How to Size a Zero Export Solar System in Ontario (2026 Guide)

How to Size a Zero Export Solar System in Ontario (2026 Guide)

Published: July 29, 2026 | Updated: July 29, 2026 | Reading time: 11 minutes | By: Solar Calculator Canada Editorial Team

A zero export solar system in Ontario is designed so every kilowatt-hour you generate is used or stored on site, with nothing sent to the grid. To size one, match production to what your home can absorb: summer daytime consumption plus usable battery capacity. Oversize it and the surplus is simply curtailed, which wastes capital and stretches payback.

Solar Calculator Canada is an independent Canadian platform that provides free solar and battery estimates and matches homeowners with vetted installers. We do not install systems, which is exactly why this guide can focus on getting the sizing math right rather than selling you a bigger array.

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A zero export solar system is a grid-connected solar setup configured so that no electricity ever flows out to the grid. In a standard net-metered setup, surplus solar is exported and comes back as bill credits. In a zero export setup, a smart inverter paired with a consumption meter watches your home's draw in real time and throttles solar output the instant production would exceed what your house and battery can take. The grid connection stays in place for buying power. It is a one-way street: electricity in, never out.

Utilities and Ontario's current incentive rules often call this design load displacement, because the solar displaces electricity you would otherwise buy rather than acting as a small power plant. Load displacement, net metering, and zero export are related but distinct terms, and mixing them up is one of the fastest ways to end up with the wrong system. If any of the vocabulary here is new, our solar glossary covers every term in this guide.

Three forces pushed this design from niche to mainstream.

First, incentive rules. As of July 2026, Ontario's provincial rebate stream for residential solar and battery projects funds load displacement systems only, and the program's official eligibility rules state that participants who take the solar and battery incentive are not eligible to hold a net metering agreement with their local utility. Homeowners must choose one path or the other. Program terms can change or end without notice, so confirm the current rules with the program administrator before signing anything. You can compare the broader landscape of current federal and provincial solar programs separately; this guide stays focused on the engineering question those rules create: how do you size a system that never exports?

Second, the shape of the rate day. For the summer period running May 1 to October 31, 2026, the Ontario Energy Board sets Time-of-Use on-peak hours on weekdays from 11 a.m. to 5 p.m., exactly when panels produce hardest. With on-peak power priced at 20.3 cents per kWh against 9.8 cents off-peak under the rates in effect through October 31, 2026, according to the Ontario Energy Board, a self-consumption system offsets the most expensive hours of the day with its own output. See how the plans compare in our TOU vs ULO Ontario guide.

Third, the connection process. For net-metered systems, utilities assess export capacity as part of the connection application, and that review can add constraints or time in some areas. A system that never exports largely sidesteps that question. It does not remove the need for utility notification, permits, or electrical inspection, and no approval or timeline is ever guaranteed.

Self-consumption ratio is the share of the solar electricity you generate that you actually use on site. It is the single most important input in zero export sizing.

Typical ranges based on Solar Calculator Canada methodology assumptions, July 2026. Actual ratios vary with household schedule, appliance mix, and system configuration.

In a net-metered system, a low ratio is fine because exports earn credits. In a zero export system, everything you do not consume is curtailed: the inverter throttles it away, and you paid for panels that produce nothing in that moment. That is why these systems are usually sized smaller than net-metered systems on the same roof, and almost always include a battery.

Step 1: Establish your daily load

Pull 12 months of bills and divide annual kWh by 365. The Ontario Energy Board's typical residential customer benchmark is 700 kWh per month, about 23 kWh per day, and larger family homes with air conditioning or an EV often run well above that. Then estimate your daytime share, the portion consumed roughly between 9 a.m. and 5 p.m. For most households it is an estimated 30 to 45 percent of daily use.

Step 2: Find your worst-case absorption day

The binding constraint is a sunny summer weekday, when production peaks and, for many families, nobody is home. On that day your system can only absorb daytime load plus battery capacity. Everything else is curtailed. Size to that day, not to an annual average.

Step 3: Size the battery before the array

Work out how much energy you need to carry from solar hours into the evening. If your evening and overnight consumption is around 14 kWh and you want most of it covered, a battery with roughly 13 to 16 kWh of usable capacity is the anchor. Our guide to the best solar batteries in Canada covers the hardware side.

Step 4: Size the array to the absorption ceiling

Add summer daytime load to usable battery capacity. That sum is your daily absorption ceiling. Then divide by your location's strong summer day production per kW. According to Natural Resources Canada's photovoltaic potential data, a well-oriented system in southern Ontario yields roughly 1,170 kWh per kW per year, which works out to an estimated June and July average near 4.5 kWh per kW per day, with clear days running around 5 to 5.5.

Worked example, with all figures as estimates. A Mississauga home uses 27 kWh per day, with about 10 kWh consumed during solar hours in summer. The owners choose a battery with 16 kWh usable capacity. Absorption ceiling: 10 + 16 = 26 kWh per day. At 5 kWh per kW on a strong summer day, the array that fills the ceiling without heavy curtailment is around 5 kW, perhaps 6 kW if they shift EV charging and laundry into daylight. On the same roof, a net-metered design might justify 9 or 10 kW. That gap is the whole point: zero export sizing is a ceiling problem, not a maximization problem.

Step 5: Stress-test winter

A system sized to the summer ceiling will undershoot winter load, since Ontario production drops sharply from November through February. That is expected. The grid covers the gap, and on the Ultra-Low Overnight plan, which prices its lowest rates between 11 p.m. and 7 a.m. according to the Ontario Energy Board, a battery may also charge from lower-priced overnight power and discharge into the 4 p.m. to 9 p.m. on-peak window. One caution: if your system was funded under a program with load displacement rules, confirm with the program administrator and your installer whether grid charging the battery is permitted under your agreement before building your winter strategy around it.

Every step above is what our free tool models with your actual address, roof, and usage.

Run your zero export numbers free in the Ontario estimator

This table compares how the two designs are engineered. Which one pays better depends on your consumption pattern, your utility, and current program rules, and the answer changes household by household.

Design comparison based on Solar Calculator Canada methodology assumptions, July 2026.

For the mechanics of how credits work where exporting is allowed, see our net metering in Canada guide.

1. Copying a net-metered quote. An installer reuses a 10 kW net-metered design for a load displacement project. The result is chronic curtailment and a payback that never matches the proposal. Ask every bidder to state their assumed self-consumption ratio and estimated annual curtailment in writing.
2. Skipping the battery. A solar-only version typically caps your self-consumption near 50 percent at best. The design rarely makes sense without storage.
3. Ignoring load shifting. Moving an EV charger, dishwasher, and laundry into solar hours can raise absorption by several kWh per day and justify a meaningfully larger array.
4. Forgetting the export limiter is a real device. Zero export is enforced by hardware: a smart inverter with a consumption meter, configured and verified at commissioning. In Ontario, electrical work must be done by a Licensed Electrical Contractor, and you can verify any contractor through the Electrical Safety Authority's contractor lookup.
5. Sizing to annual averages. Averages hide the summer peak that actually binds the design. Size to the ceiling day first, then check the annual picture, not the other way around.

A zero export solar system in Ontario flips the sizing logic Canadians are used to. You are no longer building the biggest system your roof allows; you are building the largest system your home can swallow. Anchor the design on your daytime load, choose the battery first, size the array to the absorption ceiling, and demand curtailment estimates in every quote. Then verify the whole thing independently before you sign. If a quote is much bigger than an independent estimate suggests for this kind of design, ask why.

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