Green Energy Advancements: The Latest in Solar Energy R&D

Solar energy is at the forefront of sustainable energy technology options. Despite some limitations, innovative research and development continues to expand solar energy’s potential and capabilities. Matthew Bauer, PhD, concentrating solar-thermal power (CSP) program manager at the US Department of Energy Solar Energy Technologies Office, discusses the current landscape of solar energy research, and explains the importance of focusing on CSP technologies to enhance solar energy’s adoption as a reliable source. 

Q: Can you briefly explain your role at the Department of Energy?

A: I joined the Solar Energy Technologies Office (SETO) eight years ago originally as a contractor and I've served most of that time as a technology manager, working on all sorts of projects. I've probably managed over 100 R&D projects—everything from how the optical systems work to power cycles to thermal energy storage, material science, all the way to demonstration projects. About a year ago, I took over as the program manager of the group, and I've really enjoyed working with the diverse set of people that I interact with since then.

Q: What are some of the key advantages to solar as a sustainable energy option?

A: First, there’s access to the sun from anywhere, even where there’s low resource. And it can be a passive system that can be used at very modular sizes. Whether you need under a megawatt, a couple megawatts, or very massive scale, there is a path to find the right combination of solar technologies.

Q: What are the current challenges in harnessing solar energy on a large scale?

A: There are land use restrictions to think about, and our office is focused on identifying, acquiring, and successfully preparing a specific location to host a solar energy system in partnership with local communities. You can also think about the long-term planning needed and upfront costs. But of course, the greatest limiting factor is when the solar resources are available and handling that predictability to find ways to complement solar technologies with something that firms the energy output in a manner that is most usable in the case needed. 

Q: What innovations or developments are emerging in energy storage technology?

A: The baseline right now is the molten nitrate salt system, which is the commercial concept that's been deployed. It has temperature and cost limitations and reliability challenges. 

We've been investing heavily and have done a lot to advance the commercial maturity of particle-based storage—making sand-like materials or modifications so that they can operate at any temperature and don't have corrosive limitations. It can work with any power cycle or application. For that reason, we think that there's opportunity for it to be cheaper than even existing thermal energy storage—hopefully under $15 per kilowatt hour  thermal. We think it scales down better than nitrate salts. But there's a long way to go in the research front. There are different technical challenges for solid particles that are flowing than nitrate salts and other mediums.

Q: Are there any other types of novel materials that are being pursued to boost solar energy efficiency and/or storage?

A: I touched on the solid particles already. We know stainless steel pipes or containment material don’t work at those very high temperatures; even the more advanced nickel alloys, we studied them, and we've done everything we can to move their commercial maturity. They work in a lot of places for us, but sometimes we have to go beyond that. 

So, an exciting project we're working on is modified silicon carbide and other ceramic systems. These materials have potential to work in CSP receivers, which are a very high thermal stress environment that has a risk of not lasting for the 30-year need of the product. And we even look beyond those types of materials. 

The open question is what would you use if you wanted to operate a high-stress environment and 1200 °C or higher? Because that's going to enable the very hardest applications in chemical production, potentially renewable fuels, and otherwise. That's an area that we're openly road mapping right now, and attempting to bring the early technology, readiness-level concepts to light and figure out a way to mature those.

Q: What other focus areas or current projects are in the works for SETO that are helping to progress the potential of solar energy?

A: A lot of times, material science gives us great chances to do innovative research. Another area is in the collector field. In a heliostat system, you have potentially hundreds of thousands of mirrors tracking the sun with multiple degrees of freedom and lots of loss mechanisms. And it's actually a very hard computational and metrology problem to get right and deliver energy reliably. We have a major consortium called HelioCon, which is short for the Heliostat Consortium, led by in NREL and Sandia National Labs, working to make the intellectual foundation and solve problems in that specific technical area so that we can get reliable cost-effective heliostats because we need to get costs down to have this be an affordable option, and we need them to deliver the power promised. 

The advancement of heliostats is a very different type research field than the rest of the concentrating solar power (CSP) system. Traditional mechanical engineering and material science development are the focus of the remainder of the power plant. However, the heliostat fields rely on innovations in mechatronics, communications and closed loop controls, optical measurement techniques and metrology. These are more commonly the domain of electrical engineers and computer scientists. That's an area where we need more researchers focusing on innovative solutions, and it's a unique area to CSP that isn't as cross-cutting as perhaps some of our high temperature material science. 

I'll also keep emphasizing that the area of high-temperature process heat applications is a very new focus area. Figuring out specific processes—whether it's desalination, which is at a lower temperature, or cement making at a much higher temperature—and how does that thermal system work, component by component, what is needed design, and then understanding the physics, the heat transfer chemistry and material science within those systems. A point I like to make is many people are CSP researchers and don't know it. We have so many kinds of technical expertise needed throughout a CSP team. We really try to tell folks that don't know CSP technology that they are still the folks that we need working on our problems if we're going to get the best solution possible.

Q: How do you predict the adoption/application of solar energy will evolve in the next few years?

A: For electricity production, as there is true demand for overnight renewable dispatch—which is going to happen as we get deeper and deeper into these renewable targets—that's when the CSP becomes potentially the best option. In the next few years, CSP can play a role in supporting 12 plus hours of energy storage, which goes beyond where lithium batteries have been cost effective up to this point. Such long durations of energy storage will become more necessary as we push for a more decarbonized electricity grid. The other near-term opportunity is to make inexpensive solar thermal trough systems for low-temperature process heat. It's more of a “how do you optimize design for these kind of bespoke applications and make deployment accessible?” CSP has the challenge that thermal systems aren't as easy to copy and paste as electrical systems. So repeat deployment becomes more of an engineering challenge and we need to solve those problems and make them streamlined.

Matthew Bauer, PhD, is the acting program manager for the Solar Energy Technologies Office CSP team. Since 2015, he has worked with the CSP R&D community to identify promising CSP-relevant technologies and solve technical risks impeding such technologies from commercial adoption. While primarily focused on CSP for electricity generation, Matthew also develops frameworks for technology advances in related applications including pumped thermal energy storage, solar thermal process heat, and solar thermochemical processes. He has headed SETO’s 2019 FIRM Thermal Energy Storage initiative, SETO’s 2018 Advanced Components R&D initiative, as well as the CSP program’s reoccurring seedling research initiative, Small Innovative Projects in Solar, and parallel national laboratory research. Prior to joining SETO, Matthew completed his PhD in mechanical engineering at the University of Virginia.