As energy demands continue to grow, clean and sustainable energy sources become forefront in global efforts to reach ‘net zero’ carbon emissions by 2050 [1]. While these standards may seem lofty, researchers across disciplines at UW-Madison’s College of Engineering continuously discover new ways to help make it possible.
According to the National Renewable Energy Laboratory, current renewable energy generation, most notably solar panels and wind turbines, have the capacity to produce 80% of the energy within the United States. Today, however, renewable energy only accounts for about 18% of U.S. energy consumption [2]. According to Line Roald, an electrical and computer engineering assistant professor and Grainger Institute for Engineering fellow, closing this gap means addressing the physical, logistical and technological challenges of maintaining a reliable energy supply.
“We want to maintain that people are able to access electricity at the location they need it, when they need it,” Roald says. “To achieve this, the electric grid is crucial.”
Roald notes that some of us may have access to locally generated electricity, such as rooftop solar, but many of us don’t. And for the U.S. to rely more fully on renewable energy sources, we need a more resilient grid that can compensate for uncertainty and variability in energy production—clouds unexpectedly rolling in on a sunny day—as well as transport electricity longer distances—from windy spots to calm ones.
Due to their variable nature, incorporating renewables like wind and solar into our energy mix requires strategic grid operation. Balancing and maintaining supply and demand at all times requires planning, prediction, and quick adjustments to power output. If this is not done effectively, variability can damage components and cause power outages. Alternatively, the grid can end up with an oversupply, increasing the cost of renewable energy production.
Roald is developing new methods for operating the transmission and distribution infrastructure to help overcome renewable variability, but also to transport electricity longer distances without having to build unnecessary new transmission and distribution. “We are developing new scheduling methods and software to make better use of the resources we already have,” she says.
“Another of the key challenges about an electric system is that there is very little storage,” Roald says. “We are getting better battery storage, but we are far away from having a lot of it.”
This lack in energy storage is escalated in a renewable system, Roald notes. On sunny days, there may be a spike in the grid’s energy supply from solar, but without ample storage techniques, this energy is lost, unable to meet demand on cloudier days. While battery options are available for this kind of storage, they are relatively inefficient, losing energy as soon as the charging system is removed, and they are very expensive.
Luckily, though, batteries are only one way to store energy: UW-Madison’s engineering researchers are looking holistically for other storage methods to create a more reliable supply of renewably sourced energy on the grid.
Raising the Supply
One of these researchers, mechanical engineering assistant professor Mark Anderson, uses thermal hydraulics to capture and save solar energy. According to Anderson, concentrated solar, a method which captures heat using mirrors to focus solar radiation to a single spot, provides an opportunity to store energy long-term. How is this possible? Molten salts.
Molten salts stored in large tanks can hold thermal energy for long periods of time, producing steam to power a turbine and generate electricity when it’s needed. Anderson is looking into raising the round-trip efficiency of this steam generation cycle by increasing the temperature of the molten salts from 550 degrees Celsius to 750 degrees Celsius.
Often, the feasibility of renewable sources is criticized for the economic trade-offs of making the switch from conventional sources. For the concentrated solar that Anderson researches, however, the ability of this method to help maintain the reliability of supply could make quite an impact in the energy generation marketplace.
“Because of this grid resilience—and because sometimes there’s a negative price for power and sometimes power is very expensive—you can do some arbitrages using thermal storage,” Anderson says. “If people are trying to get rid of power, then the cost goes way down.”
Anderson is not the only engineering researcher looking for new opportunities in energy storage. Grainger fellow and electrical and computer engineering assistant professor Eric Severson studies flywheel technologies for storing energy, as well as bearingless motors for reducing energy consumption. When it comes to the unpredictable nature of renewable energy sources, flywheels surpass storage methods like batteries by using stored kinetic energy to smooth out the fluctuating supply and improve the overall power quality of the energy. But improvement is still needed to increase the storage capacity of these flywheels for longer periods of time.
“Flywheels have historically been somewhat successful for the power grid for really short intervals of time; it’s called frequency regulation,” Severson says. “What we’re interested in doing is making flywheels useful to the power grid for storing energy for longer intervals of time like a conventional battery.”
