Oh boy. Here comes one of the more difficult decisions.
Which type do I buy?
Well first lets talk about the fuel, and what it's
strengths and weaknesses are.
Diesel Fuel
Diesel fuel is the safest fuel to store. It takes a lot
to make it burn. It can usually be stored in a Fuel Oil tank much like you use for heating
oil. This can be stored in your basement, garage, or outside. It's easier to negotiate a
"No-Road Tax" purchase with your local distributor, as No. 2 diesel and No. 2
heating oil is virtually identical. Although the Road grade diesel fuel does have some
additives which are often introduced in winter climates, otherwise they are the same.
Diesel fuel does have a shelf life, but can be extended by adding fuel preservatives. With
the preservatives, life expectancy is about 2 years maximum. Fuel oil tanks can be
purchased used rather cheaply, as they are often replaced when converting home heating
units to propane or natural gas.
The down side of diesel, is that it has a limited use.
Either for heating or for running your diesel engine equipment. If you purchase bulk
quantities of diesel fuel, make sure you are going to use it within that 2 year period.
Diesel fuel can be affected by bacteria, and is affected by direct sunlight.
Gasoline
Gasoline is one of the most popular and widely used
fuel sources today. It has a normal useful life of about 6 months, and with fuel
preservatives, can be extended to almost 2 years. Gasoline is used in most household
engines such as lawnmowers, gas powered trimmers, automobiles, motorcycles etc. Gasoline
also is the most combustible fuels, and generates a high amount of energy.
The down side of gasoline is it is extremely flammable
and dangerous. Gasoline fumes are heavier than air and tends to settle. This is especially
dangerous as gas soaked rags can produce enough fumes to be ignited around gas water
heaters. It requires special storage and venting considerations, especially if stored in
bulk amounts. Many ordinances disallow storage of more than 6 gallons of gasoline without
a special permit and inspections. Gasoline is also one of the most toxic, one teaspoon can
contaminate 10,000 gallons of water. So containment considerations against leakage's are
often required in bulk storage situations. Gasoline has to be stored in a safe place, out
of sunlight, and properly vented. The fumes from gasoline are easily ignited by sparks or
open flame. This can be as simple as static electricity.
Propane
Propane is a very popular source of fuel. It is very
handy in cases when it is already the primary source for heating and cooking. Propane has
an indefinite shelf life, and storage is usually a 500 to 1000 gallon propane tank. Most
propane distributors will automatically check and refuel the tank, and tanks are usually
installed at a very low cost by the distributor. Propane burns very cleanly and leaves
little or no carbon deposits in an engine.
The down side of propane is that it is not as
combustible as gasoline. Usually it derates the engine horsepower by 10% of it's gasoline
capable rating. Propane is flammable. Propane hookups restrict mobility of the generator.
Propane driven engines do not have the cooling or lubricating benefits of gasoline or
diesel fuels on valves.
Natural Gas
It is the most popular heating and cooking fuel used.
It is the most abundant and easily accessible fuel source in suburbs, and is provided
without storage concerns. Natural gas burns very cleanly with little or no carbon
deposits.
The down side of Natural gas, is it is flammable. It
derates the engine horsepower by 20% of it's gasoline capable rating. Natural gas hookups
restrict the mobility of the generator. Because you don't store it, you can not be assured
of it's availability in certain disaster situations such as earth quakes, or Y2K concerns.
Natural gas driven generators do not have the cooling benefits of gasoline or diesel fuels
on valves.
ENGINES
OK, this is where careful examination of your
expectations, generator quality, and generator design become very important. Let's review
the differences in engines, and design to establish which is your most appropriate choice.
GASOLINE ENGINE
GENERATORS
I'll classify gasoline driven engines into 3 different
design features.
1) Inexpensive or household.
2) Extended use.
3) Heavy duty Industrial grade.
Inexpensive household
generators
These are the bargain units you can buy
for under $800.00. They are typically lawnmower engines, using side valves. They use cast
aluminum cylinders, and splash bath lubrication. These are nice for occasional
non-critical uses around the house, and occasional power outages. Life expectancy of the
motor is around 300 to 500 hours of use, based on maintenance and usage of the unit. The
generator is usually a brush design, and the output is questionable for voltage sensitive
appliances. They run rather inefficient in gas consumption, run hot, and are not designed
to run continuously for long periods of time. These units run at 3600 RPM and have are
considered limited in life expectancy and somewhat disposable.
Extended use Generators
These units are a higher quality engine and generator
that you will pay around $1400.00 to $4000.00 for. They typically have a Overhead Valve
configuration which is more fuel efficient and runs cooler. They normally have a
pressurized lubrication system, and a spin on oil filter. Cylinder wall construction is
cast iron, and the generator itself is either brush or brushless in design. Power output
is not always cleaner, but more often is suitable for sensitive appliances. Life
expectancy is between 2000 and 5000 hours, based on maintenance and usage of the unit.
These units can be run for extended periods of time, but require special consideration to
cooling. These are typically air cooled, run at 3600 RPM and are very popular with
construction companies.
Heavy Duty Industrial
Grade Generators
These units are typically multi-cylinder
configurations. Sharing the same design features as the Extended Use Generators. However
they normally run at 1800 RPM, and are often water cooled. Generator design is usually
brushless, power output is expected to be clean and suitable for sensitive appliances.
