KB's Design

[kb58]

It is what it is. How best to mount and orient the panels is turning out the be the toughest part of the design. It's easy to do, but creates an eyesore, much harder to not.

[J.P.M.]

It is what it is. How best to mount and orient the panels is turning out the be the toughest part of the design. It's easy to do, but creates an eyesore, much harder to not.

Design, like life, is a set of tradeoffs. Usually optimum performance is compromised for competing priorities. My array's not pretty, but few others in S.D. county perform better.

Don't know if you've considered it yet, but if DIY, I'd get the county involved now. There's a fair amount of spec conformance to jump through, not the least of which involves mech. design, including wind and seismic considerations. For a ground mount, you will likely need a P.E. review/stamp for the mechanical part of the design.

[kb58]

Oh yes, I'm well aware of the 800-lb gorilla in the room - The City Planning Department. I have the benefit of knowing several Professional Engineers, thought I haven't asked yet whether they'd review my design. One gave me his design document that he submitted for his own solar system, so that's easy enough to use as an example.

Right now I'm looking into other possible panel array layouts; instead of the uber-low layout I had before which turned out to be a self-shading nightmare. I thought I'd share my site situation so you can see what I'm dealing with - see attached pics. The new one is still ground mount, but a more traditional single-plane array. Its optimum placement though means that when we look out into the back yard, it's right there in your face. The rear bank has a slope of roughly 30 degrees, hence the triangular layout. The new layout backs away from the trees along the south end and while there are large trees immediately behind it, they're to the northeast. Much like the first layout, it's not good in December but oh well.

Regarding the mount, if I go with an established company, I get the benefit of them supplying PE-approved drawings - for a BIG price. This ground mount would run around $4300, and that doesn't include the poles and footings. If I design it myself, then there's whatever the PE gets to review it. I've yet to find out that price in order to determine if I want to go it alone.

[J.P.M.]

Oh yes, I'm well aware of the 800-lb gorilla in the room - The City Planning Department. I have the benefit of knowing several Professional Engineers, thought I haven't asked yet whether they'd review my design. One gave me his design document that he submitted for his own solar system, so that's easy enough to use as an example.

Right now I'm looking into other possible panel array layouts; instead of the uber-low layout I had before which turned out to be a self-shading nightmare. I thought I'd share my site situation so you can see what I'm dealing with - see attached pics. The new one is still ground mount, but a more traditional single-plane array. Its optimum placement though means that when we look out into the back yard, it's right there in your face. The rear bank has a slope of roughly 30 degrees, hence the triangular layout. The new layout backs away from the trees along the south end and while there are large trees immediately behind it, they're to the northeast. Much like the first layout, it's not good in December but oh well.

Regarding the mount, if I go with an established company, I get the benefit of them supplying PE-approved drawings - for a BIG price. This ground mount would run around $4300, and that doesn't include the poles and footings. If I design it myself, then there's whatever the PE gets to review it. I've yet to find out that price in order to determine if I want to go it alone.

Looks like you've got something like a set of Hobson's choices. I terms of shading, it looks like the new location is maybe better than the others, but I'd think the support structure might be a bit involved. Also, there may be setback considerations with the city. I know the county has setbacks for arrays.

In one (or more) senses, it's good your considering a DIY job. I suspect most vendors would shy away from a design of this complexity, foundation wise, and if they didn't, my guess is they'd try to make it price prohibitive to handle what looks like a lot of unknowns that'll creep into the design.

[kb58]

I didn't phrase that well. What I meant to say was that the $4300 was just for the mounting rails and parts - not installed. I suspect it would be far cheaper to get a PE to design it and I source all the steel locally. Heck, I built a car from the ground up, this is way simpler. What's daunting is the depth of the footing to sink into sandstone, ugh.

[J.P.M.]

I didn't phrase that well. What I meant to say was that the $4300 was just for the mounting rails and parts - not installed. I suspect it would be far cheaper to get a PE to design it and I source all the steel locally. Heck, I built a car from the ground up, this is way simpler. What's daunting is the depth of the footing to sink into sandstone, ugh.

Maybe, but I got the sense of it. $4,300 for parts. Design extra. The footings are the easy part. The rest of the mechanical design is one reason why God made P.E.'s.