Lowering the Demand
Creating a smoother, more reliable renewable energy supply, while necessary, is only half the story. Motors that use less energy demonstrate how we can address another pressing challenge of renewable energy grid sustainability: energy demand that continues to grow. In a highly digitized world, there are significant opportunities for efficiency improvements that can reduce energy consumption on a large scale, lowering the overall demand.
Beyond energy storage, Severson’s newest research with bearingless technology is in increasing the efficiency of electric motors. Bearings inside conventional electric motors are a common culprit of lost energy. In electric motors that are 100-horsepower and larger, for instance, 30-80% of the energy is wasted, according to the Department of Energy. Add to that the reduction in energy efficiency when, in HVAC cooling systems, for example, bearing lubricant leaks into the refrigerant. We can avoid these losses, however, by taking these bearings out of the system. Severson notes that by implementing bearingless technology in large motors alone, we can decrease overall U.S. energy consumption by 6%.
To make demand decreases possible, Zhenqiang “Jack” Ma, the Lynn H. Matthias Professor and Vilas Distinguished Achievement Professor in electrical and computer engineering, and Bulent Sarlioglu, associate professor in mechanical engineering and electrical engineering, collaborate to lower energy consumption by improving semiconductor technology and its implementation. While Ma conducts cutting-edge materials and devices research, Sarlioglu utilizes Ma’s findings to create better and faster technology.
Right now, Sarlioglu is working on a project with NASA, developing the technology to make electric aircrafts a possibility. The compact and highly efficient semiconductor technology needed for electric aircrafts could also be used across the nation in everyday electric systems and devices to lower energy consumption and demand.
Traditional semiconductors are made out of silicon, but by changing the fundamental materials that make up semiconductors to silicon carbide, called a wide bandgap semiconductor, motors become more efficient. These principal developments in semiconductor technology can have big impacts when executed on a large scale.
In individual devices, energy improvements may seem small. Sarlioglu says existing semiconductors typically run at 95-98% efficiency, and silicon carbide moves this efficiency up to about 99%. While a 1-4% efficiency gain may not initially seem impactful, if you consider all of the things that use semiconductors—appliances, electric vehicles, air conditioning systems, fans, pumps and compressors—this wide-scale improvement could be incredibly significant.
“You can imagine in the world, in the U.S., how many there are. If you put them all together, that’s a number of the power plants,” Ma says. “Overall, we will be able to have a lot fewer power plants, and that’s good for the environment.”
Looking forward
The improvements do not end there. According to Ma, silicon carbide is just one generation of possible materials currently being investigated. While not completely ready for usage, ultra-wide bandgap semiconductors have the potential to be even more transformative than silicon carbide or gallium nitride wide bandgap semiconductors. Ma is exploring exotic materials—aluminum nitride, boron nitride, certain types of gallium oxide, and even diamond—to develop novel and highly efficient devices.
“Converting these excellent material properties and parameters into device parameters: that’s our job. We want to make that happen,” Ma says.
Across departments within the UW-Madison College of Engineering, interdisciplinary researchers seek solutions to many of the physical, logistical and technological challenges slowing the transition to a clean and sustainable energy grid. While additional infrastructure, economic, and policy considerations exist, much of the scientific research and technology development needed for a fully renewable energy grid is happening now, and UW’s engineering researchers have plans to continue generating new ideas, new research and new technologies.
Author: Katie Amdahl
Sources
[1] The UN Intergovernmental Panel on Climate Change (IPCC) issued a Special Report in 2018 saying that, “global net human-caused emissions of carbon dioxide (CO2) would need to fall by about 45 percent from 2010 levels by 2030, reaching ‘net zero’ around 2050.” The New York Times reported that the UN announced in 2019 that more than 60 countries signed onto this agreement, though only 11% of total international emissions come from those countries.
[2] The Sustainable Energy in America 2020 Factbook: Executive Summary notes that renewable power generation rose to 18% of all electricity consumed in the U.S. in 2019, most from new utility-scale wind and solar projects, along with rooftop solar systems.