U.S. speeds toward a cleaner grid, raising questions

Source: John Fialka, E&E News reporter • Posted: Thursday, April 26, 2018

When it comes to generating renewable electricity, Hawaii is leading other states in almost every category.

It gets 33 percent of its electricity from rooftop solar and has 60 utility-scale renewable energy projects feeding power into its grids. The state Legislature wants to reach 100 percent renewable energy by 2045.

Just how it does that, while preventing overloads and brownouts, is being closely watched by other states. Hawaii provides a “preview” of what states might do as the United States moves faster toward renewable energy than many experts anticipated, according to a study released this week by the National Renewable Energy Laboratory.

“If this can be done in Hawaii, it can be replicated anywhere else,” said Martha Symko-Davies, program manager for NREL’s Energy Systems Integration Facility. The report pointed to solutions for feeding large amounts of fluctuating renewable energy into the six power grids that distribute the Hawaiian Islands’ electricity.

The study shows that the use of “smart inverters,” switches that can automatically respond to potential overloads, help the grids handle the ups and downs of solar power. The growth of rooftop solar, long thought to be the wild card in controlling grids, “could actually be an asset for grid stability,” the study says.

There are days now when Hawaii approaches having 60 percent of its power come from renewable energy. It’s popular in part because Hawaii has traditionally generated most of its electricity from high-priced imported oil.

But other states are finding their own reasons to hasten the pace toward renewable energy. The record-breaking enthusiasm for more solar and wind power among utilities and consumers is pushing the management of the nation’s electric power grids into uncharted waters.

In January, the U.S. Energy Information Administration (EIA) announced that almost half of the utility-scale power generation capacity installed in the United States last year involved renewable energy. It predicted that wind power will surpass hydroelectric power this year as the nation’s largest source of renewable energy. It would be the first time in history.

The nation’s combined wind and solar power set another record, producing over 10 percent of U.S. electricity. It marked the first time since 1984 that renewable sources eclipsed the amount of power produced by the country’s nuclear power plants. And during some days last spring, California’s rapidly growing solar generation produced more than 50 percent of the state’s entire electric power demands, according to the EIA.

The bad news is that the galloping growth of solar and wind power presents a lot of unknowns. Computer modelers see a challenge in keeping the grids delivering reliable power during peak demand periods if renewable growth accelerates.

‘Fuel for free’

Apart from the experiments in Hawaii and at NREL, there has been relatively little experience to predict how to manage a big grid that functions differently when the wind stops or when the sun doesn’t shine.

“There is a bit of disagreement with the models, especially as you move out past 2030,” said John Bistline, a senior technical leader with the Electric Power Research Institute (EPRI), which does research for the public and for private utilities that produce 90 percent of the electricity generated in the United States.

Bistline met last year to explore the problem with experts from EIA and two other U.S. government agencies that model national power systems. After comparing their models formally for the first time, the groups issued a report in November. It concluded that because weather varies from year to year, multiyear data that don’t yet exist on wide-scale renewable energy production will be needed to more accurately model wind and solar.

“At a minimum, increased understanding of high penetration (of variable renewable energy) scenarios is needed to give increased confidence in model solutions that show significant evolution from today’s system,” the group concluded.

While solar power is rapidly becoming the cheapest source of electricity, the modelers found that a utility that builds facilities that produce more than it can distribute may find it becoming more expensive.

On the other hand, utilities looking to finance solar and wind farms will discover that “nearly all their cost is upfront,” the groups’ report said. Meanwhile, conventional power plants face continuing costs in fuel and the risk that those costs will increase over the life of the plant.

“Anytime you get fuel for free, it’s got to be a good thing,” said Wesley Cole, an energy system analyst who helped create the model for NREL.

Among the questions that worry modelers is how many coal and nuclear plants can survive the competition from renewables and still be around by 2030. They help control and back up the grid during periods of peak power demands. Another puzzle that Hawaii is exploring is whether large, reliable energy storage systems will emerge in time to store excess solar and wind energy at reasonable costs.

“We used a range of metrics to try to understand the impacts of different scenarios,” said Bistline. “These involve many, many billions of dollars. So there’s a lot at stake here.”

“The models are trying to measure do you have enough power to keep the system operating in the highest-risk hours. That’s been a very hot topic,” said Cole. “In general, we have a first-order approximation of things, but there’s a lot of room for improvement down the road.”

Storage and a carbon tax

The emergence of electric cars could increase power demands, but they could also lead to the development of bigger and cheaper batteries that can store large quantities of wind and solar power. Storage “is a potential game changer, particularly for solar,” said Cole. “You could get much higher penetrations of solar,” he explained, if it could be used in early evenings when sunlight fades but power demands remain high.

“Storage is a really critical piece of this puzzle,” said Chris Namovicz, the leader of EIA’s renewable energy analysis team. States that set high targets for renewable energy production present another puzzling question for modelers, he added. There are about 30 of them, led by Hawaii, New York and California, which plan to achieve 50 percent renewables by 2030.

The definitions of these targets and how states might reach them also differ. Complicating factors, according to Namovicz, include how many of these targets might be met by importing renewable energy from other states, and the cost of new power lines that might have to be built to carry the imported power.

One development that caught the modelers’ attention was a recent test by NREL of a 300-megawatt solar plant in California. The plant, owned by First Solar Inc., demonstrated that it could help balance grid supplies and demand by using electronic inverters to cycle power levels up and down. It’s one innovation that might substitute for the loss of coal- and natural gas-fired plants that provide these backup services now.

Another big question is the impact of a national carbon tax that might be passed in the future.

“We’re not in the business of trying to tell people what the policies should be in the future,” Namovicz said. “We’re trying to represent how markets behave so when you introduce different scenarios that you understand what the impacts would be, generally.”

How to model the nation’s three power grids under the stresses of more renewable energy was an area where the four teams of modelers in the separate studies disagreed. The interconnected grids amount to one of the largest and most complex man-made machines on Earth, and each team picked different metrics for policy reasons.

EPA compared data from 64 U.S. regions; EIA chose to divide the United States into 22 electricity supply regions; EPRI viewed the system using state boundaries; and NREL used data from 152 regions, some of which extended, as the grids do, into parts of Canada and Mexico.

To be sure, computer models can’t provide all the answers, noted Bistline of EPRI, but the modeling teams wanted to give utilities, government policymakers, environmental groups and other stakeholders more than just a glimpse of the challenges that having more renewable energy will pose.

“We want to make sure to get into the bark on the trees, but also present a view of the whole forest,” Bistline said.