What Peak Sun Hours Tell You

What are peak sun hours?

They are not hours of daylight. They are the daily solar energy on a surface, expressed as the number of hours the sun would need to shine at a fixed reference intensity to deliver the same amount. A day with 5 peak sun hours delivers 5 kilowatt-hours per square metre.

The idea lets installers compare locations and seasons with a single number. A summer day in Alberta can reach 6 to 7 peak sun hours, while December may be under 1. The annual average blends these, which is why published figures vary with the source, the tilt assumed and the time period. Treat any average as an approximation.

Why is southern Alberta so strong?

Southern Alberta sits east of the Rockies in a dry zone with many clear days, and its altitude means thinner air. Those factors combine to give more direct sun than coastal or lake-effect regions. The detail by city is in Alberta sunshine hours and the local case in Calgary solar potential.

Cold also helps. Panels lose a little efficiency as they heat, so a crisp day gives a better return per unit of light than a hot one. The effect is discussed in whether solar panels work in winter.

How do you turn peak sun hours into kilowatt-hours?

A rough formula: system size in kW, times peak sun hours per day, times 365, times a system efficiency factor of about 0.75 to 0.85 to cover wiring losses, inverter losses, temperature and dirt.

Example with assumptions: 7 kW, 4.2 peak sun hours, 0.8 efficiency. 7 times 4.2 times 365 times 0.8 is about 8,600 kWh a year. Equivalent to roughly 1,230 kWh per installed kilowatt. In a region with 3.3 peak sun hours the same calculation gives about 6,700 kWh. Professional tools replace the rule of thumb with hourly weather data. Once you have the energy figure, how many solar panels you need follows from your annual use.

Be aware that different tools report different things. One may give global horizontal irradiation in kilowatt-hours per square metre per day, another a value for a fixed tilt, a third for a tracking surface. These are all legitimate, but they are not interchangeable, and mixing them can inflate a production estimate by a surprising margin. Always ask which surface and period the number refers to, and prefer data covering many years, since a single sunny or cloudy year can mislead. A conservative designer will usually round down, and a good one will say so in the report. If two quotes rest on very different sun figures for the same address, that gap alone can explain most of the difference in their promised savings, so ask both to show the source of their number.

Where can you check the figure for your address?

Natural Resources Canada publishes photovoltaic potential maps and tools, and many installers use simulation software that draws on weather records. Look for the horizontal and the tilted-surface figures and read what tilt and orientation they assume. Do not mix a horizontal number with a tilted one.

Remember that the peak sun hours describe the site, not your roof. Shade, orientation and tilt change what you actually get, which is covered in the best direction for solar panels in Canada.

Does the same measure work for solar heat?

It does, since collectors respond to the same incoming energy, but thermal systems care more about winter and about storage. The Okotoks neighbourhood collected most of its heat in summer, held it in the ground, and used it months later. The seasonal timing, rather than the annual total, is what shaped its design; see borehole storage for the long version.

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