Slowing Down the Summer Sun

[AzRoute66]

I haven't read all of the Off Grid Topics yet, but I did scan all of the titles and didn't see anything like this subject.

I'm here at 31.5 degrees latitude, and when I look at the theoretical tools, I see some usable power in the mornings and afternoons between maybe May and September, well before the sun azimuth is 90 degrees and after it is 270 degrees. By the time the sun is hitting a south facing panel from the side it already has considerable altitude. I am railing right now because getting a battery [more] fully charged is just a matter of TIME, not panels - I say that this because I place a checkmark on my forehead every time I read "it is easier/cheaper just to add a panel" in all of the other threads.

An easterly or westerly facing string would only have to capture enough power to make full charging current (0 load current) in order to be 'interesting'. I 'know' it won't work financially. I know this because if it did, they would be doing it all over the place around here and the technique would be named after some grad student that needed a thesis. I am aware that the southerly faced panel is already collecting a part of those lobes as diffuse irradiance and those lobes don't exist in the winter..

That said, does anyone know of any threads here, simulations, case studies, analysis, etc. of placing some panels with more of an East - West orientation to supplement a southern oriented array? I know that when shading and weather patterns, etc. dictate, it is often desirable to offset entire arrays from true south. In fact, right here the best angle for your main array is 171 degrees due to our late afternoon monsoon storms according to a variety of sources that include weather. Must be something in that.

Butch - the '171 degrees' is not my original research, ok?

[ButchDeal]

There are several threads here about it and it is called virtual tracking. It is pretty common in off grid installs to increase charge times. Read up


i would say that this is separate and independent concept from your afternoon weather related azimurh of 171.

[AzRoute66]

Virtual tracking - appropriate term. Yes, I do see several threads and I am sure I can google up more than enough. Thank you very much.

[bcroe]

OK, Virtual Tracking. Besides stretching your sun day, it will add to the energy you can collect under
clouds, something an actual tracker cannot do. There is a lot of VT experimental info on my thread
SUN HOURS, but only you can determine what works for you. Bruce Roe

NScurJn17.jpg

[sensij]

I'll just add to the bandwagon... Yes, splitting some east and west (or southeast and Southwest) can extend the charging day. You really need to look at your expected seasonal loads... Typically, with lower insolation, winter is the most difficult time to stay fully charged, so the extra power that you imagine capturing in the summer might be overkill unless you have some additional summer loads in mind. (I get that your supply side philosophy says that if the power is available, you'll find a way to use it... It just takes some planning).

Under clouds, and assuming there is not a regular daily cloud pattern (morning marine layer here, or afternoon monsoonal clouds for you), a equatorial facing array will outperform an array of equal rating split East and West.

for off-grid, with panels relatively cheap, I would definitely plan to split the array if you have the space. For grid tie, except when you hit the point at which the service can't accept more power (as bcroe has done) the case for splitting the array is tougher to make.

[max2k]

OK, Virtual Tracking. Besides stretching your sun day, it will add to the energy you can collect under
clouds, something an actual tracker cannot do. There is a lot of VT experimental info on my thread
SUN HOURS, but only you can determine what works for you. Bruce Roe

NScurJn17.jpg

you're not only clipping in power you're also running out of paper to plot your power curve. I wonder how high would it actually go- 60-70kW?

[Mike90250]

My wife had me add an array with an eastern orientation, to get power faster in the morning for toast. Electric Toaster is the bees knees. Stove top, pan fried, all fail.

[SunEagle]

My wife had me add an array with an eastern orientation, to get power faster in the morning for toast. Electric Toaster is the bees knees. Stove top, pan fried, all fail.

If a cheap but reliable "tracking system" can be found for a homeowner then a ground mounted system can produce a lot more power. The problem in the past is the cost of running and maintaining a tracking system usually uses more wattage then what can be gained by it.

What is interesting is that the are a number of large Utility sized system (> 20MW) in S CA that have tracking systems. Some how the Engineers have found a way to make them financially worth installing. Probably by over pricing the watt hours it is selling to people covers the cost of maintaining the system.

[littleharbor]

Solar_Panels_at_California_Valley_Solar_Ranch_1_(8159038006).jpg

The Imperial Valley solar installations have a very efficient single axis tracking system. Still maintenance on a 200 megawatt installation could be a bit time consuming.

[bcroe]

you're not only clipping in power you're also running out of paper to plot
your power curve. I wonder how high would it actually go- 60-70kW?

Ha, yes it barely fits on that sheet. The intent was to have the panels adjusted to just achieve clipping
all day, making max use of the installed plant. If there were no clipping, I can assure you it wouldn't go
all that much higher; no bell curve here. It IS NOT making max use of the panels; can be justified
if panels are cheap enough.

