Los Angeles County 13kW System

[robomartin]

Hey folks, at the suggestion of some here I've been reading through a bunch of books in order to answer the many questions coming up while planning for a 13 kW system for my house. Again, thanks for suggesting I hit the books.

I am now done with CAD design of the structure and the array. The next step are permits and installation planning.

I printed what I have and visited the building and permit office. They said all looked good, both from a permit and planning perspective. The only twist is that I have to have a licensed Structural Engineer produce the drawings, verify the calculations and "wet stamp" them.

Can anyone recommend someone to do this work? I have bids from about $1,000 to $3,000 for this. They need to be familiar with Los Angeles County requirements.

The only other question that keeps coming up that I have not yet found an answer to is: What happens when you go over 10kW?

I keep seeing references to this in LA County applications and materials but they never tell you where to go or what to do if you are over 10kW. The Building and Permit guys at the counter had no clue. I think it's a power company issue. Maybe. I tried calling them but the person I spoke to had no clue what I was talking about. I am going to try again today and see if I can get any useful answers. I'm hoping someone here might have dealt with this and can point me in the right direction.

Thanks.


SOLAR ARRAY.JPG

[J.P.M.]

Since it's a POCO issue, I'd call my power provider and ask them for limits on system size for net metering.

BTW, If your considering a horizontal array as shown, be prepared to pay a performance penalty for the horizontal orientation, and also be prepared to clean the array a whole lot or be prepared to accept still more output reduction as the panels turn into mud pans in short order.

[robomartin]

Since it's a POCO issue, I'd call my power provider and ask them for limits on system size for net metering.

BTW, If your considering a horizontal array as shown, be prepared to pay a performance penalty for the horizontal orientation, and also be prepared to clean the array a whole lot or be prepared to accept still more output reduction as the panels turn into mud pans in short order.

It is tilted 10 degrees. The ideal tilt for my location is 29 degrees. At that tilt angle the structure becomes unwieldy very quickly. Right now the front edge of the front panels are at 10 feet and the back edge is about 13 feet high. At 30 degrees it gets ridiculous very quickly. I mean, it's like building a small house. This structure is roughly 50 x 16 feet as it stands now. One of the biggest problems with an array is wind loading. LA County wants the structure to handle 110 mph winds. At 10 degrees this represents somewhere in the order of about 1,000 lbs of uplift. At 30 degrees it goes up to somewhere in the 8,000 lbs range. So things quickly become exponentially more complex and expensive to build.

As far as the efficiency hit. I used PVWatts to explore a range of angles and power levels. A 10.4kW system of 30 panels at 30 degrees of tilt would do fine for my needs. This, according to PVWatts would produce 19,500 kWh/year. What I've done here is switch to a 13.0kW system with 40 panels at 10 degrees. PVWatts says this will produce 22,823 kWh/year. I could go a little more, maybe 15 degrees but frankly I don't see the point.

So, for about $2,000 more I get to build a structure with moderate tilt that looks good and end-up with about 3,000 kWh/year more energy than the ideal system. I think that's a sensible trade.

[sensij]

So, for about $2,000 more I get to build a structure with moderate tilt that looks good and end-up with about 3,000 kWh/year more energy than the ideal system. I think that's a sensible trade.

Who is your power company... SCE, or LADWP? Here is LADWP's net metering information page. You'll see a number of references to differences in requirements once you exceed 10 kW.

https://www.ladwp.com/cs/idcplg?IdcService=GET_FILE&dDocName=OPLADWPCCB547407&RevisionSelectionMethod=LatestReleased

[robomartin]

Who is your power company... SCE, or LADWP? Here is LADWP's net metering information page. You'll see a number of references to differences in requirements once you exceed 10 kW.

https://www.ladwp.com/cs/idcplg?IdcService=GET_FILE&dDocName=OPLADWPCCB547407&RevisionSelectionMethod=LatestReleased

I'm SCE. This might still be useful. I'll read through it. Thanks.

