Old Rutland landfill site of new solar microgrid

A utility-scale microgrid is underway in Rutland, Vermont’s largest utility announced Tuesday.

A solar panel and battery storage system at Northern Reliability’s test center in Waitsfield. Photo by John Herrick/VTDigger

A solar panel and battery storage system at Northern Reliability’s test center in Waitsfield. Photo by John Herrick/VTDigger

Green Mountain Power (GMP) is constructing a 2-megawatt solar facility on a closed landfill in Rutland, and includes 4 megawatts of battery storage. The company said it expects the project to be completed by December.

The stored energy will be used to shave peak electricity demand at times when solar power is less available – dusk, cloudy afternoons and winter months – and provide emergency backup power for Rutland High School during outages.

GMP says the project, called the Stafford Hill Solar Farm, could theoretically run as a microgrid indefinitely within the lifespan of the equipment. That means the project operates on a closed loop, independent of the region’s electric grid.

The utility designated Rutland City the “Solar Capital of Vermont,” but since then, several larger proposed projects have caused controversy over how solar arrays are sited. But this project’s location on a landfill is a productive use of land because it has not been used for decades, GMP says.

The 9.5-acre landfill closed in the 1990s. The company said the site has settled sufficiently to develop a solar array, and because the landfill has been closed for so long, it no longer emits biomethane, which is often used as another means of energy generation from landfills.

Darren Springer, deputy commissioner of the Department of Public Service, said the project will provide the region with readily available solar power. Typically power grid operators ask utilities to burn fossil fuels to meet high electricity demand on short notice, which, Springer said, is costly and emits greenhouse gases.

The company will hook up the high school to serve as an emergency shelter and will consider expanding to other facilities in the area.

Kristin Carlson, the spokesperson for GMP, said the project is a step toward making communities more resilient to the effects of climate change that can damage electrical infrastructure and create power outages.

GMP has not decided how to account for the renewable energy certificates for the power generated by panels and stored in the batteries. Springer said the generated power could be sold on the market as renewable power, but regulators are still deciding how to account for power coming from the batteries.

Josh Castonguay, of Green Mountain Power, said the lithium ion and lead acid batteries will have to be replaced about every eight to 12 years, depending on how often they are drained and recharged. He said the batteries would be used as little as possible for longevity.

Castonguay said the company is asking the region’s grid operator, ISO New England, to pay for the value battery storage offers for power load management. Having renewable power readily available makes it easier for grid operators to smooth out spikes in electricity demand on short notice.

The company estimates the total project cost for the solar and storage components at about $10 million. GMP received money from the U.S. Department of Energy and the state’s Clean Energy Development Fund to support the project.

South Burlington-based Dynapower will provide the batteries and White River Junction-based commercial and utility solar engineering firm groSolar will provide the panels. State regulators approved the project on July 14.

John Herrick

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  • Matt Fisken

    And to think, only two months ago I was being asked, “who do you think would undertake [building a microgrid]?”


    Although, it’s nice to see GMP prove me wrong, that “utilities are not interested.”

    Hopefully it is understood that in situations where the school/shelter is reliant on battery power means avoiding high wattage appliances like ovens, microwave ovens, toasters, etc.

  • Moshe Braner

    This report leaves us with more questions than answers. First, how large is the storage system? It says “4 MW”. That would be 4 million watts, a measure of power, not energy. E.g., if that system can really output that much instantaneous power, it could simultaneously run 4,000 toasters, each using 1,000 watts. But for how long? If it is a 4 MWH system, i.e., 4 million watt-hours, a measure of energy not power, then it could run those 4000 toasters for one hour. That is, if it can deliver that much power at once. Or it could run, e.g., 400 such toasters for 10 hours, delivering only 400,000 watts of instantaneous power, and so forth. The conflation of power and energy units is rampant in reports that have anything to do with electricity, please try and keep them straight. In this case, the official blurb from GMP http://www.greenmountainpower.com/innovative/solar_capital/stafford-hill-solar-farm/ also only says “4 MW”, so I’m still mystified. The reporters should have asked GMP for a clarification on that.

