Solar Foundation Support 1

[cmagrp]

I'm looking for a little help and guidance.

Under full disclosure, I am doing a research project to understand the different foundation / anchoring methodologies for solar farms / panel installation (non-roof) and could use some expert insight.

What are the primary methodologies used? (helical, driven steel, other?)
Why?
When to use which? (I imagine it can be site specific, but what are key criteria for each type)
What is the cost differential (or cost), perhaps by pier or by foot?)

Or, do you know of any sources where I could find some of this info?

thanks

 

[dgillette]

No actual experience with it, but I would expect that the foundations would be controlled more by pull-out than by bearing capacity, in which case helicals might be good and cost-effective. PV panels don't weigh much, and they have a lot of sail area.

You might try the National Renewable Energy Lab (

http://www.NREL.gov)

to find out what theirs are on. They are in a very windy location and might have learned something the hard way at some point.

My own PV system is anchored in place by a 3-bedroom house. So far, so good, although our place isn't as windy as NREL is. The house has an advantage over helicals because it also provides living space, which helical anchors do not.

 

[cvg]

I have experience with this, but most of this work has non disclosure agreements in place. Much of it can still be found with an internet search...

However, it is very similar to a large billboard or freeway sign. You have a large object on a pole. Wind, seismic, scour are the primary forces acting on it. Limitations include depth to bedrock. Cost is driven by time required for contractor to install. Preferred method will be cheap, quick to install, deep enough to resist overturning and also to not vibrate when it is windy.

 

[cmagrp]

I can understand projects being under non-disclosure, but why benefits of one type of method vs. another (helical vs. driven steel pile) and why cost variance (i.e. one is 25% more than another, on average)?

Any detail would be helpful. Haven't been able to find anything re: why one method vs. another for solar or price variance information on web. Have found definitional information on the methodologies

 

[cvg]

I have seen comparisons of driven steel vs cast in place concrete. the driven steel was preferred. I believe these were vibrated in place and were finned. I don't know what the difference in cost was.

 

[jhoulette]

I have designed foundations for similar light structures with a high profile.
For the smaller structures a concrete pad with sufficient weight has worked best. But when the needed weight starts to become unreasonable I have used screw piles or helical piers. I prefer screw piles (continuous round pipe with helix) over the typical helical pier (sectional, square rod with helix).
I'm assuming wet set or post installed bolts connect the solar panels base to the foundation, would be really slick if you could eliminate any concrete caps if using screw piles/helical piers. A steel base with slotted holes to allow for adjustments in dimensions.

Jim Houlette PE
Web:

http://www.evstudio.us

Online Magazine:

http://www.evstudio.info

 

[TDAA]

Same as ANY structure:

What is cheap, readily available, willing to be designed by the structural, and easy to install.

 

[jhoulette]

As luck would have it, I was just asked to design a foundation for solar panels on ground in Boulder Colorado (high wind). When doing some research to determine the best foundation I learned about AB Chance's lighting foundations. A steel screw pile/helical pier with a larger diameter to resist overturning, a variable base plate to allow for easy bolted connections, and a slot on the shaft to allow for wiring. I'm impressed so far. Learn more at

http://www.abchance.com/lighting

Jim Houlette PE
Web:

http://www.evstudio.us

Online Magazine:

http://www.evstudio.info

 

[scottiesei]

Most of the ground racks we have designed have been with concrete foundations due to owner request. When the overturning became large, we went with combined footings to connect adjacent columns. Typically, the actual panel supports limit the span of the beams or spacing of columns (we use mostly Aluminum support structures). In most cases, we need ground supports every 5'-10'. I have not designed racks with helicals but I like the idea. I think helicals would provide a much higher uplift resistance per driven depth over driven piles. If you need any additional assistance, let me know.
Scott

http://www.dbssinc.com

 

[ranlgre]

I've been doing some design on a field in AZ, the company I found most impressive was Ram Jack. They have a screw together connection instead of the conventional blot through. If the piling is more than one extension this lessens the lateral flex. They've started a subdivision dedicated to renewable energy and have a lot of interesting items on their website

http://www.ramjack.com

as well as their solar specific site

http://www.solarwindfoundation.com

 

[sunny7uc]

There is a geotechnical company

http://www.haywardbaker.com,

they are a large design-build contractor. they can do dynamic compcation, helical piers, steel piles, or can provide other economical solution depending on site conditions. I had good luck with them as they do have several techniques.