[robomartin]

Finally got a straight answer with regards to the 10kW threshold. It came from the electrical plan check guys. For my project it doesn't matter because it is considered a ground mount system. If it goes over 15kW they need additional review and it might cost a little more but that's about it. The main concern with roof mounted systems over 10kW seems to be related to fire issues. Going over 10kW kicks you out of the expedited permit process and has them look it over with a little more detail.

[J.P.M.]

Those bids at $1K to $3K sound reasonable. If I still had a license, I'd have done the review it for $250/hr., 4 hr. min., plus changes for putting my butt in the sling.

[robomartin]

Those bids at $1K to $3K sound reasonable. If I still had a license, I'd have done the review it for $250/hr., 4 hr. min., plus changes for putting my butt in the sling.

Good to know. Thanks.

[Mike90250]

When installing the array, plan on a De-Ionized water system for bi-weekly cleanings. With that shallow tilt, dirt and grime WILL collect, and you don't want hard water spots (LA water is really bad and will turn the panels white in a couple months of rinsing) Either a conventional water softener, or a DI system, to keep the Colorado River calcium from building up.
There is a Mr Clean Car wash wand system with a tiny DI cartridge or you can look into the gear car dealers use for the morning car rinse.

[J.P.M.]

When installing the array, plan on a De-Ionized water system for bi-weekly cleanings. With that shallow tilt, dirt and grime WILL collect, and you don't want hard water spots (LA water is really bad and will turn the panels white in a couple months of rinsing) Either a conventional water softener, or a DI system, to keep the Colorado River calcium from building up.
There is a Mr Clean Car wash wand system with a tiny DI cartridge or you can look into the gear car dealers use for the morning car rinse.

While being unable to measure or quantify any performance penalty associated with leftover/unrinsed Colorado river H2O spotting from Ca or other group IIa chemicals over either D.I. rising and/ or thorough wiping procedures to remove all visible spotting, I d suggest that some form of additional inspection be performed on arrays with low tilts.

I've found that rinsing with a hose and tap water what's no more than hard CO river tap water from a hose about every 4 or so rainless weeks is about as efficacious as other methods for the hassle/$$ involved vs. differential restored performance the more involved methods might produce, pretty much regardless of what the results might look like.

From observation with a good eyeball, and after cleanings of various sorts and thoroughness, I've come to the conclusion that the human eye is, at best, a poor tool to use to when estimating performance penalties due to array fouling.

As for the part lower tilts may play in the fouling question(s), the literature too seems to not have a lot of confirmed data or any strong quantitative consensus on how much, or in what ways a low(er) tilt may affect fouling, be it from spotting, water runoff velocity, mud buildup, or other issues brought on by lower tilt angles, other than lower tilts seem to fouls a lot faster.

[DanS26]

Have you been to the IronRidge design site? There is a wealth of information there and you can play with different tilts, etc. You may even find that building with Sch 40 pipe is comparable in cost to all that treated lumber.

[Mike90250]

Have you been to the IronRidge design site? There is a wealth of information there and you can play with different tilts, etc. You may even find that building with Sch 40 pipe is comparable in cost to all that treated lumber.

Treated Lumber is great for fence posts, but so much strength has been cooked out of it, it is no longer structure rated. And it soaks up water and warps like mad. At least with what they sell us in Kalifornia.

[VirgilSkinner]

Originally posted by DanS26 View Post
Have you been to the IronRidge design site? There is a wealth of information there and you can play with different tilts, etc. You may even find that building with Sch 40 pipe is comparable in cost to all that treated lumber.

Treated Lumber is great for fence posts, but so much strength has been cooked out of it, it is no longer structure rated. And it soaks up water and warps like mad. At least with what they sell us in Kalifornia.

I used the Iron ridge design site for my ground mount layout. BUT I used oil field (used) drill stem pipe for the build. It can be had for a song, and strength is far superior to schedule 40 galvanized pipe. 2 3/8 drill stem is the exact same outside diameter as 2 inch galv, so all the Ironridge hardware works just fine. I welded the pipe support structure, so top rail junction caps were not needed.