    Moreover, the article says “The stored energy will be used to shave peak electricity demand at times when solar power is less available – dusk, cloudy afternoons and winter months…” That’s nice, but to achieve that, much of the energy stored in the batteries during the sunny hours will need to be fed back to the grid at other times. This conradicts the other statement, that “the batteries would be used as little as possible for longevity”.

    Moreover, if the storage is really going to be used for “peak shaving”, which is the only economic reason for the investment, other than emergency backup power, then the system must feed into the larger grid, and cannot be an isolated microgrid. It could still be isolated during outages, to keep the emergency shelter humming with refrigeration and lighting (but not toasters). It could also keep heating systems at the shelter running, as long as their main fuel is something else (wood pellets or chips, propane, oil, etc) and enough of it is stored on site.

    • Moshe,

      Regarding lithium-ion batteries, GM uses only 65% of the 16.5 kWh battery capacity of the Chevy Volt. The available 10.8 kWh (DC) enables the car to be driven “on the batteries” for about 38 miles, after which the gasoline engine takes over.

      GM limits charging to about 90% (to prevent overcharging which is adverse for all batteries) and discharging to about 25% (to prevent too deep a drawdown of the charge to extend the battery life well beyond the 8 years/100,000 mile warrantee)

      The 4 MW mentioned in the article should be 4 MWh.

      It the batteries are lead acid, they can be drawn down to about 50% for long life, say at most 8 years for a very good quality battery. Typical drawdowns are much less than 50%.

      The charging and discharging cycle is about 80% efficient. That means 10% of the solar energy is lost during charging and 10% during discharging AND converting to from DC to AC so the energy can be used by the school’s electrical systems.

      Available energy to the school = .5 x .8 x 4000 kWh = 1600 kWh. If there are several summer days of cloudiness, then that 1600 kWh may be used up, before new solar energy recharges the batteries.

      During winter, monthly solar energy production is as low as 1/4 of summer production, i.e., not much solar energy to recharge the batteries. See below table for Burlington.

      The below table indicates the excess solar energy would occur mostly during summer, when the students are on vacation. Yikes!!!

      There would be very little excess solar energy during winter to charge the batteries.

      It looks to me this battery application should be abandoned as the minimal benefits obtainable would be at a very high cost.

      Of course, with enough subsidies even elephants can be made to fly.



      • Addition to above comment:

        If a school were to use 300 kWh/day and 4 days of storage is desired, then 1200 kWh is provided to the school, but, accounting for discharge losses and DC to AC conversion, 1200/0.9 = 1320 kWh is withdrawn from the battery.

        If stored energy in the battery is 4000 kWh, about 4000 – 1320 = 2680 kWh is left, of which only 2680 – 2000 = 680 kWh can be withdrawn at the recommended 50% depth of discharge for lead-acid batteries.

        The original solar energy fed into the batteries, accounting for charging losses, was 4000/0.9 = 4444 kWh.

        Batteries slowly discharge, even when not in use, i.e., a trickle charger is needed.

        At colder temperatures, say 40F, a factor of 1.3 applies, i.e., 4000/1.3 = 3077 kWh is the available capacity at that temperature. The factor varies from 1 at 80F to 1.59 at 20F.

        Thus, at that temperature, 3077 – 1320 = 1757 kWh is left, which is below the recommended 2000 kWh at 50% discharge.

        This means the batteries need to be stored in a heated, ventilated, lighted building, which requires:

        – Capital cost
        – O&M costs
        – Battery replacements costs.

        Is anyone still wondering why batteries for storing excess solar energy are not widely used?

        Of course, with enough subsidies, even alligators can be made to fly.


