Diesel generator power is a sensible choice

Diesel generator power
is a sensible choice

Especially when integrated into the total system

By Skip Thomsen

Issue #43 • January/February, 1997

Diesel Power? What about solar? What about the environment; don’t diesel engines use fossil fuels and create pollution? What about political correctness?

I would never suggest that anyone who has the capability of using solar power do anything but. Powering your homestead with free, non-polluting power from the sun or from a hydro-electric system is the ideal way to go. But for some of us, solar isn’t feasible. Some folks live where the sun rarely shows its face throughout the four or five coldest months of the year, coincidentally when we need the most power. Others operate home workshops and/or businesses that require more power than any affordable solar array could possibly develop. For those folks, diesel power can be a viable and efficient option.

Utilizing a generator to power the homestead doesn’t have to be an environmental disaster. A generator can be a very efficient component of your independent energy system. The key is to observe a few basics: make the generator part of the system instead of a sole source of power.

Making the generator “part of the system” means that it is always working in conjunction with the rest of the system. If at all possible, operate the generator only when lots of power is required, as on the days of the week you do your laundry, vacuum the house, operate your shop, pump irrigation water or any other heavy use. And during those times, the difference between the power you are actually using and the full potential of the machine should be going into your battery bank.

There are few solar installations that don’t require some generator backup occasionally. A generator is available in some of the best of solar homes for those times when the sky is grey for weeks at a time, and in many cases, for heavy-duty power needs. A lot of well-designed solar homes are planned for scheduled generator usage. Perhaps one day a week, all the heavy-power-demand chores are done. On this day, the generator is run all day long, and any surplus power (the difference between what the generator will produce and what is being used), gets sent to the storage batteries. Operating a generator at near its full potential is the most efficient use of the machine.

So since a generator will be required in just about any beyond-the-grid installation, why not have it be a machine that’s designed for serious use instead of a home-handyman unit that’s specifically designed for light-duty, intermittent use?

Why a diesel?

Why diesel-power instead of gasoline? Unlike gas engines, diesels have no spark plugs to replace, or carburetors to rebuild and service. Diesels generally burn less than half the fuel that gas engines do to do the same amount of work. Diesels regularly outlast gas engines ten-to-one.

For example, the average gas engine powering a generator will run for around 1000 hours before needing replacement or a complete overhaul. And that’s an average. Many don’t make it past a few hundred hours. The average diesel engine will run 20,000 hours before needing any service beyond routine maintenance, but many make it to 50,000 hours, and some a lot longer than that. At four hours a day, even 20,000 hours works out to nearly fourteen years!

Diesels are built to last. They’re built to produce their rated output for years on end. Most gas-engine generators are built specifically to be used for intermittent or emergency power. Almost all gas-engine generators run at a self-destructing speed of 3600 RPM. Most diesels run at half that speed.

The fuel-efficiency alone is a good reason for a diesel, plus off-road diesel fuel is cheaper than gasoline. It’s also a lot safer to store. It’s flammable, but not explosive like gasoline. And although diesels sometimes produce more visible exhaust, it is less toxic than the emissions from a gasoline engine. A well-tuned diesel, by the way, produces no visible exhaust except briefly, under severe load-changes.

Diesels sound scary to some people who are unfamiliar with them, but they are actually simpler in design and construction than gas engines. If you can service a gas engine, you can service a diesel. And it requires less service.

The only maintenance generally required is changing the oil, and changing the fuel, air, and oil filters. This much is the same as on a gas engine. What you won’t have to deal with is tune-ups. No carburetor adjustments, no distributor or magneto to burn out, and no spark plugs to need periodic cleaning and replacement.

Oil changes done on schedule are critical and make the difference between an engine that wears out prematurely and one that runs nearly forever.

The bad news

What about initial cost? Yep, diesels cost more initially than gas engines. But if you do the math on how the costs compare over a few years’ time, the diesel always comes out way on top. Plus, if you compare the initial costs of small diesel generators to premium-quality gas generators, the differences start to fade. Sure there are cheapo generators available, but these units just cannot be depended upon for any kind of constant service. They’re not built for it, and they won’t take it.

