Pumping water uphill: storing energy without batteries

Ross Baldick Electric Power Consulting

Jaime Luengo shows UT professor Gary Hallock how the solar-powered water pump works.

It’s been my pleasure for the past several years to supervise a senior design project in my Electrical and Computer Engineering department at The University of Texas at Austin. The project is aimed at avoiding battery storage in off-grid solar applications by taking advantage of the storability of the final product or service provided by an electric motor.

Think of an electrically-driven water pump that is filling a raised tank, with the water then being used for domestic or agricultural use by letting it flow downhill. If the pump and tank are sized appropriately, then the pump could operate when power is available and still pump enough each day to cover the needs.

Our team’s approach to powering this system from the sun without battery storage has been to use a variable-speed drive for an electric motor and vary the drive frequency to match the power output from a solar panel. When the sun is shining brightly and more power is available from the solar panel, we adjust the drive frequency up so that the motor can use all the power. When it is cloudy and the solar panel produces less power, we adjust the drive frequency down so that the motor is still pumping, but at a lower rate, and using the available power. By adjusting the drive frequency this way, we can utilize whatever power is available from the panel without battery storage. We are storing the energy by pumping water uphill.

Ross Baldick Electric Power Consulting

This year’s senior design team included (left to right): Carly Stalder, Ankit Sharma, Ji Hoon Seon, and Max Granat. Not pictured: Jaime Luengo, Cody Scarborough, Schuyler Christensen.

(There are other potential applications, such as-available air conditioning or other mechanical loads where there is inherent storage in the end-use product or service.)

Several senior design groups have been working toward this goal over the last few years. This year the students really came together and were able to build on previous groups’ efforts to build a working prototype that could harness variable light levels.

These photos show you the results: a working prototype that pumps more when the sun is bright.

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Pathways to decarbonization: ZECs, DERs, and inertia

Ross Baldick Consulting

Brad Jones (left) and Ross Baldick at the Austin Electricity Conference.

Decarbonization was the theme of the seventh annual Austin Electricity Conference, held April 20 and 21 by the UT McCombs School of Business, Cockrell School of Engineering, LBJ School of Public Policy, and School of Law.

As the name implies, decarbonization entails shifting the fossil fuel mix toward less intense producers of carbon dioxide together with reduced reliance on fossil fuels for electric generation over time. Our questions: How to implement a zero-carbon grid from a legal and policy perspective? How to achieve it from a technical perspective?

It was my pleasure to introduce keynote speaker Brad Jones, who has been an electricity industry executive for more than three decades. I first began to know Brad closely when he was Vice President for Generation Development at TXU. We  disagreed on whether to implement the nodal market, and I remember his graciousness and intelligence during that debate. He then became Vice President for Government Affairs at Luminant, the successor generation firm of TXU. He joined ERCOT as COO in 2013 and in 2015 became President and CEO of the New York ISO (NYISO), which operates the state’s wholesale electricity market and is responsible for its bulk electric system reliability.

Lower carbon dioxide emissions, green technology, and renewables, Jones said, have become front and center in New York, even making it into the headlines of The New York Times. At the NYISO, priorities include decarbonization, integration of high levels of renewables, and creating a two-way grid. The state is introducing a requirement for electrical load-serving entities to purchase zero emissions credits (ZECs) in proportion to their statewide load, with proceeds going to eligible nuclear power plants. This provides market-compatible support for nuclear generators that values their zero carbon emissions, complementing analogous schemes for renewable resources. He emphasized that ZECs are designed to be a bridge to the future, and that New York is not expecting that ZECs will be needed forever. The state, in other words, is acknowledging the social cost of carbon.

Jones also discussed distributed energy resources (DERs). We need, he said, to value the contributions of DERs, by: 1) facilitating compensation through transparent pricing and metering, and 2) offering financial credit for reducing the load on distribution systems.

Jones concluded by emphasizing the need to internalize a carbon price into the wholesale market. That price will help to do two things. First, to guide operational decisions toward existing low-carbon resources. Second, to guide capital decisions — such as building more low-carbon generation in New York and building new transmission to bring Canadian hydro power to the state.


Brad Jones (left) and Ross Baldick at the Austin Electricity Conference.

On my panel, “Managing the Decarbonized Grid,” we discussed the technical challenges of operating an electricity grid with low or zero emissions. I emphasized that these challenges depend on the mix of resources used. (Click here to download my introduction and the panelists’ introductory remarks.)

