Slowing Down the Summer Sun

[bcroe]

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.

I would expect the foundation loading not to change. The problem going on here (with this non
physical designer) is bringing the whole array to a single pivoting axis, instead of just dropping
supports everywhere. My expectation that some optional braces could be released to change
tilt, then reattached to restore full strength. Working on tilting 24 panels sitting on 6 pillow blocks
here. Bruce Roe

[sensij]

Well, examining the other threads on a 'virtual tracking' search yielded little besides mentions, and explanations, no numbers. I've only scratched the Google-sphere on this topic. So, another request for pointers to analysis, case studies, simulations is probably called for. That said, it might not be needed. The graph in Bruce's post #10 does just about all I need to see. Enough to motivate me to use PVWatts to check out a few specific scenarios anyway. Any other tools that would be quick and useful? What is 'SAM'?

SAM = System Advisor Model. Allows modeling of any combination of trackers, arrays at different directions, etc. They've been working on an energy storage module, but I haven't read up on it or played with it at all.

https://sam.nrel.gov/

A good place to start, if you really want to geek out, is the technical documentation

http://www.nrel.gov/docs/fy15osti/64102.pdf

https://sam.nrel.gov/sites/default/files/content/documents/pvsamv1-2015-errata.pdf

[J.P.M.]

Well, examining the other threads on a 'virtual tracking' search yielded little besides mentions, and explanations, no numbers. I've only scratched the Google-sphere on this topic. So, another request for pointers to analysis, case studies, simulations is probably called for. That said, it might not be needed. The graph in Bruce's post #10 does just about all I need to see. Enough to motivate me to use PVWatts to check out a few specific scenarios anyway. Any other tools that would be quick and useful? What is 'SAM'?

Bruce - Thank you so much for that perfect graph in post #10. You know I'm interested in the location, configuration, date, etc. I'm pretty sure that at some point in my burrowing I saw you have a website resource where I can get more of your stuff. If so, would you mind re-mentioning it here?

Told you in my intro post that I love me some homemade trackers. The more Rube Goldburg the better. If I had the space for a single axis tracker array, I'll bet I could rig something practical for my own use, maybe even with some seasonal tilt. Would probably get many multiple demerits if I ever wanted to sell it.

Short answer: SAM is like PVWatts on steroids. See the NREL site. Can be good and useful if you have a technical or engineering background. If not, it can be somewhat analogous to giving a loaded weapon to a 2 yr. old w/ the safety off. For most applications I've compared, it adds ~ 2-5 % ti the PVWatts output, and the economics/cost analysis can be useful for thos interested in coat analysis beyond the moron method of payback = system initial cost /1st yr. savings.

For initial/preliminary design, PVWatts will do about the same.

On virtual tracking: As others have noted, it does have some uses for things relating to limiting and/or evening out battery charging rates and a limited number of other one off applications, or some unusual climate or shading applications, but for most users, a mostly south facing and single array orientation will yield the most output for the least expense. Those who are familiar with solar resource assessment know this.

Long ago I made a single axis tracking mechanism with a couple of photo detectors, a step motor and some electronics including a wheatstone bridge. Worked great as I recall, at least through proof of concept. Then, I saw something very similar, but probably better in the journal "Solar Energy". Electronics not being my discipline of engineering interest, as well as the discovery by then that most home tracking isn't worth the slight added revenue it affords, and also not worth or the hassle, at least to me, I left it alone.

[AzRoute66]

Well, examining the other threads on a 'virtual tracking' search yielded little besides mentions, and explanations, no numbers. I've only scratched the Google-sphere on this topic. So, another request for pointers to analysis, case studies, simulations is probably called for. That said, it might not be needed. The graph in Bruce's post #10 does just about all I need to see. Enough to motivate me to use PVWatts to check out a few specific scenarios anyway. Any other tools that would be quick and useful? What is 'SAM'?

Bruce - Thank you so much for that perfect graph in post #10. You know I'm interested in the location, configuration, etc. I'm pretty sure that at some point in my burrowing I saw you have a website resource where I can get more of your stuff. If so, would you mind re-mentioning it here?

Told you in my intro post that I love me some homemade trackers. The more Rube Goldburg the better. If I had the space for a single axis tracker array, I'll bet I could rig something practical for my own use, maybe even with some seasonal tilt. Would probably get many multiple demerits if I ever wanted to sell it.

[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.

[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]

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.

[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

[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]

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

[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.

[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.

[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.

[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?

[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.