I’ve had neighbors who’ve bought those garden-variety generators for $4-500, and they used to tell me about how great the guarantees were. They smoked another generator every couple of months, and all they had to do was to haul it back to the dealer and he’d give them another new one. Now doesn’t that sound just like how you would like to spend your time? Not to mention being without power every time another generator died.

At the same time, we had our little diesel putt-putting away for years and years, without a single problem. The throw-away gas generators were screaming their little overworked hearts out, burning nearly a gallon per hour of gasoline, and our diesel was producing twice the power and running for five hours on a gallon of diesel.

OK, so what’s available?

Well, like gas-powered generators, small diesel generators come in various grades of durability, too.

Unfortunately, the general theme is this: the bigger the machine, the better it’s built. For example, most of the smaller machines, like up to about 6 KW (kilowatts), use engines that run at 3000 to 3600 RPM (revolutions per minute). I don’t know why manufacturers choose to design a generator that requires such a high engine speed, unless it’s to be able to use smaller engines. Engines develop more horsepower at higher engine-speeds (RPM), so a smaller engine running at up to 3600 RPM can produce the same amount of power as a bigger one running at 1800 RPM. Two problems result from the higher RPM: shorter engine life and, in most cases, much more noise. Fuel consumption is usually higher on the higher-RPM machines, too.

OK, for you folks who are serious about homestead power and maybe have a shop or business that will depend on a totally dependable source of clean, stable power, there’s a jewel of a machine being offered by Onan. It’s their Model Number 8.0HDKAQ.

This is a specially developed 1800 RPM, water-cooled, 8KW single- and three-phase generator that’s designed for continuous duty applications. It also has a lot of installation flexibility, with cooling-air discharge that rotates to either side- or bottom-discharge, and multiple oil-check and fill locations. All connections and controls are waterproof and sealed for safe and trouble-free installation even in harsh environments.

I just talked to somebody who has had one of these machines running for years with no repairs at all. His is the older-model unit, but the only difference between it and the new one is the better noise-control on the new one.

This genset (generator set) uses the proven Kubota three-cylinder diesel engine, and at about a 75% load, it runs four hours on a gallon of fuel.

OK, you were going to ask sooner or later: it costs around $7000. Yes, that’s a lot of money, but if you look at the long-range picture, it still looks pretty good. In the first place, if you need a machine of this capability, a serious-duty gasoline-engine generator is going to cost at least $2000, and most are higher. (The consumer-brand machines that boast of even 5KW and are available for under $2000 won’t last long enough to even consider as an option.) Figure then that most gas engines need an overhaul (or replacement) after about 1000 hours of operation. But the diesel is good for at least 20,000 hours, and quite possibly twice that.

Then factor in the fuel-consumption. Even a five-KW gas generator will burn a gallon per hour. This 8 KW diesel goes four hours on a single gallon. For the sake of a comparison, let’s assume four hours a day of use for a year. That’s 1460 hours. At a comparative figure of $1/gallon for off-road fuel, the gas unit will have used $1460 worth of fuel. The diesel, in the same amount of time would have burned $365 worth of fuel. So just the fuel savings alone would be $1100/year. Add to that the fact that the diesel will continue to faithfully produce dependable power for 13 years (figuring a 20,000 hour overhaul time), while the gas unit will likely need an overhaul at the end of its first year. The savings become obvious, don’t they?

There’s another contender in about the same price range, too. It’s the “CLC Certex” series from Power Systems Engineering, and it is available from Northern Hydraulics of Burnsville, MN. This one’s for folks who need serious power, like 20 KW. The machine uses a Detroit Diesel Engine and is built for full-time operation. It’s way bigger than any basic homestead could ever use, but if you have a shop or business that needs this kind of power, this is a good machine.

An alternative to the above generators, most of which use imported (mostly Japanese) diesel engines, are the gensets using engines made in China. Known generally as the China Diesels, these machines are notably cheaper, run at 1800 RPM (or less), and have an amazing life-expectancy.

They also use less fuel for the same output of power than any other generators I’ve found. I’ve personally seen some of these little engines with well over 20,000 hours on them, still chugging dependably along. I even wrote a book about the China Diesel I used to run my homestead for years (see end of this article).

