Optimum PV panel angle

[johnd2]

Can anyone please point me to a resource that would help in estimating the optimum panel angle for winter-time power generation?

In case you think this is a slightly oddball question, let me explain: the panel in question is being used to power some instrumentation at a remote site. The crunch issue here is not how much the panel generates in summer but to ensure that, on average, it generates at least a minimum threshold amount of power in winter. As long as it generates at least as much power in summer as in winter then the summertime generation is not relevant. Of course there will be considerable day-to-day variability, but the problem is to optimise the average daily energy capture during midwinter.

For information, this is for use at 52N - not that it should make any difference to the answer in principle, but just to confirm that there is useful solar power in midwinter, but only perhaps 10-15% of the midsummer level.

[peakbagger]

I havent seen a program that will optimize angle for a specific time of the year, but I bet they exist. Nevertheless this link may be helpfull

http://aa.usno.navy.mil/data/docs/AltAz.php. Ideally you want the panel oriented perpendicular to the sun during the months you want to optimize. What you can never know from a computer programs is how much snow is going to build up on the panel and how long it will melt and how many days of cloudy weather will you have. Many folks advocate hanging the panels vertically preferably under and overhang to prevent the snow issue.

One thing to consider is the amount of energy from the sun is considered the same winter to summer, its just that we have a lot more of it in the summer (I am at 45 degrees north). One thing that helps is reflection of sun off of snow and cold weather that increases the output sometimes over its rated capacity.

If you have the potential for reflection off of snow, I would seriously consider vertical mount as even though the angle isnt optimal, the snow reflection compensates. My panels are at 30 degrees for winter and they do occasionally collect snow, although they do melt off in a few hours in full sun.

[russ]

One member, Mountain, is a believer in the vertical mount under an overhang. He is at a ski resort in the Canadian Rockies somewhere - similar to your latitude.

[Sunking]

Go here and pick your state and nearest city. But I can tell for winter the angle will either be Latitude or Latitude -15.

[johnd2]

Apologies - I should have mentioned my location: It's southern UK (hope I'm not too much of an intruder here), approx 52N 0E.

So snow could be an issue on a handful of days a year but really too rarely to merit any consideration when deciding panel geometry. What is much more of a problem is the number of overcast days, often heavy overcast, during winter. (It's often not actually raining but 8 oktas cloud). So trying to optimise power generation by the PV panels is a real challenge.

A couple of follow-up questions:

I'm glibly talking about panel angle but without a totally definitive idea of which angle I'm referring to - I presume it's the angle that the panel makes with the horizontal plane (ie the ground) and not the angle with the vertical - right?

@SunKing: There's obviously a significant difference between Lat and Lat-15 as choices. Any guidance as to which is preferable?

Finally and in case anyone's interested, a little more info on the instrumentation application, which I should maybe have included in the original post. It's a weather station that reports live data online (or at least it does when there's sufficient stored solar energy). The power is primarily needed for the cellular data link (plus a little for the instrumentation itself, but it's the cellular modem that's the power hog - all relatively speaking of course). You can see the data at:

www.weatherlink.com/user/elydev and https://www.weatherlink.com/user/ely...mary&headers=1

(the latter screen shows a live global irradiance reading). But it went offline today at 13:43Z when the gloom descended and irradiance was down to 49W/sqm - there's a voltage cut-out that cuts power to the cellular modem when the battery gets down to 12.0v , but a separate supply continues to the logging instrumentation. Hopefully it may come back online during the day tomorrow (UK time).

[russ]

Hi John - Guess you are a few thousand km east of Mountain then!

Not to worry - we hold no grudges against our friends from the east or west.

From Peakbagger's post, ''Ideally you want the panel oriented perpendicular to the sun during the months you want to optimize.''

You are most worried about stormy seasons - which are normally winter.

I have Davis weather station as well - though not on line and grid powered. Here on the bay we have very different weather than reported at the airport some 60 km distant - interesting to follow.

Russ

[Wy_White_Wolf]

This might help

http://www.builditsolar.com/Tools/RadOnCol/radoncol.htm

I get the impression that it is designed more for use with thermal collectors instead of PV but should give you an idea

WWW

[johnd2]

This might help

http://www.builditsolar.com/Tools/RadOnCol/radoncol.htm

Thanks - that does look very relevant. Will need to do some further investigation to understand exactly how to use and present the results, but it does look like the basis for modelling the effect of changing the tilt angle of the panel. I'm not sure why it should make any real difference if it was originally intended for thermal rather than PV panels - all I'm looking for are relative effects on energy received as a result of changing the tilt angle at different times of year - no obvious reason AFAICS why this shouldn't be the same for PV and thermal.

Thanks again (and apologies for the delayed reply - been tied up with other projects!).