Actually getting a flat panel output curve probably isn't possible, more so over seasons. Here is a curve
with some adjustments of test panels. It seems to indicate that E-W panels (1 + 3 here) added together
hardly even need the S panels. This changes with the seasons. I didn't get the 1 and 3 curves to cross
at exactly noon here, because the solar noon wasn't exactly 12 standard time here. Later I got it them
exactly right taking that and my time zone position into account. Bruce Roe
PVm17Jn16.jpg

[Wy_White_Wolf]

If a cheap but reliable "tracking system" can be found for a homeowner then a ground mounted system can produce a lot more power. The problem in the past is the cost of running and maintaining a tracking system usually uses more wattage then what can be gained by it.

What is interesting is that the are a number of large Utility sized system (> 20MW) in S CA that have tracking systems. Some how the Engineers have found a way to make them financially worth installing. Probably by over pricing the watt hours it is selling to people covers the cost of maintaining the system.

Other Peoples Money. When you're using government subsidies and other forms of OPM to pay for a system you don't worry about running the cost up with trackers and such.

WWW

[bcroe]

If a cheap but reliable "tracking system" can be found for a homeowner then a ground mounted system can produce a lot more power. The problem in the past is the cost of running and maintaining a tracking system usually uses more wattage then what can be gained by it.

What is interesting is that the are a number of large Utility sized system (> 20MW) in S CA that have tracking systems. Some how the Engineers have found a way to make them financially worth installing. Probably by over pricing the watt hours it is selling to people covers the cost of maintaining the system.

Apparently single axis can be justified on a utility scale. They seem to be scanning E to W
each day, but GIVE UP the gain of a tilt angle for latitude. Not good for as far north as I am.
Another advantage would be the ability to dump snow, about the only way on this scale.
I believe the large array near the airport here is fixed.

At home I can't justify tracking. Arrays tilted for this latitude and scanned E-W need a lot
of space to get out of each others shadow. And with the ever present clouds here, the
multi alignment easily out performs a tracker. Bruce Roe

[SunEagle]

Apparently single axis can be justified on a utility scale. They seem to be scanning E to W
each day, but GIVE UP the gain of a tilt angle for latitude. Not good for as far north as I am.
Another advantage would be the ability to dump snow, about the only way on this scale.
I believe the large array near the airport here is fixed.

At home I can't justify tracking. Arrays tilted for this latitude and scanned E-W need a lot
of space to get out of each others shadow. And with the ever present clouds here, the
multi alignment easily out performs a tracker. Bruce Roe

I am still not sure if I will install a Summer / Winter angle adjustment to my future pv system. I guess it will come down to the cost since it will have to meet 130mph wind code requirements.

[J.P.M.]

I am still not sure if I will install a Summer / Winter angle adjustment to my future pv system. I guess it will come down to the cost since it will have to meet 130mph wind code requirements.

Run all the considered tilts under PVWatts, figure in annual savings per month by adjusting tilts however often for all tilts under consideration (1X/month vs. 2X/yr. for example, then calc the savings for the tilts against the increased cost/PITA/complexity of a fixed orientation.

Although retired and no longer practicing, I'd offer an opinion from an engineering/design standpoint, that the added cost of wind considerations would be mostly from adding the portions of the system that control the tilt changes, and not necessarily from changes that such a variable tilt might cause to change the design loadings on the rest of the structure. A variable tilt feature will cost more than a fixed arrangement, but more than likely any tilting design using a 130MPH design wind speed, and the gust/exposure and other design parameters used to estimate wind loadings will result in about the same design loadings for foundations, with the result of likely and probably similar or the same section moduli, design strengths, sizes and similar configuration for the supporting structure as would a system of fixed orientation. I'd never have designed a system that close to the design edge anyway.

[SunEagle]

Run all the considered tilts under PVWatts, figure in annual savings per month by adjusting tilts however often for all tilts under consideration (1X/month vs. 2X/yr. for example, then calc the savings for the tilts against the increased cost/PITA/complexity of a fixed orientation.

Although retired and no longer practicing, I'd offer an opinion from an engineering/design standpoint, that the added cost of wind considerations would be mostly from adding the portions of the system that control the tilt changes, and not necessarily from changes that such a variable tilt might cause to change the design loadings on the rest of the structure. A variable tilt feature will cost more than a fixed arrangement, but more than likely any tilting design using a 130MPH design wind speed, and the gust/exposure and other design parameters used to estimate wind loadings will result in about the same design loadings for foundations, with the result of likely and probably similar or the same section moduli, design strengths, sizes and similar configuration for the supporting structure as would a system of fixed orientation. I'd never have designed a system that close to the design edge anyway.

I understand not wanting to keep the design close to the edge. My home is rated for 150mph winds even though it only needs to meet the 130mph requirement.

I expect I will have my system sized sometime next year after I get a few months of electrical usage on it but I am hoping to get away with a 6kw system although the cost per watt may be less if I go somewhat bigger.