Solar Panel Tilt For Summer

[ChrisOlson]

Just curious how other folks set the tilt on their panels for summer time.  We live at 46 degrees north latitude and right now I have the panels tilted at 40 degrees from horizontal.  During the winter I tilt them at 70 degrees from horizontal because the sun barely makes it above the horizon in Dec/Jan.  They would need to be tilted down another 10-12 degrees (28-30 from horizontal) at this time of he year for the sun to shine directly on them at solar noon.

In summer time they need to be just about horizontal because the sun is directly overhead at solar noon.

But what I'm seeing today is that even being 10-12 degrees "off"on tilt, plus we're not quite at solar noon, my 2.7 kW array is producing over rated power, maxing the Classic controller out at 94 amps @ 30.0 volts.  If the panels stay at that output for very long the controller gets hot and starts to de-rate itself, dropping the output down to 88 amps or so until the sun goes under a cloud.  That gives the controller an opportunity to cool down a bit and it goes right back up to 94 amps when the sun comes out from under the cloud.

So the solar panels seem to be able to put out full power even though they're not perfectly aligned with the sun.

As we get more into summer, what will happen if I just leave them at the 40 degrees they are at right now?  Will I lose out on much power production?  Or will the increased tilt make them run a bit cooler and it won't make any difference if they were tilted down flat because they'll run hotter if they're almost flat?
--
Chris

[tomw]

Chris;

I just tweak mine 4 or so times a year at the equinox. Set them to be dead on at noon on a polar mount. There is some formula for  fixed something like Latitude +15 degrees maybe? but I think that is for set and forget installs in a fixed mount.

Tom

[WooferHound]

The first year I put my panels on an adjustable mount, I worked out the positioning based on the actual Sun position. I was going to move the panels 4 times a year so, on the date that the panel was supposed to be pointing directly at the Sun, I made the adjustment and measured it for my future adjustments.

I have made up a chart for myself so I can properly adjust the panels for best seasonal output. I've decided to adjust the panels 4 times a year for best output. Using this chart as listed, the panels will not be more than 1 month from directly facing the Sun. I'll explain the four lines of text relating to each readjustment.

Move Date - This is the date that you would actually move the panel to it's new position
Duration - Length of time the panel will remain in this position
Set Date - The panel should be adjusted to directly face the Sun on this date
Season - The season of the year, needs to be reversed for the Southern Hemisphere

Solar Panel Angle Set Chart

Move Date - February 21
Duration - 2 Months
Set Date - March 21 or September 21
Season - Spring

Move Date - April 21
Duration - 4 Months
Set Dates - May 21 or July 21
Season - Summer

Move Date - August 21
Duration - 2 Months
Set Date - September 21 or March 21
Season - Fall

Move Date - October 21
Duration - 4 Months
Set Dates - November 21 or January 21
Season - Winter

[ChrisOlson]

Tom and Woof,

This is pretty much what I've always done too.  They're at a steep angle in the winter so in March or so I move them to where they are now.  Then I move them almost flat for summer, back to the 40 degrees for fall and before deer hunting I tip them up to 70 degrees.

We had some panels get busted by hail one year and the insurance covered those.  But I'm wondering of there's some way to figure out how much power you'd lose out on if you just left them at the spring/fall angle during summer?

I know they get REALLY hot in the summer when the sun is beating right on them, and that can't be good.  I'm reasonably sure they'll run cooler if they're tilted at 40 degrees in the summer.  I know they'll be less susceptible to hail damage at 40 degrees.  I wonder if the fact that they'll run a bit cooler by being tilted up more will make up for the difference in the sunlight they get by being almost flat?

I'm sure there's somebody that has tried this and probably has hard data on it.

The other thing is, that in the summer with the really long days, they generate more power just because of hours of sunlight.  We've never had this much solar power before - I've over doubled my installed capacity since last fall.  And in the summer we use less power because we don't run lights as much, we cook more on the outside grille, my wife uses the clothes line to dry clothes instead of the clothes dryer, and on and on.  So we probably got WAAAY more power than we even need for summer the way it is with just one wind turbine running plus the solar.

So I'm undecided as to whether I should tilt them down for summer or just leave them where they are.
--
Chris

[Watt]

This is the calculations I use and some added theory.  http://www.macslab.com/optsolar.html 

[tomw]

Chris;

I "think" the loss due to not being perfectly perpendicular is trigonometry in action a cosine function? Or something. Gets you a % of full on solar incidence?

Probably find it on Google. This might get you some hard data:

http://www.ftexploring.com/solar-energy/sun-angle-and-insolation3.htm

Tom

[ChrisOlson]

Thanks - I'll have to study that a bit.  And maybe even try it on a nice day to see how much difference there is.  My panels are all roof mount, and the big ones are so heavy I have them mounted on the racks in pairs so they can be handled to adjust them up and down.  I have to make the rear rack brackets to lower them more from where they are now.  My thoughts are that maybe it's unnecessary to adjust them, being we probably have enough power anyway, and I wasn't sure how much difference it makes.

Edit:  Yes, thanks for those links, guys.  I read this one statement in one of the articles:
If your need for energy is highest in the winter, or the same throughout the year, you may want to just leave the tilt at the winter setting. Although you could get more energy during other seasons by adjusting the tilt, you will get enough energy without making any adjustment.

