Tag Archives: energy storage

So you’re telling me that my electric car’s battery is in the paint?

What comes to mind when you picture a battery? The familiar Duracell Coppertop AA battery? A clunky  automotive battery? The small rectangular battery in your cell phone? Researchers at Rice University are reinventing the concept of batteries and battery packaging by creating a lithium-ion battery with spray paint. That’s right, your local neighborhood hoodlum taggers can now be more energy forward than you sitting at home watching Cops.

A team of researchers from Rice University have demonstrated in a paper in Nature Scientific Reports that special “spray paints” can be used sequentially to build up the layers needed to form a lithium-ion battery. A spray-on battery could be used on a variety of materials, both rigid and flexible. They point out that the technology could be coupled to energy conversion devices such as solar cells.

Simply put, a lithium-ion battery is created by tightly layering cathodes and anodes like in the image shown below. The researchers at Rice University replicate this cylindrical design in a customizable form using the spray coatings that they developed. They applied the battery painting process to a variety of materials including stainless steel, glass, ceramic tile, and flexible polymer sheets. An SEM image of a cross section of the battery is shown below. Each of the spray painted batteries performed as a typical battery. They even applied the spray paint to a coffee mug to spell out the name of their Alma mater while also storing energy. They added that more complicated surface geometries could be possible using different spray nozzle designs that are tailored to the different viscous properties of the paints.

The are a few drawbacks to a spray painted lithium-ion battery. For one, the materials are highly toxic, corrosive, and flammable, hence why they are always tightly packaged and hidden away in their conventional form. Secondly, the batteries are highly sensitive to oxygen and moisture. This sensitivity currently restricts their widespread use because they still have to be packaged like their conventional brethren, reducing their novel promise. A spray painted battery is shown below on a glazed ceramic tile alongside its final packaged form. One of the researchers’ next steps is to develop a sealing layer to protect the batteries from these elements. Because who wants to paint their electric vehicle with a new battery but then have the painter tell them that they always have to keep the car cover on.

Typical lithium-ion battery construction.

Conventional and spray painted lithium-ion batteries.


SEM image of spray painted lithium-ion battery cross section.


Glazed ceramic tile with spray painted battery prior to packaging (left) and post-packaging (right)




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Texas Population Growth and Future Energy Demand


Photo:  Austin, TX Downtown Skyline

Forbes has released their annual list of fastest-growing cities in the U.S.  For the third consecutive year in a row Austin came out on top.  The Austin metro region grew at a 2.8% clip in 2012 bringing our regional population to 1.8 million people.  Austin has been roughly doubling in size once every 20 years since its founding in 1839.  The second and third fastest-growing cities on the list were Houston and Dallas.  San Antonio came in at #9 on the list.  Texas overall added 427,000 people to the state’s population from August 2011 to July 2012 bringing our state population to 26 million.  Texas is growing at a staggering rate of more than 1,000 people per day.  With Texas metros growing at such a breakneck pace, the challenge for Texas going forward will be to keep up with our state’s future energy demand [1][2].


Photo:  ERCOT Operations Center

The Electric Reliability Council of Texas (ERCOT), the state’s grid operator, recently released a study showing that Texas will struggle to keep pace with future energy demand especially during peak demand times for energy.  Peak energy demand in Texas occurs from 3 p.m. to 7 p.m. during the summer months.  ERCOT’s method of tracking whether the state will be able to cover its current and future energy needs is based on a reserve margin metric.  Reserve margin is a useful tool that measures how much extra generation capacity will be available based on what the anticipated future peak energy demand will be.  ERCOT’s reserve margin goal for the Summer of 2013 is 13.75%.  However, with total generation capacity expected to be 74,633 megawatts (MW) and peak demand expected to be 65,952 MW during the Summer of 2013, ERCOT will fall short of its goal with a reserve margin of only 13.2%.  ERCOT’s reserve margin is expected to decline to 10.9% by 2014, and it will eventually fall to just 2.8% by 2022.  ERCOT’s strategy going forward will be focused on introducing new market incentives for power plant operators across the state to build new generation capacity.  ERCOT will also focus its efforts on encouraging energy conservation through demand response initiatives [3].

