Solar panel pitch angle - to compensate or not

autoxsteve · May 2007

In calculating the panel mounting angle(s) for my area, they range from 11 deg (in June) to 57 deg in Dec.

I believe the pitch of my roof is 23 deg.

How much increase in efficiency am I going to gain in Summer and Winter by compensating for solar angle of approach?

Bottom line: Is it worth it to try and set up a method to compensate tilt angle throughout the year?

P.S. I'm at 34.2 deg N Latitude (sothern Kalifornia)

hillbilly · May 2007

Re: Solar panel pitch angle - to compensate or not

Depending on the cost factor, if it were me I would say that it is well worth utilizing some sort of an adjustable system. I'm a bit further north of you (something like 39 degrees), but when I change the tilt of my panels up in the fall the gain is quite pronounced (a rough guess would be in the 20% range or so). Being off grid, this is especially important in the fall/winter for us, as the time and money to do an adjustable rack didn't even factor in at all against a comperable gain with that many more solar panels. If I had to go with a fixed option (in our case, off grid) it would probably be a tilt of about 54 degrees to optimize winter sun, if you are grid tied then you would most likely do better with a tilt equal to your latitude.
In our case, the spring lowering isn't quite so obvious, as there is already a growing increase in solar production with the longer days; in our case our batteries fill up early and negate most of this gain anyways. Probably a bigger factor to look at would be any potential shading (not just now, but down the road... will that nice little ornamental tree in the neighbor's yard be an issue 5-10 years later?).

Mangas · May 2007

Re: Solar panel pitch angle - to compensate or not

In my opinion, if you can I would do it.

In my case, even though the system seems to operate well without adjusting the panels during the entire year, I think I'll reset a few of the back north panels from say December to March. The panels are ground based but very easy to move.

As Hillbilly pointed out, unnoticed shading can really effect your system's charging rates. Often, you may not realize what's in the way during the sun cycle. For example, my array is fenced off from livestock. We used rabbit fence to minimize this problem.

mike95490 · May 2007

Re: Solar panel pitch angle - to compensate or not

it's a trade off. I'm in Los Angeles, and it looks like around summer solstice, I'll be hitting inverter limits, where if I had my panels (they are on a 22 deg pitch, west facing roof) tipped more southerly, they would be less efficient at summer solstice, but I'd pick up better efficency in the winter time.
If you want yearly max, tilt more south, for better winter performance, when you have shorter days. If you need summer production, to offset Air Conditioning costs, angle accordingly, but remember, in summer, the panels get hotter, and voltage output is reduced, so don't forget to account for that.
And of course: your mileage may vary, batteries not included, ages 16 and up, light fuse and run.

SolarJohn · May 2007

Re: Solar panel pitch angle - to compensate or not

autoxsteve,

In case you're interested, I've put pictures of my adjustable mount on my blog:
http://solarjohn.blogspot.com/2007/02/mounting-solar-panels-on-your-roof.html

John

BB. · May 2007

Re: Solar panel pitch angle - to compensate or not

You can look here for the differences between various angles:

http://rredc.nrel.gov/solar/pubs/redbook/ (link does not work for me at this moment--but it should be good)

And this solar calculator does a very good job of estimating kWhours and utility bills (even Time Of Use) using direction of panels and roof angle. It was pretty accurate for my home... However, it does not take into account local weather conditions. I am behind a coastal mountain range that blocks most of the summer coastal fog/marine layer (near San Francisco, CA)--but it gives the same results for the two zip-codes. So, if you are in an area with local fog/marine layer--take the numbers with a grain of salt.

http://www.sunpowercorp.com/homeowners/solar_calculator.html

If you are on-grid and have a 1 year net metering connection, then you don't need a fixed angle maximized for winter production. You can either mount at latitude angle (maximum production across whole year, or even maximize summer production when your TOU rates are the highest (my peak rates go from $0.11/kWh to $0.29/kWhr for May 1st through October 31st). So, if you have A/C (heavy peak summer loads) or a very good rate of peak power pay-back if you generate more than you use (high summer rates) then you may actually gain if your fixed array is set to favor summer generation.

My roof is a bit steeper than yours, and is a 2nd story with only ladder on gutter access, plus I will be 70 in 20 more years--all leading me to the conclusion that I will not be up on that roof changing angles at least twice a year--and it would not be cost effective to pay anyone to do it either. Plus walking on most types of roofs is a good way to cause them to fail faster.

There are advantages to having arrays above the roof plane (either raised or tilted) as cooler solar PV panels generate more power, shed snow and dirt better, etc.. There are also disadvantages to having panels mounted at angles to your roof (catch storm winds better, are more obvious to neighborhood--possible complaints about looks, targets for kids with rocks/thieves).

In the end it is your decision but, if you are grid-tied with TOU power and/or heavy summer loads, I would probably go for the fixed angle design (either 34 degrees, or just at your roof angle of 23 degrees) and not bother with the tilt feature unless you have really good roof access.

-Bill

System2 · May 2007

Re: Solar panel pitch angle - to compensate or not

SolarJohn wrote:

autoxsteve,

In case you're interested, I've put pictures of my adjustable mount on my blog:
http://solarjohn.blogspot.com/2007/02/mounting-solar-panels-on-your-roof.html
John

Some good info and links there, thanks John.
Wayne

autoxsteve · May 2007

Re: Solar panel pitch angle - to compensate or not

Thanks. I did a few calculations and it appears that I can get thru 7 months of the year at 23 deg roof pitch, and adjust the panels up by another 28 deg from Oct thru Feb. This approach will make the max angle delta (at peak for the day) as follows:

Month Delta from ideal noon angle
JAN 2.8
FEB -6.2
MAR 11
APR -1
MAY -9
JUN -12
JUL -9
AUG -1
SEP 11
OCT -5.2
NOV 2.8
DEC 5.8

Months in italics include a 28.2 degree increase in panel height from std 23 deg roof pitch.