I suspect this is the case for us.  We weren't short on power last summer and I have added both wind and solar capacity since then.  I have kept building and adding on our power system for the worst case days.  This is the first year ever that we have not had to run the generator for the entire month of March.

It appears that they take into account only the solar insolation, and don't factor the operating temperature of the panels into the figures they give as "optimum" for summer time angles.  That's the part I'll have to try for myself to see how much difference it makes.
--
Chris

[Wolvenar]

At the risk of hijacking this topic

Well I played around with making a calc available here just for this kind of thing,
but I never publicly posted it. 

I do not know if its accurate I have not had the time to verify,
it was one of those thing I picked up along the way years ago, and had to tweak and modify to work at all in today's servers/browsers.

Just posting so you guys want to give it a try.
 Let me know  how good or bad it is, or if you have something better that is legit to put on here.

I plan to put up a bunch of these kind of tools in time with a page listing them out,
if/when I can find the time to do it.
Ideas for such are welcome.
(post the ideas here please)

[WooferHound]

I thought that this was interesting from Watt's link

[ChrisOlson]

I went out and tried just the six big panels this afternoon.  We had a high thin cloud layer that came in, but not real bad.  The panels were putting out 2365 watts.  The winter time legs fold down on the racks so I folded those up and raised the three big pairs of panels up to 70 degrees.  The controller said about 2325 watts.

When I tipped them back to to 40 degrees the output on the controller said 2360 so it agreed pretty close with the first reading.

The ideal would be about 30 degrees right now, probably.  They were at 40.  At 70 degrees the big panels lost 40 watts.  The big panels are 1,460 watts of the total 2,690 installed capacity.  And we were well past solar noon when I did this.  So it looks to me like, possibly, a guy would lose out on about 700-800 watt-hours per day by leaving them at 40 degrees vs moving them down to a summer time angle.

Not very scientific, but that's what I came up with.
--
Chris

[oztules]

I am currently at 40 deg south. Panels are set for 45 deg. In summer I loose a bit, in winter I should do better than all the 15-20 degree roof mount ones.

This is pretty silly for me, as I have the grid to act as the storage from summer to winter. This is it's first year of full operation, but I suspect next year I will change the angles to perhaps 16 deg and leave it. I should get far more from the longer days with correct angles than averaging over the whole year.

The interesting thing at this time is to see how like systems fare in winter at this latitude and at what angles.

For you Chris, without that storage, (I'm 400 kwh in front at this time since Dec8... tough to store that any other way) I'd be tempted to increase pitch for insurance, and for when you need the power .... winter months.

45 degrees  and I still can't use it all... lets see this winter.


..............oztules

[ChrisOlson]

oz, I'll definitely tip them back to 70 degrees for winter.  They work really good there when we get sun and it's easy to sweep the snow off.  Sometimes the snow even slides off by itself.

After seeing that the panels don't drop a lot in power output even at 70 degrees tilt (which is about 40 degrees off what it should be to be "perfect" for this time of year) I think I'll leave them at the 40 degree angle for the whole year except for when we get into November - end of February.  They are less prone to getting damaged by hail that way, and with over doubling our capacity since last year I think we will not need to use them at full power thru the summer months.

Sure, it seems like a "waste" to not use them to full capability.  But we bought them for the extra winter time power, and they're paid for.  I don't have grid power to "bank" for another time of the year so it doesn't really make much sense to try to get everything out of them if I don't need it.
--
Chris

[rossw]

I went out and tried just the six big panels this afternoon.  We had a high thin cloud layer that came in, but not real bad.  The panels were putting out 2365 watts.  The winter time legs fold down on the racks so I folded those up and raised the three big pairs of panels up to 70 degrees.  The controller said about 2325 watts.

When I tipped them back to to 40 degrees the output on the controller said 2360 so it agreed pretty close with the first reading.

The ideal would be about 30 degrees right now, probably.  They were at 40.  At 70 degrees the big panels lost 40 watts.  The big panels are 1,460 watts of the total 2,690 installed capacity.

If your panels are 10 degrees off "ideal", you stand to lose approx 1.6% of your output.
If your panels are 30 degrees off "ideal", that increases to about 13.4% of your output gone.

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.

[kenl]

I only adjust twice a year and only change the angle 15-20 degrees when I do. I have a low slope roof so lay them flat in the summer and add 6 inches of tilt in the winter. Probably not the ideal setup but gets me 80% rated output summer and winter and 100% spring and fall.
 More tilt in the winter would probably give me a earlier start up on the charge controller though. So it isn't optimal.

[ChrisOlson]

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 darn things are developing over their rated power again today with the tilt "off" about 10-12 degrees, and we got an hour and a half to go to solar noon yet.  The wind ran all night at low output around 1.0-1.5 kW so the bank has dropped into float already.  It'll heat water for 2-3 hours @ 2 kW and then the thermostats will kick out on the water heaters and don't really have anything to run beyond that unless we turn something on just to soak up juice.

I think I got my system oversized for our needs in summer unless I find some more loads to run.  So this might all be somewhat of a moot point anyway.
--
Chris