MDI High School Hopes to be Carbon Neutral by 2030

And Carbon Negative by 2050

Jul 08, 2024

BAR HARBOR—Can MDI High School be carbon neutral by 2030 or carbon negative by 2050? One teacher wants to make it happen and she’s getting the data that she hopes will help get the school there.

MDI High School science teacher Ruth Poland and A Climate To Thrive’s Renewable Energy Solutions Coordinator Corey McVay recently gave presentations on data that was collected regarding energy use and carbon emissions by MDI High School. They presented to the High School Board, the AOS, and the High School Board of Trustees.

Poland’s presentation was based upon the different types of energy and fuels used at the high school, the carbon emissions related to this energy and fuel use, and ways to reduce the high school’s carbon emissions. Poland’s data and presentation was a teacher and student collaboration and students from the ECO team, the honors environmental science class of spring 2023, and the AP calculus class of spring 2024 all assisted with data collation and analyzation.

The goal of Poland’s and the students’ work is to help move the high school closer to one of the goals in a set of commitments passed by the High School Board in 2021 . Those commitments are Project Legacy

ELECTRICITY AND FOSSEL FUEL COSTS

The electricity data gathered was from the electric meter that provides power to the majority of the school. However, there are more meters on campus including electric bus charging stations and athletic field lighting that were not captured so the data does not include the complete power use of the school, but these other meters, by usage, are fairly inconsequential in the overall electricity use of the school.

MDI High School opened in the fall of 1968 and was built with, and still relies on, older and less efficient heating technology that runs on fuel oil. There have been some heat pumps added in recent years for heating and cooling, but they play a small role in the overall system. For that reason, fuel oil is the number one cost center for energy costs at the high school and also the highest emitter of carbon dioxide and other greenhouse gases.

In addition, some propane is used for other heating systems and there are school vehicles that use diesel fuel and gasoline. The school does have two electric school buses that are helping to cut out the vehicle-based carbon emissions.

CARBON DIOXIDE EMISSIONS

On an annual basis, the school emits an average of 575 metric tons of carbon dioxide. According to the energy use by fuel type that would break down to:

183 metric tons due to electricity usage,
364 metric tons due to fuel oil usage,
30 metric tons due to propane usage.

ELECTRICITY AND POSSIBLE SAVINGS

The high school has a 435-kilowatt (kW) rooftop solar array that went online and started producing electricity in the winter of 2019. It is currently owned, operated, and maintained by Sundog Solar, but the school will have the opportunity to purchase it at the end of 2025. The purchase price is not exactly known but the agreement is that it will cost no more than $364,500. Sundog Solar paid for the initial construction of the solar array.

The solar array was constructed as a behind-the-meter system. This means that the school can use the electricity generated by the array as it is generated and only excess electricity not being used at the time by the school goes into Versant power’s grid. For this excess power, the school is given credits to offset any use of Versant electricity.

The school currently purchases the electricity produced by the array from Sundog Solar for $0.089 per kilowatt hour (kWh), which is well below the rate that Versant offers. The Versant rates vary from $0.13 to $0.24 per kWh for the school’s accounts.

According to McVay, if the high school does not purchase the solar array in November 2025, “the price for electricity produced by the solar array will be set annually at 12.5% below Versant Power’s standard offer rate.”

It is estimated that if the school purchases the solar array when it is available, that it will save the school approximately $1,160,391 over the following 20 years. If the school does not purchase the array and continues to purchase the power from Sundog Solar, it is estimated that it would save the school $203,870 over that same 20-year period.

To date, it is estimated that the solar array has saved the school approximately $111,524 in electricity costs and reduced greenhouse gas emissions by the following amounts.

393 metric tons of carbon dioxide,
.74 metric tons of sulfur dioxide,
.65 metric tons of nitrogen oxide.

STILL PAYING FOR ELECTRICITY

While the solar array has the capability to power everything that is covered under the main meter, there are unavoidable issues that cannot currently be mitigated as the system is currently set up. Periods of poor weather with low sun or shorter winter days reduce the effectiveness of the system as does darkness.

In addition, the net energy billing plan that the school is under with Versant Power does not cover demand charges. Because the school uses large amounts of power at any one time, the demand charges for the high school are set at a higher rate. Even if the solar array produces enough excess power to be credited sufficiently to cover all of the grid provided electricity, there can still be substantial demand charges.

According to McVay, electricity demand is “the amount of instantaneous power being used from the electric grid at one time. Since the high school uses large amounts of electricity at once, it has high electricity demand on some of its accounts.”

Energysage.com explains demand charges this way: “At its core, a demand charge shifts the charge on your electric bill from how much electricity you consume over an entire month to the maximum electricity you need at a single point during the month.

Below is a sample bill from the high school for the period of October 18–November 15, 2023.

This bill shows that the school’s solar array produced enough unused electricity to cover all of the school’ grid provided electricity usage and there is no charge for any kilowatt-hours of electricity. However, due to the high demand rate the monthly charge for that time period was still $3,614.87.

POSSIBLE PATHWAYS TO MEET THE GOAL OF REDUCED EMISSIONS

There are three potential pathways to meet the commitment to reduce emissions.

Purchase the solar array,
Manage the demand, perhaps with a battery array,
More closely track the school’s electricity usage with smart meters.

Purchasing the solar array was a topic of conversation at the June 24, MDI High School Board of Trustees meeting as was the subject of selling Renewable Energy Certificates (RECs), which was brought up in Bar Harbor’s Higgins Pit Solar Array proposal as well.

When renewable energy is generated, RECs are also generated in the form of credits that are used to offset greenhouse gas emissions. These RECs can be sold to others and the purchaser can claim the credits towards their own greenhouse gas emissions. If the producer sells them, they do not get to make any claims of emissions reduction, but they do get reimbursed monetarily for the RECs. The sale of RECs can be negotiated on a yearly basis so a producer can sell them one year, but not the next.

During the trustees’ meeting, board member Keri Hayes asked about the possibility of purchasing the solar array in November of 2025 and then selling the RECs for a certain number of years to make money to then invest in infrastructure that would work in tandem with the solar array to further reduce emission, such as more heat pumps for heating and cooling the school or a battery array to avoid demand charges.

The subject of the solar array was only a discussion based on the presentation at this meeting so no decisions were made and no votes were taken on the subject.

All images are from the presentation.

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