      • Addition to the above comment:

        “The stored energy will be used to shave peak electricity demand at times when solar power is less available – dusk, cloudy afternoons and winter months – and provide emergency backup power for Rutland High School during outages.”

        During the months of the above table, the on-peak average was 8.14 c/kWh and the solar-weighted, on-peak average was 6.98 c/kWh.

        There was a shortage of gas last winter causing higher wholesale prices compared to prior years, thus raising the SIMPLE AVERAGE (8.14) and the SOLAR-WEIGHTED, AVERAGE (6.98) wholesale price, for the year!! Had the gas shortage not happened, BOTH average prices would have been lower, i.e., more in line with prior years.

        Current New England annual average grid prices are about 3.5 c/kWh, off-peak, and about 8 c/kWh*, on peak (7 AM – 11 PM), for a daily average of about 5 c/kWh.

        * solar-energy weighted it would be about 6.5 c/kWh.

        Recent bids in response to a PSB PV solar RFQ indicate daily average quotes of about 13 – 15 c/kWh, these quotes are low because of the extensive state and federal subsidies.

        With solar weighted, wholesale, on-peak, prices of 6.5 c/kWh, no economic case can be made for peak shaving or for emergency backup with solar panels.

        There are much less costly ways to reduce CO2 by means of increased energy efficiency.

        I hope GMP personnel read this so they will not waste their valuable time and our valuable taxpayer money on another costly boondoggle.

        With enough such boondoggles, Vermont’s near-zero-growth economy will become less and less competitive.

    • Wow all this talk about toast is making me feel HUNGRY? These solar power banks are a great idea and are becoming more and more common even here in the UKIt does not say much about the battery system though. thanks eric roberts http://www.batteriesontheweb.co.uk

  • Annette Smith

    I’m curious how the batteries will be managed.

    “used as little as possible for longevity” doesn’t really explain it.

    I use a laptop and was recently told by a computer technician that I should not leave it plugged in because that will shorten the battery life and instead I should run it down to 10% and back up to 100% and down and up. I also read recently that 40/80 is what some people recommend, but the computer technician said go down as far as possible, then back up to 100%. So that’s for a laptop lithium ion battery.

    My off-grid solar system uses lead acid batteries, and if I’m understanding how they operate, you can get x number of cycles out of them, and it’s important not to drain them.

    So will GMP keep these batteries always charged, will they cycle them, or something else? Or do they know? What’s the best way to extend the battery life to 8 years or more?

    Or will they burn up in a fire the way the First Wind’s Hawaii battery warehouse did (twice) http://www.kitv.com/news/hawaii/-Blaze-in-battery-warehouse-shuts-down-Oahu-wind-farm/15936674. I hope someone has studied what happened there and incorporated safety measures to put out a battery fire if it were to happen at this Rutland GMP Solar landfill site.

    To Moshe’s question, that First Wind Hawaii battery storage (built with a $117 million federal loan guarantee) is variously discussed in news stories as
    –a 15 MW battery storage system
    — a 15 MVA, 10 MWh battery and power-management controls
    –supported by a 1.5-MW Xtreme Power energy storage and power-management system
    I have no idea what that means, since it is all describing the same system.

    • Moshe Braner

      Annette: I think your computer tech is wrong. Some “exercising” of the batteries is good for the batteries, but really deep cycles are not. Not sure what’s the optimum for Lithium Ion batteries. For NiMH, 40/80 is a good compromise if you want to get real use from them (not just emergency backup), and that’s what the Prius does. My Prius is 13 years old and the battery is still OK (but not forever!).

      The reports on the Hawaii facility are another example of the way most journalists conflate the units of power and energy. This makes it impossible for the curious readers to interpret. My _guess_ is that it can supply 1-1.5 megawatts for about 7-10 hours. The reason I am guessing so is because the whole point of building these things is to store enough energy for several hours’ use. And the charging would also be accomplished in several hours. And the “power management system” needs to be beefy enough to handle the maximum instantaneous power it would be called upon to accept or provide. So the 1.5 MW is probably correct, and so is the 10 MWH, while the “15 MW” was probably supposed to be “15 MWH” – perhaps it’s 15 in, 10 out, due to the inherent losses when you convert electricity to chemistry and back again.

