Sizing Your System

Solar system size is calculated by adding up the rated DCThe type of electricity produced by solar panels. DC power only flows in one direction and must be converted to AC by an inverter. power of each solar panelA device made up of photovoltaic cells that converts sunlight into DC electricity. Solar panels are also referred to as modules., measured in watts (W). Each panel has a nameplate rating (usually in the range of 400–600+ W) and the total system size is simply the sum of all panels installed. For example, a system using 18 panels rated at 500 W each would have a total system size of 9,000 watts or 9.0 kW.

Most Ontario homes land between 5 kW and 15 kW but a properly sized solar system is one that:

• Does not significantly exceed your expected annual electricity use
• Fits on your roof
• Complies with Canadian Electrical Code requirements for your electrical panel
• Remains within your budget

In Ontario, residential solar systems (net meteringA solar system configuration that allows excess solar electricity to be sent to the grid in exchange for hydro bill credits. These credits can then be used to offset future electricity imports. In Ontario, unused credits expire after 12 months. and load displacementA solar system configuration where any excess power sent to the grid does not receive hydro bill credits. Because exported electricity provides no financial benefit, these systems often include battery storage to capture surplus energy for later use rather than sending it to the grid without compensation.) are subject to a 10 kW AC size limitIn Ontario, residential solar systems are limited to 10 kW of AC inverter capacity. This is a regulatory limit, not a technology limit.. This limit applies to the total ACThe type of electricity used in your home and by the grid. Solar panels produce DC electricity, which must be converted to AC by an inverter before it can be used in your home. output of the inverterA device that converts DC electricity from solar panels into AC electricity for use in your home or export to the grid. Every grid-connected solar system requires an inverter., not the total DCThe type of electricity produced by solar panels. DC power only flows in one direction and must be converted to AC by an inverter. capacity of the solar panels on the roof. This means that while the inverterA device that converts DC electricity from solar panels into AC electricity for use in your home or export to the grid. Every grid-connected solar system requires an inverter. is capped at 10 kW ACThe type of electricity used in your home and by the grid. Solar panels produce DC electricity, which must be converted to AC by an inverter before it can be used in your home., the solar panelA device made up of photovoltaic cells that converts sunlight into DC electricity. Solar panels are also referred to as modules. array (DCThe type of electricity produced by solar panels. DC power only flows in one direction and must be converted to AC by an inverter. size) can be larger.

Most string inverters allow a DC-to-AC ratioThe ratio between the solar panel array size (DC) and the inverter size (AC). Ratios up to 2:1 are possible but some clipping will occur. of up to 2:1, meaning that up to 20 kW DCThe type of electricity produced by solar panels. DC power only flows in one direction and must be converted to AC by an inverter. of solar panels could technically be connected to a 10 kW ACThe type of electricity used in your home and by the grid. Solar panels produce DC electricity, which must be converted to AC by an inverter before it can be used in your home. inverterA device that converts DC electricity from solar panels into AC electricity for use in your home or export to the grid. Every grid-connected solar system requires an inverter.. In these cases, the inverterA device that converts DC electricity from solar panels into AC electricity for use in your home or export to the grid. Every grid-connected solar system requires an inverter. limits the maximum power output and excess production during peak sun is clipped.

While it is technically possible to install a system with more than 10 kW of ACThe type of electricity used in your home and by the grid. Solar panels produce DC electricity, which must be converted to AC by an inverter before it can be used in your home. inverterA device that converts DC electricity from solar panels into AC electricity for use in your home or export to the grid. Every grid-connected solar system requires an inverter. capacity, doing so reclassifies the project as a large distributed energy resource (DER). This comes with significant additional permitting, engineering studies and hydro company approvals. Such projects are treated more like small commercial installations and are cost-prohibitive for residential homeowners. As a result, systems above 10 kW ACThe type of electricity used in your home and by the grid. Solar panels produce DC electricity, which must be converted to AC by an inverter before it can be used in your home. are uncommon in the residential market.

Solar offset is the portion of your home's electricity use that your solar system is expected to cover on an annual basis. Because solar production is higher in summer and lower in winter, net meteringA solar system configuration that allows excess solar electricity to be sent to the grid in exchange for hydro bill credits. These credits can then be used to offset future electricity imports. In Ontario, unused credits expire after 12 months. allows excess summer production to offset electricity used later in the year by accumulating credits.

Some homeowners assume that solar only makes financial sense if the system is sized to offset 100% of annual electricity use, but this is not the case. In Ontario, net meteringA solar system configuration that allows excess solar electricity to be sent to the grid in exchange for hydro bill credits. These credits can then be used to offset future electricity imports. In Ontario, unused credits expire after 12 months. credits expire after 12 months, which means oversizing a system can result in unused production that provides no additional financial benefit. In many cases, it is better to size a system slightly below 100% offset. Even when roof space, electrical limits or inverterA device that converts DC electricity from solar panels into AC electricity for use in your home or export to the grid. Every grid-connected solar system requires an inverter. caps restrict system size, solar can still deliver strong value.

If roof space, budget or electrical code constraints limit your system size to below 100% offset, the overall financial return can remain similar. While a smaller system produces less electricity and results in lower annual savings, they also come with a lower upfront cost, maintaining comparable value.

To create an accurate custom solar design your HSA Advisor and our installer partners require the following information:

• A recent, complete hydro bill: Your rate structure is an important input for the financial analysis.
• 12 months of electricity use data (kWh): Used to size the solar system. If not shown on your hydro bill, this can be found by logging into your hydro account.
• Photos of your main electrical panel and any subpanels: This helps confirm what the capacity of the solar system will be and if there is breaker space on your panel to connect it.
• Clear satellite imagery: In most urban areas, satellite images provide sufficient detail to assess roof layout and shading.
• Your goals and priorities: Such as maximizing savings, minimizing upfront cost or planning for future battery storageA system that stores solar electricity for later use, typically during power outages. Batteries are optional and are not required for net-metered solar systems..