For off grid homes or for backup systems, generators provide a charge to batteries or keep critical electrical loads active during a power outage. Backup systems can be extremely expensive for plug-and-go preconfigured setups, but it is relatively simple and cheap to automate a standard generator to perform the same task. I standard generator, like the one used on a construction site, will run you less than $500 while a preconfigured setup can cost thousands. You can spend a bit more, around $900, to upgrade your standard generator to a quieter, more compact option as well. The preconfigured system will likely require professional installation but it will be setup to automatically turn on when your other power source is depleted or losses power.
To obtain this same setup with a standard generator, you will need an automatic generator module (AGM) to control when the generator turns on. With the AGM you can select a certain battery voltage to turn the generator on or turn on when the grid is down. The generator will then be started either with some of the remaining power in your battery system or from an isolated battery connected directly to the generator. Many standard generators are already equipped with a battery and starter, so setup is simpler. If your generator does not have a starter and battery, you will need to size and install appropriate components. Generally a riding lawn mower battery will provide enough power for startup.
The AGM will also need to operate the generators choke, which means if your generator uses a manual choke lever, you will need to install an actuator (similar or the same type as is used in car door lock mechanisms). The trickiest part of the AGM system is determining the appropriate wiring schematic to combine the generator to your system. For this, you will need to compare the generators wiring diagram to the AGM wiring diagram and locate the wires in the generator to splice into.
Forgoing the AGM, you can install a manual start generator to be used at times of higher electrical needs. Automatic start and manual start generators can run on gasoline or propane. Generators are an excellent method of making a battery powered system more economical, since they can be used on only the most extreme days (either hot or cold or long stretches of time without sunlight for solar systems), allowing you to size your battery bank for a more average time of year/day.