Optimising array angle

ron45 · December 2009

Hello, Don't know the current thinking on this. We are in a stand alone situation in central New Mexico. I just went out to change the angle on my trackers in anticipation of Dec 21st. I generally do this several times a year. I also have a larger fixed array on the roof that was set at what was considered the optimal angle in the early 90s sometime.

I'm wondering if the thinking has changed since then. I think I used 42 degrees but I could be wrong about that. I was wondering if I should change that angle to one more favorable to winter conditions since that's when we need the most power. Any thoughts. We are in the process of upgrading our system but currently it is:

about 700+ watts of pv, Out back chargers MX 60 and Flemax 60 for each array respectively, Outback inverter VFX 3524, and 12 Surrette S 560s.

Ron

BB. · December 2009

Re: Optimising array angle

Try the PV Watts program and plug in different angles and you can get a month to month comparison with a few different numbers (hour by hour, if you want those details are available too).

Note that the program uses 1 kW as the minimum array size--you will have to past into a spread sheet and multiply by your 0.700 kWatts for your system estimates.

Use Derating = 0.52 for an off grid AC inverter with flooded cell batteries and see how the numbers agree (or disagree) with your numbers.

"Station Identification"
"City:","Albuquerque"
"State:","New_Mexico"
"Lat (deg N):", 35.05
"Long (deg W):", 106.62
"Elev (m): ", 1619
"PV System Specifications"
"DC Rating:"," 1.0 kW"
"DC to AC Derate Factor:"," 0.520"
"AC Rating:"," 0.5 kW"
"Array Type: Fixed Tilt"
"Array Tilt:"," 35.0"
"Array Azimuth:","180.0"

"Energy Specifications"
"Cost of Electricity:"," 8.7 cents/kWh"

"Results"
"Month", "Solar Radiation (kWh/m^2/day)", "AC Energy (kWh)", "Energy Value ($)"
1, 5.33, 84, 7.31
2, 6.06, 84, 7.31
3, 6.44, 99, 8.61
4, 7.16, 102, 8.87
5, 7.40, 105, 9.13
6, 7.10, 95, 8.27
7, 7.13, 98, 8.53
8, 7.02, 98, 8.53
9, 6.71, 91, 7.92
10, 6.55, 97, 8.44
11, 5.73, 85, 7.40
12, 5.14, 81, 7.05
"Year", 6.48, 1119, 97.35

And for +15 degrees as a winter average tilt:

"Station Identification"
"City:","Albuquerque"
"State:","New_Mexico"
"Lat (deg N):", 35.05
"Long (deg W):", 106.62
"Elev (m): ", 1619
"PV System Specifications"
"DC Rating:"," 1.0 kW"
"DC to AC Derate Factor:"," 0.520"
"AC Rating:"," 0.5 kW"
"Array Type: Fixed Tilt"
"Array Tilt:"," 50.0"
"Array Azimuth:","180.0"

"Energy Specifications"
"Cost of Electricity:"," 8.7 cents/kWh"

"Results"
"Month", "Solar Radiation (kWh/m^2/day)", "AC Energy (kWh)", "Energy Value ($)"
1, 5.75, 91, 7.92
2, 6.32, 88, 7.66
3, 6.34, 97, 8.44
4, 6.63, 95, 8.27
5, 6.49, 92, 8.00
6, 6.05, 80, 6.96
7, 6.21, 85, 7.40
8, 6.39, 89, 7.74
9, 6.48, 88, 7.66
10, 6.72, 99, 8.61
11, 6.13, 91, 7.92
12, 5.61, 89, 7.74
"Year", 6.26, 1084, 94.31

So for December, that would be:

89kWhr per month / 81 kWhrs per month = 1.10 or 10% performance increase for December to do a +15 degree winter tilt.

Tilting to a 65 Degree tilt gives an estimated 91 kWhrs per December... A bit more of an improvement...

-Bill

Dave Angelini · December 2009

Re: Optimising array angle

Ron,

If you are actually tracking the sun from east to west you have pretty much achieved the big bang. Setting the angle of the panels to the sun is a small gain for an offgrid user. For my offgrid customers the 2nd axis tracking is mainly for snow and high winds. The units will program for flat at night or maximum angle for snow loads.

Remember once you get through absorption you are not using the energy that a grid tie would and the angle can't help you as much or, at all. Bad weather in a winter location such as yours is the best reason to track the sun. Your batteries will last because you will be charging them completely more often and discharging them less often.

Are you getting float time? This should happen by 2PM on decent winter days!

