What size solar battery do I need?

It depends on what you want it for, and the arithmetic is short: your daily electricity use, times the number of days you want covered, times the share of your normal use you would actually run. A typical Ontario home using 9,000 kWh a year uses about 24.7 kWh a day. Running everything for a full day therefore needs about 24.7 kWh of usable capacity, while running a fridge, lights and the internet at roughly thirty percent of normal use needs about 7.4 kWh. That is the difference between two Powerwall-sized units and one.

Why does the calculator ask what share of my use I would run?

Because inventing that number would be the single worst thing this page could do. Plenty of sites state that essential loads are some fixed percentage of a household's normal consumption, and no source we could find publishes a figure for Ontario homes. It also varies enormously: a house with a gas furnace and a gas water heater has a much smaller electrical baseline during an outage than one with a heat pump. So we ask you, and we show the arithmetic so you can try different answers.

How much does a home battery cost in Ontario?

Home battery storage in Ontario runs $8,500 to $24,000 installed for a system, according to Solar X Canada, and the figure that scales with capacity is $700 to $2,000 per usable kWh installed, from Green Building Canada. Named products sit inside that: a 13.5 kWh Powerwall is quoted at $19,000 to $24,000 fully installed in Ontario and an Enphase IQ Battery 5P at $8,500 to $11,200 per 5 kWh module. Adding a battery to a solar system rather than buying it standalone is generally quoted lower.

Where do the Tesla figures come from?

From Solar X Canada, not from Tesla. Tesla's own Canadian site returns an HTTP 403 error to us, and this site's rule is that a source we cannot read ourselves cannot carry a number. So the Powerwall capacity and price here are attributed to the Canadian installer who publishes them and whose page we can actually open. If you want the manufacturer's specification, get it from Tesla directly rather than from us.

Does a battery earn back what it costs in Ontario?

That is a harder question than it is for panels, and this page does not claim to answer it. Panels displace electricity you would otherwise buy, which is straightforwardly worth money. A battery mostly moves electricity you have already generated from one hour to another, so what it returns depends on the gap between the price at the hour you store and the hour you use, which on a time-of-use plan is real but modest. The other half of its value is not financial at all: it is whether your house has power during an outage, which is worth what it is worth to you.

Solar battery sizing calculator

Battery sizing is one short multiplication, and the hard part is one honest input: how much of your house you would actually run on it. Get that right and the capacity falls out. Get it wrong and you buy twice the battery you needed.

Last updated August 28, 2026By The SolarPanelFinder Rooftop Desk

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How many kWh of battery do you need?

Electricity you use in a yearFrom your bill. The OEB treats 9,000 as typical.How long it should cover youOne day is the usual answer for an outage.Share of your normal use you would actually runFridge, lights and internet only is a much smaller number than running the whole house.

24.7 kWh a day, 30% of it, for 1 day

7.4 kWh of usable capacity

Which at the $700 to $2,000 per installed kWh that Green Building Canada publishes comes to $5,178–$14,795. For scale, whole home battery systems in Ontario are quoted at $8,500–$24,000 installed.

Your daily use, being 9,000 kWh over 365 days: 24.7 kWh
Times 1 day at 30%: 7.4 kWh
1 × 13.5 kWh unit would do itTesla Powerwall 3 (13.5 kWh), fully installed in Ontario - Solar X Canada, Home Battery Storage Ontario 2026: $19,000–$24,000
1 × 10 kWh unit would do itTypical 10 kWh battery unit, Canada - Solar Guide, Solar Panels Cost in Canada 2026: $7,000–$20,000
2 × 5 kWh units would do itEnphase IQ Battery 5P, installed - Solar X Canada, Home Battery Storage Ontario 2026: $17,000–$22,400

The share field is an input rather than a built-in figure on purpose. “Essential loads are thirty percent of normal use” is the kind of plausible number no source publishes, and putting an invented one at the centre of the answer would be worse than asking you. Work yours out from what you would actually run: a fridge, some lights, the internet and phone charging is a very different number from keeping the air conditioning on. Three things also mean a real battery covers slightly less than this arithmetic suggests, and none of them is modelled here because we could not source a figure for any: round-trip efficiency losses, depth-of-discharge limits beyond whatever a product already calls usable, and degradation over the years.

Ontario program money for a battery has conditions that rule out most retrofits

The ones that matter: a battery only qualifies when it is installed together with a NEW solar system rather than added to panels you already own, a home that already has solar or storage is excluded outright, and taking the provincial route means giving up a net metering agreement with your utility. Those interact, so they belong on one page with every condition attached rather than as a footnote here.

Read the conditions in full before you let anyone build a quote around them.

