Off-grid Solar 101 | modern offgrid living

Solar battery Generators system

System / January 20, 2017

This picture of a model 4000 Generac brand generator looks just like my 7000 watt electric start modelAC Generators for back-up power and running large loads Generators are best used for backup power during long periods of little or no sun. Under these circumstances you would run the generator just long enough to provide the batteries with their Bulk stage charge and for a portion of the Absorption charging stage. The 3 stage charge cycle is explained under Charge Controllers The reason you would not attempt to charge the batteries fully with the generator is that towards the end of the Absorption stage, the batteries are drawing much less current and most of the generators' power is not being used. Very inefficient. This would be a good time to run your large loads (like washing machine, vacuum, etc) that would normally put a real drain on your batteries.

If you charge the batteries up to about 85% to 90% capacity this way, not only will that prevent them from being too deeply discharged, but also a small amount of winter sun could charge them the remaining 10% to 15%.

Most good Power Inverters have a battery charger built in. When you run the generator and apply the AC to the inverter, it will charge the batteries and transfer the AC to your loads (appliances). This is the most efficient technique. It would be much more expensive to run a generator full time to supply power. Also, it would wear out much faster and let's not forget the noise.

This Solar Home runs a freezer, computer, 27 inch color tv, microwave, and assorted other lights and devices. In the winter I run my generator for 45 to 60 minutes per day to charge the batteries up to about 90%. Since some winter days are sunny, the generator is not used every day.


For a small to medium sized Solar Energy System, a 4000 to 7000 watt generator will work nicely. The price range is $500 to $1500 dollars depending on brand & features. You can spend much more on Auto-Start capability, diesel fueled, or propane fueled generators but I believe only large systems would make these generators economical. I bought a Generac 7000 watt model with electric start at Home Depot for $1100 and after almost 5 years of use, realize it is bigger than I needed. Still, it's nice to have the extra power.