It would appear that I would not lose as much by doing this. I'm going to wade back thru an estimate/package that I got from a supplier to see if there is a slick way I can add a threaded jackscrew to the mix to minimize the effort.... Maybe a monthly adjust is not too far out of the question...

niel · May 2007

Re: Solar panel pitch angle - to compensate or not

steve,
i will simply say that for those that can do it without much difficulty or costs they should. it means being able to physically move the pv's angle twice per year for a 2 position arrangement or more often for those with more than 2 positions. it is a diminishing return type of a thing, but you do gain. i favor 2 positions to optimise winter and summer averages making the angle changes around the equinoxes. your roof angle is good for your summer average, but you may need a special length for the adjustable mount to come up with the winter average you desire. the requirements for your mount will be from flat on your roof to up off the roof by another 28 degrees. most adjustables don't go from flat (correct me if i'm wrong on this one) and they usually go in increments of 15 degrees compromising your 28 degree goal by 2 degrees, but it is workable.

crewzer · May 2007

Re: Solar panel pitch angle - to compensate or not

Bottom line: Is it worth it to try and set up a method to compensate tilt angle throughout the year?

P.S. I'm at 34.2 deg N Latitude (sothern Kalifornia)

Steve,

I think you need to check your local insolation data to see if the “seasonal adjustment” approach is worth the combination of the initial installation investment as well the effort of climbing up onto your roof twice a year to make the adjustments.

30-year data for Los Angeles shows that the annual daily average energy harvest for a fixed-tilt (~34 degrees) south-facing array is 5.6 hours per day. This ranges from 4.2 hrs/day in December to 6.6 hrs/day in July and August.

See: http://rredc.nrel.gov/solar/old_data/nsrdb/1961-1990/redbook/sum2/23174.txt

The same array tilted up at ~51 degrees (lat + 15) will harvest an annual average array in your location will collect an average of 5.4 hours per day of “full” Sun. This ranges from 4.5 hrs/day in December to 6.0 hrs/day in August.

If you set your array to ~19 degrees (lat – 15) of tilt from ~March 21 through September 22, and then to ~51 degrees from ~September 22 through March 21, it will harvest an annual average of 5.8 hours/day.

The increase from 5.6 hrs/day (fixed tilt) to 5.8 hrs/day (dual settings) is +3.6%. Other ways to realize this gain are to:

1) Increase wire size to reduce wire and cabling inefficiency
2) Consider an MPPT controller instead of a PWM model
3) Use VRLA batteries instead of flooded-cell models
4) Buy and install a slightly larger PV array
5) Clean the environmental “crud” from the array ~ 2X a year

I’m not trying to steer you in any particular direction… just trying to make the point of considering your installation from a systems perspective. I hope this information helps you make a practical decision.

Regards,
Jim / crewzer

niel · May 2007

Re: Solar panel pitch angle - to compensate or not

all good advice from crewzer and as i said if you opt for it it has a diminishing return meaning slight gain. crewzer pegged it at 3.6% for la with 2 positions and going from 2 positions per year to say 3 may give another fraction of a percent gain, hence the diminishing return. most opt for no more than 2 positions as winter is a time most of us suffer from the lack of sunshine and we in the areas of snowy winters like the feature of the steeper angle allowing snows to fall off faster. as pointed out before it isn't for everybody and it does cost more for mounting. you could gain more with going from a standard deep cycle lead acid battery to an agm style battery as the agm is more efficient at taking a charge saving you the cost of producing the extra power the standard battery would need.

Aguarancher · February 2015

Houston we have a problem. Until i logged in. this is what i got trying to read this post? [h=1]Solar panel pitch angle - to compensate or not[/h]

An internal error has occurred and the module cannot be displayed.

BB. · February 2015

I confirm. If I use Internet Explorer, not logged into forum, using this link:

http://forum.solar-electric.com/forum/solar-electric-power-wind-power-balance-of-system/general-solar-power-topics/600-solar-panel-pitch-angle-to-compensate-or-not

I too get:

An internal error has occurred and the module cannot be displayed.

-Bill

ggunn · February 2015

autoxsteve wrote: »

In calculating the panel mounting angle(s) for my area, they range from 11 deg (in June) to 57 deg in Dec.

I believe the pitch of my roof is 23 deg.

How much increase in efficiency am I going to gain in Summer and Winter by compensating for solar angle of approach?

Bottom line: Is it worth it to try and set up a method to compensate tilt angle throughout the year?

P.S. I'm at 34.2 deg N Latitude (sothern Kalifornia)

I would suggest going to PVWatts and running some test cases. Do a simple cost-benefit analysis. Compare the output of a system tilted at 23 degrees all year with one the same size tilted at 23 degrees for part of the year and some greater angle the rest of the year. make sure you have the correct azimuth entered for your roof. Consider the cost addition for an adjustable tilt racking scheme (and think about wind loading) plus the PITA factor in having to go up on the roof to make the adjustments.

I'll bet it's not worth it.

BB. · February 2015

We really do not need to address the original post's question... This thread is almost 8 years old and came up because of (I guess) a database error.

-Bill

Aguarancher · February 2015

The reason it came up is a spammer had replied to it this morning. You have since banned the poster. Only reason I brought it up was because of the error reported.

BB. · February 2015

Not a problem. The spammer hit something like 5-6 threads before I got there to remove the posts/ban the poster.

-Bill

Solar panel pitch angle - to compensate or not

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