Presentation at the 2019 Massachusetts Sustainable Communities and Campuses Conference on March 29, 2019 in Cambridge, MA

1. CITY OF CAMBRIDGE
Municipal Facilities
Improvement Plan
Photovoltaic InstallationsFletcher Maynard Academy 76.6kW
Completed 2018

2. Agenda;
1. Existing conditions analysis
• Daylight
• Comfort
• Ventilation
2. Temporary solutions
3. Strategies
“The goal of the Municipal Facilities Improvement Project
is to use whole building thinking to define a plan for the
City of Cambridge to provide and maintain high-
performance buildings for staff, occupants, the public and
the environment.”

3. Agenda;
1. Existing conditions analysis
• Daylight
• Comfort
• Ventilation
2. Temporary solutions
3. Strategies
The philosophy of looking at a building as a
series of interrelated systems and buildings as
part of an integrated portfolio.
A high performance building is not only low
carbon and energy efficient, but also provides a
comfortable and healthy indoor environment, is
resilient, easily maintained and responds to the
larger community it serves.
WHOLE BUILDING THINKING

4. City of Cambridge Initiative Timeline
• 2012 Municipal Solar Feasibility Study by CDM Smith
• “Rooftop review” identified the top 15 City-owned sites
*See Dept. of Energy Solar Mapping Resources
• 2015 Municipal Facilities Improvement Plan (MFIP)
• 2015 Net Zero Action Plan
• 2015 5% Onsite Renewable Goal by 2020
• 2016 Cambridge Community Shared Solar (CSS) - Additional Site Feasibility
Review by Cadmus
• CDM’s shortlist of 15 City-owned sites starting point.
• Phase 1: First Street Garage - carport CSS project.
• Phase 2: Feasibility of rooftop solar development
• 2016 MFIP projects evaluated solar in existing building portfolio

6. Cambridge Solar Installations
Photovoltaic (PV) systems in operation include:
MLK School
670.3kW
Main Library
66.6kW
DPW Frazier Building
2.5kW
Cambridge Rindge and Latin School
72.8kW
Sullivan Water Treatment Plant
840.3kW
Frisoli Youth Center
3kW
Kennedy Longfellow School
175kW
Russell Youth and Community Center
36.1kW
Citywide Sr. Center
12kW
Fletcher Maynard School
76.6kW
859 Broadway City Hall Annex
26.5kW

7. Cambridge Solar PV in Construction or Design
PV Arrays in construction or design:
King Open School
2.386.5kW
Graham and Parks School
219kW
Russell Youth and Community Center
Expansion
53.3kW
Taylor Square Firehouse
24.4kWac
• City is on target to exceed 5% goal by 2019, one year ahead of schedule with the opening of the King Open School.
• Several additional arrays are under consideration, as the City looks beyond 2020 toward Net Zero Action Plan and
GHG 2020 and 2030 emissions reduction targets.

8. Solar Photovoltaic (PV)
Installation….. Parts and Process
Site Selection
Owner or with Designer
Designer
Selection
Solar (Electrical)/
Architectural/Structural
Design Documents
Feasibility Study
Schedule
Budget & Funding
Eversource Evaluation
MassACA Registration
Bidding &
Contracting
Inspectional Services,
Eversource & MassACA
Commissioning
(Cx)

9. Getting Started….Design Considerations
• Electrical Infrastructure Assessment
• Network or Radial Grid
• Historic Buildings
• Occupied Buildings
• connect to the grid; safety; access; staging area; parking.
• Structural Assessment
• Coordinate PV design with structural engineer.
• Uplift from wind is critical.
• Allowable loads may vary on a building.

10. …additional Design Considerations
• Data Acquisition System (DAS) Reporting
• Shading assessment and tree management
• Orientation & Roof Edge Setbacks
• Roof Warranty
• Access to all roof levels for O&M
• Ballasted vs. mechanical fastening for installation of racking
• DC or AC runs along rooftop – Locate inverters accordingly. Essential
to manage wire runs & identify trip hazards in snow with flags.
• Cx is essential

11. Case Study: Kennedy Longfellow School (Klo) 175kW
Initial design was peer reviewed by SDA and
nearly doubled size of array.
Assess existing conditions
• Occupied school
• New roof
• Tree canopy
• Structural integrity of the roof
• allowable psf may vary
• Ballasted or mechanically fastened
• Wind uplift
• Electrical infrastructure – work with utility
• network vs. radial grid
• Condition of switchgear
• Location of utility required AC
disconnect
• 521 CMR MAAB – accessibility triggers
Tree shading Roof access
Loading varies
Edge Setback New roof
Shading

12. Case Study: Kennedy Longfellow School PV Array Layout
• Allowable structural loads
varied 5.9 to 8.6 psf with no
structural modifications
undertaken.

13. Case Study: Kennedy Longfellow Design 175kW
• Occupied building with limited
access
• Summer construction
• Followed installation of new roof
with 30 year warranty.
• No electrical upgrades – network
grid
• MAAB upgrades - toilet room &
entrance.

14. Case Study: Kennedy Longfellow School (KLo) 175kW
• East/West facing panels
• Minimized DC runs
• Ladders provide for O&M
• Trees trimmed prior to
construction & ongoing
scheduled maintenance
• Roof inspected at start and
finish - warranty requirement.

15. • 12kW
• Structural upgrades at underside of deck to accommodate wind
uplift
• Network vs. radial grid connection
• Design by Arup
• Electrical Contractor subconsultant Solar Design Associates
refined design in shop drawings
Citywide Senior Center
Rooftop Patio PV Canopy 12kW

16. Citywide Senior Center
Rooftop Patio PV Canopy 12kW

17. • Participator Budget Project
• Array size of 33kWac was
increased to 66.6kWac
• Larger capacity panel
• additional panels
• Newer roof
• Occupied building
• Adjacent to High School
Cambridge Main Library
System Size: 66.6kW ac

18. • SunPower 360 W PV modules
• Helix mounting racks
• SolarEdge P800 DC-DC optimizers
(1 optimizer per 2 PV modules)
• 33.3kWac SolarEdge inverters.
• East/West panel orientation
Cambridge Main Library
System Size: 66.6kW

19. Thank you