Tilt angle worth the effort?

stmoloud2

Just finished wiring up an additional 300W to the system but my best tilt location would be a NW direction, not the optimum North. (I am located in the southern hemisphere).

So is it worthwhile doing the extra to set up angles as per the usual North-facing angles (here 25 degrees summer, 50 degrees winter) or maybe just leave them flat? Thanks. 

mike95490

I set my panels up to maximize winter harvest.  The short, cloudy days of my winters leave little time for charging, so optimum angle is required.   Summer I have many more hours to harvest, and generally clear weather, so the winter angle is not a problem

 Flat will quickly foul with debris and reduce your harvest in all seasons

BB.

You can use a solar harvest program and see what the changes may be... here is a simple one:
http://www.solarelectricityhandbook.com/solar-irradiance.html

Auckland (Facing North West)
Average Solar Insolation figures

Measured in kWh/m2/day onto a solar panel set at a 53° angle from vertical:
(For best year-round performance)

Jan	Feb	Mar	Apr	May	Jun
5.51	5.26	4.84	4.06	3.30	2.98
Jul	Aug	Sep	Oct	Nov	Dec
3.22	3.63	4.40	4.67	5.14	5.29

Auckland (facing due North)
Average Solar Insolation figures

Measured in kWh/m2/day onto a solar panel set at a 53° angle from vertical:
(For best year-round performance)

Jan	Feb	Mar	Apr	May	Jun
5.80	5.54	5.10	4.27	3.47	3.14
Jul	Aug	Sep	Oct	Nov	Dec
3.39	3.82	4.63	4.92	5.41	5.57

If you are off grid, and needing "winter" power:
June NW / June North = 2.98 Hours of sun / 3.14 hours of sun = 0.95 or 95% of North

More or less, 10% accuracy is probably the best you can measure power/energy harvest with non-laboratory instruments... And it is not usual for a +/- 10%-20% or even greater year to year average harvest variability.

Here is another solar harvest website:

https://pvwatts.nrel.gov/

Local weather conditions will make a difference (generally, these harvest calculators use actual measured energy harvest over 10+ years... And in some places (such as Florida where they have afternoon thunder storms/cloud cover in summer, facing more towards the South East to harvest earlier sun is actually better.

And, there is of course other issues, like shading form hills/mountains, down in valley, trees/buildings, overhead power lines, chimneys, roof stacks, etc... all have effets too (any shading on a solar panel can dramatically cost harvest energy, by 50% or more is typical for even a a single cell shaded in a series string of panels).

So, don't worry too much. This "less than optimum" change in panel orientation is not going to be hurting you by very much... And if it does, just add some more panels to make up for the loss. Solar panels are relatively inexpensive these days and adding a few (and saving generator fuel, longer battery life) is generally a good thing.

-Bill

stmoloud2

Thanks, I guess then I'm not getting any less amps than if the panels were flat. That would be a problem as now it appears the lowest I can mount them is at an angle of 20 degrees in that NW direction. But providing I'm not making losses I can go up to 50 degrees.   

stmoloud2

Panels are getting cheaper, problem is finding the space to put them. But nice problem to have even if they can't always be located where one would wish. I've been using your formula's Bill to get a better balanced system. It is slowly coming together thanks to you.

BB.

You are very welcome... And to clarify a few questions on my part.

What do you mean by mounting the panels "flat"? You can use the SolarElectric (or PVWatts) link to see what works best for you... With panels mounted "flat" or horizontal, in Summer, you do get some more hours of sun... In Winter you get less.

Auckland
Average Solar Insolation figures

Measured in kWh/m2/day onto a horizontal surface:

Jan	Feb	Mar	Apr	May	Jun
6.41	5.65	4.59	3.31	2.35	1.96
Jul	Aug	Sep	Oct	Nov	Dec
2.18	2.83	3.96	4.82	5.86	6.26

Also, when you say the lowest angle is 20 degrees, is it 20 degrees from Horizontal or Vertical... The SolarElectric link, the panel angle is actually a little bit unusual. It uses Vertical as Zero Degrees. The PVWatts and many other software packages use horizontal as Zero degrees.

