This commentary is by Andrew K. Gentile, an electrical engineer who lives in Sheffield.
Green Mountain Power has made the unrealistic promise that soon it will rid Vermont of all power outages. GMP’s plan, as explained on WCAX News, consists of burying power lines and supplying customers with battery backup systems.
The utility said the project would cost $1.5 billion over the next seven years and would eventually lower costs for customers.
The claim that there will be zero power outages is nonsense. However, almost every Vermonter I know owns a generator, which underscores the fact that power in Vermont is unreliable. Therefore, it is worth considering whether the changes GMP is proposing would decrease outages, and how much those changes might cost.
Because most of Vermont’s outages are caused by trees falling on lines, converting overhead lines to underground would certainly help reduce outages. Underground lines do not get hit by trees; however, they are prone to damage from flooding, earthquakes, lightning and rodents. In addition, they are sometimes accidentally dug up by humans.
The cost of converting overhead lines to underground is dependent on, among other things, the voltage of the line. The higher the voltage, the higher the cost.
Transmission lines are considered high-voltage and are very rarely installed underground. The cost of underground transmission lines can be five to 10 times the cost of overhead lines. Furthermore, the life span of an underground transmission line is less than half that of an overhead line. Under most conditions, it is not cost-effective to install transmission lines underground.
Distribution lines constitute most of Vermont’s power infrastructure, and they account for most of the outages. These lines are considered medium-voltage and are commonly installed underground. Despite that, the cost of underground distribution is still more than double that of overhead. Under the right conditions, moving distribution lines underground can be a cost-effective measure to reduce outages.
The second idea proposed by GMP was to provide Tesla battery backup systems to its customers. According to a New York Times article, these batteries are the core of the GMP plan. The batteries would be indirectly tied to the grid, and GMP would remotely control them to absorb excess energy.
Given that Vermont imports most of its electricity, it’s not clear how much excess energy would be available. But the point is, with a home battery backup system, a house would instantly and automatically switch to battery power during an outage.
Despite this convenience, the battery backup system is neither practical nor a cost-effective solution for most Vermonters. A Tesla Powerwall home battery capacity is 13.5 kWh, which can provide enough power to get through most outages, but not enough for an extended one. Even with a battery system, homeowners would still need a generator.
According to the Energy Information Administration, the average U.S. household uses 11,000 kWh per year, or about 30 kWh per day. As such, a 13.5 kWh battery backup would provide enough power for about half a day. A house that didn’t have electric heat, an electric stove, and an electric hot water heater might get a full day out of it. Ironically, a battery backup system would clash with Vermont’s shortsighted push toward an all-electric state.
A Tesla battery pack costs about $12,000, and given that you might need it for 100 hours a year, it would take over 200 years to pay for itself. It would be more economical to purchase a 7.5 kW Champion generator for about $900.
Considering the expected costs of providing battery packs and installing underground power lines, GMP’s predicted project cost of $1.5 billion over the next seven years is grossly underestimated. If GMP were to provide each of its 270,000 customers with a $12,000 battery system, the cost for that alone would be $3.24 billion. And the installation of underground lines would cost even more than the batteries.
In 2008, the state of New Hampshire funded a study that came up with similar conclusions regarding the costs and benefits of moving overhead lines underground. In that study, the N.H. Public Utility Commission concluded that converting its overhead lines to underground would be prohibitively expensive and, in many cases, impractical. “According to data supplied by the New Hampshire utilities, in good soil conditions, the cost of a 34.5 kV line may be in the range of $2,000,000 per mile. If built in granite, that cost could increase by another $500,000 per mile.”
GMP has 22,000 miles of power lines, and if it converted just 25% of its overhead lines to underground, it could cost over $10 billion, upward of $37,000 per customer, and that’s based on 2008 estimates.
The New Hampshire study also concluded that, if the financial burden of the underground lines was transferred directly to customers, rates would increase by 110% to 150%. And here in Vermont, we have the added cost of a very expensive battery backup system, pretty much guaranteeing that our rates would triple.
I agree that we need improvements to Vermont’s power grid. In Sheffield, our power has been out so many times this summer I have lost count. I have the utility service department phone number on speed dial.
I would welcome any improvement in Vermont’s electric grid, but the costs proposed by GMP are unrealistic. I would need to see a lot more details on this one before I would sign off on it.
