Help in understanding the correct angle setting.

Texas Wellman

Set up is near Houston, Tx. Lat/Lon 29* 95*. If the angle is supposed to match the lattitude that means I would need to set the angle at 29* for a good year-round result? How do you figure out the best summer/winter angles? I did a quick search but didn't see anything that would directly answer my question.

Also, when the angle recommended is 29*, do you count that from the horizon up? As in straight level is 0* and straight up is 90*? I know these seem like simple questions but it's a little fuzzy at this point.

Edit: I found some interesting information at these links:
http://www.macslab.com/optsolar.html

http://solarelectricityhandbook.com/solar-angle-calculator.html

ggunn

Re: Help in understanding the correct angle setting.

Texas Wellman wrote: »

Set up is near Houston, Tx. Lat/Lon 29* 95*. If the angle is supposed to match the lattitude that means I would need to set the angle at 29* for a good year-round result? How do you figure out the best summer/winter angles? I did a quick search but didn't see anything that would directly answer my question.

Also, when the angle recommended is 29*, do you count that from the horizon up? As in straight level is 0* and straight up is 90*? I know these seem like simple questions but it's a little fuzzy at this point.

Edit: I found some interesting information at these links:
http://www.macslab.com/optsolar.html

http://solarelectricityhandbook.com/solar-angle-calculator.html

The tilt angle is calculated as a displacement from vertical. If you were at the equator, your latitude would be zero degrees and modules with latitude tilt would be pointing straight up.

Altitude and tilt are complementary angles, i.e., they sum to 90 degrees. Altitude is measured from the horizon and tilt is measured from the vertical. The altitude of the sun at solar noon on the equinoxes is 90 degrees minus your latitude, so setting your modules at latitude tilt points them directly at the sun at that time.

The range of the sun's altitude at solar noon from solstice to solstice is 47 degrees, which is twice the 23.5 degree angle between the earth's plane of rotation and the plane of its orbit around the sun, and the center of that range is its altitude at the equinoxes. That means that on the winter solstice your modules would need to be tilted at 29 + 23.5 = 52.5 degrees to point directly at the sun, and conversely on the summer solstice at 29 - 23.5 = 5.5 degrees. If you were to realign your modules twice a year, you'd want them to be in the middle of the summer range half the year (17.25 degree tilt) and the middle of the winter range (40.75 degrees tilt) for the other half.

It gets more complicated at higher latitudes because of the sun's extended path around the horizon in the summer months.

Anyway, all that said, you'd have to look at the projected output of your array (in PVWatts, for example) at the different tilts for the summer and winter months versus leaving them at latitude tilt to decide if the difference justifies the pain and expense of building and realigning an adjustable array. The closer you get to pointing directly at the sun, the less difference a few degrees of deviation makes.

Coach Dad

Re: Help in understanding the correct angle setting.

Hi Tex...
Here is another link for you....
http://mapserve3.nrel.gov/PVWatts_Viewer/index.html
- Enter either your zip code or your Lat/Lon numbers...
- Zoom
- send to PV watts
At that point you can try different tilt angles to fine tune the ones for your location.

SolaRevolution

Re: Help in understanding the correct angle setting.

If you are going to be installing a fixed array you should also consider when you will need the most power.

-Many utilities charge more during summer peak hours so it cam make more sense to maximize production by setting a tilt to maximize summer sun.

-Most off-grid full-time residences use more power in the winter when there are less daylight hours. I know some folks who have been in the solar industry since the early 1980s who keep their fixed arrays at latitude +15° all of the time. I think this is a bit extreme. I prefer to set fixed off-grid at latitude or lat +5°. In my area we often have the most cloud cover in the winter so it does not necessarily make sense to optimize the tilt for when there is there is not much sun and you will typically need to supplement with a generator anyway.

-Many 'cabins' are for summer use only so it can make sense to set them at latitude -15°.

-Some off-gridders use air-conditioning in the summer or pump a lot of water in the summer with their residential systems.

-Direct water pumping PV systems usually need to pump more in the summer.


-Alex Aragon