BB. · December 2009

Re: Optimising array angle

Sorry, I blanked out that you are using 1-axis trackers... The PV watts program can be used to check optimization for those too.

-Bill

ron45 · December 2009

Re: Optimising array angle

BB. wrote: »

Try the PV Watts program and plug in different angles and you can get a month to month comparison with a few different numbers (hour by hour, if you want those details are available too).

Note that the program uses 1 kW as the minimum array size--you will have to past into a spread sheet and multiply by your 0.700 kWatts for your system estimates.

Use Derating = 0.52 for an off grid AC inverter with flooded cell batteries and see how the numbers agree (or disagree) with your numbers.

And for +15 degrees as a winter average tilt:

So for December, that would be:

89kWhr per month / 81 kWhrs per month = 1.10 or 10% performance increase for December to do a +15 degree winter tilt.

Tilting to a 65 Degree tilt gives an estimated 91 kWhrs per December... A bit more of an improvement...

-Bill

Thanks Bill. I'm not much of a numbers guy. We have had the system so long we take it for granted. Except for equalizing and keeping the water levels up it's just in the background most of the time. We're off grid since 1983. But our use of ac has gone up over the years . So all the upgrade stuff we're doing is like starting over again. I will try the angle change once I get the mods done to the array frame supports. I'll probably not get to it till next fall. I'm sure the fixed array is less of an angle than 65 degrees. We are adding between six and ten KC 130s. Six of these will go on the two ancient, and still working great, Zome Works Trackers. This will get us a more robust charge capability.

Ron

ron45 · December 2009

Re: Optimising array angle

Dave Sparks wrote: »

Ron,

If you are actually tracking the sun from east to west you have pretty much achieved the big bang. Setting the angle of the panels to the sun is a small gain for an offgrid user. For my offgrid customers the 2nd axis tracking is mainly for snow and high winds. The units will program for flat at night or maximum angle for snow loads.

Remember once you get through absorption you are not using the energy that a grid tie would and the angle can't help you as much or, at all. Bad weather in a winter location such as yours is the best reason to track the sun. Your batteries will last because you will be charging them completely more often and discharging them less often.

Are you getting float time? This should happen by 2PM on decent winter days!

Right now the system is too small for our power consumption and we are getting ready to add six to ten KC 130s to go on the old Zome Works trackers. Only six will actually fit on the trackers. They currently have 12 old arco 35 w dinosaur pannels on them. I'll probably put the twelve on a fixed array between the hot water collectors.

I have some pics of our hand built adobe on my page at myspace. No pics of the system there yet if I remember correctly. I'll upload some when I get the KC 130s installed. I'm collecting info to build my own 10', 700w wind charger from parts available at Otherpower.com. We'll probably just get the metal parts and magnets from them and make the stator and prop ourselves.

Here's the link to my page

www.myspace.com/ron45becker

Ron

vcallaway · December 2009

Re: Optimising array angle

Love the photos of your house.

Can you post some of your solar setup?

ron45 · December 2009

Re: Optimising array angle

vcallaway wrote: »

Love the photos of your house.

Can you post some of your solar setup?

I've been waiting to get the new KC 130 mounted but I could take some today and uplaod them this eve. It's fairly modest for an off grid system but we began in 83 with 4 arco 35's and four trojan T 105 and some wire and dc lights. This seems like downtown but it needs to grow to keep the macs and my recording studio happy. Everywhere else we are very frugal with water, we have our own well, and power. Everything's on power strips and all compact flourescent lighting. We have a 10.5 back up generator that runs on propane.

I'll go snap some pics.

Ron

ron45 · December 2009

Re: Optimising array angle

ron45 wrote: »

I've been waiting to get the new KC 130 mounted but I could take some today and uplaod them this eve. It's fairly modest for an off grid system but we began in 83 with 4 arco 35's and four trojan T 105 and some wire and dc lights. This seems like downtown but it needs to grow to keep the macs and my recording studio happy. Everywhere else we are very frugal with water, we have our own well, and power. Everything's on power strips and all compact flourescent lighting. We have a 10.5 back up generator that runs on propane.

I'll go snap some pics.

Ron

Ok they are on the page now. I already forgot what I called the folder but something with Alternative in the title. We are of the alternative persuasion in all things.

And thanks for the kind words about our home. We are thrilled every day to be here.

Ron

n3qik · December 2009

Re: Optimising array angle

I like the:

This is the give a damn dept. and trouble shooting crew.
 We were fortunate enough to hire these two away from Maytag

I have 3 on my crew.

Optimising array angle

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