ASK THE EXPERTS: Selecting a Small Backup Generator

Beginner

I’ve been living off-grid for about 10 years with PV and microhydro  systems, a small battery bank, and a generator. While I very rarely need to use the generator, I can’t do away with it completely. It’s getting old now and the manufacturer no longer supports it, so I’m wondering what other generators might currently be available.

A 2 to 4 kW generator will be adequate. It needs to run on propane, have a remote two-wire battery start feature with no external power input required (other than an onboard starting battery), and a weatherproof enclosure. Any suggestions?

Ray Bowkley • Blue Grass, Virginia

The smaller the generator power output, the more difficult it is to find features like propane and remote electric start. There are a few options out there, but you won’t likely be able to find them locally and will have to have them shipped.

On the lower end of the cost spectrum, Durostar, Powermate, and Power Trust Equipment all have electric-start propane generators in the 3 to 5 kW range. The higher-priced Cummins Onan has propane RV generators that will work for you. You may have to add the remote starting cable and switch yourself, but that’s a relatively simple project.

Another option is propane conversion kits for gasoline generators. The kits are relatively simple to install, and come with detailed instructions.

There are a few features to consider when selecting an off-grid generator:

Fuel. Propane is an excellent choice because it never goes bad in storage, and water can’t condense and get into the fuel. Trifuel models that use gasoline, LP, or natural gas are also available. Diesel is also a good choice for long engine life and low fuel consumption.

Power. Choose a generator powerful enough to charge your battery and cover all the loads you run—with extra capacity for any high startup loads (such as well pumps). And derate the output for altitude—3.5% less efficient per thousand feet above sea level; temperature—about 1% to 3% less efficient for every 10°F above rated “full-power” temperature; and fuel type—propane has a lower energy density than gasoline, making the generator about 10% less efficient.

Engine speed. Most generators spin at 3,600 rpm, but 1,800 rpm generators are available. They last longer and are quieter, but are also more expensive.

Remote start. Almost any generator with electric start can be retrofitted with a remote starting kit, which can even be homemade.

Automatic generator start (AGS). Many inverter/chargers can automatically start and stop a generator based on your battery bank’s voltage or state of charge. This is controlled by the inverter’s auxiliary relay and an add-on control module that can also convert a two-wire starting system to three-wire. I don’t recommend AGS in most cases—there are too many things that can go wrong (see my article on vacation cabins in HP174).

Warranty. Generators can be finicky, and have lots of moving parts that can fail, so selecting a generator brand with a long warranty is often worth any extra cost. Be sure the warranty does not exclude off-grid use.

Dan Fink • Buckville Energy

Comments (7)

Paul Scheckel's picture

Off grid (wind/solar) with 5k Alaska Diesel genset, 1800RPM with >8,000 hrs. minimal maintenance, biodiesel friendly, rugged, reliable, remote start. Other off-gridders i know with LP generators pay less up front but over time service adds up. Off-grid RE systems are summed up nicely in "The Homeowner's Energy Handbook." Should be powerful enough not to clip the wave form under full house load.

raydarby@sustainableenergygroup.com's picture

I have a Trace/Xantrex 6048 (120VAC) grid-tied battery backup system and the Honda EU2000. It's a gas-sipper thanks to the eco-throttle. No auto-start so I just monitor battery SOC and fire it up manually. Love it!

off-grid solar's picture

Any suggestions for hooking up a portable Honda EU 2000 watt generator to a Schneider - Conext SW4024 inverter? It's an off-grid solar system for a small container home, and we don't anticipate needing to to use the generator much, but in the winter there may be occasions where the batteries need to be re-charged from the generator. Not planning to use the generator to run loads, just re-charging the batteries. Pull-start generator so trying to figure out the best way to connect into this inverter...

Michael Welch's picture
Hi there. Normally you attach the generator to the AC In inverter terminals, per the inverter's documentation. Why not do that?
raydarby@sustainableenergygroup.com's picture

We've found diesel to be a better choice for off-grid systems, as propane generators have much more frequent service intervals and expensive repairs when used as frequently as generators are in off-grid applications. Propane units are best suited for grid-tied homes and occaisional power outages. That said, I'm really interested to see what others experiences have been!

Forrest Jones's picture

Perhaps someone more knowledgeable than I, can state this more clearly, but the way that I hear it, generators do not have a stable enough sine wave to match the 60 cycle electricity that is being generated from your PV microinverters or string-inverters. Therefore, you can not use both at the same time. You may therefore need an automatic transfer switch for when the PV gets too low, that will switch from one to the other. Sad that they can't work together.

sunrnr's picture

Please also consider portable solar plus storage, but be sure to compare specifications such as high-load inverter, testimonials, and country of production.

Show or Hide All Comments

Advertisement

X
You may login with either your assigned username or your e-mail address.
The password field is case sensitive.
Loading