[RE-wrenches] Off-grid ground mount: Can it be done cheaper

[Kent Osterberg]

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
>
>
>