However, the China Diesels seem to be happiest in the hands of owners who have a certain amount of mechanical savvy. Although I ran one for many years without a glitch, I have interviewed lots of owners who haven’t been so fortunate. In many cases, there had been problems, but most were easily solved with a bit of ingenuity. In almost all of these cases, once the bugs were worked out, the machines performed well from then on.

If you need a machine that you can just plug in and forget about (except for routine maintenance, of course), the name-brand commercial units are a safer, if more expensive bet. But buyer beware: for the generators with the high-speed (3000-3600 RPM) diesels, I’ve heard time-before-overhaul figures ranging from 1000 to 3000 hours, and fuel burn promises of two hours per gallon. To me, that’s unacceptable.

Maintenance = long life

As with any internal combustion engine, proper maintenance is essential. Diesels are no exception, and the most important maintenance is oil changes. An oil change every 100 hours of operation is normal operating procedure for a diesel engine, and it will assure a long and trouble-free life.

Regular air- and fuel-filter maintenance is also essential, and fuel filtering is one area where diesels are more demanding than gas engines. Diesels use precision fuel injectors that are ultimately dependable as long as they are kept clean. Even a tiny speck of debris can clog a fuel injector nozzle, so it is essential to keep a good-quality fuel filter in the system.

The normal setup is to have a large, paper-element fuel filter somewhere in the fuel line between the fuel tank and the engine, and another filter, usually the canister-type that comes with the engine or genset, right on the engine itself. The first filter, available at most auto/truck supply stores, can be mounted on the wall of the generator shed. An outside location is usually preferred because of accessibility and the propensity to spill a splash or two of fuel when changing the filter element. If your generator shed has a wooden floor, spilled fuel (or engine oil) can create a serious fire hazard.

Operating tips

There are two things to remember to keep your diesel healthy as long as possible:

The first is that these engines do not like to be started up for short runs. In other words, don’t start your generator for a 10-minute project. Ideally, the generator should be started and allowed to reach normal operating temperature before any big loads are applied, and it should again be allowed to run at a light load for a few minutes before shut-down. The reason is to avoid rapid temperature fluctuations. One secret of long life (of any engine, actually) is to allow it to make its necessary temperature fluctuations gradually. Shutting down an engine after it’s just been running at full load for a while means that it will cool more rapidly than is healthy for it.

The second thing to remember is that diesel engines like to work hard. Matter of fact, they don’t do very well when they’re not working hard. Running a diesel engine at a fairly high load ensures enough combustion pressure to keep the piston rings seated firmly against the cylinder walls, and this is important to the long life of the engine. Running a diesel for long periods of time with only light loads can cause the rings and cylinders to form a glaze, which then keeps the rings from doing their job when the engine is next expected to work hard.

The trick, then, is to run the generator only when you’ll be using a large portion of its potential power. Sometimes, this requires scheduling high-power-use operations for the same day of the week, or organizing your workday to do the power-tool chores while the generator is on-line.

What I did for all the years I ran my diesel-powered homestead was have a small, very portable 1800-watt gas generator handy for those times when I just needed a little bit of power for a few minutes, especially somewhere out of reach of extension cords. I used this little machine for pumping water out of our creek, for field-repairs, and any time I needed more short-term power than I wanted to subject my inverter to. That’s the kind of service these little gas generators are designed for, by the way.

Never operate your generator without a properly installed and serviced air cleaner. It doesn’t take much abrasive dust to dramatically shorten the life of an engine.

Use only engine oil marked for service in diesel engines. Diesels run at much higher operating pressures than gasoline engines, and they need this grade of oil. The cheapest way to go on oil is to check with your favorite discount store to find what brand they carry, and then buy several cases at a time when it’s on sale. Which brand you use (as long as it’s marked for diesel service) is immaterial, but most mechanic-types recommend staying with one brand. I’ve always used Valvoline HPO 30W, as it is a high-quality diesel-rated oil and it always seems to be on sale somewhere.

Safety equipment

We’re talking safety of your generator here. We’ll get to your personal safety later.

Any permanent generator installation needs to be protected with automatic shut-down equipment. Most manufacturers offer shut-down kits for excessive coolant (engine) temperature and oil-pressure loss, and some also have overspeed shut-down kits. I recommend all three.