So, the 53 degrees from vertical would be 37 degrees from Horizontal (90 degrees - vertical angle = Horizontal angle).

The second method (horizontal as zero degrees) is a bit "more natural". Usually, the best yearly harvest = your latitude. I.e., Auckland is at 37 degrees South. "Best yearly total harvest" = 37 degrees from Horizontal, or 53 degrees from vertical.

Even at the Equator, where "flat" or zero degrees is "optimum", having a 5 degree tilt makes the panels better at self cleaning (wind/rain removing leaves and dust).

Anyway--Just want to make sure we are clear in our discussions here.

Take care,
-Bill

ScoobyMike

I have a camper with a 100W panel lying flat on the roof, and a portable 100W panel that I deploy with an angle on the ground.  Last Thanksgiving in Southern California the rooftop panel provided 2A to the battery, while the ground panel provided 6A to battery. So, ~3x increase with late year, low solar angle.

stmoloud2

Bill, I am mounting one end of the array on a fence-line, the other on a shed nearby. So that is why I'm restricted in direction. The angle is from the horizontal, 20 degrees being where the other end of the array comes to rest on the roof of the shed. So can't go any further down towards the horizontal.

ScoobyMike, I have exactly the same panels mounted horizontal on my bus roof, so will take some readings and compare. I have a multimeter but that's only good for 10A max for 30 seconds. I would want that meter in circuit for more than 30 seconds. Any suggestions as to suitable meter would be appreciated.

petertearai

Im a bit north of auckland , set to 45 deg . Good for winter . But as said summer there is more hours of sun so angle not so important . Especially off grid . There is an app called solar tilt which gives you the optimal angels for winter and summer .

stmoloud2

That must be the winter tilt you are referring to. Kaitaia is 35 degrees latitude, supposedly add 15 degrees to that for winter tilt. I'm not going fuss with it too much now, we're getting loads of sun & between now and winter I should have gotten a decent amp-meter to make some comparative measurements. 

softdown

I'm at 37 degrees and happy with a 45 degree tilt for winter optimization. Battery bank maintains a slightly higher summer time low voltage ~50 volts. Compared to ~49.8 in the winter. The difference is slight because the fridge works much less in an ~55 degree room.

Sitting at 49.6 at 5:20am because the fridge compressor is on and I nuked some breakfast in the microwave - can't sleep this morning.  Purgatory - can't sleep yet too tired to cook a proper breakfast. 

littleharbor2

softdown said:

I'm at 37 degrees and happy with a 45 degree tilt for winter optimization. Battery bank maintains a slightly higher summer time low voltage ~50 volts. Compared to ~49.8 in the winter. The difference is slight because the fridge works much less in an ~55 degree room.

Sitting at 49.6 at 5:20am because the fridge compressor is on and I nuked some breakfast in the microwave - can't sleep this morning.  Purgatory - can't sleep yet too tired to cook a proper breakfast. 

Could winter vs. Summer temperatures be affecting your batteries voltage.

softdown

littleharbor2 said:

softdown said:

I'm at 37 degrees and happy with a 45 degree tilt for winter optimization. Battery bank maintains a slightly higher summer time low voltage ~50 volts. Compared to ~49.8 in the winter. The difference is slight because the fridge works much less in an ~55 degree room.

Sitting at 49.6 at 5:20am because the fridge compressor is on and I nuked some breakfast in the microwave - can't sleep this morning.  Purgatory - can't sleep yet too tired to cook a proper breakfast. 

Could winter vs. Summer temperatures be affecting your batteries voltage.

Yes they are. Adjusting for that my winter time low voltage is ~50.2. My summer time temp has gone up to 61 - so still kind of cool. 

Good point. 

I've also been working harder at lowering usage when the sun is down. Having instant access to system voltage is a fantastic thing.