Alternative Power sources - Basic backup generator questions

Author

Basic backup generator questions

Mike Ruskai

2007-09-03, 11:12 am

I'm looking for some basic information about automatic backup
generators to run on liquid propane.

My house has 200A service, and I'm not interested in a generator that
requires me to pick a fixed number of circuits. The whole house needs
to be on backup. I'm not sure at this point what my power needs would
be, but my preliminary guess is that a generator in the 10-15KW range
would be sufficient.

My questions:

1) What's the lowest power output that's available for whole-house
backup?

2) How important is liquid cooling versus air cooling in a normal NJ
climate?

3) How large a propane tank is best? Besides the future generator,
there's an existing oven/range and a future gas grill to consider. I
already have a tank for the oven, of course, and I believe it's
capacity is 200 pounds. It's oversized because after our initial
propane company let us run out of gas on Xmas Eve day a few years
back, then wanted a $100 emergency fill fee to come and rectify the
situation, we requested a tank with a gauge (if possible) from the new
company. I expect the 200-pound cylinder is the smallest they had
with a pressure gauge attached.

I'm comfortable doing research on details myself, so I'm only looking
for basic pointers, and appreciate whatever helpful answers towards
that end that I get.

philkryder

2007-09-03, 11:12 am

On Sep 2, 9:14 pm, Mike Ruskai <BUTthann...@DONTearthlinkLIKE.netSPAM>
wrote:
> I'm looking for some basic information about automatic backup
> generators to run on liquid propane.
>
> My house has 200A service, and I'm not interested in a generator that
> requires me to pick a fixed number of circuits. The whole house needs
> to be on backup. I'm not sure at this point what my power needs would
> be, but my preliminary guess is that a generator in the 10-15KW range
> would be sufficient.
>
> My questions:
>
> 1) What's the lowest power output that's available for whole-house
> backup?
>
> 2) How important is liquid cooling versus air cooling in a normal NJ
> climate?
>
> 3) How large a propane tank is best? Besides the future generator,
> there's an existing oven/range and a future gas grill to consider. I
> already have a tank for the oven, of course, and I believe it's
> capacity is 200 pounds. It's oversized because after our initial
> propane company let us run out of gas on Xmas Eve day a few years
> back, then wanted a $100 emergency fill fee to come and rectify the
> situation, we requested a tank with a gauge (if possible) from the new
> company. I expect the 200-pound cylinder is the smallest they had
> with a pressure gauge attached.
>
> I'm comfortable doing research on details myself, so I'm only looking
> for basic pointers, and appreciate whatever helpful answers towards
> that end that I get.

It sounds like you are seeking is a "backup only in emergency"
solution.
Please verify that.

It sounds like you don't want to reduce load in an emergency.
Again, please verify that you have no load you could "shed" during an
emergency.

What do you use for HEAT?
Is it an electric heat pump?
If it is, then you need to be sure you can start it.
If not, what fuel do you have on hand and how do you store it today?

You ask:
> 1) What's the lowest power output that's available for whole-house
> backup?
Wouldn't that depend on the house?
You've implied that you want 200 amps if needed.
Do you really use that much?
Do you know **your** peak load or have an upper bound for it?
How many kwh do you use per month?

Assuming the 200 amp from above, and continuing:
200 amps would be about 24kw, if you really needed all that.

It is likely that your 200 amp service exceeds your actual
consumption.
If you could "get by" with 18kw then this unit might suffice:
http://www.generac.com/Products/Res...ooled/18KW.aspx
Note the fuel consumption.
Note it provides only 18kw which is LESS than the 120volts times 200
amps max that you originally asked to have.

Fuel consumption may exceed 2 gallon per hour.
The above specs 2.85 for only 18kw at max output.

Water cooling would not be needed.
But, you may not find many air cooled units larger than the 18kw.

It would seem 10-14 days might be a good minimum.
that would be
10*2.85*24= 684 gal.
14*2.85*24 = 958gal.
at 80% full, a 500 gallon tank would only give you 400 gallon usable.
If you really use much less than 18kw, then check the other fuel usage
specs.
Do you have storage space for two of them?

