For the purposes of our discussion, “Intermediate backup power” is for those who want to be prepared to be off-grid for 200-500 hours per year, or who for other reasons prefer a more permanent or automatic solution to their needs.

As with those needing basic backup power, intermediate power is also most easily provided using a generator. To understand why intermediate backup power for the off-grid-capable home does not yet consider solar, wind, or micro-hydro power, see the discussion in Part 4.

Intermediate backup power shares many of the same concepts as Basic backup power. The chief differences are:

  • Choosing a generator designed to be a backup/standby generator vs a portable generator
  • More expensive generators
  • More complex installation to support the permanent installation
  • The possible addition of additional fuel supplies of storage capabilities.

When you expect or desire to spend more than 200 hours a year disconnected from the grid, it’s time to begin thinking about a permanently installed generator. This is true whether or not you intend to add alternative energy solutions to your home because such a generator will become a vital part of such systems.

Generator selection should still be based on anticipated needs based on the data you’ve collected about your critical loads. Avoid the temptation to just buy a larger generator that will power everything in your whole home. This temptation will be strong for two reasons:

First, that is what most vendors and installers would prefer to sell you. If you don’t know what your real needs are, you’ll almost certainly be sold an over-sized generator.

Second, it is easier and less expensive to wire in a large generator  to the entire house, than to isolate the generator power to only the critical loads. You’ll be told that “ will cost more to have a smaller generator and isolate the critical loads.” Yes, this is probably true – but you’ll save resources over the life of the generator by not burning excess fuel every hour it runs! An over-sized generator will be burning through more fuel and faster as well – all so that you can run loads that are ridiculous, to run off a generator, to begin with! This could be a very big problem in a protracted power outage if fuel is in short supply.

An over-sized generator will be burning through more fuel and faster as well – all so that you can run loads that are ridiculous, to run off a generator, to begin with! This could be a very big problem in a protracted power outage if fuel is in short supply.


With the above in mind, select a quality standby generator. Your main decision points will be:

  1. Wattage
  2. Fuel type
  3. Brand
  4. Installation options

As mentioned, wattage should be limited to your needs. Fuel type is something to spend some time considering. Each fuel has its advantages and disadvantages:

  1. Gasoline
    1. Pros: Abundant, inexpensive, easy to obtain
    2. Cons: does not store well for long periods of time
  2. Propane
    1. Pros: Relatively abundant, stores indefinitely
    2. Cons: Can be expensive, not easy to obtain
  3. Natural Gas
    1. Pros: In most, if available on your properly, is indefinitely available without transport or travel, except for some emergencies. Propane could be an alternative.
    2. Cons: Not available everywhere.
  4. Diesel
    1. Pros: Abundantly available, similar fuels can sometimes be used (home heating oil, jet fuel, kerosene, biodiesel-diesel). Diesel engines often outlive other combustion engines. Fuel efficiency.
    2. Cons: Does not store well for long periods of time. Additives can help some.

Once you’ve decided on your fuel source and generator brand and size, all that is left is installation.

Installation considerations

When installing a backup generator, it is common to also install an ‘Automatic Transfer Switch’ (ATX) which does the job or sensing the loss of grid power, starting the generator, and then powering the home electric panel, or sub-panel, with the generator power.

Some ATX include a built-in critical loads/generator loads panel. These are designed so that your critical home circuits – those that should be serviced by the generator – are wired into the ATX panel and are automatically serviced by the generator when the generator is running and the utility power is unavailable.

This is a fine option if there are enough circuits available in the ATX panel for doing so. If not, consider moving critical loads to a new sub-panel that can be serviced by the ATX. Prepare for some expenses to have a professional isolate, move, and re-wire these critical circuits. If building a new house, do this from the start and you’re home will be well-prepared for off-grid-capable power.

This is not an average DIY project and should be left to the professionals.

A less-expensive, but less automatic option would be to install the generator output to a manual switch such as a generator interlock. This will be less complex and costly to install, but requires far more manual process to switch between the generator and utility power. However, this is an option worth considering as temporary if one intends to install alternative energy components such as solar, batteries, wind, etc.