Energy conservation efforts such as Austin’s Pecan Street, Inc. smart grid demonstration project is a great example of how Texas’ booming metros can reduce overall peak energy demand.  Pecan Street’s smart grid demonstration project is leveraging a $10.4 million DOE grant as well as resources from the University of Texas at Austin, Austin Energy, and a consortium of industry leading high tech companies.  Pecan Street is studying the benefits of integrating rooftop solar, energy storage, electric vehicles, natural gas, smart appliances, and home energy management networks to manage peak energy demand within neighborhoods and also to help customers reduce their monthly utility bills.  Pecan Street’s smart grid demonstration project has grown to include 600 residential homes.  Lessons learned from Pecan Street’s research projects will go towards helping cities across the state and country better understand how to satisfy future energy demand when facing rapid population growth [4].

Introducing Pecan Street, Inc.

[1]  Austin is America’s fastest-growing city: http://www.bizjournals.com/austin/blog/morning_call/2013/01/austin-is-americas-fastest-growing-city.html

[2]  Forbes; “America’s Fastest Growing Cities”:  http://www.forbes.com/sites/morganbrennan/2013/01/23/americas-fastest-growing-cities/

[3]  Future electric outlook shows improvement:  http://www.ercot.com/news/press_releases/show/26358

[4]  Austin’s Pecan Street, a Smart Grid ‘City Bloc,’ Adds PV Solar and EVs:  http://www.pecanstreet.org/2011/10/austins-pecan-street-a-smart-grid-city-bloc-adds-pv-solar-and-evs/


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New Future for Paper? Think Energy Storage Devices

The coming years will see more and more renewable sources, plug in electric vehicles, and even more electronic devices requiring energy storage. All these require an inexpensive , light, scaleable, and efficient energy storage. Energy storage is especially critical to further development of some intermittent renewables like wind and solar. From the policy standpoint, having reliable and inexpensive energy storage can make it easier to achieve renewable portfolio standards, help with electricity peak demands by offsetting them, or make electric vehicles more accessible. Well, paper just may be the answer. 

Recently, scientists at Stanford coated office paper with nanotubes and nanowires to make it conducting. Moreover, they produced lightweight, flexible battery and supercapacitor (high-energy density capacitor). The discovery was unexpected as the researchers substituted paper for plastics in their previous research as a base-layer for the coating [1]. More porous paper holds this special “ink” made with carbon nanotubes better, making for a more durable battery and capacitors. 

The device is made from an off-the-shelf office paper. The paper is coated with carbon nanotube “ink”. Because of its porosity and good absorbance, the ink rheology is not very important and nanotubes bind well to it. The Proceedings of National Academy of Sciences paper [2] reports a resistance of 1 Ω (Ohm)/sq (per square). This is comparable to a resistance of a 100W light bulb (its metal filament) and not very different from an internal resistance of a regular AA alkaline battery. This paper can be folded, crumpled or even dipped in acid and it still retains its unique properties. Professor Yi Cui, said that one day, he could use a brush to paint his walls with an energy storage device (energy-storing wallpaper, anyone?) [2,4]. 


Conducting paper rolled into a tube, Ref. 3

Conducting paper rolled into a tube, Ref. [3] 

Paper for Supercapacitors 

For comparison, a 50nm layer of gold (very good conductor) deposited on a sheet of standard Xerox paper had resistance of 7 Ω (Ohms)/sq (it was 1Ω for the coated paper). By coating both sides of paper with the carbon nanotube ink, the researchers created a supercapacitor with capacity of 200F/g (Farad per gram) in sulfuric acid electrolyte. This capacity was not severely diminished even under high current loadings of 40A/g. The gold-based supercapacitors made in a similar fashion had about 4-5 times lower capacity. Ultimately, the supercapacitor performed well even at 40,000 cycles with capacitance losses less than 3%. In MIT Technology Review article [5], Nicholas Kotov, professor of chemical engineering at the University of Michigan, says that the dipping method to make the supercapacitors is “simple and nice”. 

Paper for Batteries 

Because a large weight of batteries, up to 20% is due to heavy metallic current collectors, the paper can also be used in batteries to reduce weight while still maintaining reasonable resistance. Thus a higher gravimetric energy density can be accomplished [1].  Such battery proof of concepts made by the Stanford group achieved over 500 cycle times with high capacity retention. Paper was stable in the electrolyte over the period of 3.5 months and the battery showed only small self-discharge. 

