Martin Luther King Jr. School
CED Greentech held the distinct honor of supporting the development of the solar photovoltaic (PV) system at Martin Luther King, Jr. School in conjunction with Wayne J Griffin Electric Inc. (WJGE), Zapotec Energy, and the project's solar designers from In Posse. Located just across the Charles River from Boston, the Cambridge MLK school represents the city's commitment to both education and sustainable construction. Although providing a safe and productive learning environment was the paramount goal of the project, energy efficiency and energy conservation were areas of intense focus during the planning and construction of the building. In addition to industry-best plumbing and HVAC practices, the use of geothermal wells and a gray-water storage system is in the process of helping the school building achieve LEED Platinum certification. Going beyond energy conservation, from the onset the project called for solar energy generation to take place on site to offset as much of the energy to be consumed as possible. Altogether, the new school is over 80% more efficient than the average American school.
To aid in design and engineering support WJGE worked closely with CED Greentech who brought in Zapotec Energy to assist and ensure the needs of both the district and the building were met. In contrast to a typical ground or flat roof installation, the MLK plans called for multiple subarrays on roofs of varying heights, solar awnings and large rooftop pergolas to provide shade to outdoor space below. All together, the consortium of In Posse, CED Greentech, WJGE, and Zapotec Energy implemented a cutting edge 592 kilowatt (kW) PV system.
In September of 2014 initial meetings between CED Greentech and WJGE were comprised of evaluating the bid specifications called for by the school district. The design was developed to hit aggressive energy offset goals using best-in-class materials. Unfortunately, the initially-proposed solar modules were not commercially available within the project's timeline, causing the need for a mid-stream pivot in the design. Further, during the design and approval phase for the school project there emerged on the market a new breed of inverter -- the commercial string inverter -- that offers numerous benefits over traditional central inverters, including lower cost, increased safety, increased system performance, increased design flexibility.
Working in harmony with our manufacturer partners and the project's designers and owner, CED Greentech proposed a design shift that would satisfy the project's goals and budget constraints while providing the district with visually striking PV arrays. The first change was a transition from central inverters to a distributed commercial string inverter architecture. Under this design each roof array and awning was strung to its own Solectria transformerless three-phase inverter. The design flexibility and production gains afforded by the use of string inverters makes the Solectria PVI-TL a perfect fit for the multiple arrays on the MLK building.
The next major decision centered around module selection. Despite numerous roof lines and arrays, space was still limited. Highly efficient and energy dense modules would be needed to make a significant impact on the school's projected energy consumption. Sunpreme modules offered desirable power characteristics at the best price tag for the number of watts the school needed to install to accomplish its energy offset goals.
“There was only one panel capable of meeting the energy production requirements within the constraints of available rooftop space, timeframe, and budget – Sunpreme’s Maxima GxB370,” noted CED Greentech President Stuart Rentz. With the commitment of their full engineering team, Sunpreme accelerated production of the 72-cell panel, an astounding 370 W bifacial frameless module, for this project. Bifacial panels absorb light from both sides to increase energy yield. Over 1,500 of these high energy density panels were installed to meet the project requirements.
The MLK project represents perhaps the most challenging solar project pursued in the City of Cambridge to date. With the help of Perkins Eastman, In Posse, Wayne Griffin Electric, CED Greentech, and Zapotec Energy, the MLK School now enjoys a cutting edge solar system that will serve as a benchmark for future Cambridge Schools’ projects and other rooftop solar projects across the country. This outcome would not have been possible without the teamwork and successful collaboration between all involved. All 1,599 panels and 21 inverters successfully came online in January, 2016.
Cambridge, MA 02139