Inverter and battery vs generator: how to compare the real cost
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A generator is cheap to buy and expensive to run. A battery system is the opposite. The only fair comparison is over several years, using your own numbers. Here is a method that works anywhere, whatever your currency.
Step 1: what the generator costs you each year
Track a typical month, or estimate from receipts:
- Fuel: litres (or gallons) bought per week × price per litre × 52.
- Servicing and repairs: oil changes, spark plugs, filters, repairs and parts over a year.
- Replacement: the generator’s price divided by how many years it lasts at your level of use.
Add them up. That is the yearly cost of the generator, before counting noise, fumes and trips to buy fuel.
Step 2: what a battery or solar system costs over its life
Get two or three quotes for the system the calculator suggests. For each:
- Upfront cost, installed.
- Battery replacement: if the battery is expected to last fewer years than the rest of the system, add the cost of replacing it. Lithium batteries usually last much longer than lead-acid; see lithium vs lead-acid.
- Grid charging, if the battery recharges from the grid rather than solar: the extra electricity on your bill.
Divide the total by the number of years you expect to use it (often 8 to 10 years for the inverter and panels) to get a yearly cost you can compare with the generator.
Step 3: compare, and work out the payback
Payback in years = upfront cost ÷ (generator cost per year − new system’s running cost per year)
If the generator costs more each year than the new system’s yearly running costs, the difference pays back the purchase. When fuel is expensive and outages are long, paybacks can be short. When outages are rare, a generator can stay the cheaper choice.
Things the numbers don’t show
- Safety. Generator exhaust contains carbon monoxide, which has no smell and kills. Never run a generator indoors, in a garage, or near windows and doors, and fit a carbon monoxide alarm. Health authorities such as the US Centers for Disease Control and Prevention publish clear guidance on safe generator use.
- Noise and neighbours, especially at night.
- Availability. Fuel shortages and price spikes often come at the same time as long outages.
- Instant switching. An inverter takes over in a fraction of a second, so computers, routers and medical devices don’t lose power. Most generators need starting and a changeover.
The hybrid option
Many homes don’t need to choose. A modest battery system can cover the short, frequent outages and the night, while the generator only runs occasionally to recharge the batteries during long outages. Running a generator at a steady, efficient load for a few hours uses far less fuel than running it all evening for a few lights.
If you go hybrid, check that the inverter can accept a generator input and charge batteries from it, and size the generator to cover the battery charger plus anything running at the same time.
Size the battery side of a hybrid system: set the hours without power to the outages you want the battery to cover.