A battery and a generator can look interchangeable on a specification sheet and behave nothing alike on the third day of an outage. The difference is not power. It is what happens when the stored energy runs out.
Who this helps
A homeowner comparing stored energy against combustion equipment, often with solar already on the roof or under consideration.
When to read it
Read this once you know roughly how long the outages here last. Duration is the input that decides this chapter.
What you can decide afterwards
Whether this household's exposure is to short interruptions, which stored energy handles well, or to long outages, where the deciding question becomes how the system gets replenished.
Quick answer
Both carry a house; they differ in what happens when the stored energy runs out. A battery discharges and then needs recharging, from the grid that is down or from an array that may not be producing. A generator runs as long as fuel keeps arriving, so its endurance is a supply question rather than a capacity one. Decide from the length of the outages this property actually gets, and confirm whether any existing solar can even produce power while the grid is down — many arrays cannot.
What this chapter can help you determine
Which failure mode this household cares about: the flicker and the short interruption, or the multi-day event where replenishment decides everything.
How each system's energy is replenished, and what each depends on to do it.
What the household experiences during a short outage compared with a long one.
How an existing or planned solar array changes the question.
How does the system get its energy back?
Stored energy, refilled from the grid or an array
A battery system discharges to carry the household and then has to be recharged — from the grid once it returns, or from a generating source on the property.
This points here when:
Outages here are brief and frequent rather than long and rare.
Silent, emissions-free operation matters because of siting, neighbours, or household sensitivity.
A solar array already exists or is planned, giving the battery a way to refill while the grid is down.
Nobody wants an ongoing fuel relationship or engine service schedule.
If this is the wrong call: A multi-day winter outage with no sun and no grid, where the system carries the house until the stored energy is gone and then cannot refill.
Fuel delivered continuously
A generator converts fuel to electricity for as long as fuel keeps arriving, so its endurance is a fuel-supply question rather than a capacity question.
This points here when:
Outages here have lasted long enough that endurance is the real concern.
A fuel supply already reaches the property, or can.
Loads such as heating, cooling, or pumps make sustained output the point.
The household accepts engine service, exercise cycles, exhaust, and noise as part of ownership.
If this is the wrong call: Taking on service obligations and running costs for endurance the household's actual outages never demanded.
Both, doing different jobs
Stored energy covers the instant and the short interruption; combustion equipment covers the long event. The household is then buying two systems and the coordination between them.
This points here when:
Both short interruptions and long outages are genuine problems here.
Sensitive equipment cannot tolerate the gap while any engine starts.
A solar array makes stored energy productive outside outages too.
If this is the wrong call: Buying two systems whose interaction was never specified by anyone, and discovering during an outage that they do not coordinate the way the household assumed.
What you probably already know
Whether the property has solar, or whether solar is being considered.
Whether short flickers or long outages are the recurring complaint.
Whether noise or emissions would be a problem at this location.
Whether the household wants an ongoing fuel and service relationship.
What is commonly still unknown at this point
How long the household's actual loads would run on stored energy, which depends on the loads and cannot be assumed.
Whether an existing solar array is even configured to produce power while the grid is down, which is not automatic.
Whether the property's electrical arrangement suits either system without changes.
How each system behaves during the switchover, and whether the household would notice.
Information to gather
Whether an existing solar installation can operate during a grid outage, confirmed with its installer rather than assumed.
The lengths of the outages this property has actually experienced.
Which loads must ride through a momentary interruption without dropping.
Whether a fuel supply reaches the property already.
Any siting constraints — proximity to windows, neighbours, and living space — that would rule either option in or out.
Questions to ask
For a solar installer: does the existing array produce power when the grid is down, and what would it take to make it do so?
For a generator contractor: how does the transfer arrangement behave if both stored energy and a generator are present?
For either: which of the household's priority loads does this system carry, and which does it not?
When this does not apply
The property has no solar and no interest in it, and outages here are long.
The question is really about who operates the system rather than how it is replenished.
A system is already installed and the question concerns its condition.
What would change the decision
An existing solar array turns out to island during an outage, or turns out not to.
Outage duration at this property changes materially.
A load that cannot tolerate the switchover gap is identified.
Siting, noise, or emissions constraints rule one option out.
What requires a qualified professional
Whether an existing array or battery can support a generator, or the reverse, is a design determination for the installers of both systems.
How long any system carries any household is a calculation from measured loads, done by a professional with the real equipment list.
What this page cannot determine
How long a battery system would carry this house.
Whether solar at this property can recharge a battery during an outage.
Whether either system suits this property's electrical arrangement.
Deliberately out of scope here:
Capacities, run times, and any figure describing how long a given system lasts.
Whether either system can be installed at this property.
Which combination is appropriate here.
Bottom line
Short, frequent interruptions favour stored energy. Long outages make replenishment the whole question. If both matter here, the honest answer is that two systems are being considered, and how they coordinate is a design question for the installers of both.
What to do next
Do this chapter's work on paper: Home load priority worksheet. Turn a vague sense of what matters into a written, prioritised list plus an explicit inventory of what you still have to look up.
The next decision is Whole-home backup or essential loads only? — Which coverage scope this household wants, and how to state it so that every contractor prices the same project.
Standby generator or portable generator? — Whether this household needs equipment that operates without anyone present, or can rely on equipment a person sets up and runs.
Should I get a home backup generator? — Whether this household should spend further time and money investigating backup power, or resolve something else first.
what drives cost on the generator side of this comparison — This chapter compares the two on how they behave rather than on price. If the generator side is the one you need to put a number against, that chapter names the installation scopes that drive it — there is no equivalent breakdown published here for the battery side yet.