What Size Home Battery Do You Need? A Practical Ontario Guide
Choosing a home battery is not as simple as buying the largest capacity available. The best system is the one that matches your household’s energy use, backup priorities, electrical service and future plans.
The first distinction is between kilowatts and kilowatt-hours. Kilowatts describe how much power the system can deliver at one time. Kilowatt-hours describe how much energy is stored. A large battery can provide longer runtime, but the inverter and electrical design still determine which appliances can operate together.
Smarter Power offers SBSS configurations in 10, 20 and 30 kWh ranges, subject to the home, installation location and applicable electrical requirements.
Start with your real usage
A monthly hydro bill shows total consumption, but interval data is even more useful because it shows when electricity is used. A home that consumes 30 kWh over an entire day may only need a fraction of that amount to cover essential circuits overnight or through a typical peak period.
Decide what “backup” means to you
Some homeowners want only refrigeration, lighting, internet, a sump pump and heating-system controls. Others want broader household coverage that may include air conditioning, well pumps or selected kitchen loads. High-power appliances can reduce runtime quickly, so they should be identified before the battery is selected.
Consider your operating strategy
A 10 or 15 kWh system may be appropriate for a household focused mainly on essential backup and modest ULO peak shifting. A 20 kWh system provides more flexibility for evening load coverage and longer outages.
A 30 kWh configuration may suit a higher-consumption home, an EV household or a customer seeking more extended backup, where the site and Ontario installation rules permit it. These are planning examples, not universal sizing rules.
Solar and future electrification also matter. A homeowner planning to add an EV, heat pump, electric water heater or larger solar array should size the electrical system with those future loads in mind. It is usually more economical to plan correctly once than redesign the system later.
Battery runtime can be estimated with a simple relationship: usable battery energy divided by average supported load. For example, 15 usable kWh supporting an average 1.5 kW load is approximately 10 hours before accounting for changing loads and reserve settings.
Smarter Power reviews hydro bills, interval data, panel capacity, outage goals and solar potential before recommending an SBSS. Ontario’s Electrical Safety Authority also sets residential energy-storage requirements related to installation location, separation and aggregate capacity, making site-specific design essential. Review the ESA residential energy-storage guidance.
Use the Smarter Power Residential Savings Calculator as a starting point, then confirm the recommendation through a home assessment. More battery is not automatically better. Right-sized storage usually delivers the strongest balance of cost, savings, backup runtime and long-term value.