Add: Just a thought, NOMB and not trying to rain on the parade: Between the shading you've got and how it impairs resource availability, the possible to likely rather large extra cost of a ground mount, particularly on less than flat ground, the hassles that less than experienced in such matters DIY'ers are likely to get from the city, and the rather small electrical usage you have, all may conspire to make your application less cost effective than others, stretch payback/lower ROI. Time shifting off/away from peak pricing periods may be a better way to keep the electric bills low(er). It's sunny around here but not every property is a good solar application.

[max2k]

Oh yes, I'm well aware of the 800-lb gorilla in the room - The City Planning Department. ... If I design it myself, then there's whatever the PE gets to review it. I've yet to find out that price in order to determine if I want to go it alone.

If I were you I'd go to City Building Department and simply ask what they require and take it from there. At the end of the day they'll be the ones reviewing / inspecting your project you might just do what they require. They might not give you all the details but you should be able to get a feeling how much freedom you have there.

[kb58]

I thought I'd seen the post in this (my) thread but couldn't find it... I need a reality check:

Someone mentioned taking into account daylight savings time when running simulations in SAM. The giant spreadsheet I created per JPMs helpful input is working well, but which way do I shift the cells? In March, clocks are turned forward until November, making the sun stay up an hour longer per the adjusted clock, so do I shift the ~4000 hourly rates back an hr between those times? Part of me would like to ignore it for simplicity sake but an hour is a sizable chunk of exposure time, especially during the upcoming summer TOU times.

[edit] I just realized that maybe SAM has an option for daylight savings time... I'll check but don't remember seeing one. (answer: it does not)

[sensij]

I thought I'd seen the post in this (my) thread but couldn't find it... I need a reality check:

Someone mentioned taking into account daylight savings time when running simulations in SAM. The giant spreadsheet I created per JPMs helpful input is working well, but which way do I shift the cells? In March, clocks are turned forward until November, making the sun stay up an hour longer per the adjusted clock, so do I shift the ~4000 hourly rates back an hr between those times? Part of me would like to ignore it for simplicity sake but an hour is a sizable chunk of exposure time, especially during the upcoming summer TOU times.

[edit] I just realized that maybe SAM has an option for daylight savings time... I'll check but don't remember seeing one. (answer: it does not)

During standard time (in winter), the hour that SAM reports is intended to represent the energy production during that hour... the 7:00 AM output from SAM (or PVWatts) represents the 7:00-7:59 hour on the clock.

During daylight savings time (in summer), the hour that SAM reports needs to be increased by 1 hour to represent clock time... the 6:00 AM output from SAM (or PVWatts) represents the 7:00-7:59 hour on the clock.

If you start looking at sub-hourly modeling, you should also be aware that SAM uses the position of the sun at 30 min after the hour for the calculations representing the output during that hour. To overlay a clear day's output in SAM with actual data from a system, the adjustment could be 1.5 hours, depending on how your "actual" data source is handling time (averaging data vs instantaneous output, etc). I understand that SAM now has a sub-hourly interpolation function, but I haven't dug into it yet.

[kb58]

Thanks. Increased annual production by about 1%.

[J.P.M.]

During standard time (in winter), the hour that SAM reports is intended to represent the energy production during that hour... the 7:00 AM output from SAM (or PVWatts) represents the 7:00-7:59 hour on the clock.

During daylight savings time (in summer), the hour that SAM reports needs to be increased by 1 hour to represent clock time... the 6:00 AM output from SAM (or PVWatts) represents the 7:00-7:59 hour on the clock.

If you start looking at sub-hourly modeling, you should also be aware that SAM uses the position of the sun at 30 min after the hour for the calculations representing the output during that hour. To overlay a clear day's output in SAM with actual data from a system, the adjustment could be 1.5 hours, depending on how your "actual" data source is handling time (averaging data vs instantaneous output, etc). I understand that SAM now has a sub-hourly interpolation function, but I haven't dug into it yet.

Agreed on the time shift. I probably should have mentioned it, but all my solar calcs etc. always stay on standard time just as railroad schedules once did. If I was thinking, I would have mentioned it.

I haven't done subhourly w/SAM yet and it may be some time before I get to it.

I think I might have beat SAM to it on that one. I've got spreadsheets I've done at 1 minute intervals for 1440 minute days for HDKR and recorded Davis 1 minute interval GHI for comparison of theoretical vs. actual clearness indices and also used for the fouling estimates I do when it's "clear". That's also used to compare my model of system output with the monitored 5 minute data from the Sunpower monitor.