      • Annette Smith

        I did a search about laptop and deep cycle batteries and found these:

        Battery Maintenance
        Standard Maintenance
        A Mac portable is just that: a portable computer. It was designed to be plugged and unplugged to allow the battery to discharge and recharge on a normal cycle. As such, if you use your machine plugged in all the time, then it is important that you discharge (or calibrate) your battery every so often. If you rarely use the battery, then Apple recommends completely discharging the battery and charging it again at least once a month. If you use your notebook frequently on the battery and plug it in to “top off” the battery, then a full discharge cycle is required less often.

        Deep Cycle Battery Care and Maintenance (there is more at the link above but this is the relevant portion)
        For best battery life, batteries should not be discharged below 80% of their rated capacity. Proper battery sizing will help avoid excessive discharge.

        • Glenn Thompson

          To add to this discussion, look into the suggestions electric car manufactures offer to maximize electric vehicle battery life! I’m surprised this one site recommended not to discharge batteries below 80% of rated capacity. Never heard that one before.


          As for the topic…..I understand the concept of adding battery storage to solar power but question the feasibility of doing so given the existing technology? Won’t that drive up the costs of solar power?

      • Moshe,

        For lithium batteries the maximum charge is about 90% of capacity and the minimum charge is about 20% of capacity, which gives 70% of capacity as usable energy.

        The in and out losses are less than of lead acid batteries.

        The battery cost/kWh of lithium ion batteries is much higher than lead acid.

        It is important the charging energy is “smoothed/conditioned” before entering the battery to prolong life.

        In case of PV solar and wind energy, the charging energy is variable, which is a no-no for all batteries.

    • Annette,

      The best way to extend lead-acid battery life from 6 – 8 years, to 10 – 15 years is to:

      – charge to about 90% of capacity
      – not discharge below 20% of capacity

      Do not:

      – deep-cycle greater than 50% of capacity, i.e., exceed going from 90 to 40%, or from 70 to 20%
      – charge too fast
      – discharge too fast

    • Annette,

      The Hawaii battery units were used for “smoothing” short term variations of the energy produced by the wind turbines, similar to the $10.5 synchronous-converter system used by GMP to smooth Lowell energy so as not to be too disruptive to the high voltage grid.

      They were NOT used for energy storage.

      They may have been charged to quickly causing them to overheat and catch fire.

    • Annette,

      What your computer person does not know is that Apple limits to maximum charge (which SHOWS 100%, but is not) and the minimum charge (which shows a warning and then shuts down the computer before the minimum is reached) of the lithium-ion battery.

  • rosemarie jackowski

    Every day I become more convinced that we need to place increasing emphasis on conservation in order to limit the use of all forms of energy… wind, solar, oil.

    I am not suggesting just turning the lights off. But maybe some houses are too large. In the future, we could encourage smaller homes, more windows on the south side, less unnecessary travel… More public transportation. Local, small, and simple is best.

    I have a small house. I designed it so that most windows would be on the south side. It makes a big difference.

    • Moshe Braner

      Rosemarie: you are right. And it is easy to conserve a lot of electricity, mostly with simple behaviors, and with rather modest investments. E.g., turn the lights off when you leave a room. Replace incandescent bulbs with CFLs or LEDs. (CFLs are now only $1 each, have a nice color (get the “warm white”), don’t flicker, and save dozens of $$ EACH relative to indandescents. Some LED bulbs are down to $5, and are even more efficient, and give their max brightness immediately upon turning on, and make no hum nor RF noise.) Don’t light up the outdoors. Use air conditioning sparingly, and close windows and doors if and when you do. Shade windows on hot sunny days and open windows at night to get cool air in. When your appliances are old, replace with “energy star” models. In particular, refrigerators and washing machines (only get the front-loading kind). Dry clothes on a line. (Yes, choose to wait and do the laundry on sunny days, it won’t kill you.) These things may seem petty, but they easily add up to $1000 saved per year for a typical household.