Below is a video from Dr. Cui’s group at Stanford showing how simple it is to make this paper (of course, the “secret sauce” of the nanotube ink is not revealed) 

Nanotubes + ink + paper = instant battery

What I personally like about this technology is that is seems “ready to go”, or pretty close to commercialization. Who knows, in a strange twist of fate, maybe in a year or two, our electronic readers such as kindles and iPads will rely on paper they replaced for their energy storage. 


[1] Paper Battery Shows Promise for Grid, Vehicle Energy Storage

[2] Hu, L., Choi, J.W., Yang, Y., Jeong, S., La Mantia, F., Cui, L., Cui, Y., 2009, “Highly Conductive Paper for Energy-Storage Devices,” Proceedings of National Academy of Sciences

[3] “Battery Made of Paper Charges Up,” BBC News, Tuesday, December 8, 2009, 16:38 GMT

[4] “Making Powerful, Lightweight Batteries From Nothing But Nanotube Ink and Paper” Popular Science, Clay Dillow, Posted 12.08.2009 at 11:15 am

[5] “Batteries Made from Regular Paper”, MIT Technology Review, Katherine Bourzac, December 8, 2009

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Wind Will It End?

Please forgive me for the cheezy post title, but if you choose to read on I think you will see it is relevant. When we discuss the challenges facing wind energy we hear about the intermittency and storage issues, destroying the visual landscape, lack of transmission and even the dangers posed to birds. Many people also raise valid concerns regard whether or not wind can be economically feasible without government subsidies, regulations and mandates. A recent Scientific American article shows that wind proponents should also worry about the challenges we don’t hear about every day.

Not surprisingly, a lot of these less discussed challenges are coming from wind’s competitors. The Coalition for Fair Transmission Policy believes wind producers should fork over the funds needed to expand the transmission infrastructure from the areas of the country where wind energy is produced (the Midwest) to the areas with the highest energy demand (the East Coast). While this seems like a reasonable idea on the surface you should be asking yourself who is this Coalition?  Turns out the Coalition for Fair Transmission Policy is made up of East Coast utilities.

Closer to home we have players in the natural gas game demanding that wind developers be held responsible for some of the costs associated with running backup natural gas generators. These generators are essential in providing electricity when the wind slows down and is unable to produce the needed amount of electricity. As before this appears to be a reasonable suggestion. Why shouldn’t wind energy producers help foot at least part of the costs generated when a gas turbine is turned on to make up for a decline in wind energy? At the same time this seems like an attempt by the natural gas industry to increase their competitions costs and help keep natural gas competitive on price.

Anyone who is familiar with the wind industry understands the large role played by the government. While people can certainly debate whether the government should be involved at all and if so to what level, nobody can deny the importance of politics in the past or in the future. In my podcast I touched on the concerns Senator Charles Schumer raised regarding the spending of stimulus funds on projects that were creating more jobs in China than in the United States. Now Schumer and three other Senators proposed a plan that would prevent federal grants being issued to any project used blades or turbines manufactured outside of the U.S. opponents of the Senators’ plan claim that the U.S. cannot afford to slow or limit the growth of the wind industry because it will only put us at risk of falling behind Chinese and European manufacturers. They also point out that Schumer and his colleagues are simply trying to funnel jobs to their states and the number of jobs going overseas has been exaggerated. As with most things in politics the number of jobs being created in and outside of the United States differs significantly depending on who you talk to and before you know it the whole issue has taken a nasty turn towards “he said, she said”-ville.

It is obvious each of these parties (Senators, utilities, the natural gas industry) and their actions are motivated through their own self-interests, but it should be just as obvious that we cannot simply dismiss these legitimate concerns simply because we do not support the people raising them. In a perfect world we would be focused on finding solutions for the “natural” problems facing wind instead of creating additional artificial roadblocks. In that same perfect world everyone would be working towards the common goal of creating clean renewable energy and the traditional utility, natural gas and coal industries would be okay with that. Reality is the world isn’t perfect and the future of wind energy is hardly certain. For the wind industry to continue its impressive growth they will have to learn to be just as focused on navigating the wonderful world of politics and viciously competitive energy industry as they are with coming up with solutions to their storage issues.

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Isentropic Energy – A Breakthough in Energy Storage?

