Is a national high voltage transmission system the cheapest way to cut emissions?

Scientists call for HVDC lines connecting the nation’s wind, solar, and power markets

Numbers from a new modeling tool built by top scientific researchers have sparked new talk of a national transmission system.

A high voltage direct current (HVDC) grid expansion to connect the nation’s best utility-scale wind, solar, and other renewable resources to 256 electricity markets is the cheapest way achieve big emissions reductions from the power sector by 2030, according to a recent peer-reviewed article in the journal Nature Climate Change. 

But while support for a better transmission system is common in the utility sector, several sector insiders told Utility Dive they are not sure the grid design envisioned in the paper is the panacea the research suggests it is.

“Using future anticipated costs for wind and solar, carbon dioxide emissions from the U.S. electricity sector can be reduced by up to 80% relative to 1990 levels, without an increase in the levelized cost of electricity,” reports “Future cost-competitive electricity systems and their impact on U.S. CO2 emissions.”

The software modling that produed that conclusion — the National Electricity and Weather Systems (NEWS) tool — “allows us to look at possible energy futures,” explained study co-author Alexander MacDonald, the recently retired director of the National Oceanic and Atmospheric Administration (NOAA) Earth System Research Laboratory.

“People probably aren’t willing to pay more for electricity so cutting most of the CO2 that drives climate change from the generation sector without increasing the price is important,” he said.

“We can place the generators in better areas when we are thinking about the highest value energy to meet the grid’s hourly demand, as this model does,” said Chris Clack, a research scientist with Cooperative Institute for Research in Environmental Sciences at NOAA.

Significant carbon reductions can be achieved with existing technologies if generation is more efficiently connected to load centers, the NEWS tool found.

The news from NEWS

NEWS was programmed to optimize for the least expensive U.S. system. It produced two high-level insights, MacDonald said.

First, the larger U.S. electricity markets saw greater emissions and cost reductions as a result of the model. Second, a U.S. low carbon future does not have to mean more costly electricity.

Conclusions depend on the variables in NEWS, MacDonald acknowledged. Its input included comprehensive cost and price information from the Department of Energy’s Energy Information Administration (EIA) database and a target date of 2030.

The solution NEWS lands on incorporates wind, solar PV, natural gas, nuclear, and hydroelectric generators. It assumes the build out of a nationwide HVDC transmission network, which the paper reports “is more efficient and cheaper” than high-voltage alternating current (HVAC).

The “key constraint” in the model, according to the paper, was “it must provide electrical power for every hour to every market while operating within current technology limits.”

Key to the cost savings achieved in the NEWS model is that the wind and solar PV plants “are geographically dispersed over the entire contiguous U.S.,” the paper reports.

“All the sensitivities show a bigger area connected by HVDC transmission costs less and mitigates more carbon,” Clack said. “That is the main result from the paper.”

The researchers also considered modeling for enhanced penetration of distributed resources, MacDonald said, but their model did not take into account potential system benefits that could mitigate for their higher installed cost compared to central-station generation.

“The answer is costs," he said. "They go up 50% to 100%. Our job was to find the lowest cost solutions for the entire electricity sector. Any argument in favor of more distributed generation would have to justify higher costs and higher emissions.”

What an optimized transmissions system could look like, according to the NOAA paper.

Transmission and the regulatory process

“Plans for national HVDC transmission to link our renewable energy resources have been proposed before and they are exciting because they remind us of our solar and wind riches,” said Nancy LaPlaca, energy consultant for the clean energy advocacy group NC WARN. “But these proposals also remind us how difficult it is to get new transmission through the regulatory process.”

Even the Obama administration’s landmark Federal Rapid Response Team for Transmission (RRTT), created to streamline federal agency cooperation and move proposals through permitting complexities and delays, has had limited impacts, LaPlaca said. Projects like the Clean Lines in the Midwest and Tres Amigas in the Southwest are still in limbo.

NEWS didn’t consider the challenges of transmission development like rights-of-way (ROWs) and permits, Clack said. But among their 500 simulations were those that doubled the cost of the transmission build out.

“If it was undergrounded along railroads and interstate highways, there would be nowhere near the resistance,” Clack said. “We looked at that instead of going into the nitty gritty of policy and regulations.”

Transmission was about 4% of the total cost assumed by NEWS, but doubling of that cost factor would still result in the GHG reductions, while only raising average retail electricity rates from about $0.104/kWh to $0.107/kWh, Clack said. Today, average retail price is around $0.12/kWh in the U.S., though costs vary greatly by region.

"The experts we’ve consulted say that doubling the cost of the transmission build would cover the cost of undergrounding the build on average across the country," he added. In places like the Rocky Mountains, they were told, it would be more expensive. But in places like the Midwest, they were also told, it would cost little more than overhead lines.

Telegraph lines were built along railroad ROWs in the nineteenth century and much of today’s fiber optic network was undergrounded along them, MacDonald pointed out. In both cases the railroads were paid for their cooperation.

Since this would be a national undertaking, he added, the federal government could also grant undergrounded ROWs along interstate highways.

Railroads and highways “go wherever these lines would need to go and I am confident the railroad companies could see the economic opportunity,” Clack said. "In addition, having trains lay these cables would be easier than doing it with trucks.”

It would require a national plan but "it could be done in conjunction with the private sector,” MacDonald said. “Third parties with private capital could bid to do the build like toll roads are built.”

NEWS shows “the economics are truly there,” Clack added. “It should help get projects moving forward.”