Life expectancy can exceed 10,000 hours. These are more critical applications equipment
and are more expensive. Prices range from $3500.00 to $6000.00
DIESEL ENGINE
GENERATORS
Diesel generators are typically classified as more
durable, more fuel efficient, and longer lived than it's gasoline cousins. There are some
distinct advantages of a diesel engine over a gasoline engine. Most have to do with the
RPM the unit runs at, as diesels have more torque, they are better suited to run a lower
RPMs. Diesel generators are much more expensive to purchase, but when you start
approaching the 5000 hour mark, they become much cheaper to operate. Diesels are usually a
bunch noisier than gasoline generators. Again I'll classify the diesels in somewhat the
same fashion as I did the gasoline driven generators with one notable difference, the
cheapest of the diesel generators will probably outlive the better of the gasoline
generators, so it will be hard to label a diesel as an Inexpensive household generator.
1) Least Expensive
2) Industrial Grade
3) Heavy Duty Critical Use
Least Expensive Diesel
Generators
These units can vary all over the map. From acceptable
to pretty good. Many run at 3600 RPMs like their gasoline cousins. They are air-cooled and
often don't have pressurized lubrication systems. They are usually pretty fuel efficient,
but are quite heavy. One of the favorite of the least expensive diesel generators are
often Chinese Imports, which vary in design and quality. While these units are usually
quite reliable, some imports require some modifications, and aren't well documented. Often
times the owner of such import units is required to have some stronger mechanical aptitude
in order to make them more functional. Parts availability in imports is often a concern
and retrofits to more accessible parts is very common. Domestic versions of the
inexpensive diesel generators are usually pretty good, air-cooled, 3600 RPM, splash bath
lubrication, they often are found to have good voltage output. The inexpensive diesel
generators are often available in a portable version, although they are very heavy and
require some serious consideration when moving them about. These units are quite noisy,
and require special considerations for sound and location. Life expectancy is usually at
least 5,000 to 10,000+ hours, and prices range from $2,000 to $5000.00
Industrial Grade Diesel
Generators
These units run at 1800 RPM. They are quite fuel
efficient, using half the fuel per gallon as it's gasoline version. They usually are
a bit quieter, and often are water cooled. They have fully pressurized lubrication
systems, and sophisticated fuel systems. These units are sometimes found to be available
in a portable version. They are typically 6000 watt to 50000 watt and higher, used
in automatic standby systems for non-critical applications. These units offer clean power
output, and very low maintenance. These units are a favorite in smaller commercial
applications, and are often the system of choice with the best home standby units, and are
often used as the sole power source in remote areas. Life expectancy is easily 10,000 to
30,000 hours and more. Cost can vary between $3500.00 for the smallest 6 kW units,
to $20,000.00 for the larger 50,000 kW units.
Heavy Duty Critical Use
Diesel Generators
These are the critical and big bad boys of the
generator world. These are usually 25 kW into the Mega-watt reserve power units. These
units are designed with utmost reliability in mind. Used for critical applications such as
hospitals, communications stations, TV & Radio Broadcasting backup power, Military,
etc. Life expectancy is probably bettered measured in term of years. Power output is as
good as it gets. Price is more than you would ever want to spend on a generator anyhow.
Figure $20,000 for the tiny units on up into the 7 figure range. Most of us never realize
we see them on a daily basis. Locomotive engines are actually big bad diesel DC generators
if that gives you any idea how much power diesel generators can produce.
Diesel versus
Gasoline Generators
I wanted to get the opinion of those who have some
extensive experience in answering questions objectively regarding the comparison. Many
times it is too easy to "rubber stamp" an opinion about which is better or not,
based more on popular vote, than real thought provoking considerations. It turns out that
either gasoline or diesel can be the best choice when applied to a specific set of
circumstances and requirements. Many people are concerned about the life expectancy
of gasoline engines. I turned to Bruce Perrault who is clearly an expert in answering such
questions.
"Speed can be a difference. I
really think if you took a commercial grade engine like a Vanguard and put it up against a
3600 rpm diesel, it could compete very well. I can speak from experience when I tell you
that I have 1800 rpm two cylinder gas Onans out there with thousands of hours and still
running strong. In one case the hours are above 10,000. It all depends on maintenance and
type of use. Technology is the thing now and today's V-Twin is a far cry from yesterdays
L-Head engine. Very few of today's engines resemble anything that was produced 30 years
ago when I was starting in this business. I believe today's engines are far advanced in
both technology and the way they can handle poor conditions. The commercial grade engines
have come a long way, although some of the old cast iron engines of yesteryear were hard
to beat when it came to long life. "
Bruce Perrault, Master Service
Technician, (Check out his site at Precise Engine Repair
)
Another great article to read about
this comparison is written by Dave Pascoe, 25 year veteran Yacht Surveyor. While his
comparison is in regards to boat engines, I think it is very relevant to the comparison. Gas Vs Diesel
Because the quality of the units can vary wildly, I was
reluctant to do a one on one comparison. However, because we have some reasonably credible
data, input and experience on a couple of popular choices in both the diesel and gas
models, I decided I would stick my neck out and make a rather generic comparison between
the Diesel and Gasoline. I have also solicited the experience of experience professionals
just to make sure I was being reasonably accurate and fair.
The assumption here is that you are going to use the generator a
bunch, let's say 3 to 4 weeks continuos every year or 500 to 700 hours a year. The key
here is to remember the "Use it or Lose it" life expectancy of any motor. Most
engines aren't going to last much longer than 20 years whether you run the heck out of
them or not. In the example below, our goal is to run about 10,000 hours of generator
provided power, or perhaps around 15 to 20 years of service based on the 500 to 700 hours
a year usage.
The comparison is between a good solid 3600 RPM gasoline generator,
based on the Extended Use Description above, and the Industrial Grade 1800 RPM Diesel
Generator. The comparison is between 4 very popular models with similar output
requirements. I left out the actual manufacturers as I didn't want to listen to one or the
other complain. Life expectancy of the gasoline generator is around 5000 hours, the diesel
is 20,000 hours easily.
