Solar battery calculator
See how long a battery would power your home, how many you would need, and what a Renon Xcellent or Tesla Powerwall could save each year by charging overnight at ultra-low rates. Upload your bill or adjust your usage below.
Comparing batteries first? See our guide to home battery backup and Tesla Powerwall installation in Canada.
How big a solar battery do you need?
Start with your daily use: divide the kWh on your electricity bill by the number of days in the billing period.
Backup time = battery size ÷ hourly use. A home using 30 kWh a day averages 1.25 kW. One 13.5 kWh Tesla Powerwall covers that for about 11 hours, and a 16 kWh Renon Xcellent for about 13 hours.
Essentials last much longer. A fridge, furnace fan, lights and Wi-Fi together draw roughly 0.5 kW, so one Powerwall runs them for about 27 hours. That is why backup systems usually put these circuits on a protected panel.
Batteries for a full day = daily use ÷ battery size, rounded up. At 30 kWh a day that is three Powerwalls or two Renon Xcellents. Most homes size for less than a full day: one battery is usually enough to shift the expensive peak hours on time-of-use rates, and solar panels recharge it during a long outage.
The calculator above does this with your own numbers. Upload a bill and it shows backup time, how many batteries you would need and what one would save.
How a battery saves on time-of-use rates
On time-of-use pricing, power costs more at peak hours and far less overnight. A battery charges overnight at the ultra-low rate and runs your home the rest of the day — so every kWh is effectively bought at the overnight price.
More than just bill savings
Solar battery & Tesla Powerwall FAQ
Cost, rebates, lifespan, and how a battery pays off on time-of-use rates.
How much does a Tesla Powerwall cost in Canada?
A standalone Tesla Powerwall installed by Xolar in Ontario is about $23,997 before tax (roughly $27,100 with 13% HST).
Ontario’s Home Renovation Savings Program battery rebate only applies when the battery is installed together with new solar panels; in that case it pays $300/kWh, about $4,050 for one 13.5 kWh Powerwall 3.
A Powerwall added on its own does not qualify.
Enter your usage in the calculator above for a personalized cost, rebate, and payback estimate.
What is the Ontario battery rebate, and do I qualify?
Ontario’s Home Renovation Savings Program (HRSP) offers up to $5,000 back on a qualifying home battery for Ontario homeowners. The calculator applies it to your net cost automatically. You can see every current program on our Ontario rebates page.
How long does a Tesla Powerwall last?
Tesla warranties the Powerwall for 10 years.
In practice it’s expected to keep a meaningful share of its capacity well beyond that, especially under gentle daily time-of-use cycling rather than heavy fast-charging.
How many Powerwalls do I need for my home?
It depends on your daily use and what you want covered.
One Powerwall (13.5 kWh) handles daily peak-shifting and essential backup for many homes.
To cover a full day of use, divide your daily kWh by 13.5 and round up: a home using 30 kWh a day would need three.
The calculator above works this out from your bill.
How long can a Tesla Powerwall power a house?
On essentials (fridge, lights, internet and furnace fan, roughly 0.5 kW together) one Powerwall runs about 27 hours.
For the whole home it depends on your use: at 30 kWh a day the average draw is 1.25 kW, so about 11 hours, and less while heating, air conditioning or cooking are running.
Pairing with solar lets the battery recharge during an outage and run far longer.
Does a home battery pay off on time-of-use or ULO rates?
A battery saves by charging overnight when power is cheapest and powering your home the rest of the day.
On the Ultra-Low Overnight (ULO) plan that overnight rate is just 3.7¢/kWh, so every kilowatt-hour you’d otherwise buy at peak prices is effectively bought at the overnight price — that swap is what this calculator estimates.
A battery pays off fastest when paired with solar, which adds production and delivery-charge savings on top.
Tesla Powerwall vs. other home batteries?
Xolar’s main battery offering is the Renon Xcellent (16 kWh), a high-capacity battery at a lower installed price.
The Tesla Powerwall (13.5 kWh) remains popular for its built-in inverter and app.
Compare both using the battery selector in the calculator above.
Make the most of your battery
A battery saves more when it's part of a full system — and the rebate above is just the start.
