Peak Solar Production Hours

[Chris Jacobson]

I'm not sure if my title accurately describes my thread. I have charted solar noon for each day throughout the year for my location here in Southwestern Ontario. It seems the general opinion I'm reading is that "peak production" occurs 3 hours either side of solar noon. Is this just an average or could we say that in the depths of winter, the peak hours gradually drop and could realistically be only 2 hours either side of solar noon? Or is the six hour window an average for the entire year?

Again, I'm just trying to wrap my head around a shading issue for my own piece of mind and so I can study the installer's evaluation with a critical eye. The shading issue just happens to occur very close to the outer ends of the peak hours each day from approx. Oct. - March (and the trees are not mine so removal is not yet an option).

Thanks!

Chris

[Rob Beckers]

Hi Chris,

To put some numbers to the various solar windows (I model them with the Solmetric 210, but they don't exactly make that easy so this is approximate):

The base number if you have sun from 8am through 4pm all year is 89% of energy production with no obstructions at all (ie. solar window 5am - 7pm). Honestly, that number sounds somewhat exaggerated in its losses; I know people with that kind of solar window still do very close to the 1,140 kWh/kW/year I use as the base number. Possibly the software doesn't take the properties of the glass on the modules into account, where light beyond a certain angle largely bounces out again. In any even, use that as somewhat of a base number.

If I gradually tighten the solar window for winter from 8am to 10am, and from 4pm back to 2pm, the energy production number goes to 82%. In short, a 7% additional loss.

In your particular case, if I recall, you have some shading early morning. But at that time the leaves are gone too. So it's only during late March or April and early October that there are more serious shading issues while the leaves are present. My earlier estimate of a 4% or so loss due to the trees still sounds reasonable in that scenario.

Weren't they silver maples? I have a number of those as well: They are 'junk trees'. Once fully grown they tend to split and fall over within a few short years. So there is hope! :nuts:

-RoB-