An Underseas Cable to Power Puerto Rico

A big idea to solve a couple of big problems

An Underseas Cable to Power Puerto Rico
Rendering of submarine communications cable, Adobe Stock

Across Puerto Rico, the quality of life and economy is more precarious than anyone would tolerate anywhere else in the United States. And the reason largely comes down to a singular problem: the electric system is dirty, fragile, and expensive.

On the mainland, Americans face a very different problem, the challenge of finding a follow-on project after the commissioning of two new reactors in Georgia. These reactors have brought a strong a supply chain, a cadre of workers with highly specialized skills, and a complete design for what could become a series of cookie-cutter plants that would cut costs and make a dent in our carbon problems.

Can we put these problems together? Yes, but it requires something we don’t do much of these days: thinking big. It’s time to turn the planners loose on some feasibility studies and start building a political consensus on serious paths to a zero-carbon economy.

The United States could solve the two problems with a one project, an underwater cable. Such cables are increasingly common around the world and in the United States as we seek to move clean energy longer distances. Many more are planned. They have very low line losses and are highly reliable.

And that reliability could make them an attractive alternative to Puerto Rico’s current unreliable grid.

Puerto Rico has problems on three sides of its electricity system. One is the distribution side—ordinary utility poles and low-voltage lines, and submarine cables won’t help that. But it also has problems on the generation and transmission side. Most of the island’s generation infrastructure is on its south side, and it is antiquated. It runs on heavy oil, one of the more carbon-heavy fuels. (Displacing a megawatt-hour of heavy oil helps the climate than displacing a megawatt-hour from natural gas.) Between the old generators and the load center is a range of mountains and transmission lines vulnerable to hurricanes.

A cable transmitting clean energy close to San Juan would be much sturdier and more efficient. In addition to slowing climate change by building reactors that will displace something dirtier than natural gas, a cable would help harden the island’s infrastructure against storms, allow economic expansion in a place that needs new jobs, reduce poverty among U.S. citizens by lowering living costs, and move everyone up the learning curve in a nascent technology that will be critical in years to come.

Experience with Underwater Cables

Building the cable would be a massive challenge, to be sure, but engineers are increasingly turning to direct current cables—on land and underwater—as they figure out how to move clean energy where it is needed.

From Miami to San Juan is about 1,000 miles. That distance is not long for a data cable, but it is long for a power cable. At present, the United Kingdom is studying a DC cable from Iceland, called Icelink, which would carry geothermal energy about 750 miles.

Of the submarine power cables already in service in North America, the newest is a 53-mile (85 km) cable from Pittsburg, California, to San Francisco. It opened in 2010, allowing the closure of the Potrero fossil plant inside San Francisco. The Champlain-Hudson Power Express line will be 339 miles (548 km) and carry 1.2 gigawatts, from a Hydro-Quebec substation near the New York State line to Astoria, Queens. It is mostly submarine, running under Lake Champlain and the Hudson River, but part is above ground.

Around the world, even longer cables have been laid. In June 2021, the North Sea Link, a 1.4-gigawatt cable, opened to carry electricity between the north of England and southern Norway. At the time it was commissioned, it was the world’s longest, at 447 miles (720 kilometers). The plan is for excess power from offshore wind to flow east to Norway on windy days, and hydroelectric power from Norway to flow west when the wind isn’t blowing. And the Viking Link, another 1.4 gigawatt line running from Lincolnshire in England to Jutland in Denmark, began construction in 2020 and is supposed to be completed this year. It is 475 miles (765 kilometers).

Longer cables are planned, notably the EuroAfrica Interconnector, which would connect Egypt, Cyprus, and Greece in a 876-mile (1,396-kilometer) chain

Transmitting Nuclear Energy via Underwater Cable from Mainland to Puerto Rico

The cable may be technically feasible, but what about the power to fill it? On the mainland side, there is a happy confluence of circumstances. The reactor model in question is the Westinghouse AP1000. Georgia Power will finish a twin-unit plant near Augusta in the next few months. The price was roughly double what was expected. That is a pitfall of first-of-a-kind projects, and the way to get the price down is to take advantage of the lessons learned on the first pair.

Georgia Power has a wider gift for the world: a complete set of design drawings, and a cadre of workers with the skills to build. Those workers have done better on Vogtle 4, the second new unit, than on Vogtle 3. It’s time to turn them loose on a follow-on project.

And it happens that such a project is already licensed; Florida Power & Light (FPL), during a natural gas price spike earlier in this century, applied for a license from the Nuclear Regulatory Commission and has been sitting on it ever since. It is a combination construction/operating license. Regulatory approval is simple if the company builds the plant as designed, and after the Vogtle experience, a second builder has a much clearer idea of precisely how to do the job.

The new plant would not be a perfect carbon copy of the current Vogtle designs, to use an antiquated pun. For example, the water discharge system would be different: Vogtle uses cooling towers but in South Florida, the water warmed by the plant would be injected into permeable rock beneath the surface. But the painful work of detailed design is done. And, at considerable expense, a lot of insight has been gained.

