In process of updating – completing by 15/06/16

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 – yet achieving that 99% will also cost many times that of one providing 80%-90% – despite the latter’s cost of a generator and its fuel. This is primarily because of the very high cost of the hugely more battery capacity required, and that of more solar. 

The amount and reliability of solar energy (insolation) that is most likely for your area can be found via https:[email protected]gov You need the tables Parameters for Tilted Solar Panels – and the data for maximums and minimums. I suggest also to read my article How much solar energy is available.

 Increasing solar capacity substantially assists 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 and the cost of fuel used – versus the cost of solar and battery capacity and space. As a rough guide it is generally not worth increasing battery capacity capacity beyond 24 hours. 

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 and having much the same output as the solar system’s inverter. This enables the entire electrical system to be run (if needed in the event of solar system failure) from that generator.

At all other times however, use a high current output battery charger running from the generator to charge the system’s batteries if/when they drop below about 60% remaining charge.This will also very much extend the life of the battery bank.

Onan 4.0 kVa good

Onan petrol and diesel generators (made by Cummins) are very much quieter than most. Pic Onan Cummins.

Visitors increase energy use

Another, and rarely considered need for a generator (for your first solar system) if you have city-bred friends staying (or worse, a caretaker looking after your property). This is because people living on solar power tend to be far more careful to turn off anything electrical that is not in use. Those not accustomed to solar may double the energy usage and truly increase the need for a generator with a home solar system !

Where a grid power supply is readily available, it is far better and cheaper to have battery capacity for only one day – and use that as a ‘virtual generator’ to cope with possible breakdowns – and peak loads. 

Currently most generators are noisy and polluting (but so it is solar panel and battery production). A hopefully near future, silent and pollution-free substitute for a generator will be a fuel cell. Many are available but currently cost many times the price of a generator of the same maximum 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 was in an area where there was 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.

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 motorhomes.