Updated July 2017

A generator for home and property solar optimally supplies 5%-10% of yearly energy. This article explains why and the costs involved if more or less.

Relying on solar alone is feasible. But even 99% reliability implies three days a year without power. Achieving that 99% costs many times that of 80%-90%, despite the latter’s cost of generator and fuel. This is primarily because of the huge cost of the far more battery capacity required. Furthermore, that of more solar capacity. 

The amount and reliability of solar energy (insolation) that is most likely for your area can be found via: https://eosweb.larc.nasa.gov/cgi-bin/sse/grid.cgi?email=skip@larc.nasa.gov You need the tables Parameters for Tilted Solar Panels – data for maximums and minimums. Also: How much solar energy is available.

 Increasing solar capacity substantially assists. This is because more energy will be captured in semi-overcast conditions.

Because fuel costs vary hugely it is not feasible to give meaningful examples. It can however be estimated in terms of acceptable percentage of the generator’s cost over (say) ten years. Similarly, the cost of fuel used versus that of solar and battery capacity. As a rough guide it is rarely worth increasing battery capacity capacity beyond 24 hours. 

Generator for home and property solar

Where there are no unusual peak loads (such as an arc welder or big air compressor) you will need a generator capable of supplying 110 or 230 volts. It must have much the same output as the solar system’s inverter. This enables the system to supply full power (if needed) independently of solar.

Use a high current output battery charger running from the generator to charge the system’s batteries. Do this if/when they drop below about 60% remaining charge.This usefully extends the battery life.

Onan 4.0 kVa good

Cummins Onan diesel generators – not silent , but quieter than most. Pic: Cummins

Generator for home and property solar – visitors increase energy use

Another, and rarely considered, need for a generator is when city-bred friends visit. Or worse, a caretaker looking after your property. People living on solar turn off anything electrical that’s not in use. Those not accustomed to solar do not. This can double energy usage. 

Where grid power is available, it’s far cheaper to limit battery capacity to one day. Use the grid as a ‘virtual generator’ to cope with breakdowns, peak loads etc. 

Currently most generators are noisy and polluting. As is solar module and battery production.

A hopefully silent, pollution-free substitute will be a fuel cell. Many are available but cost hugely more than a generator of similar output. Fuel cells and their use are covered in depth in my book Solar Success (for home and property systems).

Coconut well from air jpg

Our self-designed and built Broome (in the very isolated Northwestern Australia) solar system. It is in an area where there is almost constant sun year-round. We had a generator but used it for less than twenty hours a year). For details of this system see All Solar House.

Generator for home and property solar – further information

All you need to know about the need for a generator with a home solar system, its choice and usage is included in my book Solar Success. That book provides all you need to know to buy, design and/or install stand-alone solar systems for homes and properties. My book, Solar That Really Works does the same for boats, cabins, camper trailers, caravans and motor homes.