For example, our main path to decarbonization in recent years has involved renewable resources such as wind and solar, which are generally connected to the grid via power electronic converters. Power electronics interfaces have a crucial difference with traditional grid-connected rotating machinery in that they do not “natively” provide inertia. Inertia has been essential in the control of the electricity system since its inception, because it enables stable synchronization of the electric waveforms in the grid and serves to limit the rapidity of changes after a disturbance. In order to decarbonize with renewables, we need to deal with this reduction or elimination of inertia.

One solution is to utilize the renewable resources to “synthesize” inertia using the flexibility of their power electronic converters; however, the drawback here is that some of the renewable production is sacrificed. A second solution, being developed and tested by panelist Brian Johnson of the National Renewable Energy Laboratory in Golden, Colorado, explores controls for power electronic converters that do not rely on inertia to provide synchronization.

Click here to access all four of the conference panels.

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John Goodenough, batteries, and steam trains

Ross Baldick Consulting

John Goodenough

My wife and I often enjoy BBC documentaries, and historian Dan Snow is a favorite host.  In his series about the history of railways in England, he observed that, as the industrial revolution increased manufacturing in England, there was a need to move product around more cheaply, which in turn encouraged transportation innovations such as the steam train.

In a previous post, I’ve talked about the fraught nature of technical predictions. The same applies to predictions about costs, but the history of railways suggests that invention will be applied to reduce the costs of parts of the supply chain that are growing relatively more significant. For example, as relative costs reduce for any one particular contributor to electricity production, attention turns to bringing down the costs of other components.

In the context of renewables, we have seen ongoing reduction in the cost of wind and solar. To support the utilization of that energy, various ancillary services are required, including “regulation ancillary service.” If you had asked me a decade ago about renewable integration, I would have predicted that regulation ancillary service would become an increasingly significant part of the cost of renewable integration. However, in recent work  with Juan Andrade and Yingzhang Dong, we investigated why, in fact, the amounts (and costs) of regulation ancillary service have not increased in the Electric Reliability Council of Texas (ERCOT), despite a huge increase in renewable penetration.

The fundamental answer is that there have been a multitude of changes to the ERCOT market design that has allowed the generation capacity for regulation to be utilized more effectively. The biggest change was the move from the zonal to the nodal market, but other changes have also contributed. These changes have enabled significantly more wind power to be utilized without increasing the cost of regulation ancillary service needed.

As with locomotives and manufacturing, as the need and costs of ancillary services seemed to be looming larger, imagination and innovation have resulted in better ways to utilize ancillary services to complement the production of renewable energy.

As many of the contributors to costs of renewables decrease, the issue of intermittency and the need for storage becomes more significant. Battery storage is currently too high-cost for bulk storage. But John Goodenough, inventor of the lithium-ion battery and my colleague in mechanical engineering, has recently published a paper describing a solid-state lithium-ion battery that may significantly improve the economics of battery storage. Lower cost batteries may be the new locomotive of renewable development.

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“Smart Grid” highlights

Guest lecturer Andres Carvallo (L) and Ross Baldick. Photo by Hunyoung Shin.

Guest lecturer Andres Carvallo (L) and Ross Baldick. Photo by Hunyoung Shin.

My “Smart Grid” course continues apace. Highlights have included lectures by Andres Carvallo on the architecture of the grid, and several lectures on existing and upcoming “smarts” at the wholesale generation and transmission level, including wholesale operations by Dave Maggio, new transmission technologies by Brad Bell, and human factors by Mike Leggatt.

Guest lecturer Scott Hinson (L) and Ross Baldick. Photo by Hunyoung Shin.

Guest lecturer Scott Hinson (L) and Ross Baldick. Photo by Hunyoung Shin.

The class has now shifted to topics at the heart of the “conventional” smart grid, namely distribution and end use, including smart grid ecosystem analysis by Ingmar Sterzing and residential power quality by Scott Hinson. Oh, and yes, we just had a midterm.

To access any of the lectures to date, click here.

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“Smart Grids” course features industry experts

Ross Baldick Consulting

Dr. Ross Baldick hosts industry experts for his new UT course, “Smart Grids.”

I’ve been in the thick of it recently, putting the finishing touches on a new course I’ve designed about smart grids for my students at UT Austin. “Smart Grids” begins in less than two weeks.