Having all the automatic shut-down capability in the world is no substitute for proper maintenance, however. It’s a good idea to do at least a cursory inspection of the machinery at every oil-change. Keep the engine clean so that any leaks are easily spotted, and should there be a leak, tend to it at once. The shut-down switch that’s supposed to protect your engine in the event of an oil-pressure loss may stop catastrophic damage, but it’s doubtful that any engine operating at a load will fully survive zero-oil-pressure for even the amount of time it takes for the switch to shut down the engine. Diesel engines are highly dependent on proper oiling at all times because of the high pressures on internal parts.

Another important consideration is proper ventilation of the generator enclosure or shed. Even with a good cooling system on the engine itself, the entire machine needs to have substantial access to fresh, cooling air. The shed must have either a large enough screened opening for natural convective airflow, or if a smaller opening is dictated by the amount of noise you’d like to have escape from it, a blower must be installed.

A blower that forces airflow through the enclosure can be plugged directly into the 110 volt power of the generator so that it will come on any time the machine is running. In very cold climates, you can connect the blower through a temperature-sensitive switch, so that the blower will operate only after the room temperature has reached 80 degrees or so.

Temperature control is important to the long life of the electrical equipment as well as the engine. Excess heat is what ultimately kills alternators.

One last piece of equipment I highly recommend is an hour-meter. Most commercial-duty generators already have one installed, but if not, it’s a convenient and inexpensive way to monitor oil-change and other maintenance intervals. Keep a notebook and pencil handy in your generator shed and make notations of all service and repairs done to the machine, too.

Your safety

If you’re not intimately knowledgeable on things electrical, remember that the current produced by your generator can kill you. Before making any connections, changes, or repairs that you are unsure of, please seek the help of somebody who is competent in these matters.

Don’t remove guards that are designed to keep your fingers, clothing and what-not-else out of harm’s way. If you need to temporarily run your equipment without belt or other guards, be acutely aware of their absence. Belts and pulleys have a habit of locating and catching anything they can get, like shirt-sleeves, shirttail, rags, tools, fingers, and worse.

An engine that is or has been running is hot. Some parts, like exhaust components, are hot enough to inflict serious burns. Be careful.

Oil spilled on a wooden floor is a serious fire hazard. Best keep a suitable metal drip pan under your engine if your shed has a wooden floor. Never leave oily rags in the shed, either. Spontaneous combustion is a very real hazard.

When designing your shed, leave enough room to get around the equipment, and place the equipment in the shed for best access to common maintenance areas. Protect the exhaust pipe with shielding to prevent accidental contact.

Oil changes are best done when the engine is hot, or at least warm. Try to develop a system in which you can remove the drain plug without touching the engine or the hot oil with your hands.

Have a 12-volt light (wired to the engine’s starting battery) in your generator shed so that you can see what you’re doing, even at night, with the generator off.


Noise is another consideration, of course. All diesel engines are noisy, and the noise must be controlled if the machine is within earshot of your home or your neighbor’s. The Onan machine mentioned above comes in its own sound-barrier enclosure, and it’s one of the best I’ve seen (and heard). Installing that entire unit in a well sound-insulated shed will make a quiet installation. Just make sure that you don’t impair the supply of cooling air in your quest for quietness.

In conclusion, when you figure the long-term costs of operation, diesels always win out over gas engines, and commercial-duty equipment always wins out over the home-handyman variety.

Once you acquire your diesel generator, install it carefully and thoughtfully and make sure it receives the proper maintenance.

Keep your machine clean. Wipe it down at every oil change, and you’ll be able to spot any little leaks before they become a real problem. Clean equipment is also easier to service, and, well, haven’t you ever noticed how much better your car runs after you wash it?

Your electrical system is going to be with you for a long time. It deserves to be thoroughly researched, thoughtfully designed, and carefully constructed. It should be built with dependability and permanence as the primary focus. Plan your electrical needs not only for right now, but for the foreseeable future as well. It’s a lot cheaper to build your system with the future in mind than to upgrade it later. Buying cheap components not intended for full-time use may save you a little at first, but you’ll pay more than the difference when you have to replace them.


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