It would seem that with some compromises or if your true load is less
than the 24kw, that a 500 gallon tank and the 18kw air cooled would
"suffice."
But, if your heat is from a heat pump, you need to be sure you have
plenty of capacity to start it.

Best
Phil

Ron Rosenfeld

2007-09-03, 11:12 am

On Mon, 03 Sep 2007 00:14:45 -0400, Mike Ruskai
<BUTthannydI@DONTearthlinkLIKE.netSPAM> wrote:

>I'm looking for some basic information about automatic backup
>generators to run on liquid propane.

There are very very few that run on liquid propane. You probably mean
liquid propane vapor, which are common.

>
>My house has 200A service, and I'm not interested in a generator that
>requires me to pick a fixed number of circuits. The whole house needs
>to be on backup. I'm not sure at this point what my power needs would
>be, but my preliminary guess is that a generator in the 10-15KW range
>would be sufficient.
>
>My questions:
>
>1) What's the lowest power output that's available for whole-house
>backup?

You can use most any size for backup. You should get the smallest that
will do your job, as it will burn less fuel when at lower outputs (which is
where it will be most of the time).

>
>2) How important is liquid cooling versus air cooling in a normal NJ
>climate?

For short-term backup, probably either will work well. In general, the
water-cooled generators will last longer, if they are used for long-periods
of time. I use a liquid-cooled 1800 rpm generator that runs about 150
hrs/year. We've had no problems with about 1800 hrs run time.

>
>3) How large a propane tank is best? Besides the future generator,
>there's an existing oven/range and a future gas grill to consider. I
>already have a tank for the oven, of course, and I believe it's
>capacity is 200 pounds. It's oversized because after our initial
>propane company let us run out of gas on Xmas Eve day a few years
>back, then wanted a $100 emergency fill fee to come and rectify the
>situation, we requested a tank with a gauge (if possible) from the new
>company. I expect the 200-pound cylinder is the smallest they had
>with a pressure gauge attached.

That will depend on how long you think you will have to run your generator
before you can replace the propane. For a generator in the size range you
mention above, figure 1 gph at "idle" and 2 gph at peak load.

>
>I'm comfortable doing research on details myself, so I'm only looking
>for basic pointers, and appreciate whatever helpful answers towards
>that end that I get.

You really need to know what your maximum draw will be (and startup surge),
and also make a decision as to how many days of fuel you require.

Probably the biggest questions for your area are whether you will need to
run a/c during a power failure; and also whether you have an electric
stove, or other heavy duty electric appliances.

I see from above that you have a gas stove. If you have no a/c, then I
would guess that your estimate of 10-15 kW is accurate.

We have a 3200 sq ft well-insulated home. We have gas stove, gas dryer,
electric refrigerator as well as the "usual" kitchen appliances -- coffee
makers, toaster oven, mixers, etc. We also have a 0.5amp/240V well pump.
Heat is via a propane fueled furnace, with forced hot water heating.
(Forced air heating would use more power for the blowers).

Our "peak" surge is probably about 5kW -- probably due to several items
starting up at once. Our average daily usage is much less, however. But
you need to size your generator to take care of the surge.

There are a number of generators available for backup in the size range you
specify. You should also get an ATS (automatic transfer switch) that will
also automatically exercise your generator weekly or so. The ATS will need
to be rated at your 200amp and will probably need to be installed by a
licensed electrician.

HTH,
--ron

(PeteCresswell)

2007-09-03, 11:12 am

Per Mike Ruskai:
> I'm not sure at this point what my power needs would
>be,

If I were in your place, I'd either spend some money on a device
that measures total consumption at the meter - or take the time
and figure out how to deduce consumption by timing the
revolutions of the meter disc.

Then I'd fire up as many appliances as I thought constituted a
full load and see how much they're drawing at the meter.

Then I'd be able to shop for a specific capacity.
--
PeteCresswell

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