Not for lack of ideas: an interview with NREL’s Dr. Peter Green


Editor’s note: We at pv magazine are big fans of the U.S. Department of Energy’s National Renewable Energy Laboratory (NREL). For years, NREL’s reports have informed our coverage by providing highly detailed technical insights into many aspects of renewable energy, including everything from the composition of PV system soft costs to issues of integrating very high levels of wind and solar on the grid. As such, it is a great honor to present an interview with Dr. Peter Green, who serves as the deputy laboratory director for Science and Technology and the chief research officer for NREL.


Dr. Peter Green. (Photo by Dennis Schroeder / NREL)

pv magazine: NREL has so many different program areas, and produces work on so many different facets of renewable energy. For our readers, can you summarize the main areas of work that NREL engages in, and how they relate to each other?

Peter Green: So let me do that. The lab as a whole is one of seventeen national labs in the United States, and we are generally focused on renewable energy and energy efficiency. The laboratory, which was founded in 1977 as the Solar Energy Research Institute and later becoming NREL in 1991, engages foundational scientific research, technological innovation and energy analysis.

One key area is building energy efficiency – residential and commercial buildings, and communities.. The first net zero-energy office building in the United States was built at NREL.

With regards to renewable power generation, the major areas are solar, wind and water, geothermal, bioenergy and hydrogen. In fact the first  wind turbine-specific air foils were developed by NREL, in collaboration with a number of industrial partners. Today NREL leads collaborative efforts to develop the next generation wind turbines and wind farm efficiencies. In the area of solar, we hold the world record for the most efficient multi-junction solar cells. We have made significant advances in improving the stability of perovskite solar cells (over 1000 hours) and developing manufacturing capabilities for roll-to-roll production of perovskite-based solar cells. This could be a game changer, with regard to the availability of truly cheap solar power.

Another area of research is bio-energy, where we work on the conversion of biomass to fuels and chemicals. Interestingly we are working on optimizing the performance of fuels for internal combustion engines and powertrains, with other labs; this is the DOE co-optima program. There is also work at NREL on the hydrogen economy: hydrogen fuel cells for vehicles, in collaboration with other labs and industry.

From the point of view of energy systems, we are working on the grid modernization initiative with a number of other national laboratories, utilities and private companies. We are looking at deployments of distributed energy resources, within the United States as well as in remote places, places like Alaskan villages and even parts of South America and Africa. NREL is also seriously engaged in the future generation autonomous energy grid, where artificial intelligence will be used to guide operational decisions, instead of humans. This should lead to a more resilient and secure grid.

Companies spend a lot of time at NREL, working with staff. For example Eaton has employees who are at NREL permanently, working in our state-of-the-art, one of a kind, energy systems integration facility (ESIF). ESIF is a facility dedicated to advancing the integration of clean energy technologies. 

And there are other areas of interest outside of renewable energy. We have collaborative  projects in the areas of oil and gas and nuclear energy, with other national labs. This is important because the globe is in the midst of an energy transition. Renewables aren’t ready to meet current global energy demands. So it makes sense to work with partners to understand how to increase the penetration of variable renewables (wind, solar) into the energy system which relies other non-renewable sources. Our goal is to increase efficiency, reliability, security, resiliency and reduce costs as much as possible for consumers.

To give you a sense of NREL’s impact, we are a lab of 1800 full-time employees, and about 500 non-permanent staff, and we have established over 800 partnerships, with cities (such as Los Angeles), towns, utilities, corporate entities in the US and around the world. We publish an average of 500 scientific papers, and approximately 200 other reports etc. Our economic impact just exceeded one billion dollars, annually, for the first time, in the history of the lab.


pv magazine: To delve more deeply into those partnerships, NREL has been working with Mexico’s INEEL in particular. Why are these partnerships a priority for NREL and what role do they play in the organization’s work?

Green: That’s a very good question. We have engaged with countries, cities and towns around the world for a very long time. This has involved, for example, disaster relief efforts in the US and abroad, helping people to develop more resilient energy systems.

Now with regards to Mexico our interactions go back almost three decades with IIE – that’s Mexico’s electric research institute – where we have done collaborative work on wind mapping in Oaxaca, for example. There have been collaborations on off-grid solar and wind installations; we’ve worked on microgrids, PV and water pumping systems – even training initiatives in Mexico collaboratively with IEE, going back more than two and a half decades.

Our work with INEEL is a natural evolution of our relationship. We are hoping to work in all areas of renewable energy, if possible. Regarding the energy grid, we’d like to continue to expand our activities on distributed energy resource  projects. We have significant activities with other national labs and utility companies in this areas. We are working with partners on solar installations in various places, as well as understanding markets, and educating the consumer.


pv magazine: So NREL has conducted a number of studies on integrating very high levels of renewable energy on the grid over the last decade. How has the understanding of integrating higher levels of wind and solar changed over time, and why is it important for NREL to do this work on this issue?

Green: Based on our knowledge the science and technology of various renewable power generation sources, our high performance computing facilities and our expertise on techno-economic analysis, we’re in a unique position to do this kind of work.

With the integration of larger penetrations of variable renewables (wind, solar) into the energy grid, many questions including voltage stability (two-way energy flow because consumers can sell power generated at their homes back to the grid) and indeed grid stability need to be addressed. We performed a study a few years ago – the EGRIS study – where we considered a realistic number of consumers across the eastern United States, a huge number of generation facilities (renewable and non-renewable) and their operations, and using realistic time intervals, we performed the world’s most sophisticated computer simulations to understand potential challenges for power generation. These kinds of studies provide insights into planning for future infrastructural needs, including power electronics device performance requirements, for high penetrations (>50%) of variable renewable energy.  NREL has since published other papers on this topic.


pv magazine: I think we’ve all noticed the calls by certain politicians to cut funding to both renewable energy and basic research, yet NREL has retained relatively stable levels of funding in the recent budgets that have gone through the U.S. Congress. Can you talk about the base of political support that NREL has, and why it is so broad?