FPL has a somewhat conflicted view of nuclear energy. Its parent company, NextEra, operates mostly in unregulated markets around the country to build wind turbines, and it stresses its renewable bona fides. NextEra dropped out of the nuclear industry’s main trade association and runs extensive advertising campaigns boosting its green image by stressing wind and solar, not nuclear.

And after Georgia Power’s experience with Vogtle, NextEra might be forgiven for showing some reluctance to make the leap. But there are good reasons for the federal government to make the numbers work. The stress is on reasons, plural, because this is a project that makes more sense from a national perspective than from a local, corporate one.

For example, powering Puerto Rico with clean electricity advances our national climate goals. Making electricity reliable and reasonably priced will improve the business environment on the island, stimulating job growth, boosting tax revenues, and generally raising living standards there. If the project draws in other Caribbean islands along the way, it could be a form of foreign aid for needy neighbors, whose ties to the United States would be strengthened. And it would be an important step in making the AP1000 a desirable product and a useful tool for decarbonization.

Here, FPL—or maybe Congress and the Joe Biden administration—could take a cue from the battery industry. Energy analysts have a method for measuring the value of batteries: seeing if the benefits of their various functions can be “stacked.” That is, making the right decisions depends on taking into account all the different functions batteries can fill: adding reliability, reducing the need for a transmission upgrade, matching supply to demand, stabilizing the grid, etc. It may be time to apply this structure to a nuclear project.

Potential Opportunities for Nuclear Energy

The new reactors would add production to the grid roughly equal to what Puerto Rico consumes, but they would not be hard-wired directly to the undersea cable, any more than any power plant today serves a single factory or a single town. The cable would essentially extend the U.S. mainland grid to Puerto Rico, bringing the reliability of a diverse supply. (That’s how you keep the lights on for the few weeks once every 18 months when you shut the reactor for refueling and maintenance, or once every year or two, on average, when a glitch of some kind leads to a reactor shutdown.) On the island end, the cable would come ashore at a substation, possibly one that already exists. It would require new equipment, to convert the direct current back into alternating current, the kind that the Puerto Rican grid carries, but this is a well-developed technology. And generally speaking, substations are much easier to site than power plants or power lines.

If the cable had to come ashore somewhere en route, for engineering reasons, there are lots of possibilities. All the islands in the Caribbean burn fuel oil, which is expensive and environmentally dirty. There are good engineering reasons for them to prefer a cable as at least a partial replacement for fuel oil. Solar and wind can play a role in plans to get off fuel oil, although both are highly vulnerable to hurricanes, and intermittency is a particular problem in environments where grids are fractured and can’t tap into distant areas where the wind is blowing or demand is lower so surplus power is available.

The Nuclear Alternative Project, made up of a group of Puerto Rican engineers across the United States, has been working toward a small modular reactor or two for the island. (Puerto Rico’s load is too small to host a reactor the size of the AP1000, although its annual energy consumption, 18 million megawatt-hours, is almost as much as a twin-unit AP1000 plant would produce.)

Laying a cable to Puerto Rico would not replace all the generation on the islands; some would be needed for backup. But it would vastly improve reliability and resistance to storms.

A Caribbean business group estimated in 2014 that the cost of such a line would be $5 billion, but didn’t provide a basis for the estimate. In 2022, a company called Alternative Transmission said it could build the line for $5.5 billion to $6 billion. It called the plan “Project Equity,” and said it would deliver 2.1 gigawatts from up to two points on the east coast of the mainland to two points in Puerto Rico. (Coincidentally, 2.1 gigawatts is about the output of two AP1000 reactors, although the company said it would eventually look for renewable power; it didn’t mention nuclear power.) The president of the company, Adam Rousselle, the project would take transmission “out of the hurricane’s wrath.”

Can we think big about a single project with diverse goals?

The idea of using new generation in Florida to power an offshore territory is difficult because it requires planners, who are often specialists in a narrow field, to think about more than one factor at a time. Investor-owned utility companies, who are the traditional builders of reactors, do not make investments for reasons of economic development or domestic policy. And they will invest in resilience only if compensated for doing so.

A publicly-owned electric system may make investments to spur economic development and a higher standard of living, but Puerto Rico’s long-time government utility, known as Prepa, was never up to the job, and since 2021, the transmission and distribution system has been run by a private operator.

In fact, that operator, Luma, which took over the system nearly two years ago, is already thinking big. It has asked for more than $8 billion from the Federal Emergency Management Agency. But it does not own the old fossil-fueled generators, and the next move may be to re-place or upgrade those.

Why think big now? Because we are probably on the cusp of an era of big changes: big land areas abandoned to rising seas, big migrations driven by climate, and maybe even big efforts to tinker with the climate in ways that will produce uncertain results, like launching reflective material into the stratosphere to bounce some solar energy back into space. Better to jump in now with some big initiatives whose consequences are relatively calculable.

But doing that requires thinking on a bigger scale, the scale of, say, the Trans-Alaska Pipeline, the Panama Canal, or the transcontinental railroad. The energy transition will require grander thinking, harnessing emerging technologies, like long-distance, high-voltage direct current submarine cables plus more modern nuclear reactors, to the problems at hand. And here is a place to start.

*April 24, this article has been updated to correct a typo that identified the reactors at Vogtle as 4 and 5 rather than 3 and 4.