Back story: During more than a year of preparation, I could not find any text suitable for engineering students. That’s when I started enlisting the help of colleagues, who generously agreed to serve as the “text” for the course. Fortunately for us, we have a wealth of expertise in Austin and Texas. More than a dozen industry guests, including Brewster McCracken of Pecan Street and Bill Muston of Oncor, will lecture on topics from generation and transmission to end-use. We will be asking: What is a smart grid? What does a self-healing grid mean? What are the costs and benefits of a smart grid?

Each lecturer has assembled slides, and each one will be made publicly available on the course webpage: http://users.ece.utexas.edu/~baldick/classes/379K/EE379K.html

So far, the webpage features only my course introduction, but you can see the topic headings laid out for the whole semester. You’re invited to check back for the slide presentations as they become available throughout the semester.

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How much storage is even feasible?

Ross Baldick ConsultingIn response to my last post, about the challenges of wind integration, a reader asked: “Is building storage of this scale even feasible?”

If you had asked me in 2000, “Could wind get to 18GW wind in ERCOT by 2016?” I would have answered no!

I would have been concerned about technical feasibility as well as cost. Technical feasibility has not turned out to be a  problem at that level of penetration, so I would now shy away from claiming technical non-feasibility for storage.

Indeed, I think one can contemplate large-scale dispatched storage (end even some way to dispatch small scale distributed storage) that would make it compatible with existing grid control paradigms at even very high penetrations of storage. Certainly, the battery regulation AS providers are taking ISO signals that look like standard dispatch signals.

The big stopping point continues to be cost. If Elon Musk can make it cheap, and can add some dispatchability, there could be a lot of storage. However, I’d prefer to first wring out from the thermal generators as much controlability as we can get before we blow a lot of money on storage.

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ERCOT: meeting the challenges of wind integration

Ross Baldick (left) receives Outstanding Engineer Award 2015 from Joel Sandahl, Chair of Power and Energy Society, Power Electronics Society, Industry Applications Society, and Industrial Electronics Society Austin Texas Chapter.

Texas has, by far, the highest penetration of wind among the three main US interconnections (Eastern, Western, and Texas), and the Electric Reliability Council of Texas (ERCOT) has met the challenges of wind integration. ERCOT is set to get even more wind power, which will present even greater challenges, because of the relationship between wind production and electricity demand.

Several of my students, most recently Dr. Duehee Lee, have investigated the statistics of wind production to understand this relationship. Recent joint work with Lee (reported at Wind Farms in Dallas in May, and more recently at the Austin IEEE Power and Energy Society chapter meeting and the Berlin Conference on Energy and Electricity Economics) analyzed the relationship between wind and load variation at various timescales. We want to understand how the variability of wind at various timescales will affect the operation of ERCOT, and what resources will therefore be necessary to compensate for this variation, whether it is agile generation or battery storage.

West Texas inland wind presents a particular problem, because it tends to be negatively correlated with load, while near-coastal wind is weakly correlated and therefore a better match to load. This means that increased amounts of inland wind will not offset the need for other generation capacity to cover the peaks in demand. Moreover, this generation capacity will also need to be increasingly flexible to accommodate wind production that occurs off-peak.

Furthermore, while aggregating large numbers of farms tends to smooth intra-hour fluctuations of wind, in contrast, the longer term fluctuations of wind, and particularly the negative correlation of inland wind and load will not be “solved” by aggregation of West Texas wind.

Coastal Texas wind has better correlation with load from this perspective, but it may be more difficult to build much more coastal wind due to environmental and other considerations. An open question is how much more wind can be accommodated in the ERCOT market before we need to build large-scale storage.

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Solar in a Quito hotel

I recently had the pleasure of staying at a hotel in the old town of Quito, Ecuador, and saw a photovoltaic (PV) installation that would seem strange in most of the world.

We typically see PV panels tilting toward the south in the northern hemisphere or toward the north in the southern hemisphere, in order to capture the sun’s rays. A variation is to tilt toward the west in afternoon-peaking locations, such as Austin, Texas, where air conditioning drives peak loads. (Click here to read the work by Pecan Street that considers the tradeoffs between maximizing energy production and maximizing the value of that energy).

At my hotel in Quito, however, the courtyard had been covered by horizontal PV panels:

quito-solar-1 | Ross Baldick Consulting

As well as being an attractive building-integrated PV awning, it was also perfectly oriented, since Quito is almost on the equator. It allowed some light through to the courtyard below, because the PV cells were mounted on a transparent support (see below), and also provided shade for the courtyard.

quito-solar-2 | Ross Baldick Consulting

The combination of an old colonial building with updated decor and energy sources made for a lovely stay in this charming town.

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