Limits to Green Energy May Curtail Future Net Metering

This is the final installment of a series examining the V.I. Water and Power Authority’s net-metering program, its challenges, and its future. For previous installments see Related Links below.

If net metering has proven so successful and popular, why wouldn’t the legislature and the Water and Power Authority work to raise the 15MW maximum production cap to keep the program around? It’s a simple question with a complicated answer, and one that has little to do with policy.

In the next few years, the U.S. Virgin Islands will have to contend with an engineering problem that has bedeviled the renewable energy industry around the globe – there is a physical limit to the amount of energy from solar arrays and wind turbines that energy grids can handle before becoming unstable.

All sources of energy can be separated into two major categories: dispatchable energy and intermittent energy. Dispatchable energy provides the bulk of the electricity on utility grids, often referred to as the base load.

Electrical engineers like dispatchable energy because it’s easy to control. This category includes any type of energy from a power plant in which the input of fuel can be adjusted to increase or decrease the output of electricity.

Nuclear plants as well as those that burn fossil fuel, such as diesel or coal, are dispatchable power providers. There are some renewable sources of dispatchable energy as well, such as biomass and trash-to-energy plants.

Intermitment energy providers are those in which the input of fuel and output of electricity are out of the hands of engineers. Wind and solar are the two most common examples. No one can force the wind to blow or the sun to shine. As a result, the energy output from these sources is sporadic and difficult to predict.

Melton Smith, design and construction manager for WAPA, said that for utilities to ensure that the lights don’t go out, they must find a balance between the amount of electricity they know will be available at any given point and the electricity that might be there.

“If we have sufficient renewable energy systems out there that we can turn off a generator, that’s a good thing on one side and a bad thing on the other side,” he said.

He explained that on a sunny day, solar panels could provide enough energy to allow WAPA to idle some of its generators, thereby saving money on fuel costs. But what happens if a cloud goes by? Smith says WAPA would have to scramble to get its generators restarted to compensate for the sudden dip in energy production.

If that dip is too large, he said, it could cause blackouts while generators at the power plant are coming back online.

In order to integrate solar and wind into their energy mix, utilities must conduct studies to determine how much intermittent energy their grid can sustain before they begin risking service interruptions.

Clinton Hedrington, director of transmission and distribution for WAPA, said they’ve conducted two such studies on the Virgin Islands’ grids. The first suggested they could tolerate a 10-percent penetration rate from intermittent sources. The second estimated 20 percent. Exactly where the threshold lies will take experimentation and very careful planning.

So just how far away are we from hitting our intermittent energy limit? It’s closer than you might think.

Since there is no electrical interconnection between the St. Croix and St. Thomas/St. John districts, the total Virgin Islands electrical grid, which would be tiny by stateside standards to begin with, is divided into two even smaller grids, so the amount of intermittent power needed to hit the 10- to 20-percent mark on either isn’t much.

Hedrington said he believed the territory could handle the 15MW of intermittent energy allotted to the net-metering program as well as the 18MW that will come from industrial solar arrays slated to come on line next year. Anything beyond that, he said, will raise complications.

“If you have so much penetration by solar, and then you add wind, you become much more unstable. And that’s a big deal,” he said, referencing a proposed industrial wind farm at the Bovoni landfill on St. Thomas. “You know, we’re doing all of this wind study and then we’re also at max with solar, that’s going to cause a problem, and we know that.”

Hedrington said a possible solution is to install industrial-sized batteries throughout the grid to help even out the flow of electricity from intermittent sources, though exactly how this would be implemented has not yet been planned.

The Virgin Islands government is negotiating with the Clean Energy Coalition, a stateside nonprofit group, to launch a pilot program on St. John that will attempt to raise the penetration barrier through the use of batteries. The study could start next year and, if successful, could establish a roadmap for the rest of the territory to follow suit.

Hedrington said another possible solution would be to connect the territory to Puerto Rico’s grid. As part of a much larger grid, the amount of renewables the territory could install would skyrocket.

“The interconnection to Puerto Rico raises our penetration to infinity,” Hedrington said. “We could add renewables, add renewables, add renewables and just rely on them to deal with the intermittency.”

The interconnection to Puerto Rico is still just a proposal, however, and there are presently no plans to build it.

So what does this mean for the net-metering program? In all likelihood, when the 15MW production cap is reached sometime in the next two to four years, the program won’t be extended. Those in the program will continue to enjoy the benefits of net metering, but new customers will not be added.

Hedrington made it clear that as the territory begins to flirt with its intermittent penetration limit, every new proposed megawatt of solar and wind energy will require extensive planning and potentially infrastructure improvements. With a large solar farm on the way and several proposed industrial wind projects on the drawing board, there may not be any room left for small-scale net-metering installations beyond the 15MW cap.

“While we don’t want to be against the penetration of renewables, we have to protect the grid. Because it will be detrimental at the end of the day,” Hedrington said.

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