Ballasted ground-mount array

[Hillsider]

I am pretty much committed to doing a ground-mount system, due to structural & shading issues with a roof-top system, but in the course of checking out all the permitting issues in L.A. County, I came across a requirement that pretty much scuttles any configuration that requires a concrete foundation. The county building code section 1805.3 requires foundation setbacks adjacent to up & down slopes, based on the height of the slope, that can range as high as 40'. My ideal site is a "flat" terrace ( 15' wide x 120' long, E to W ), bounded by an 80' down-slope and a 70' up-slope, so any excavation to satisfy the code would result in a building site totally useless for a solar array.
I reviewed my earlier data on ballasted ground-mount systems, & came up with the same objections that caused me to reject them before. All of the systems were either restricted to "utility scale" ( > 75KW ) arrays, or were "one size fits all" mini racks with a 30* tilt. Engineering data that would allow a homeowner to customize an array to his specific site, does not appear to be available to the general public. I probably have not yet put together the proper "search terms" to find either an Engineering firm, or an installer willing to just do the structure, but perhaps someone on this forum has come across the information that I am seeking. FWIW, driven or helical piles are also not feasible, as my soil has too many large rocks in it.

[Naptown]

Look at schletter and unirac ula
Both have a ballasted system

[sensij]

What is wrong with 30 deg tilt?

[Poway]

... My ideal site is a "flat" terrace ( 15' wide x 120' long, E to W ), bounded by an 80' down-slope and a 70' up-slope, ... FWIW, driven or helical piles are also not feasible, as my soil has too many large rocks in it.

If you were thinking about putting in a concrete pad with a ballasted system then the area must be pretty much flat with rocks underground (picture?). I would revisit the assumption about too many large rocks. If some of the poles (conventional approach) hit large rocks then you can drill and epoxy in anchor (rock becomes footing for pole, instead of pouring concrete).

[Hillsider]

Thirty degree tilt

What is wrong with 30 deg tilt?

The PNMini offered by Schletter, with a 30* tilt is not a show-stopper, however PVWatts recommends a tilt of 18* for mty location. The AltE store offers that structure for $500, without the ballast, so I would still have to come up with a wet-stamped engineering design for the ballast blocks, in order to submit a request for an expedited permit. L.A. county is like a "10-million person third-world country." I am afraid a submittal for a comprehensive solar system would disappear into the bowels of the Dept. of Public Works.

[Naptown]

The PNMini offered by Schletter, with a 30* tilt is not a show-stopper, however PVWatts recommends a tilt of 18* for mty location. The AltE store offers that structure for $500, without the ballast, so I would still have to come up with a wet-stamped engineering design for the ballast blocks, in order to submit a request for an expedited permit. L.A. county is like a "10-million person third-world country." I am afraid a submittal for a comprehensive solar system would disappear into the bowels of the Dept. of Public Works.

Schletter will provide engineered stamped drawings for your install.
The 30 d tilt is I believe maximum.
You can order a lower tilt. Or set to a lower tilt if desired.
Just need to specify location terrainodules and tilt.

[sensij]

The PNMini offered by Schletter, with a 30* tilt is not a show-stopper, however PVWatts recommends a tilt of 18* for mty location. The AltE store offers that structure for $500, without the ballast, so I would still have to come up with a wet-stamped engineering design for the ballast blocks, in order to submit a request for an expedited permit. L.A. county is like a "10-million person third-world country." I am afraid a submittal for a comprehensive solar system would disappear into the bowels of the Dept. of Public Works.

That is surprising. What azimuth? In San Diego, most southerly facing system max out annual production at around 30 deg. LA, somewhat north, should be the same or steeper.

[Hillsider]

Update to tilt angle

That is surprising. What azimuth? In San Diego, most southerly facing system max out annual production at around 30 deg. LA, somewhat north, should be the same or steeper.

My error! I did a system review with PVWatts, but also did an analysis of the system using the CSI calculator, as it allowed for a more detailed description of the shading for the entire year. I have a very severe southerly shading problem during the winter months, due to a bunch of 60' tall trees on my southern horizon. Some of the trees belong to me ( and I may cut them down ), but two or three giant Blue Gum windbreakers belong to the county. BTW, my azimuth with the current "compact" Ironridge structure is 192*. If I am forced to go with a "worst case" distributed array ( single-row portrait ), 12 panels on the West end of the terrace would remain at 192*, but the 12-panel sub-array at the East end would face an azimuth of 205*.

