Solar monitoring: what normal output looks like

Your monitoring app is the best tool you have for keeping a solar system healthy. A quick look once a month catches most problems early. The trick is knowing what normal looks like, because solar output in Canada swings enormously between seasons and from day to day. This guide shows typical monthly numbers, the warning signs worth acting on, and how to check your system against the estimate you were sold.

Where your data comes from

Almost every modern inverter connects to the internet and reports production to an app or web portal run by the inverter maker.

• String inverters usually report total system output, sometimes split by string.
• Microinverters and power optimizers report output for each panel, which makes it easy to spot one weak panel.
• Your utility's smart meter records what you import and export, which you can usually see in your utility's online account.
• Consumption monitoring is an add-on that shows what your home uses. It is useful for understanding self-consumption and battery behaviour.

Ask your installer to set up the app in your name and show you how to read it before they leave. Make sure you own the login, not just the installer.

What normal output looks like by season

Here is our Toronto sample system (7.3 kW of panels) month by month. Scale it to your system by dividing by 7.3 and multiplying by your system size in kW.

A few things stand out:

• July produces roughly nine times as much as December.
• November to February together produce only about 10% of the year.
• Cities with more sun, like Regina and Calgary, produce more per kW over a year; Vancouver and St. John's produce less. Our model's yearly output per kW ranges from about 870 in St. John's to about 1,300 in Regina.

Day-to-day swings are normal

Monthly averages hide a lot of variation. In the app you will see:

• A bright June day producing well above the monthly average, and a rainy June day producing a fraction of it.
• Zero or near-zero output for a few days after a snowstorm.
• A smooth curve on clear days, rising from morning to a peak around midday and falling in the evening. Cloudy days look jagged.
• Slightly higher peaks on cold, clear spring days than on hot summer days, because panels are more efficient when cool.

Don't judge your system on a single day or week.

Signs something is wrong

Act on these:

• Zero output on a clear, sunny day. Check whether the inverter shows a fault or the app has lost its internet connection. A tripped breaker is a common cause.
• No data for several days. Often just a Wi-Fi change, but production may have stopped too.
• One panel consistently lower than its neighbours in panel-level data, when shade can't explain it. It may be a failed panel, optimizer or microinverter, a loose connector, or damage from squirrels.
• A sudden step down in output that persists across sunny days.
• Error codes or a red or orange light on the inverter.
• Gradual decline faster than expected. Panels lose about 0.5% per year on average, according to US National Renewable Energy Laboratory research. Losses much larger than that over a few years are worth investigating.

Seasonal patterns are not faults. A steady fall in output from August to December is expected. So is a new shadow from a neighbour's tree that has grown over a few summers, although that one is worth noting.

Comparing with your estimate

Your installer's quote, and any SolarMyBill estimate, gives expected annual production in kWh. To check it fairly:

1. Wait a full year. Comparing a single month is unreliable, because weather varies a lot.
2. Compare the annual total. Within about 5% to 10% of the estimate in either direction is normal year-to-year weather variation.
3. Allow for degradation. Year five should be a little lower than year one.
4. Compare like with like. Some estimates are for AC output at the meter and some for DC output at the panels. Ask your installer which theirs is.
5. Check the weather. An unusually cloudy summer will pull a year down. Natural Resources Canada's photovoltaic potential maps give typical monthly output per kW for municipalities across Canada, which is a useful sanity check.

If your system falls more than about 10% short for a full year without a clear explanation, contact your installer with the data. Many contracts include a production estimate, and some include a production guarantee. See how much electricity a solar panel makes.

Check your bill too

The app shows production. Your bill shows what you actually paid. Once a quarter, compare your bill to the same period last year. Make sure net metering credits are showing correctly and carrying forward. Our guide on reading your electricity bill explains what to look for.

Next step

See your own estimated month-by-month production: check your roof.

Common questions

How much should my solar panels produce each month in Canada?

In our Toronto model, each kW of panels makes about 0.6 kWh a day in December and about 5.5 kWh a day in June and July. Your location and roof will shift those numbers.

Why is my solar production so low in winter?

Short days, a low sun and snow cover all cut winter output. November to February is only about 10% of the year in Toronto, which is normal.

How do I know if my solar system is underperforming?

Watch for zero output on sunny days, a panel lower than its neighbours, or error codes. Over a full year, falling more than about 10% short of the estimate is worth raising with your installer.

Should I compare my production to the estimate monthly?

Monthly comparisons are unreliable because weather varies. Compare the full-year total to the annual estimate instead.

Sources

• Natural Resources Canada: Photovoltaic potential and solar resource maps of Canada
• NREL: Photovoltaic Degradation Rates, An Analytical Review
• CertainTeed Canada: Homeowner's guide to solar maintenance