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‘The Engineered Difference’ Foundation Designs and Cost Comparisons for Panoche Valley Solar Project Phase I

Best Base completed extensive design work for the foundations required for Phase I of the solar array at the Panoche Valley project, generating designs for the Sun Edison, Solarflex, and Array Tech racking systems. The structural, geotechnical, and environmental engineering aspects were considered, as well as advanced supply-chain, local component-based manufacturing, installation, and pricing methodologies.

MKM & Associates (Santa Rosa) led an in-depth engineering effort, working with PJC & Associates geotechnical engineering (Cotati) and environmental consultant Sam Altshuler (Danville) to complete the foundations designs. The preliminary criteria, provided by the racking companies to perform the engineering, included the spacing of supports, panel layouts, panel angles, and preferred posts. Some wind tunnel test results were also supplied and used to determine alternate designs.

Four foundation designs for each racking system were developed: a Helical Anchor (rotary installation), a Wide Flange Pile, a Pipe Pile, and a Pipe Pile with accompanying wind test results (all vibration installation).

In summary, the installed cost of each of the four foundation designs, ranging from $11.70 - $22.96 per ft, is significantly less than the installed cost of a concrete pile, which can easily run over $45 per ft.

In addition, the total cost per foundation of the four designs ranges from $176 - $427 (with an average of $285), also significantly less than the $450+ total cost of the 10 ft. driven concrete pile previously assumed. This represents a difference, when multiplied by the hundreds of thousands of foundations necessary for all phases in the project, equating to tens of millions of dollars.

The designs utilized soil parameters as given in the geotechnical report by Engeo, dated March 26, 2010, project number 8924.000.000. The assumed solar support spacings (based upon information from the suppliers) were 13.33’ for Array Tech, 18’ for Solarflex, and 19.7’ for Osolar. Somewhat different foundation designs would occur if the solar racking systems were modified.

All structural work was performed in compliance with ASCE 7-05, 'Minimum Design Loads for Buildings and Other Structures.' Wind loads were developed using Chapter 6, Method 2, 'Analytical & Wind Tunnel Procedures,' or Method 3, ‘Wind Tunnel Procedures.’

Finally, these preliminary foundation designs are useful in determining overall costs of the three potential systems. Additional refinements can be done once a racking system is chosen, with all aspects of the refinements being considered so desired performance, cost, and installation objectives can be achieved. Foundation Specifications/Content/Costs Four foundation options were developed for each of the three companies providing racking systems. Specifications and accompanying costs vary due to requirements necessary to support each array. The first option is a helical anchor, made of a pipe with helical flights, tips, and ears necessary for rotary installation. The second, or wide flange option, utilizes steel sections designated by ‘W,’ and then depth and weight per foot of the section (e.g., W 8 x 10 designates a steel flange 8” in depth, weighing 10 lbs per linear foot). Options three and four utilize pipe piles and are designated by HSS (hollow structural steel) followed by the outside diameter and wall thickness (e.g., HSS5.563 x .258 designates a round hollow steel section with a 5 5/8” outside diameter, a wall thickness of .258 inches). All material is galvanized for corrosion protection.

Costs for the Phase I preliminary foundation designs given below include material and installation, and are to be used for estimating purposes only. Installation time is based on the use of one rig; two rigs would cut estimated time in half, three by two thirds, etc.

Panel Co Foundation Type Length Cost Quant. Total Cost Install Array Tech Helical Anchor 13.5 ft $310 18,000 $5.58 M 4.7 mo. Wide Flange Pile W8 x 10 15 ft $176 18,000 $3.17 M 4.9 mo. Pipe Pile HSS5.563 x .258 13.5 ft. $223 18,000 $4.02 M 4.9 mo.

With wind tunnel testing Pipe Pile HSS4.5 x .237 13.8 ft. $181 18,000 $3.26 M 4.9 mo.

Solarflex Helical Anchor 14.7 ft. $328 6,400 $2.10 M 2.0 mo. Wide Flange Pile W 10 x 12 17.5 ft. $239 6,400 $1.53 M 2.2 mo. Pipe Pile HSS6.625 x .280 14.7 ft. $295 6,400 $1.89 M 2.2 mo.

With wind tunnel testing Pipe Pile HSS6.625 x .25 14.0 ft. $258 6,400 $1.65 M 2.2 mo.

Sun Edison Helical Anchor 17.5 ft. $427 10,000 $4.27 M 3.0 mo. Wide Flange Pile W 10 x 17 20.0 ft. $332 10,000 $3.32 M 3.2 mo. Pipe Pile HSS8.625 x .250 17.5 ft. $357 10,000 $3.57 M 3.2 mo.

With wind tunnel testing Pipe Pile HSS6.625 x .250 16 ft. $288 10,000 $2.88 M 3.2 mo.

Environmental Engineering Best base is the only product company today to supply a carbon footprint analysis for every installation, a custom report detailing the project’s carbon savings when compared to alternative foundation designs. Based upon a model developed by recognized environmental engineer Sam L. Altshuler, the analysis performs production cycle CO2 emissions and cost savings calculations relating specifically to a structure’s foundation, then quantifies and documents accompanying carbon reductions.

2 A preliminary review of the environmental attributes considered and quantified (in relative order of importance) for the Panoche Valley project are:

 carbon footprint  noise  site restoration  criteria pollutants (mainly vehicle emissions and windblown dust)  water quality

The helical anchor should have the minimum environmental impact, driven concrete piles the most, with lower noise, air pollutant emissions, and potential impact on water quality and native flora and fauna. Potential worker and public health impacts are also likely lower compared to driven piles or drilled piers.

Conclusions/Recommendations The four foundation designs given are engineered to exceed all performance criteria. Each is also very environmentally friendly, and will provide a superior adjunct to any Environmental Impact Report. And, since every power project will eventually be decommissioned, it is significant that helical anchors, wide flange piles or pipe pile designs ‘come out as easily as they go in.’

Engineering also supplied remarkable insight into the material make up of each design, providing the ability to develop extremely cost effective solutions – especially when compared to driven concrete piles. For example, if the total per pile cost for each wide flange solution is added ($176, $239, and $332) and then averaged ($249), it is significantly less than the estimated total cost of $450 for a 10 ft. concrete driven pile.

To go one step further, even if the highest wide flange pile cost of $332 is taken and multiplied by the 10,000 foundations necessary for the Sun Edison system ($3.32 million), it would still be $1.18 million less than if 10,000 concrete piles were installed at a cost per unit of $450 and a total of $4.50 million.

In terms of recommendations, the obvious consideration involves vibration vs. rotary installation, as the costs associated with producing a helical anchor – although less than a driven concrete pile – are slightly higher than either the wide flange pile or pipe pile vibrated into the ground (Note: all four designs take approximately the same amount of time to install, and are all quicker than driven concrete piles).

Finally, the primary focus of every project seen seems to be on what’s ‘above’ ground, and what’s ‘below’ is often considered unimportant. However, in the case of the Panoche Valley project, there will be hundreds of thousands of foundations necessary equaling tens of millions of dollars, and the engineering and product management/delivery process necessary to optimize the designs in terms of performance and cost are critical elements in the project.

The Best Base core competency centers on all aspects of the foundation, our business to bring 20+ years of expertise to this market. Our structural, geotechnical, and environmental engineering approach, along with our supply-chain, local component-based manufacturing, installation, and pricing methodologies, are key elements in our product development & delivery process, and differentiators for our offerings.

3 Panoche Valley Solar Project Sample Foundation Design

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4 Sample Connections of Foundations to Solar Racks