This Week in Green Tech: Heavyweight Energy Storage, Wind Farm Insights, Virtual Career Fair
Tom Lombardo posted on May 20, 2020 |
A heavyweight energy storage system, wind farm R&D, virtual fair and more.

It is a good week to shelter in place and read up on the advances in renewable energy. This time we examine an interesting energy storage system, some research about long-term production from wind farms, and a renewable energy company delivering a virtual career fair.

Heavyweight Energy Storage System

As the world moves from fossil fuels to renewable energy sources, energy storage becomes more of a necessity, due to the intermittent nature of solar and wind power. Giant banks of Li-ion batteries are popping up all over the grid, but these batteries are made from toxic chemicals and have limited life spans. A cleaner, less expensive, and more durable system continues to elude engineers, but one self-described “serial innovator” thinks he has a solution, and it’s massive … literally.

Gravity-based energy storage has been around for years, primarily in the form of pumped hydro facilities, where water is lifted to a reservoir when electricity supply exceeds demand and flows back down to generate electricity when it’s needed. The system is responsive, efficient and nontoxic, but it depends on geography. An upstart called Gravitricity developed an energy storage technology that uses weights instead of water, and the company thinks that it will become a serious contender in the long-duration energy storage arena.

Weights go up and down to store and release energy. (Image courtesy of Gravitricity.)
Weights go up and down to store and release energy. (Image courtesy of Gravitricity.)

The principle is simple: when an energy source like a solar or wind farm is generating more energy than the grid requires, the excess energy is fed to motors that lift a heavy mass. When the renewable resource diminishes, the mass is allowed to fall in a controlled manner, and the motors become generators. Since energy equals force times distance, it takes a lot of weight and a great height to get an appreciable amount of energy out of this arrangement. Deadweight is easy to come by (feel free to insert your own political jokes here), but for the height requirement, we either have to dig or build to achieve it. Gravitricity has two solutions: first, it plans to use abandoned mine shafts, some of which are over a kilometer deep, and already have existing infrastructure for bringing electricity in and out of them. Once the technology is established and the costs come down, the company plans to dig its own shafts, making it less dependent on geography. Here’s the company promo video:

Gravitricity says that its system can accommodate masses of 500 to 5,000 metric tons with shafts between 500 and 1,500 meters, giving energy levels ranging from 204 kWh to 20 MWh. At the high end, that’s enough to power more than 8,000 homes for two hours. The company claims that it has a response time of less than one second, is 80 to 90 percent efficient, and can last for more than 50 years with no degradation. All of those claims appear feasible given today’s technology, but I question the system’s cost-effectiveness. Gravitricity says that it can get the price down to $171/MWh—less than half of the cost of Li-ion technology, which it claims is $367/MWh. I don’t know when Gravitricity obtained those figures, but at the time of this writing, the levelized cost of energy (LCOE) for Li-ion batteries is well under $200/MWh and falling faster than… well, lead weights down a mine shaft. By the time Gravitricity hits its target, Li-ion could break the $100/MWh threshold. Nonetheless, the company is investing over $1.2 million to build a small-scale demonstrator plant in Scotland. I’m skeptical about its commercial prospects, but I won’t be disappointed if Gravitricity proves me wrong.

A 16-meter tower with 50 tons of mass will serve as a demonstrator. (Image courtesy of Gravitricity.)
A 16-meter tower with 50 tons of mass will serve as a demonstrator. (Image courtesy of Gravitricity.)

Wind Turbines Show Very Little Degradation Over Time

Researchers at the Lawrence Berkeley National Laboratory examined the performance of wind farms as they age and found that during the first 10 years, the output decreased by 0.53 percent per year in farms that housed older turbines, while more modern turbines experienced a paltry 0.17 percent annual decline in performance. After 10 years, however, the performance of older turbines took a sharp 3.6 percent hit before settling into a steady 1.27 percent annual decrease. The scientists noted that wind farms in Europe experienced a slow, linear decline that didn’t abruptly shift after a decade. What’s the difference? In the U.S., wind farms are eligible for a tax credit during their first 10 years of service. The researchers concluded that once the credit elapsed, utilities spent less money on maintenance, allowing the turbines to slip into disrepair.

Annual performance of newer wind farms compared to older wind farms. (COD = Commercial Operation Date.) Image courtesy of Hamilton et al., “How Does Wind Project Performance Change with Age in the United States?,” Joule (2020).
Annual performance of newer wind farms compared to older wind farms. (COD = Commercial Operation Date.) Image courtesy of Hamilton et al., “How Does Wind Project Performance Change with Age in the United States?,” Joule (2020).

On the positive side, even with the steep drop-off, U.S. turbines still fared better than their overseas counterparts. Researchers attributed this more to terrain than technology or maintenance. Many U.S. wind farms are located in the flat Midwest, while those on other continents often reside in hilly or mountainous regions. Rough terrain can lead to more turbulent winds, which cause additional wear and tear on the turbines. The study, which provides insights for utilities, investors and policy-makers, was published in the energy journal Joule.

Green Power Education

To prepare tomorrow’s workforce for careers in sustainable energy, sPower, an independent utility with more than 150 renewable energy plants across the U.S., is hosting its first Virtual Renewable Energy Career Fair, which puts the spotlight on some of the company’s youngest professionals as they describe their paths to the renewable energy industry.

Wind and solar analyst Skye Mooney talks about her career in renewable energy. (Image courtesy of sPower.)
Wind and solar analyst Skye Mooney talks about her career in renewable energy. (Image courtesy of sPower.)

In addition to the career fair, sPower’s “Careers in Renewable Energy” presentation, which the company had been delivering in classrooms, is now being made available via online conferencing. Interested educators can make a request using the contact information on the career fair website.

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