One of the primary problems that the electric power industry has faced since its inception is the fact that electricity cannot be economically stored throughout the grid. Electricity is generated and transported via transmission lines, but it must be either used or disposed of: either too much or too little power on the grid causes instability problems that can lead to system-wide failure. Unlike oil or gas, there are no storage tanks to help buffer against even hourly supply and demand changes.

This is why the price of power varies as much as 3X from off-peak hours in the middle of the night to peak demand in the afternoon.  Although demand varies, there is no way to smooth out the supply. Further, the entire grid is overbuilt to ensure that the worst case local demand on the worst case days is met. The so-called “peaker plants” that are built to handle these demand spikes are intentionally run at reduced capacity the majority of the time just so they have enough available extra capacity to “spin-up” and meet the peak demand. This approach is very costly.

Today, there are really only two economically viable electricity storage options for bulk power: pumped hydro, and compressed air energy storage (CAES).  But unfortunately, even these two options have significant geographical limitations and their net environmental impact is still being debated. While advances in batteries (Li-ion, NaS, Flow, advanced lead acid) are taking place, they are still currently far more expensive than pumped hydro and CAES. Considering that the average price of generation is around $0.04/kWh and the average retail electricity price to end customers is ~$0.10/kWh, you can quickly see how a utility would only be interested in storage technologies that can get to pennies/kWh or less.

The chart below, from the Electricity Storage Association (ESA), shows the overall cost of the various storage options.

Apart from cost differences, not all of the storage technologies are necessarily a good fit for bulk time-shifting applications. The plot below, also from ESA, shows the various storage options plotted against two of the most important variables: discharge time (how long power can be delivered) and rated power (how much power can be delivered). For time-shifting applications, what we want is the ability to deliver lots of power for long periods of time.

Further  complicating things is that as more renewables come online and become a greater percentage of overall generation capacity, their weather-dependent intermittency will only pose further problems for utilities and grid operators.

What is desperately needed is cheap, reliable, ubiquitous, bulk electricity storage.

That’s what this new company Isentropic Energy could provide. Their system uses the First Ericsson Cycle and improves on a thermodynamic heat engine from the 1800’s to convert electricity into a temperature difference, store that temperature, and then use the temperature difference in reverse to create electricity.

From the company’s website:

“Isentropic has designed a system that uses the Isentropic heat pump to store electricity in thermal form (“Pumped Heat”). The storage comprises two large containers of gravel, one hot (500C) and one cold (-150C). Electrical power is input to the machine which compresses/expands air to (+500C) on the hot side and (-150C) on the cold side. The air is passed through the two piles of gravel where it gives up its heat/cold to the gravel. In order to regenerate the electricity, the cycle is simply reversed. The temperature difference is used to run the Isentropic machine as a heat engine.”

Here’s a schematic of their system:

Apparently, they have used advancements in aircraft technology to make significant improvements in the heat engine mechanics, resulting in roundtrip efficiencies in the range of 72-80%. Also, because the system uses gravel, which is a cheap and readily available material, they project installed costs at around $55/kWh, and as low as $10/kWh at scale. This translates into very low $/kWh costs over the lifetime of the system as shown in their table below:

The overall benefits of this system are that it is very low cost, is not geographically constrained, has high overall roundtrip efficiency, is environmentally inert, and is both modular and scalable. While the technology is still in early development (according to this GreenTechMedia article, they have completed prototype number 3), it definitely holds promise for solving one of the power industries biggest challenges.

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Energy Storage Breakthrough?

A cost-effective solution for energy storage, that is not geographically limited, is one key ingredient missing from the vision of a solar and wind dominated electricity generation profile.  Currently, the only cost-effective storage solution for load shifting of renewables are Pumped hydro and Compressed Air Energy Storage (CAES).  Unfortunately, both technologies are limited by geography.  Pumped hydro needs water bodies separated vertically and CAES needs an underground cavern with specific geology.  Other solutions, up to this point, have been batteries that are too expensive and limited by inadequate cycle lives.

Isentropic Energy, a UK-based startup, claims that they now have a solution.  Their technology is the Pumped Heat Electric Storage System (PHES). The storage device works by taking advantage of a heat pump that uses electricity to compress air into a gravel tank on one side and expand air into a second gravel tank on the other side.  The result is one tank with compressed air at 500 degrees celsius and one with expanded air at 150 degrees celsius.  The energy differential can then be used as needed to run a heat engine.

