OT: Fixed solar panels and daylight hours

[Andy Champ]

... or maybe not OT. Except I'm not really intending to fit any...

It occurs to me that in winter the sun runs across an arc of the horizon of 140 degrees or so (ICBA to find out exactly what) and so at all times if it's above the horizon, and there's no cloud, it's shining on the front of a panel.

But in summer the sun rises and set further north. It's enough that at this time of year the evening sun gets into the windows on the north of our house - which it never does in summer. Does this mean that near dawn and dusk it's "behind" a panel?

Andy

[John Rumm]

Yes. (true at sunrise as well)

[NT]

You get a good bit more out with tracking, but its not really doable on a roof.

NT

[harryagain]

It does. If you look at the panel output you get a bell curve for this reason.

The other similar factor is local sunrise/sunset which varies depending if you are on top of a hill or in a valley.

[Brian Gaff]

Maybe you need winter and summer panels.

Brian

[Martin Brown]

On mid winters day it is closer to a pathetic 100 degree arc and barely getting 13 degrees above the horizon at best. The light travels through a lot of atmosphere and so is weaker as well as short on daylight hours.

Yes. The summer azimuth range of the sun in the northern UK is something close to 270 degrees. Confuses lots of people this.

If the solar panel is exactly horizontal then the incident light scales as cos(solar_altitude) but if it is installed on a sloping roof then there will come a point where the sun is below the artificial horizon imposed by that construction when its azimuth is more than +/- 90 degrees away from the direction of slope of the roof.

Another easy one is that at the equinoxes it is exactly 180 degrees.

[Dave Liquorice]

Yes. ATM our solar thermal doesn't really kick in until some time after 0830, sunrise is about 0530. Like wise it will stop about 1800. It's not exactly centered on 1300 (solar noon) as the roof is aligned slightly west of south.