, is likely to be mobbed and beaten senseless by the creatures who live in his hood. The modern view is that we all need to suffer together, regardless that the person worked hard, saved his money, stayed home and ate sandwiches instead of fancy diners, and worked to buy a backup generator.
. Christ> As others have stated, it's about the peak, not the average.
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I think others tripped on a few ideas. Change the greenhouse to propane vented wall heater. What is the heat source for your house? If you already use propane for heat, that is provided in bigger tanks, and I think the propane is a bit less expensive.
Do you live some where that AC is needed? Window units or central AC in your house?
. Christ> I'm thinking of getting a propane-powered whole-
house backup generator with the automatic switch on when the power fails. I went through the electric bills for the last twelve months and found that we used an average of 54.9 kilowatt hours per day or about 2.3 per hour. Quite a bit, but we have a well with pump and my wife keeps the greenhouse warm all winter with an electric heater.
6,500 watts that I use to power the pump, boiler, refrigerators, etc., but it would be nice not to have to run out in the rain to start and fuel it during an outage.
to power a house, and we wouldn't be using the electric oven or dryer during outages. That would be almost 5 times the average usage, which should give coverage for start-up peaks.
sort of thing?
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Another question is the quality of the propane generator. I can't remember the details, but some brands are very poor quality. Not likely to last very long, and won't put out good quality electricity. Makes a bit of snow on the television picture. What's a backup generator, without television?
. Christ>
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My hood is mainly folks like me and most have their own generators. They put in a McMansion development up on the ridge a few years back but I think a few rounds of .308 would convince them to go back home and freeze in the dark.
Unfortunately, the home is heated with oil. I was thinking of getting a die sel powered generator to run off the fuel oil tank but I don't know if such things are available for residential applications. I'll have to put in a 2
50-gallon propane tank if I get the generator.
We're in Maryland so we need AC in the summer. It's an old farmhouse so we have window units that we turn on or off as needed.
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