PHES Device Schematic

So key questions are how big, with what duration, and how much does it cost?  As for size, Isentropic claims a land footprint of only 120 square meters for a 16MWh system.  The system would be able to deliver 2MW of power for a duration of 8 hours.  And best of all they claim that they can deliver this solution at a cost of $55/kWh of storage, they hope to be able to get this number down to $10/kWh as they scale up.  This compares favorably to pumped hydro at a fraction of the footprint, would be slightly cheaper that CAES, and would be significantly cheaper than battery technologies like sodium-sulphur and lithium-ion.  (see table below)

A technology like this could be the key to the large-scale integration of wind and solar.  Currently, the intermittency of both technologies is thought to limit the potential for either or both to provide the majority of our power.  However, with a low-cost storage option, like PHES,  that intermittency could be evened out with storage, and wind and solar would then be able to provide consistent power.

As promising as this technology sounds,  Isentropic Energy is still in the prototype development stage.  They are currently developing their fourth prototype and are still probably have another year or two until they are ready for commercial development.

Even if everything goes according to plan and PHES becomes a reality, there is still one more ingredient necessary for a wind and solar dominated grid.  That ingredient is sufficient transmission to access the tremendous wind resources in the Midwest and solar resources in the Southwest.  That’s where we still need policymakers to get things done.  Due to the locally focused structure of electricity transmission and the failure of the national government to step in and get transmission funded and built, a transmission infrastructure necessary to get to most of the wind and solar resource seems very far away.  I mean a 750Kv national transmission infrastructure would only cost $60 billion and what is $60 billion amongst friends or a nation of 300 million people (approx. $200/pp).

Our clean energy future is just two steps away:

1.  Energy storage for wind and solar grid integration

2.  Legislation from the congress and directives from FERC to allow for a nationwide high voltage transmission infrastructure.


1.  www.greentechmedia.com/articles/read/breakthrough-in-utility-scale-energy-storage-isentropic/

2.  www.isentropic.co.uk/

3.  www.aep.com/about/i765project/docs/WindTransmissionVisionWhitePaper.pdf

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Energy Storage and Economics

Renewable energy sources are a fantastic idea, but what is the key to making them most accessible? Energy storage. You know, AA batteries, superconductors, a flywheel, a reserve hydroelectric dam. If the goal is to power the grid with renewable energy, then storage systems are necessary to confront the problem of an energy source that produces electricity only at certain times.

The Electricity Advisory Committee of the Department of Energy published a report in December 2008 entitled Battling Electricity: Storage as a Strategic Tool for Managing Variability and Capacity Concerns in the Modern Grid. In it, the committee analyzes the prospective applications of energy storage systems, from generation to transmission and distribution to the end user. They separate the major storage systems into a few categories: first, bulk or distributed, and second, long-term and short-term (energy storage measured in hours as opposed to minutes/seconds).

I can see that renewables have a bleak future unless accompanied by energy storage. I do, however, take issue with two of the committee’s conclusions regarding economics. First, they repeatedly emphasize that energy storage systems can provide “a way to defer investments in transmission and distribution (T&D) infrastructure to meet peak loads…for a time” (EAC 3). While they give convincing evidence that T&D updating does not occur incrementally (which means that putting it off could save money and provide time to more fully research T&D infrastructure), I believe that putting off something that needs to be done is wasteful and lazy, even if you have technology allowing you to procrastinate. Even if it is true that T&D investments should be deferred for the time being, it seems to me that optimism about energy storage is a slippery slope leading to complacency about the grid.

A second benefit they see from energy storage is that it can allow Americans to continue their present lifestyle with no change in electricity consumption, or even an increase in electricity consumption if electric cars get their groove back. On the right-hand column on page 4, there is a delicately worded paragraph basically confirming that people don’t like to pay high prices for something they are used to paying less for. While I agree that transitions are difficult and should be kept as smooth as possible, I also believe that economics is a worthy tool in the hands of those attempting to regulate electricity consumption. Why flinch at charging a higher price for electricity used at peak load times? If the goal is less consumption during those times, once people figure out that electricity costs more at that time, they will fall over themselves to find a way to use less electricity then.

Finally, the report addresses the applications of energy storage systems while brushing over the actual technology. If you are looking for more detail on energy storage technology, go here for a 2001 report by Ribeiro et al.

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