Green: Yes, the good news for us is that our operational budget right is in excellent shape and we hare hiring additional researchers for a diverse range of our programs. I think that the large number of meaningful partnerships with power utilities, industry and academia have proven that we add value. The administration understands what we actually we bring to the table.

Hosting visits from the Energy Secretary Perry, the deputy secretary and the under-secretary, have enabled us to demonstrate our capabilities and actual impact and to tell them about the serious work that the laboratory actually performs on behalf of the nation. They have all been pleased, and that has really helped.

In short,  there is a lot of support from people, and organizations, with whom we have worked, and this has been helpful.


pv magazine: You’ve talked about how NREL is very active in looking into how to boost the penetration of renewables, including solar. How do you see battery storage developing? What kind of pace of adoption can we expect next year and the years that follow?

Green: All indications are that the adoption is going to increase because battery prices are continually dropping, at a more rapid pace than expected, due to scientific and manufacturing advances. There is a wide range of battery chemistries, beyond lithium ion batteries, being investigated by labs across the globe. We anticipate a continued trend towards prices reductions and increased reliability; as prices drop there is going to be more adoption.

EVs are continuing to be adopted at a rapid rate, across the globe, with China providing the largest markets. The Chinese have developed policies to ensure the growth of the markets. All the big auto makers have plans for increased EV adoption. 


pv magazine: You actually see that various battery technology are going to be involved? It won’t be dominated by lithium ion? What’s your sense?

Green: For the next decade of so lithium ion batteries are going to be dominant. But there are new opportunities out there. For example, new battery chemistries are available and others are soon be discovered. This is clear from the scientific literature.

The work on flow batteries for grid storage applications, is promising. Vanadium flow batteries is a good example. NREL is engaged in all of these areas, including next generation batteries -beyond lithium ion – and battery safety and performance.


pv magazine: It is very interesting how NREL is also involved on the automotive side. You mentioned your partnership with big auto companies. So you really have an understanding of how storage and lithium ion is being deployed, and what these carmakers need. So you can also factor that into your simulations, in terms of what batteries have to deliver, what energy storage has to deliver, to really pump up the share of renewables in power generation.

Green: When I think about renewables in the transportation system, three things typically come to mind. First, bio fuels – produced from plant waste (not corn) – will play an important role.  This will particularly be true for heavy-duty vehicle long distance transport (not withstanding short-haul electric trucks used on some European cities). 

The second case involves hydrogen fuel cell powered vehicles. Hydrogen powered vehicles (many of which are driven in southern California), have a range of up to 400 miles. Such vehicles are available on the NREL campus. NREL has significant activities in this area, collaboratively with other national labs and the auto industry.  The challenge is cost and the lack of a large-scale fueling infrastructure; this will be solved with time.

Finally, most automobile manufacturers expect that the cost of ownership of EVs will be sufficiently cheap, by 2023 , that most people will want to own EVs. The cost of maintenance of EVs is also cheaper than the internal combustion engine vehicles. Of course, the widespread adoption of EVs will be limited by the charging infrastructure.


pv magazine: I wonder how that will pan out, because you know it’s difficult to invest in charging infrastructure if you don’t have that many EVs, but you also don’t want to be pushing EVs if you don’t have charging infrastructure. It’s kind of a chicken/egg problem.

Green: Actually, this is more straightforward than it would appear. NREL has published work that evaluates different scenarios of electric vehicle adoption and the charging infrastructure that would be required. States like California and Colorado are making plans for an eventuality of widespread EV use. We have also published  a study that evaluates the effects of different percentages of adoption of EVs and the effect of uncoordinated charging on the performance of the electric grid. Research in this area will provide the appropriate guidance to community planners.


pv magazine: What would be your main recommendations for developing countries that could benefit from PV?

Green: Virtually all places around the globe recognize the importance of PV. The price has dropped, and continuing to drop, to the point where it is competitive with basically every other form of power generation. So it is becoming more and more affordable everywhere. Customers are going to use PV only as long as they can realize savings, and they certainly can.


pv magazine: I have one more question. The bigger picture now, one is increasing the penetration of renewables like solar, the other is, we haven’t gotten too good of feedback lately, the meeting now happening in Katowice to continue what happened in Paris, and you had that rather negative assessment from the IPCC on staying below 2 or 1.5 degrees Celsius. The IEA has even said that there are more coal-fired power plants coming along in Asia and other regions.

Do you think we can still stop this warming? Do you think that solar and other renewables can play an even bigger part to help out here?

Green: Solar and wind will play a bigger part, in the future. The research on the next generation wind energy (much larger and more efficient wind turbines, and more efficient wind farms), and cheap, stable, and more efficient solar cells (e.g.: perovskites and low cost high efficiency multi junction solar cells), will provide terawatts of power needed to provide energy for the globe.  Other renewable sources, together with new cost effective storage technologies, are eminent. Researchers across the globe are highly motivated.  I believe that the final analysis, the economics will drive decisions.

The other good news is that in cities and towns around the world, the behavior of individuals is influenced by local policies. In other words, grassroots efforts around the world are proving to be effective.

In short, it is not for lack of ideas. The ideas are here. The technologies are here. It is only a question of whether we can make things sufficiently cheap and will people adopt it at a sufficiently high rate.

It is going to take an effort on the part of everybody, in every part of the globe -literally every single person.


Interview conducted by pv magazine Managing Director Eckhart Gouras, pv magazine Americas Editor Christian Roselund and Energía Hoy CEO Santiago Barcón Palomar.

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