103-Attachment B.pdfSolar Power Generation Site Viability Evaluation -
City of Cupertino
SITES:
Corporate Yard Parking Lot
Quinlan Community Center
City Hall Parking Lot
PREPARED BY
IN PARTNERSHIP WITH
CH2MHIL 1
JUNE 2, 2010
1.0 Solar Analysis and PV System Potential Evaluation
The solar analysis evaluation is based upon information provided by the City of Cupertino (City),
including original/as-built design drawings and LiDAR data. Photovoltaic (PV) system energy generation
and AC capacity are estimated using PVWatts v.I by the National Renewable Energy Laboratories,
climate data San Francisco, DC to AC derate factor of 0.77, 10 degree tilt, and azimuth of due South.
Solar radiation is calculated using the ESRI Solar Radiation Tool and Critigen/CH2M HILL's S.A.F.E.
Solar Mapping Tool.
The results of the solar analysis are summarized below in Table 1.
TABLE 1.
PROJECT DETAILS FOR PHOTOVOLTAIC SYSTEMS FOR SITES IDENTIFIED BY THE CITY OF CUPERTINO
�Pl/ Syttern Capacity
[kW Alternating Current
Annual kW hour (kWh)
Site
Location
(kWAc)]
generated by PV SY+e#ern
Corporate Yard Parking Lot
10555 Mary Avenue
331.25
450,502.50
Quinlan Community Center - Roof
10185 North Stelling Road
138.29
188,067.60
Quinlan Community Center -
10185 North Stelling Road
103.36
140,564.16
Parking Lots
Quinlan Community Center -
10185 North Stelling Road
241.65
328,631.76
Total of Roof and Parking Lots
City Hall Parking Lot
10300 Torre Avenue
349.27
475,005.02
All figures included in this evaluation are aerial images of the facilities with indicating areas where a PV
system can be located to maximize the system capacity. Solar radiation hotspots are displayed on the
facilities as a Yellow -Red gradient. Yellow areas represent an annual average of at least 6 hours of solar
access a day while Red areas represent an annual average upwards of 11 hours of solar access a day. The
areas shown reflect the building data represented in Table 1 above. Also shown are the potential systems
on future covered parking lots or structures that could be installed.
SOLAR POWER GENERATION SITE VIABILITY EVALUATION - CITY OF CUPERTINO
1.1 Cupertino Corporate Yard Solar PV Recommendations
Decreasing the tree coverage over the East parking canopies would allow for greater solar access and
further increase the PV system size and annual return.
FIGURE 1.
CUPERTINO CORPORATE YARD, 10555 MARY AVE, CUPERTINO, CA — AREAS FOR PROPOSED PV SYSTEM PER THE MAXIMUM
ROOF SPACE AND PARKING AREA AVAILABLE WITH A SUITABLE SOLAR RESOURCE
(Source: S.A.F.E. Solar Mapping Tool, CH2M HILUCritigen)
SOLAR POWER GENERATION SITE VIABILITY EVALUATION - CITY OF CUPERTINO
1.2 Quinlan Community Center Solar PV Recommendations
Decreasing the tree coverage over the parking lot southwest of the building would allow for greater solar
access and further increase the PV system size and annual return.
FIGURE 2.
QUINLAN COMMUNITY CENTER, 10185 N. STELLING RD, CUPERTINO, CA — AREAS FOR PROPOSED PV SYSTEM PER THE
MAXIMUM ROOF SPACE AND PARKING AREA AVAILABLE WITH A SUITABLE SOLAR RESOURCE
(Source: S.A.F.E. Solar Mapping Tool, CH2M HILUCritigen)
SOLAR POWER GENERATION SITE VIABILITY EVALUATION - CITY OF CUPERTINO
1.3 City Hall Parking Structure Solar PV Recommendations
The City Hall Parking lot is surrounded by trees which severely inhibits solar access to canopies on the
East edge of the parking lot. Decreasing this tree coverage will further increase the PV system size and
annual return.
FIGURE 3.
CITY HALL PARKING LOT, 10300 TORRE AVE, CUPERTINO, CA — AREAS FOR PROPOSED PV SYSTEM PER THE MAXIMUM ROOF
SPACE AND PARKING AREA AVAILABLE WITH A SUITABLE SOLAR RESOURCE
(Source: S.A.F.E. Solar Mapping Tool, CH2M HILUCritigen)
SOLAR POWER GENERATION SITE VIABILITY EVALUATION - CITY OF CUPERTINO
2.0 Structural Facility Evaluation to Support the PV System
The structural evaluation is based on information provided by the City, including original/as-built design
drawings and the proposed PV system described above. The City expressed its preference to use
penetrating PV systems for all facilities.
The intent of this evaluation is two -fold. The first is to determine the suitability of the existing facilities to
support the installation of the proposed PV system per the requirements of Chapter 34 of the 2007
California Building Code (CBC). The second is to outline the structural design requirements for new PV
Canopy Shade/Support structures as well as to identify structural design considerations for these
structures. This evaluation is limited to the ability of the structures to accommodate the self weight
contribution of the PV system.
The results of the structural evaluation are summarized below in Table 2.
TABLE 2.
SUMMARY OF STRUCTURAL EVALUATION
Loads
Available to
Adequaoy tc
Support Weight
Support
of PV/Systems
Proposed PV/
Facility or Shedd Structure
Description
Location
psf
System?
