Including a Generator With Your Solar Array

April 2014

Some customers want or need additional security that power will be available to their solar powered house.  In this case, whether solar batteries are part of the solar array or not, adding a generator can add peace of mind.


Generators Fulfill Three Objectives for Off-Grid Systems:

  1. Backup Charging – producing power in any weather.
  2. Battery Equalizing – certain batteries need a planned overcharge several times a year to increase performance and service life.
  3. Running Loads that Exceed the Inverter Capacity – for example, well pumps.

For on-grid systems, a generator may decrease the battery-bank size, or eliminate it all together.  For instance, a customer with a relatively reliant grid and an incentive structure that doesn’t offset battery costs may be better off maximizing their funds to increase their solar array as opposed to adding batteries.  If back-up power remains important, then a generator may provide an appropriate solution without batteries.  In the scenario where there is a grid-tied solar array and a generator, the two must be wired to ensure that grid-tied solar array doesn’t recognize the generator output as energy from the grid and attempt to feed power back to the grid.  This can be accomplished with appropriate automatic disconnects and wiring design.

Much like batteries, generators add a layer of complexity to the solar system and may require maintenance and have a shorter life span than the solar array itself.  The generator’s life expectancy can be increased by choosing a well-regarded manufacturer with a good warranty (minimum two-year warranty is recommended).

Additional considerations include sizing the generator and the AC voltage output.  For off-grid systems, a generator is typically sized to supply the full charging capacity of the inverter plus additional loads needed during charging.  Most generators in home systems are 2,500 watts or greater.  Regarding AC voltage, some generators only produce 120V and others are either field-configurable or are 120/240V with a switch.

As noted in the previous article, combining a generator with your off-grid solar array will provide additional capacity to the system and potentially allow you to consider a smaller battery bank since the generator can offset the shortfall when there is limited sun.  Or, adding a generator to your grid-tied (no battery) solar array may provide back-up power while maximizing your solar production.

*Reference Article:  Engine Generator Basics by Allan Sindelar, Home Power Magazine 4/30/12