Calculators · Renewables

Solar PV

Array capacity, annual energy and yearly savings for a rooftop system, from the roof area, the sun hours at your site and the panel efficiency. A first number before a site assessment.

Free. No sign-up. Not sealed engineering. By Ali Mazloum, P.Eng.

Inputs

Enter an area above 0.
Use a value between 0.5 and 10.Halifax about 3.8, Toronto 4.0, Calgary 4.5
Use a value between 5 and 50 %.
Use a value between 30 and 100 %.
Enter a rate of 0 or more.
Defaults: 50 m², 4.5 sun hours, 21 % panels, 78 % performance ratio, $0.14/kWh.
System capacity (DC) –
Annual energy–kWh/yr
Annual savings–/yr
Panels of 400 W–
Capacity per m²–W

A simple production model. Tilt, orientation, shading, snow and local tariffs are not modelled. Educational use; not sealed engineering.

Formulas  Capacity (kW) = area × efficiency at 1,000 W/m²   Annual kWh = capacity × peak sun hours × 365 × performance ratio   Savings = annual kWh × rate. Panels are counted at 400 W each.

Sizing a rooftop array

Five minutes

Estimating what a roof can produce is the first step in deciding whether solar makes sense for a building. This tool gives a first number from the parameters you can read off a drawing and a solar map, before anyone climbs on the roof.

How the production is calculated

Three things set the output: the sunlight at the site, measured as peak sun hours; the panel area and its efficiency; and the performance ratio, which is how much of the theoretical output survives the inverter, the wiring, soiling, shading and temperature. Modern monocrystalline panels reach 20 to 23 % efficiency at standard test conditions of 1,000 W/m².

Peak sun hours are not daylight hours

A peak sun hour is one hour at a full 1,000 W/m². A day with twelve hours of weak light might deliver four peak sun hours. Halifax averages about 3.8 a day over the year, Calgary about 4.5. Natural Resources Canada publishes the maps through RETScreen.

Who this is for

Engineers, installers, building owners and students who need a number before a full assessment. For a proposal, run PVsyst, SAM or RETScreen with the real roof orientation, tilt, shading and the utility’s rate structure.

FAQ

Straight answers
How many solar panels do I need for my home?

An average Canadian home uses about 10,000 kWh a year. With 400 W panels and 4 peak sun hours, that is roughly 20 to 25 panels, or 35 to 45 m² of roof. This tool counts panels from the computed capacity at 400 W each.

What performance ratio should I use?

The performance ratio is the share of the theoretical output a real system delivers. Well-designed systems reach 75 to 85 %. Use 75 to 78 % in cold climates with snow, 80 to 85 % for a well-oriented system in a temperate one. Inverter losses, wiring, soiling, shading and temperature are what take it below 100 %.

How do I find my peak sun hours?

Natural Resources Canada’s RETScreen and NREL’s PVWatts give solar resource data by location. Rough annual averages: Maritimes 3.5 to 4.0, Ontario and Quebec 4.0 to 4.5, Prairies 4.5 to 5.0, US Southwest 5.5 to 7.0. Summer is far higher than winter.

Does this account for net metering or feed-in tariffs?

No. Savings are annual production times your electricity rate. Net metering credits, time-of-use rates, feed-in tariffs and demand charges all change the real number, as does how much of the production you use on site.

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