The Clean Energy Corridor Clarified

You have seen the signs and the TV ads literally littering Maine regarding the New England Clean Energy Corridor (NECEC), aka the CMP transmission line from Quebec to just above Lewiston. Some oppose and others support. No doubt when people go to vote in May they will be approached by advocates and opponents of the line.

While the following goes into great detail about the Corridor, the bottom line to voters is simply this: building the Corridor requires a tradeoff, the loss of 53 miles of a 115-foot swatch of commercially harvested forest, for at least a 10% reduction in the carbon content of electricity delivered to New England customers.

Unfortunately, this issue has not been immune from what has become a common tactic with many political issues – grossly misleading, if not downright false statements to rationalize a position. Hopefully, the following will allow people to be better informed when they are asked to vote on this topic in November.

The delivered electricity does not go to Massachusetts.

When the power leaves the NECEC just north of Lewiston it enters the 6 state New England Power Pool and is instantaneously blended with all the power in the system. There are no direct paths to Massachusetts or any other states, there are no state grids. It is all interconnected. Massachusetts residents are paying for that power and getting most of the environmental credit, but many people do not understand that in power grids, dollars do not flow with electrons.

One way to think of this system is to visualize a very large bathtub that has multiple faucets filling it and multiple drains emptying it. The tub is the grid, and grid operators must constantly match “water” coming in from power plants and other transmission lines with water draining (consumption) to keep the level of water perfectly level. The NECEC is just one more faucet and when its water is released it blends with everything there.

The details:

There are 9 regional grids in the US, referred to as either regional transmission operators (RTOs) or Independent System Operators (ISOs). They are all interconnected through interties (except for Texas, whose interties have such low capacity they are effectively an island).

ISO-NE is part of the Eastern Interconnection, along with ISONY, Ontario, Quebec and New Brunswick:

In the case of New England, ISO-New England (ISO-NE) is the regional grid, and it has 13 interties with other systems. Interties 10 and 11 are with Quebec Hydro, 12 and 13 with New Brunswick:

With the exception of these interties, the 6-state region functions as one system without consideration for state boundaries. Geographically it looks like this:

But if you show the actual system network it looks like this:

Since this system is Alternating Current (AC) current moves through wires back and forth 60 times a second. Physics tells us that when you put current into a circuit, network or grid, it flows everywhere. Even though there are contracts for the sale of electricity from point A to point B within a grid, these are merely accounting for the dollars involved; the idea the electricity actual goes directly from A to B is a fiction.

High Voltage Direct Current (HVDC) lines are point to point and do not interact with the rest of the grid between entry and exit. The NECEC itself is an HVDC line. At its terminus in Maine, the DC electricity is converted to AC and enters the ISO-NE grid.

When the NECEC operates, natural gas power plants are displaced and their carbon emissions stop.

Referring back to the bathtub analogy, that new NECEC faucet adds a huge amount of water into the tub, but no new drains are added (consumption stays the same). So in order to keep the tub level and equal amount of electricity that had been pouring into the tub needs to be shut off. In the New England pool, the units shut to allow for the NECEC’s influx would all be natural gas fired plants. Millions from natural gas power plant and pipeline operators are funding opposition to the line, as it represents a real threat.

By displacing these natural gas plants with zero emissions electricity, the NECEC could lower the greenhouse gas intensity of New England grid power by between 10% and 15%.

The details ISO-NE operations are described in more detail here, but briefly put, the operators are constantly trying to both monitor and forecast

demand. They then dispatch generation, according to cost from low to high, to meet that demand. Since there is always some level of demand, many generators run 24/7.

At a capacity of 1.2 Gigawatts, NECEC will import 10.5 billion kilowatt hours (kWh) annually. ISO-NE consumption in 2019 was 97.8 billion kWh. Coming in all at once, and without reducing demand, an equal amount of generation will need to be turned off. The following chart shows which type of units were dispatched to meet that load last year.

Natural gas units are the ones that will be displaced.

There are 89 natural gas fired power plants in ISO-NE that operated in 2019. Their carbon emissions vary widely from plant to plant, irrespective of size. Not all these plants would necessarily shut down when the NECEC operates, because some are only used to meet a few hours of high peak demand. The top 85% largest units have an emissions average of .00056 tons/kWh. However, the system average for all of these plants, according to EPA data, is .0005 tons CO2 per kWh. The largest of these units (Lake Road in CT and Fore River in Mass) , emit .00043 and .00044 tons/kWh. Using the metrics from these two largest plants, the NECEC offsets 10 billion kWh, or about 4.3 million tons of CO2. The ISO-NE system emitted 30 million tons in 2019, so the NECEC would cause a 15% reduction.

Another analysis concluded that the minimum reduction would be 3 million tons, or about a 10 % reduction.

Reducing Maine’s baseline carbon intensity for grid electricity is therefore between 10% and 15%

Maine ratepayers do get lower electricity costs.

Whenever electricity moves around the grid, the amount flowing is dependent on where the demand might be. By putting all this new capacity into the grid in Maine, it reduces the amount of power flowing north, and thereby reduces transmission costs for Maine ratepayers.

The details

ISO-NE (as well as other grids) use locational marginal pricing at pricing nodes (points of delivery to the local distribution utility). LMP’s are calculated for over 1,000 nodes (171 in Maine), in 5 minute and hourly increments. LMPs include the cost of energy, transmission constraints and losses.  

An analysis of the impact of the NECEC on LMPs is provided at  A chart of the LMP reductions by state is shown below.

Maine is estimated to save about $450 million.

When Quebec Hydro exports this power, it will not replace it with fossil units.

Quebec Hydro generated 213 Terawatt hours (TWh) of electricity in 2018, of which less than 1% is fossil. This includes is domestic load, including exports. The NECEC export is about 10 TWh. Hydro Quebec has at least 40 TWh of excess capacity, none of which is fossil. In addition, it has a collection of reservoirs that, when full, exceeds one and a half times the demand of all of New England.

The details

Hydro Quebec’s energy generation sources include the following (source: Canada Energy Regulator):

Data on surpluses:

Cut down trees reduce what the carbon the forest absorbs, but the NECEC offsets that lost absorption 4,000-fold.

Only 50 miles of the corridor is newly clear-cut, a 150 wide swath. The remainder of the line is already cut and will be slightly widened. But if, hypothetically, a 130 mile, 150 foot swath were cut through the forest it would remove about 430 acres. Maine’s forest absorb about 3 metric tons per acre. That “lost” forest would have absorbed about 1,290 metric tons of carbon a year. When the NECEC operates between 3 and 4.5 million metric tons of carbon will not be emitted from natural gas power plants. There is clearly a tradeoff here.


Unfortunately, very few initiatives necessary to avert a climate crisis come without some kind of tradeoff, whether it be economic or environmental. Achieving Maine’s and the region’s climate goals by replacing fossil fuel use with decarbonized grid electricity is a key path in our strategy portfolio. The NECEC is vital to climate action by substantially reducing the greenhouse gas content of New England grid electricity.

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