Choosing the Proper Backup Generator

Published by: Nick Meissner

Our goal for being off the grid has been to produce all of our power from renewable sources (solar, hydro, wind, wood gas, steam, hydrogen, etc) and not rely on fuel sources that must be purchased (gasoline, diesel, propane, etc).  But particularly in northern climates, it takes time to achieve that unless one has a bundle of money up front to invest in a very large renewable energy system.  Because of this, many people getting started with renewable energy begin with a small basic system and build up from there as budget allows.  Many times this initial system is not "renewable" energy but rather "alternative" energy as it involves the use of a fuel powered generator, to a greater or lesser extent.

The smallest and most basic system is often a battery bank with an inverter/charger that uses AC electricity from a fuel powered generator to charge the DC batteries and then converts the DC power from the batteries into AC that is usable in the house.  This arrangement means the generator is only running periodically to charge the batteries rather than running continuously whenever power is needed.  As soon as the owner is able to afford it, renewable charging sources are added and perhaps a larger battery bank installed.  Once enough renewable sources are added, the generator is used less and less until it takes on the role of only a backup power source.

When deciding which generator to purchase, there were a number of items I took into account (not necessarily in order of importance):

  • Fuel Type
  • Mobility
  • Power Production
  • Cleanliness of Electricity
  • Fuel Efficiency
  • Price vs Durability vs Amount of Use

Fuel Type

Other than the durability issue, there are other factors to consider when choosing which fuel type.  Diesel engines have been successfully run on a variety of different fluids, including vegetable oil, hydraulic fluid, and used engine oil.  There is a process involved in preparing it for use, but it is very nice to have other options that could be less expensive or easier to get during hard times.  Diesel is also less volatile and doesn’t spoil as easily.

While I took all these issues into account, the conclusion I came to was that in my situation, they didn’t overcome the first issue mentioned above.  However, for some people it might.


Gasoline generators are often more portable than a heavy duty Diesel unit.  If your generator needs repair that you can’t handle at home, it is much easier to move a 5 kW Honda than an 8 kW Diesel, unless you have the equipment to do the job easily.  Maybe not a major factor for me, but still something to take into account.  On the other hand, you probably won’t be needing to have your Diesel repaired if you take care of it.

Power Production

For generator size, I chose to go with 5 kW.  Too small and you won’t be able to use the valuable run time of the generator to multitask and accomplish all your big energy consuming projects while charging the batteries.  Too large and the unit will not only be overly expensive, but may also use a lot of fuel while wasting much unused electricity.  So for me, 5kW is a good compromise.  For many, a little larger may provide an extra margin of power.  And it can be difficult to find good Diesel generators smaller than 8 kW.

Cleanliness of Electricity

Low end generators often have cheap electrical parts that produce poor quality electricity.  This can not only be hard on equipment, but can also increase the amount of time required to charge one’s batteries.  Because of complicated reasons that only an electrical engineer would fully understand, poor quality electricity cannot push as much charging power out of a charger as good quality sine wave electricity.

Companies such as Honda and Yamaha have come out with generators equipped with an inverter so that  they can produce pure sine wave electricity.  This is a very nice feature, but it also comes with a price tag.  Many of the good Diesel generators have quality electrical components that produce clean electricity, so cheaper gas models would be the main culprits to be concerned about.  I have heard of “Honda” generators being sold by large chain stores that do indeed have a Honda engine, but the electrical components are greatly inferior to the “full” Honda models.  Buyer beware!  If it looks too good to be true, it probably is.

Fuel Efficiency

Diesels generally win here, but gasoline models with inverters built in (to produce sine wave electricity) are often able to lower RPMs to run only as fast as needed to produce the amount of power you are consuming at that moment.  That means fuel savings and less wear and tear on the engine.  We compared two large generator’s fuel cost to operate.  One was Diesel and the other was propane.  The Diesel won hands down.  But that was years ago and with the price of fuel fluctuating the way it is, who knows what it would be now.

Price vs Durability vs Amount of Use

If I had an unlimited budget and could easily afford the best and most durable generator, then I probably would have chosen a different model.  But since I am on a limited budget, the price was certainly a major factor in the decision.  On the other hand, I am a firm believer in not buying “junk”.  It ends up wasting more money in the long-run.

So for me, a deciding factor in this dilemma was the amount of use the generator would get.  Since I will only be running it periodically during a few months of the year, it could take many years to wear out a good average generator, if properly maintained.  If, on the other hand, I it would be used in a generator only application which would require extensive use, I would go for the most durable unit I could afford.

So far, we have been talking theory, but what does this mean in real life?  A good quality Honda gasoline generator, for instance, I would consider to be in the “good average” generator class.  It is good quality and reliable and if taken care of can last for many years under the kind of intermittent use I would be giving it.  For the high-end very durable end of the spectrum, I would go with a good quality Diesel generator made by Kubota or Isuzu or similar brand.

The Final Verdict

A good Kubota Diesel would have been my first choice.  A Honda inverter model (such as EU6500is) would have been my second choice.  But when I plugged in the price vs durability vs amount of use dimension, I changed my mind.  The final choice was a Honda EM5000SX.  No, it isn’t an inverter model producing pure sine wave electricity, but since it is a 2011 model, it has an updated voltage regulator (iAVR) and other features that reportedly produce fairly clean electricity.

When running hooked up to my system, the charger is producing full power.  Works for me!  And as far as fuel efficiency, I am sure it uses more than an inverter model and probably more than a comparable Diesel, but its only .75 gal./hour at its full rated load and slightly more than .5 gal./hour at half load.  Not as good as my Dad’s 12kW Diesel (.5 gal/hour at 5-8 kW) but still pretty good.


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