  • One positive of this project is that it isn’t being placed in a Rutland neighborhood or in a meadow along a Vermont scenic roadway.

    Hopefully, this will be the start of some common sense thinking in siting industrial solar developments.

  • Wayne Andrews

    Moshe: The problem I have with electric conservation is the fact that it costs dollars to accomplish this task. Saving electricity is not always saving dollars out of your pocket.
    To implement all those topics you describe above would take a lot of money and then add to some major projects the possibility of a cost of a loan.
    I do believe in conservation along with creating new forms of electric generation but each one of these saving devices have drawbacks and could take up a lot of space here.

    • Wayne:

      Your point on the cost of electric conservation is a good one.

      I just got our Green Mountain Power statement that shows an energy efficiency charge of $7.35 or 5.9% of our total bill.

      Maybe someone can say if a 5.9% charge is a good investment of rate payer’s money by telling us if Vermont is achieving at least a 5.9% reduction in annual electrical consumption?

    • Moshe Braner

      Costs of my proposals above:

      $negative – Turn the lights off when you leave a room.

      $50 – Replace a couple of dozen incandescent bulbs with CFLs or LEDs. And save $2000 in power bills over 5 years – any of your financial savings giving you returns like that?

      $negative – Don’t light up the outdoors.

      $negative – Use air conditioning sparingly, and close windows and doors if and when you do. Shade windows on hot sunny days and open windows at night to get cool air in. OK, getting shades, if you don’t have them, may cost you $100.

      $300 (extra over inefficient models, good for 10+ years) – When your appliances are old, replace with “energy star” models. In particular, refrigerators and washing machines (only get the front-loading kind).

      $10 – Dry clothes on a line. I recently replaced my clothesline, after 20 years of use. The trees were free.

      Alas, saving on heating costs is a lot harder and more expensive up front than saving electricity. Sealing drafts, adding insulation, etc. Still worth doing, as it will pay for itself in a few years. This is where the government could help by arranging low-interest (should be zero-interest) loans. the “PACE” program arranges for repayment of such loans via the property tax bill, so it’s secured, and passes on to the new owners if the house is sold. With repayment spread out over 5 years or more, the total impact on the homeowner’s cash flow is positive, since the heating fuel bills are reduced.

      If you heat on electricity, in the inefficient way (baseboard or space heaters) then there is no cheap way to cut that out, you’d need to install either a “heat pump” (3x more efficient) or a fuel-burning boiler or furnace or space heater. Either way that’s $thousands. But that’s because a house built with only electric baseboard heating is really incomplete. If your house lacked a roof you wouldn’t leave it like that, uh?

  • John Greenberg

    First, thanks to Moshe Braner for all his comments here, all of which are right on key.

    Second, to generalize his specific comments in response to Wayne Andrews, energy efficiency is a global term for a variety of specific projects (like replacing bulbs, or insulating). The financial return on each of these is easily calculable and can be tailored to precise circumstances.

    There are PLENTY of improvements to be made in Vermont (and elsewhere) with financial returns which make the decisions truly no-brainers, as his examples amply show. Any energy investment which returns far more than any other possible investment fits in this category, and at the rate we waste energy in our society, these remain shockingly abundant. Conservative studies estimate these in at least the 20% range: that is, at least 20% of our electricity could be saved at a “cost” which would be negative.

    There are some projects, of course, where the returns would require more thought. Legitimate policy questions do arise when the returns are sufficiently marginal that they need to be compared carefully with competing uses of the funds. However, we’re a LONG way away from the point where such projects predominate.

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