PROJECT INFO

Name: Water Treatment Plant Solar Photovoltaic Array
Owner: Chelmsford (Mass.) Water District
Cost: $2.88 million
Project delivery method: Design-build
Construction: May 2010 – November 2010
Project management team:

  • Chelmsford Water District
  • Massachusetts Department of Environmental Protection
  • Massachusetts Department of Energy Resources
  • Stantec Consulting
  • Contractor: Nexamp and Florence Electric
    Estimated annual savings:

  • $68,880 on electricity with 574,000 kWh of alternative energy
  • 405.7 short tons of carbon dioxide
  • The American Recovery and Reinvestment Act of 2009 couldn't have come at a better time for state and local authorities in Massachusetts.

    Two years earlier, the state had pledged to increase solar capacity at public facilities by up to 132 megawatts. At the same time, a water district was examining ways to conserve resources. The two goals dovetailed perfectly to qualify for the stimulus requirement that states devote at least 20% of their water and wastewater revolving-loan allocations to energy and water efficiency, green infrastructure, and environmental innovation.

    Today, the Chelmsford Water District's 3-mgd treatment plant in Crooked Spring has one of New England's largest solar photovoltaic arrays. The recently completed 485-kilowatt solar field is expected to supply about 55% of the plant's annual power requirements, but on any given day it may produce more than the plant needs. When that happens, the local electricity utility applies a credit to the district's bill.

    DESIGN-BUILD FOR TIGHT DEADLINES

    Electricity burns up to 40% of a treatment plant's operating budget. In 2007, to help local governments reduce pollution and save money, EPA and the Massachusetts departments of Environmental Protection and Energy Resources launched a pilot planning initiative to evaluate renewable and energy-efficiency options.

    Thinking back to Chelmsford Water District's operational evaluation, Environmental Compliance Manager Todd Melanson says “we could've made small changes like changing all of our light bulbs. But we knew that wouldn't get us where we wanted to be: reducing energy consumption 25% to 30% over the next 10 to 15 years.”

    Melanson and his colleagues had been attending quarterly energy roundtable discussions the state was hosting with the University of Massachusetts (UMass) Lowell. There they learned that although wind energy is more economical (see “Sea breeze” on page 35 of the July issue), most of the state's inland sites don't have the recommended 13-mph minimum velocity to be technically feasible. But Massachusetts does have sufficient insolation — the sun's energy incidence on a region in a calendar year — for photovoltaic power.

    In February 2009 — with passage of the economic stimulus just around the corner — the district engaged a graduate student from UMass Lowell's Renewable Energy Engineering Department to analyze shading and evaluate potential panel layouts at its mostly flat, 30-acre Crooked Spring site. The plant treated 596 mgd total in 2009 — well below its peak hydraulic capacity of 4.5 mgd — and its 150-hp, high-head pumps consumed 1.2 million kilowatt hours (kWh) of electricity at a cost of $127,000.

    The report concluded that ground-mounting panels at 22° F could produce 40% of peak hourly demand. That was enough to convince Melanson and the state that solar power was feasible.

    The stimulus gave Massachusetts $186 million for water and wastewater revolving loans. After deciding to use one-third to fully fund the 14 green projects the state's pilot program had identified, water authorities began looking for projects that could meet “shovel-ready” deadlines.

    The district's project was already planned and approved, so authorities fast-tracked the project using the two-year-old Chapter 25A procurement law, which allows for design-build.


    IT'S ALL ABOUT COMPROMISES

    The art and science of solar photovoltaic power

    Components: An array of cells, called panels, and an inverter.

    Operation: The panels convert the sun's radiation to direct current (DC), which the inverter converts to alternating current (AC). Whenever the panels produce more than a plant needs, the excess electricity is routed to the grid and the customer's bill is credited. When the sun's not shining, the grid supplies power conventionally.

    Considerations: The more radiation they receive, the more power the panels produce.

    Ideally, panels should face due south at an angle roughly equal to the latitude. To maximize production in the summer, when electricity's more expensive but the sun's farthest from the earth, a shallower angle increases the normal incident of radiation; i.e., the amount of sunlight that hits the panel perpendicular to the plane of the face of the panel.

    In reality, the tilt and azimuth are usually a compromise based on available area, site conditions, shading issues such as trees, power poles, and other panels, and architectural concerns.

    Another factor is response curve. Different types and sizes of panels react differently with different sun conditions and positions.

    The “perfect” installation would be in the desert facing due south tilted at the site's latitude. But you'd have to somehow transport that power to the consumer, who's probably nowhere near the installation. That's how you end up with rooftop arrays in Ohio that are facing southwest and tilted at 10 degrees.

    It's all about getting the best layout for a given application.



    CUTTING NEED FOR TRADITIONAL ENERGY IN HALF

    “Using the revolving-loan program with design-build was an ideal way to disperse the funds because we had so much experience with the bidding language, contracts, and getting contractors and cities together to move things forward quickly,” says Patricia Arp, Green Program revolving-loan coordinator for the Massachusetts Department of Environmental Protection. (See timeline sidebar.)

    Some pilot projects experienced difficulties with utility interconnections and unexpected shading concerns, but for the most part construction went smoothly.

    Because the design-build team was juggling new technology and new funding requirements, the state set aside 5% of the project budget — $141,400 — for contingencies like change orders. This foresight paid off.

    For example, a means for communication between the solar array and the plant's SCADA system was not included in the original design, since the system was designed to monitor just the treatment processes. Yet as the project neared completion, the team determined it would be useful to connect the solar components to the system so that operators could monitor the whole system remotely.

    They tapped into unused funds from project contingencies to cover the $46,000 cost of those connections.

    Currently, stimulus-funded loans are at work on 34 contracts that are expected to lower the state's energy consumption by 25 million kWh/year. That translates to 18,000 fewer tons of carbon dioxide annually.

    “If not for the stimulus, this project would've been three to five years down the road,” Melanson says.

    — Allan (george.allan@stantec.com) is a principal in the Westford, Mass., office of Stantec and helped the Chelmsford (Mass.) Water District manage the design and construction of the solar farm project.


    LESSONS LEARNED

    Four steps to a successful grant or loan application.

    Think outside the box. Chelmsford Water District Environmental Compliance Manager Todd Melanson and his colleagues doubted state authorities would consider preliminary plans for a solar photovoltaic installation as “shovel-ready.”

    Thinking fast, they turned to a local engineering school for a student to study the project's viability and potential economic benefits. They used the resulting report as a planning document to show how the installation could help lower public-sector energy consumption.

    Be proactive. Managers gave themselves a crash course in building, energy, and environmental compliance trends to identify the technologies best suited for their application and funding-program requirements.

    By having planning documents prepared and organized, they were able to meet the application deadline for a stimulus-funded revolving loan.

    Develop partnerships. Managers cultivated relationships with state environmental protection and energy resources department employees, met with local legislators, and attended educational initiatives sponsored by academia and utilities.

    “The way we went about this and used our resources, we were able to create a functioning cycle of how to get something like this project done,” Melanson says.

    Foreknowledge is forewarned. Explore all the possible contingencies of alternative technology. Have an electrical engineer review plans for utility interconnection. If there's another renewable energy system nearby it may affect your potential installaion. Determine what impact studies, upgrades, or other requirements you'll need to complete for project approval.