[Hillsider]

Schletter ballasted pvmini structure

Schletter will provide engineered stamped drawings for your install.
The 30 d tilt is I believe maximum.
You can order a lower tilt. Or set to a lower tilt if desired.
Just need to specify location terrainodules and tilt.

Thanks for the update. It appears that you have significant experience with Schletter's products and business model. While the pour-in-place system of ballasted arrays is the easiest for a home-owner to accommodate, due to lower weight of delivered components ( aside from the pumped concrete itself ), recent searches have produced no results for residential-scale arrays. Pre-cast ballast components weigh around one ton each, so obviously have to be delivered & placed using heavy equipment. Articles on ballasted array requirements seem to indicate that most projects are custom designs, requiring the participation of a structural engineer. I have yet to call Schletter's customer-service rep for additional information, but perhaps you can give me the benefit of your experience, as to my available options. If an on-site in-depth survey of my site is required, I suspect the cost will be well beyond my reach. If on the other hand, public-domain data on wind, soil, weather & seismic particulars, along with the assessor's property description ( and perhaps, Google Earth scans ) are sufficient to create a cost proposal, then I may still be able to go forward with my project.

[Poway]

Going down the wrong path??

If you were thinking about putting in a concrete pad with a ballasted system then the area must be pretty much flat with rocks underground (picture?). I would revisit the assumption about too many large rocks. If some of the poles (conventional approach) hit large rocks then you can drill and epoxy in anchor (rock becomes footing for pole, instead of pouring concrete).

I looked at 30+ residential ground mounts in san diego. Many (including mine) in boulder territory. All used metal posts/poles with concrete footings. When impossible to dig thru a large boulder to make room for the footing epoxied rebar into bolder made the boulder part of the footing. I would get a few opinions to make sure you can't take a more traditional approach.

[Naptown]

Thanks for the update. It appears that you have significant experience with Schletter's products and business model. While the pour-in-place system of ballasted arrays is the easiest for a home-owner to accommodate, due to lower weight of delivered components ( aside from the pumped concrete itself ), recent searches have produced no results for residential-scale arrays. Pre-cast ballast components weigh around one ton each, so obviously have to be delivered & placed using heavy equipment. Articles on ballasted array requirements seem to indicate that most projects are custom designs, requiring the participation of a structural engineer. I have yet to call Schletter's customer-service rep for additional information, but perhaps you can give me the benefit of your experience, as to my available options. If an on-site in-depth survey of my site is required, I suspect the cost will be well beyond my reach. If on the other hand, public-domain data on wind, soil, weather & seismic particulars, along with the assessor's property description ( and perhaps, Google Earth scans ) are sufficient to create a cost proposal, then I may still be able to go forward with my project.

You tell them the zip code
They will look up the wind snow and seismic data which is readily available in public domain
They will tell you the specifications on the ballast blocks.

[Hillsider]

Boulders Not The Problem

I looked at 30+ residential ground mounts in san diego. Many (including mine) in boulder territory. All used metal posts/poles with concrete footings. When impossible to dig thru a large boulder to make room for the footing epoxied rebar into bolder made the boulder part of the footing. I would get a few opinions to make sure you can't take a more traditional approach.

First, let me congratulate you for residing in San Diego County ( I lived in San Diego myself, from 1950 1958 ). I too reviewed many of the ground installs in your county, & downloaded the PDF drawing package on of the forum members attached to a forum post. I also reviewed the San Diego Standard Solar Plan, to compare with requirements in L.A. County, to qualify for an expedited solar permit application. The difference is like day-to-night. San Diego's requirements make no mention of the IBC ( International Building Code ), whereas L.A. county makes explicit reference to IBC Section 1805.3 --- the H/3 rule. Three Geotechnical Engineers who were queried by clients about enforcement of that rule, said "don't take a chance that the inspector wouldn't catch it". Based on the rule's definition of "bottom of slope", to allow a 5' setback from the edge of the down-slope for the North piles, would require that those footings would be driven 46' into the soil. Hence, my current retreat into the area of ballasted structures, which require no soil penetration.