does anyone in here know the optimal angle from horizontal and degree of rotation in respect to the compass for a PV arrray located on an offshore platform (for a coast guard light) 2 miles due south of Fort Morgan, Alabama?
It is very close to Mobile if that helps in the calculation. The plan we have calls for the frame holding PV panels to be mounted at a 45 degree angle, 12 in 12 pitch, and I thought that was wrong the first time I looked at it.
I am betting someone in here will know right off the top of their head! Thanks.
Replies
I'm no expert on optimizing solar design, but simple geometry says that you'll get maximum exposure by aiming the panel due South. In the summer you'll get maximum gain by tilting the panel up from the horizontal about 7°, in the winter by about 54°. If you are storing the energy in batteries for nighttime use I'd imagine you'd want to lean toward the winter angle since the days are shorter and you'd have to maximize gains in the winter more so than in the summer. Same if you are trying to use the energy for heating; possibly the opposite if for cooling.
There may be someone here who can explain subtle considerations such as the above more authoritatively.
Good basic advice, the weater patten form NOAA records need to be researched.
53.75 tilt first cut, and first cut direction would be straight south. Winter solstice is worst time, shortest day. Cosine of direct sun is <1 rest of time, but days are longer.
For East west orientation, you should look at a few years of weather for the solstice. Often, since storms likey come from a prevailing direction (the west on the west coast) if may be advantages to bias the southern direction a little by where the clouds are the most during daylight.
Also, weather patterns vary by time of year. Last study I did for the angle found that the worst time for daily solar insolation was in Utah (insolation is the total solar energy at the earth at a given spot = kW-hrs per day available) in February for the location I was looking at, so the angle was set to about 46 degrees.
I'm interested in this stuff. Can you comment on the tracking bases that some arrays use? Do they do much to improve output?
Key words for a search are "solar insolation"
2 best hits on google of the first 10 below.
Yep, tracking is a big Plus.
http://www.windsun.com/Solar_Basics/Solar_maps.htm
http://edmall.gsfc.nasa.gov/inv99Project.Site/Pages/science-briefs/ed-stickler/ed-irradiance.html
well i am amazed! when i did a previous investigation about installing solar on a custom home in california 2-3 years ago the decision was to install at 18 degrees and that a 4 in 12 pitch facing south was as good as it would get.
Of course this was a preliminary investigation, and solar was not installed at the time of construction, however I thought I had incorporated into the design of the home a roof that was at the proper angle so panels could be added later with no structural revisions.
I am very surprised to find out that the proper angle is 46 in Utah! I realize that Mobile Alabama is quite a bit south but it sounds like 45 might be right. I am absolutely shocked that my previous information was so far off. I am no expert on the subject but I ask a LOT of questions, it bothers me to think i got such wrong information. Thank you all!
If you face due South and tilt your panel up at at angle equal to your latitude, it'll be square on to the sun when the sun crosses your longitude at the equinoxes. To be square on for the solstices, you need to add about 23.5 degrees for winter, and subtract 23.5 degrees for summer.
Of course, the sun is lower in the sky before and after meridian transit, and weather trumps all the basic geometry.
-- J.S.
Regarding South, you may want to investigate whether that should be geographic South or solar South - my guess is solar South. There is a difference, in my area about 15 degrees. (Note, I am not confusing matters further by suggesting magnetic South, which moves from time to time. Yes, the magnetic poles move.)
Alfie, can you explain "solar South"? Even having studied navigation I've never heard of it. I'm imagining how the earth rotates and revolves and can't see how the sun can be higher in the sky at any point other than true South (or North, depending on one's location on Earth).
I have an intuitive understanding of it, but could not explain it accurately. You'd be better of Googling "solar South". For example, depending on where ones lives, the sun may rise 15 degrees South of East, and set North of West. Or, I have got it all wrong and some body will set me straight.
In Googling "solar South" it is apparent that what they mean is South. "Solar South" is not a scientific term, but a term someone made up trying to explain the difference between South and magnetic South. In my opinion it is bad to use such a term because when someone makes up their own term they have to explain what it means, and to explain what it means the correct terms would be used in the explanation anyway. So they just end up with a longer explanation that is less clear than if they used the real words to begin with.
Thanks.
hey could it be that the optimal angle for a PV array that is hooked up to the grid would be just under 20 degrees from horizontal?
when i was going over my thinking in how i got so far off i realized that maybe, if you are tied into the grid the goal would be to have the most exposure on a yearly total basis, not on a daily basis in which the angle needs to be optomized for the shortest days of the year.
i guess what i am trying to say is that if you are tied into the grid and just selling juice back to the power company is it better for the yearly total to orient the grid on a 4 in 12 pitch? does that sound correct?
"...if you are tied into the grid and just selling juice back to the power company is it better for the yearly total to orient the grid on a 4 in 12 pitch?"
Basically, yes. Especially if you have Time-of-Use metering, where they pay more for electricity generated during peak time (noon to 6 pm in CA). Peak summer rate is 4x baseline while winter peak is 2x base. Since there are more generating hours in the summer, and you are getting paid more for it, optimizing for summer generation gives you the best ROI.
optimal angle for a PV array that is hooked up to the grid
Whole different scenario than the bouy out in the ocean. As mentioned by the prev. poster, the rate you get from the power you sell is a big factor.
You need to put the payoff numbers into the weather pattern data to get your optimal. You may even want to set your arrays up for being able to manually tilt the array every few weeks to optimize payback.
Best I have ever done with a 60 sq foot tracking array on a clear day is about 16 kW-hrs*. A whole $1.50 per day at 10cent kW-hr. doesnt even start to cover the cost of the array without a big infusion of government subsidy.
* the system description attachment is 3 MB, so you may not want to bother if you are dial-up.
awesome dude, thanks
Segundo,
A google search shows quite a bit of information. Here is the first link shown:
http://www.macslab.com/optsolar.html
Bill Koustenis
Advanced Automotive Machine
Waldorf Md
Segundo,
Did you mention whether this thing would be floating? If it's floating, the best orientation is horizontal.
Ron