The prices

Every published figure this page uses

Home battery storage in Ontario and Canada, from named sources. The per-kWh row is the only one that scales with the size this tool computes; the rest are reference points.
Item	Typical range	Unit	Source
Home battery storage, Ontario, installed	$8,500–$24,000	per system, CAD, before incentives	Solar X Canada, Home Battery Storage Ontario 2026
Tesla Powerwall 3 (13.5 kWh), fully installed in Ontario	$19,000–$24,000	per unit, CAD, before incentives	Solar X Canada, Home Battery Storage Ontario 2026
Installed battery cost per kWh of usable capacity, Canada	$700–$2,000	per kWh installed (CAD)	Green Building Canada, Solar Panels Cost in Canada (updated 14 Jan 2026)
Typical 10 kWh battery unit, Canada	$7,000–$20,000	per unit (CAD)	Solar Guide, Solar Panels Cost in Canada 2026
Home battery storage, Ontario, common mid-market band	$13,000–$22,000	per system, CAD, before incentives	Solar X Canada, Home Battery Storage Ontario 2026
Tesla Powerwall 3 added to a solar system, before HST	$13,000–$17,000	add-on to system price (CAD)	Xolar, Cost of Solar Panels in Ontario (2026)
Enphase IQ Battery 5P, installed	$8,500–$11,200	per 5 kWh module (CAD)	Solar X Canada, Home Battery Storage Ontario 2026
Growatt APX HV modular battery (5 to 30 kWh), installed	$8,000–$14,000	per system depending on capacity (CAD)	Solar X Canada, Home Battery Storage Ontario 2026
Solis hybrid inverter plus Renon battery added to a solar system, before HST	$9,500–$11,000	add-on to system price (CAD)	Xolar, Cost of Solar Panels in Ontario (2026)
Battery added to a solar installation, Canada-wide	$8,000–$15,000	per unit added to system cost (CAD)	Volts.ca, Solar Panels Cost in Canada 2026
8 kW solar array plus Tesla Powerwall 3, complete	$35,900–$45,100	per project, CAD, before incentives	Solar X Canada, Home Battery Storage Ontario 2026
Solar plus battery, 5 to 12 kW systems, before HST	$30,000–$46,300	per project (CAD)	Xolar, Cost of Solar Panels in Ontario (2026)

The limits

What this calculation leaves out

Three losses, all real, none of them modelled here, because we could not source a figure for any.

A real battery covers slightly less than this arithmetic suggests, and it is worth knowing in which direction the error runs. Round-trip efficiency means some of what goes in does not come out. Depth-of-discharge limits can hold back capacity beyond whatever a product already describes as usable. And capacity falls over the years, as it does in every battery anyone has ever owned. Each of those would need a number to model, we did not find one we could cite for Canadian conditions, and so this page states none rather than guessing three.

The practical consequence is simple: size a little generously rather than exactly, and treat a result here as a floor rather than a target.

On the Tesla figures specifically, an attribution note. Tesla's Canadian site returns an HTTP 403 to every request we make, and the rule on this site is that a source we cannot read ourselves cannot carry a number. So the Powerwall capacity and price above are attributed to Solar X Canada, a Canadian installer who publishes both and whose page we can open. That is a weaker source than a manufacturer's own datasheet, and naming it honestly is better than implying we read something we did not.

The last thing worth saying is about what a battery is for. Panels displace electricity you would otherwise have bought, which is straightforwardly worth money. A battery mostly shifts electricity you already generated from one hour to another, so its financial return depends on the price gap between those hours, and on a time-of-use plan that gap is real but modest. The other half of the case is not financial: it is whether the house keeps working during an outage. That is a genuine reason to buy one, and it is not something a calculator can price.

Frequently asked questions

What size solar battery do I need?: It depends on what you want it for, and the arithmetic is short: your daily electricity use, times the number of days you want covered, times the share of your normal use you would actually run. A typical Ontario home using 9,000 kWh a year uses about 24.7 kWh a day. Running everything for a full day therefore needs about 24.7 kWh of usable capacity, while running a fridge, lights and the internet at roughly thirty percent of normal use needs about 7.4 kWh. That is the difference between two Powerwall-sized units and one.
Why does the calculator ask what share of my use I would run?: Because inventing that number would be the single worst thing this page could do. Plenty of sites state that essential loads are some fixed percentage of a household's normal consumption, and no source we could find publishes a figure for Ontario homes. It also varies enormously: a house with a gas furnace and a gas water heater has a much smaller electrical baseline during an outage than one with a heat pump. So we ask you, and we show the arithmetic so you can try different answers.
How much does a home battery cost in Ontario?: Home battery storage in Ontario runs $8,500 to $24,000 installed for a system, according to Solar X Canada, and the figure that scales with capacity is $700 to $2,000 per usable kWh installed, from Green Building Canada. Named products sit inside that: a 13.5 kWh Powerwall is quoted at $19,000 to $24,000 fully installed in Ontario and an Enphase IQ Battery 5P at $8,500 to $11,200 per 5 kWh module. Adding a battery to a solar system rather than buying it standalone is generally quoted lower.
Where do the Tesla figures come from?: From Solar X Canada, not from Tesla. Tesla's own Canadian site returns an HTTP 403 error to us, and this site's rule is that a source we cannot read ourselves cannot carry a number. So the Powerwall capacity and price here are attributed to the Canadian installer who publishes them and whose page we can actually open. If you want the manufacturer's specification, get it from Tesla directly rather than from us.
Does a battery earn back what it costs in Ontario?: That is a harder question than it is for panels, and this page does not claim to answer it. Panels displace electricity you would otherwise buy, which is straightforwardly worth money. A battery mostly moves electricity you have already generated from one hour to another, so what it returns depends on the gap between the price at the hour you store and the hour you use, which on a time-of-use plan is real but modest. The other half of its value is not financial at all: it is whether your house has power during an outage, which is worth what it is worth to you.
Does a battery qualify for Ontario program money?: Only under conditions that rule out most retrofits, and they are on our rebates page rather than here. The important ones: the battery has to be installed together with a new solar system rather than added to panels you already own, a home that already has solar or storage is excluded outright, and taking the provincial route means giving up a net metering agreement. Those interact in ways that decide the answer, so they belong on one page with all of them attached.

Sources

Where these figures come from

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