Wind potential mapped on the left, solar on the right

What about storage and the distribution system?

There is nothing wrong with an effort like a national transmission and renewable energy plan, LaPlaca said. “But we have to keep building solar and wind near existing transmission and we have to keep working on distributed energy resources at the grid edge because cutting greenhouse gas emissions isn’t something we can wait to do.”

Some think a bulk power system solution may also overlook some technical difficulties and miss some opportunities.

If a system like the one proposed is built, observed SolarCity Grid Engineering Solutions Sr. Director Ryan Hanley, it creates the risk of stranded assets if demand falls off or technology evolves. 

“The BPA transmission project was recently cancelled due to changed load scenarios," he noted. "The use of HVDC does not insulate grid planners from incorrect forecasts or the risks of massive, inflexible grid investments.”

The proposal is not in conflict with the pursuit of a distributed grid, but but has many of the same challenges as today’s grid, Hanley said. Distributed assets are more flexible and can target system weaknesses.

“The trickiest part is getting the system to balance continuously,” pointed out Strategen Consulting Co-Founder and Managing Partner Janice Lin, the Co-Founder and Executive Director of the California Energy Storage Alliance. There are additional costs for that, she added.

Distribution system costs were implicitly included in NEWS because it assumed today’s 68% to 32% transmission to distribution cost ratio, Clack said. “For each $0.68 spent by the model on transmission, it is assumed another $0.32 is needed for the distribution system.”

Distributed resources make the delivery of electricity from the transmission level to the distribution level and into homes and businesses where it is ultimately used more reliable and cost-effective, Lin said.

“The system has to operate at 60 Hz and things happen at a local level,” she said. “That is why we have backup generators and resources to support the grid. What if a tree falls on a line?”

The NOAA researchers’ proposal offers “significant improvements in the transport of renewable energy over long distances,” Hanley said, “but it does not solve the challenges of centralized planning itself.” 

The NEWS model does not explicitly model system regulation costs but is required to balance frequency and voltage at all times, according to Clack. NEWS applied grid system operating standards to keep the power flow in balance, allocated 7% of the calculated costs as load following reserves, and held 15% of peak load as planning reserves.

The geographic scale removes much of the sub-hourly higher frequency regulation now necessary, according to Clack. “The hourly variability is explicitly modeled and the load is matched in each market each hour for an entire year…while providing 7% following reserves and accounting for the electric losses for shuffling power across the U.S.” 

In theory, MacDonald added, variability of wind, solar, and demand over large areas can be balanced with a real time control system that determines power flow over the whole network, including power input and output from multiple stations.

“Such a control system has to interface with the AC distribution system,” MacDonald said. “But the engineers I have talked to indicate the DC tie tends to stabilize smaller scale AC distribution systems.” 

Without addressing the NEWS authors’ plans specifically, Lin believes storage and other distributed energy resources (DERs) would improve any bulk transmission system scenario because they would “optimize the load side.”

Even with supply that is completely sufficient, DERs can make the load less peaky, she said. “And why have a purely supply-driven solution? Being smarter about load and smarter about supply will help cost-optimize transmission and distribution and make the whole system more reliable.”

NEWS showed there would be “extraordinary costs to get to higher levels of distributed resources,” Clack said. “One of the biggest costs will be upgrading the distribution system because it is not designed for two-direction power flows. Utility-scale renewable sources would be just like other traditional generators with one way power flows.”

DERs offer the “unique advantage” of stacked revenue streams that many valuations do not account for, observed GTM Research Grid Edge Analyst Andrew Mulherkar. They benefit utilities, the grid, and help reduce GHGs, and they also provide value streams like lower customer bills, backup power, and increased control of energy use.”

The possibility of transitioning to a national bulk power system is intriguing but has challenges, he said. “There is a very high growth potential for DERs because they are drivers for the utility, for consumers, and for commercial and industrial customers.”

Different perspectives

Formidable challenges come with “a large transformation of the U.S. electrical power system by the 2030s,” acknowledges the NOAA researchers paper. They include “the integration of variable generators; changes to the existing regulatory, commercial and legal system; and investments in an HVDC network and new power plants.”

At the same time, it offers the potential for benefits beyond an 80% GHG reduction from power generation, MacDonald noted. “The electric system is only about 37% to 38% of U.S. carbon emissions. There are also autos and trains and space heating that generate emissions.”

Electricity is increasingly being used for those purposes, he said. “If that means more coal, we have lost. But if you decarbonize electricity generation, you decarbonize those things, too.”

This plan, with existing technology, will also work in other major world economies like China and India and Europe, he added. “There is an opportunity here to do something in the immediate future.”

The transition “would be a difficult transition,” the paper concludes. But it is "not dissimilar to previous U.S. projects for the creation of national markets, such as the transcontinental railroads of the nineteenth century, and the interstate highway system of the twentieth century."

Utilities charged with the responsibility for keeping the lights on and the air conditioning running often don’t have the same a historical perspective as researchers.

“Pumped and battery storage are definitely areas that need to expand as we incorporate more renewable energy on the grid,” observed Duke Energy Spokesperson Randy Wheeless. “But the need for new transmission will not go away – especially as we move to a world where generation could be distributed all around our system.”

“Grid design requires the use of a diverse set of assets to minimize risk,” Hanley said. “Making the grid more distributed supports greenhouse gas emission goals while also introducing more flexibility into the grid to mitigate the risk of large, centralized outage events.”

Filed Under: Transmission & Distribution Solar & Renewables Distributed Energy Regulation & Policy