Backup generators. [RE-wrenches]

[Travis Creswell, Ozark Solar]

Hi Carl,

I can answer a few of your questions generally speaking.  I also highly
recommend you double check me.  I know of no study.

Propane, also know as liquefied petroleum gas, is not environmentally
friendly unless you only are considering the site where it is being used.
It is very clean burning.  It is the least energy dense (~91,000 BTU's /
gallon) by volume of the 3 fuels.  Propane stores for many years (10+?, who
knows?) without ruining and is very safe to store.  It's main danger is that
is does not easily dissipate and is heavier than air so it will settle into
any low areas such as crawl spaces, basements, even ditches and risk being
ignited should a leak occur.

If the generator is only used to back up a renewable energy system
(occasional battery charging and intermittingly running loads that are to
big for the inverter such as table saws etc) my recommendation would be to
use propane.   In non-farming location there is no need for diesel on the
property but propane is commonly used for the cookstove, clothes dryer and
for space heating.  The 1800 RPM Kohler propane models are excellent propane
generators but are very pricey.  Depending on initial budget and how long
you expect the unit to operate per year you can convert a less expensive gas
powered generator to propane quite easily with readily available kits for
less than $300.  Propane generators start relatively easily in the cold
although I would recommend an electric start model with plenty of battery
should the temp be expected to get cold.

Diesel is the most energy dense at ~140,000 BTU's gallon (I think).  The
untreated fuel easily spoils and treated diesel is not to be trusted more
than a few years. If you are talking about the running a shop all day long
most of the year and need to be storing diesel for other farm equipment then
diesel for sure.  It's stinky raw and stinky when it's burning (actually I
like, it as it reminds of my days on the carriers flight deck) and stains
everything it touches but is relatively safe to store.  Diesel is commonly
believed to be the most reliable but I cannot attest to that.  I can attest
that when they do break they are expensive to fix and parts are always
special order.  I own three deisel service trucks.  There is little to no
chance of making a diesel work with parts available locally.

Gas is the 2nd most energy dense, is the most dangerous to store, and does
spoil easily.  If the generator carb. is not drained you could come to back
to a very badly varnished bowl and jets within 6 months of not operating the
generator and the carb requires a rebuild.  Propane models won't do that to
you.

Natural Gas can't be stored by readily available technology so it requires
that you be in a town with natural gas or be nearby a pipe line.  I have
several customers with unlimited natural gas as they own the well head and
live on the property.  You might not have that.

In terms of gallons/kva.  You asked about that didn't you?  Just looking at
energy density, assuming the btu's/kva  and efficiency remain constant
regardless of the fuel source then 1000 gallons of diesel would run a
generator about 40%-50% longer than 1000 gallons of propane.  Assuming the
diesel doesn't spoil before then.  Locally propane is down to $.85 per
gallon and farm diesel is under a dollar so diesel is cheaper per btu then
propane.  Diesel at the pump is nearly $1.35 per gallon.

Travis Creswell
Ozark Solar




----- Original Message -----
From: "Carl Emerson" <freepower at freepower.co.nz>
To: <RE-wrenches at topica.com>
Sent: Thursday, November 08, 2001 7:09 PM
Subject: Re: Backup generators. [RE-wrenches]


> Hullo There..
>
> While I can see this topic becoming a good thread, is there an answer to
the
> original question ??
>
> Does anyone know of a study done on the pro's and con's of Petrol vs.
Diesel
> vs. LPG or natural gas backup generators. I need to consider initial cost,
> economy, maintenance, environmental, reliability etc.
>
> Or maybe no such study has been done ?
>
> Carl Emerson
>
> - - - -

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