Chilmark weighs backup power options

The town could end up with over a week's worth of backup power, or one to four hours' worth.

A diagram of what a full microgrid could look like. —Courtesy of Rob Hannemann

With climate change in mind, including the potential for severe storms, Chilmark is considering energy resilience options for its town center.

Chilmark could pursue three levels of resiliency, with the most resilient providing over a week of backup power in the event of an outage, and the least providing one to four hours.

The most resiliency would be achieved with a full microgrid. This involves powering the town hall, fire, and EMS buildings with solar energy, adding a battery, and connecting all of these features in a microgrid — a small-scale electricity network.

Chilmark could also choose to simply outfit the buildings for solar energy and add a battery. Adding a battery for the buildings could lower electricity costs for solar energy, and would add resilience for outages of up to 48 hours.

Chilmark could also choose the path of least resiliency, which would provide one to four hours of backup power in the event of a power outage.

The buildings in question are ready now for solar energy, says town energy committee chair Robert Hannemann. This would likely be the first step in any of the three options. “The wiring is all there to install solar panels, and we’re ready to go with that … We could put solar on all of the buildings or selected buildings … that’s one immediate option we can think about.”

Hannemann presented the options to the select board at its Tuesday meeting. How much resiliency the town ends up with also depends on how much money it wants to spend, he said. “The key question here, that I have no answer to, is how much resilience do we want going forward?” Hannemann asked. “Do we want, basically, one to four hours? Do we want one to four days? Do we want to prepare for a Hurricane Bob-type outage of a week or more? That’s a decision that is going to impact the costs of getting that resilience.”

That question, Hannemann said, is not for the energy committee to decide. He also suggested that Chilmark officials not make the decision alone. “I believe we need the emergency managers across the Island to understand fully where we’re going here,” he said.

Hannemann also told the board that these levels of resiliency are not mutually exclusive, and can be completed in phases instead of as one major project.

Hannemann says that the buildings will be connected at some point. “The firehouse, town hall, EMS building are all going to be, at some point, tied together from an electrical standpoint,” he told the board.

These different options largely come from work since June 2022 between Chilmark, Aquinnah, and the Lawrence Berkeley National Laboratory in Berkeley, Ca. This partnership is under the federal Energy Transition Initiative Program (ETIPP), which assesses the use of microgrids to increase energy resilience in town buildings.

Hannemann said that a full microgrid comes with multiple advantages. This microgrid would include a generator, as batteries cannot be counted on when the grid fails. Chilmark also has such a generator already, located in the EMS building parking lot.

And were the microgrid to fail, Hannemann said, a control system would isolate the microgrid so as to not affect the larger energy grid.

Hannemann added that the working partnership with the Lawrence Berkeley lab has allowed Chilmark to build models of its monthly energy use and peak electricity loads by day of the year, as well as to determine how much solar energy can be installed in the town center.

Once the town chooses a resiliency approach, it will also be able to determine its potential solar energy output, related capital cost estimates, and any operating costs for a microgrid. A scoping study to understand the cost and benefit of approaches for the town centers will also be completed midyear.

Adding a battery would yield some financial benefits, as power utility Eversource would be able to use the battery at times of peak energy use. “You can think of it as a way that Eversource can smooth out their needs and have a … smaller amount of capital on the Island. They’re really buying access to this for four or five times in the year when they need it,” Hannemann said.

With a battery, 15 diesel generators down-Island, used during peaks in power, could also be discontinued.

Who owns the buildings’ solar arrays will also affect costs. Owning and managing the solar arrays would provide the lowest possible utility bills, as the town would have access to the full power output of the arrays. However, installing and maintaining the solar power arrays could be a significant cost. “I’m not sure we’re prepared and have resources available to manage and maintain it, but we could. So we need to think about that,” Hannemann said.

Leasing the building’s roofs to a developer is a cheaper option, with which a developer would own and operate the solar power array for a period of time. In that arrangement, Chilmark would likely pay for the energy, but would pay a lower rate and receive a leasing fee.

Hannemann added that a solar array should last 25 years once installed.

Select board chair Bill Rossi asked Hannemann about the availability of government subsidies for the work.

“There are. Depending on what happens in November, they’ll continue to be available,” Hannemann said.


  1. leasing the roofs to a developer is A BIG MISTAKE!!!! the town should own the solar panels and any income from it. NO TO DEVELOPERS.

  2. I’m glad to see that the specter of climate change is being taken seriously, and preparations are moving in the right direction.
    However, my latest research and calculations indicate that both the economics and the battery capacity are in reality much better than indicated in your article.
    I have been delving deeply into this issue, and have just completed a comprehensive analyses of what it would take for me to convert my property to 100% solar power – become totally energy independent and self-sufficient, with enough PV panels and batteries, and enough solar-thermal and heat storage to stay fully functioning even through a week or more of no sunshine. In other words, I will never need fossil fuels or grid electricity again.
    And I will reduce my carbon footprint by 30-40 tons a year!

    My calculations show that the annual cost of the loan I will need, in order to do the conversion (including the cost of replacing/recycling the batteries after 10 years), will be less than what I will save annually by no longer needing to buy propane or grid electricity.

    By doing this, we will save more and more as the cost of heating fuels, gasoline and grid electricity keep rising.
    No grants are needed for Chilmark to do this. All you need is a loan at reasonably low interest.
    And since you know your energy requirements, and it’s easy to see how much solar potential you have available, it is also easy figure out how many PV panels and batteries you’ll need, and what that’ll cost. And what will installation cost?
    I’d be happy to show you my calculations and help you figure out the best and least costly way for you to reach your goal – reliable energy security no matter what, and profitable too.
    Onsite independent solar is definitely the most reliable and cost-effective way to go.

    • Anna! I’m thrilled to hear someone else saying this! Can you imagine the changes to our society when electricity becomes nearly free? The ramifications are enormous!!!
      My mantra: buy your OWN solar panels. Do NOT lease your roof.
      Solar panels on every roof!

    • Anna, your batteries could last 20-30 years or more if you care for them carefully. Use them in a 20 percent low state to an 80 percent high state. You can buy switches to do this for you automatically. Your batteries could last indefinitely. Does your system include a backup generator? Lowe’s sells them for around $3k

  3. For clarity could we get an explanation on how it is possible that a battery for 3 buildings in chilmark will allow the island to discontinue the use of 15 diesel generators

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