William,
There are auger mounted systems that don't require any concrete. For
locations with suitable soil, they probably save some time and are a
little less expensive than concrete. But it takes a substantial
structure to withstand 85 mph, or greater, winds. There's no getting
around the physics of that.
Oregon also requires PV mounting structures to be engineered unless they
meet conditions prescribed in the solar installation code. The
prescriptive rules only apply to roof mounted systems, so ground mounts
require a structural engineer to sign off on the construction plans.
Kent Osterberg
Blue Mountain Solar, Inc.
www.bluemountainsolar.com
On 3/24/2012 10:29 AM, William Miller wrote:
Daryl:
Thanks for the photos and description of the mounts you are
installing. We have installed many of the DPW ground mount systems in
similar configurations.
http://millersolar.com/MillerSolar/Portfolio/ground-mount/engineered_ground_mount.jpg
We are realizing two things:
1. Concrete footings of any type are expensive. The cost of
excavation, forming and concrete really adds up.
2. For off-grid, when the module tilt angle increases to 45 degrees,
the foundations need to be substantial. During one install we had our
heavy PV trailer blow over due to high winds. We decided to have the
foundations reviewed by an engineer and when we received the results,
we had to go back and double our piers and strut. We had bid the job
so the updates came out of our pocket. See:
http://millersolar.com/MillerSolar/Portfolio/ground-mount/full_size_photos/engineered_ground_mount.JPG
We are now required by the AHJ to provide a wet stamp from a
structural engineer for every PV structure over 6 feet in height.
This means every off-grid. We know the engineers will require massive
foundations which will cost a lot. I am looking for a cheaper way to
install these racks. I have not found it yet.
Thanks for your input.
William Miller
At 04:37 AM 3/24/2012, you wrote:
William,
I'm attaching a picture of a system we just completed in Eleuthera
using DPW racks on concrete pilings. We tied the pilings and rebar
reinforcement into the limestone bedrock with rebar down 16 inches and
used 12 inch sono tubes as forms.
We do a lot of ground mounting since our summer work is mostly in New
England and snow removal is always a factor. I have two pole mounted
arrays at my home, but it is the most expensive option, and therefore
do a lot of this type of ground mounting. We also have an economical
"cribworks" type structure made from solid railroad ties and weighing
in at about 2800 lbs each that we will sometimes offer to customers in
off grid situations.
Daryl
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