Solar Panel Tilt For Summer

[rossw]

In a real system, you need to take the cosine of the dot.product of the off-axis angles. Within about 10 degrees is "almost insignificant". At 20 degrees it's just over 5% down.

Ross, have you ever determined if the cell operating temperature is higher when the panels are aligned "perfect" vs "off" bit?  I'm wondering if the cells do run hotter with "perfect" alignment if that affects output, vs having them "off" a bit and have the cells run cooler.

The testing I've done seems to indicate that the loss due to extra heat is less than the gain due to extra radiation.
However I've noticed several times that the "sweet spot" is not necessarily when the panel is completely perpendicular to the sun. I haven't had time to investigate much further, but my gut feeling is that with the panels dead square on, there's a fair bit of surface reflection, and slightly offset at least some of that light gets refracted and reflected within the glass back onto the cells.

More work required - when I get time!

I think I got my system oversized for our needs in summer unless I find some more loads to run.

Thats rarely a bad situation to be in!

[ksouers]

I think I got my system oversized for our needs in summer unless I find some more loads to run.

Thats rarely a bad situation to be in!

Damn the bad luck!

[ghurd]

I get emails...

People need to remember the "BEST" day of the year is the lowest tilt of the whole year for that ONE day.
364 days a year will be steeper.

And vice versa.

I used fixed brackets for installs.  About 12 degrees less than worst case angle.
Most of what I do does not need a whole lot of power in mid-summer, and mid-summer has pleny of sun to get it done (IE: do not need a whole lot of lighting in a barn when the sun sets at 9PM, but need it when the sun sets at 5PM).

There are exceptions such as cash registers being busier in Dec, but exceptions are few in what I do.
If the solar and battery is sized properly, it should get past 98% of the worst case. That's not cheap considering various back-up sources for the few required times a year.

A little common sense goes a long way.
G-

[ChrisOlson]

A little common sense goes a long way.

That's a good summary statement.

The solar panels, for us, are more backup than primary.  And I could use a couple more 250's yet for winter time power in the poor conditions when the wind don't blow.  So common sense says to stick with the original plan - I bought 'em for winter time to fill in the gaps in wind power so we can always have hot water.

I think my tendency to always look for a little more stems from years of trying to figure out where the next kWh was coming from.
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Chris

[ChrisOlson]

I'm happy to report that I did not change my solar panel angle from 40 degrees (used for spring and fall) for summer and they still hit rated power in perfect solar conditions, and well over rated power during periods of "cloud edge effect".

We're only three weeks from the summer solstice, and from that point the angle starts getting better again.

I have arrived at the conclusion that it is a waste of time for me to adjust the angle of our panels four times a year, and down to 20 degrees for summer.  Simply tilt them up to 70 degrees in late fall/early winter, and back down to 40 degrees in early spring, and they work fine.  On any day with sunshine they make WAAAY more power than we can use in the long days.  They're still putting out enough power to hold the bank in float at 7:00 in the evening most days.  And if we got both wind and solar I just shut the turbines off and leave just one running because we can't use them.  On cloudy days it don't make a bit of difference what angle the solar panels are at.

I can't say this is a "rule of thumb" for everybody, because some off-grid people might not have enough installed solar capacity.  So a tracker or religious tilting of the panels to get more out of them might pay off.  But we sized our system for winter-time power needs and this is the way it plays out.
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Chris

[Rover]

One of the benefits I see in my area to a closer to horizontal angle is on mildly cloud yet overcast days. I have two arrays , one of which I can't move much closer to horizontal than ~ 60 degrees , the other is at 30 degrees.

Identical panels in each array as far as cells (yet with different physical panel dimensions, same models etc, but it appears that Solar Cynergy panels have changed sizes while keeping same model and output numbers)  with different total  wattages per array  (the 60 is 300W the 30 is 600W) , both running through their own ts 45 mppt's .. yet on cloudy days I get way way more than a 2:1 that one would expect from the the 600W 30 degree.

Yes there are other factors, but I can see the difference on sunny days when the ratio is close to 2:1

Rover

[rossw]

yet on cloudy days I get way way more than a 2:1 that one would expect from the the 600W 30 degree.

I currently only have a pyranometer, but I'd love to be able to justify a pyrheliometer.
I most certainly observe a similar thing, Rover - even with tracking panels. On mostly overcast (as opposed to merely scattered clouds) days, I frequently see more power from panels pointing higher in the sky than pointing in the direction of the sun.

I have no research to support my theory, but I think it has a fair bit to do with the total "sky area" the panel can see, weighed of course by the cosine angle.

[David HK]

One factor I have noticed in power production with a tracking array is the cleanness of the air/atmosphere,

Twice a year as the seasons change it is very noticeable to observe extraordinarily clean sky so that the blue really appears as a true blue colour. Usually the humidity is way down to less than 40% on occasions, and the sky is cloudless. As a result my ammeter shows a much higher than usual power production. These occasions only last for a week or so.

For the rest of the year in high humidity power production is good but not as good as mentioned above.

David in HK

[Dave B.]

I'm happy to report that I did not change my solar panel angle from 40 degrees (used for spring and fall) for summer and they still hit rated power in perfect solar conditions, and well over rated power during periods of "cloud edge effect".

We're only three weeks from the summer solstice, and from that point the angle starts getting better again.

Chris,

  Exactly what I have learned here the first 8 months of my voltaic. Enough to know that tilting twice a year (about 45 and 70 deg. here where my adjustment holes are closest) will work fine. 3 weeks to getting closer to more ideal again and then 3 months the other side before tiliting them for Fall / Spring is looking very good to me. Mine are very easy to reach and tilt but more often and for how much gain ? I plan to add more panels as well instead of a "neat" tracker.  Dave B. 

[ChrisOlson]

I plan to add more panels as well instead of a "neat" tracker.  Dave B.

On the last ones I bought, I was going to put them on a tracking setup.  But then I said to heck with it.  I could get two more 250 watt panels for only $700.  I KNOW I'll get a couple kWh from those every day.  I don't think $700 stuck in a tracker is going to get that for me with what I had.  So I just bolted them to the shop roof on a tilting rack.

We got a conglomeration of panels - Sharp 123's, Schott 250's and Helios (made in Milwaukee, WI) 250's.  I just kept bolting on panels until we had more than enough, from whoever had a good deal at the time I decided to get some.  I never search around for the cheapest dollars per watt like some people do.  I usually call up this RE outfit in Eau Claire and ask them what they got and how much.  If it sounds good I jump in the Dodge Cummins and go pick up a load.

I got 2.7 kW on one Classic with three different arrays.  And every array is wired for a different Vmpp, all fed into that one Classic 150 from the combiner.  That Classic seems to be able to figure it out, because it quite regularly gets rated power from all them combined   
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Chris