Corporate Yard Parking Lot Shade
New
10555 Mary Avenue
N/A
Adequate
Structure
Quinlan Community Center Building
Existing
10185 North Stelling Road
12
Adequate
City Hall Parking Lot Shade Structure
New
10300 Torre Avenue
N/A
Adequate
NOTES:
The estimated self weight PV loading is 5 pounds per square foot which assumes SunPower 315 solar panels attached to the supporting
roof/canopy structure with the SunPower SF or SM Panel mounting system.
2 See Section 2.1 for Additional Facility Considerations.
In addition to this evaluation, a detailed structural analysis for the entire building/canopy structure(s) will
need to be performed after the layout of the new solar PV system is determined. The analysis will be
preceded by a field inspection by a Structural Engineer to assess condition of the existing construction
and magnitude of existing dead load. The analysis will include gravity, wind, and seismic load
considerations in accordance with the requirements of the 2007 CBC, and specifically Chapter 34 for
existing structures. The final type and layout of the solar PV systems may be affected by the structural
capacity of various building elements as determined by the detailed structural analysis. This analysis will
most likely occur during the design phase of the project and will be included with the permitting and
construction documents package.
The City of Cupertino currently adopts 2007 California Building Code. The Code requires building and
canopy roofs be designed for a minimum roof live load of 20 pounds per square foot (psf), as well as dead
load of roof construction, framing members, building services and finishes suspended from the roof, and
roof top equipment. As per code the 20 psf live load can be reduced for the roof members supporting
tributary areas of more than 200 square feet. The minimum reduced live load is 12 psf for the members
with tributary areas of more than 600 square feet. The code prescribed ground snow load for Cupertino,
CA is 0 (zero) psf.
SOLAR POWER GENERATION SITE VIABILITY EVALUATION - CITY OF CUPERTINO
The code's definitions of the roof live loads are:
2007 CBC Section 1602.1: "Those loads produced (1) during maintenance by workers, equipment
and materials; and (2) during the life of the structure by movable objects such as planters and by
people."
It is expected that no additional roof live load could be imposed on the areas occupied by the PV systems.
Based on the code interpretation, it is concluded that the design roof live load can be counted towards the
loads available to support weight of the solar PV systems mounted directly on the roof.
This evaluation addresses the gravity load capacity of the structures to support the proposed PV system.
The equivalent uniformly distributed load of a particular PV system is used to compare with the total
design roof live load of the structure to obtain a general indication of the structure's capacity to support
the solar PV installation. The actual load distribution on the roofs will depend on the type, layout,
geometry, and weight distribution of a selected solar PV system. Additional wind and seismic loads due
to solar PV installation will also be imposed on the existing structure. The magnitude of these loads will
depend on the layout, wind characteristics, and weight of the systems.
Wind load analysis was not included in the scope of work of this assessment. Adding significant projected
area to existing structure roofs as with angled solar panel systems will increase wind load on the structure.
The wind load resisting system of existing structures may be required to be upgraded to meet the code
requirements for the increased wind loads. It is foreseeable that when specifying the PV array components
(mounting system, modules, etc.) and layout, the wind load will need to be considered.
Seismic load analysis was also beyond the scope of this assessment. The building code requires seismic
design for the structures in the City of Cupertino. Review of the structure drawings indicated that the
older structures were designed to the previous CBC and Uniform Building Code (UBC) Seismic
requirements. The newer structures were designed to the more recently adopted CBC Seismic Design
requirements. If the seismic base shear is increased by more than 5% the code requires upgrading the
seismic load resisting system to meet the code. It is foreseeable that when specifying the PV array
components (mounting system, modules, etc.) and layout, the seismic load will need to be considered.
2.1 Additional Facility Considerations
Parking Lot Shade Structures
Parking lot shade structures are planned for the following sites:
• Corporate Yard
• City Hall
The shade structures will be new and engineered to accommodate the PV system and existing parking lot
layout. The superstructure and foundations must be designed for the vertical and lateral requirements of
the 2007 California Building Code for roof live load, wind, and seismic. The minimum roof design live
load will be 20 psf and may be reduced to for members with tributary area greater than 200 square feet.
Material construction options include steel, concrete, and Fiberglass Reinforced Plastic (FRP). Steel
framing is typically the preferred and most cost effective material used for this type of structure.
Consideration must be given to protect the support columns for these structures from vehicular traffic.
This may consist of strategically placed concrete curbing and or Bollards.
SOLAR POWER GENERATION SITE VIABILITY EVALUATION - CITY OF CUPERTINO
3.0 Electrical Facility Evaluation to Support the PV System
The electrical evaluation is based on information provided by the City, including original/as-built design
drawings and the proposed PV system described above.
The City Hall, Community Hall, and the Library are co -located at the same site, each with their own
electrical service entrance. The proposed PV array was evaluated in Table 3 as a single PV system. This
349 kW system is too large for a tie-in to the Community Hall, is adequate for a tie-in with City Hall, and
it is recommended that it be tied into the Library because of the larger service entrance size and greater
energy usage than City Hall.
The other option for the Civic Center complex is to separate the PV arrays into up to 3 separate systems
and tie into multiple buildings. This option will allow more flexibility to closer match the ideal PV system
size for each of the buildings, which as a rule of thumb is 75% of the annual kWh used at the electrical
service. The disadvantage of this option is that the hardware will likely cost more.
SOLAR POWER GENERATION SITE VIABILITY EVALUATION - CITY OF CUPERTINO
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