Hawaii Energy Storage 8: The fascinating world of phase change materials

They’re not batteries, they’re not thermal storage systems, but they still store energy.

You haven't heard much about phase change materials. You will.  Phase change materials are a range of compounds that have a huge energy signature when they change forms, or change phase, from liquid to solid or solid to liquid.

A common example is ice in a cooler. As long as ice is melting, it is absorbing heat from the beer and the outside of the cooler, and it keeps the temperature of everything around freezing. The temperature stays stable as long as the ice is changing phase and turning into water. Once the ice is gone and the melting process stops, the stuff in the cooler warms up.

You can develop materials that change phase at almost any temperature, and they work both ways--they can keep things cold, or alternatively, can keep things hot.

Japanese researchers at a recent energy storage conference said they are studying phase change materials to keep bentos hot. In this application, the materials changes from liquid to solid at the assigned temperature. As the food starts to cool, the phase change starts, the liquid changes to solid, and the process throws off heat. As a result, your bento stays at the assigned temperature and can't get cold.

You have heard of lithium ion batteries in laptops and Boeing jets that heat and even explode. You’ve felt your cell phone battery heat up. One researcher said a phase change material blanket could automatically a begin liquefying when a battery heats up, thus keeping it cool and preventing the explosion.

Researchers said you can dramatically increase the capacity of a home water heater by inserting rods with phase change materials inside. The phase change material stores a great deal of energy, and releases it as it changes phase. In this application, as the water temperature drops when you take a shower, the phase change material—presumably inside pipes in the water heater--begins solidifying, releasing heat into the water, without having to turn on the electric coils.

This means you could charge up a water heater when power is plentiful and cheap, and it could produce far more hot water for longer than standard water heaters of the same size.

I talked to a man whose company uses phase change materials to keep medical supplies cold for a week while they are being delivered to the military or third world countries.

A New Zealand researcher is mixing phase change compounds into drywall, keeping a house from getting too warm in summer or too cold in winter--without having to use electricity. It basically makes half inch drywall act like a thick concrete wall.

A German researcher talked about designing a modern supermarket to reduce lighting loads and improve cooling loads. They build icemakers into their big coolers to buffer their temperatures, and so they can turn off the power during times of high-cost power and still keep food cold. On stormy nights, when German windfarms produce more power than there is load, the price of electricity to supermarkets goes negative; they are paid to take power—they make ice with it.

When power rates go up, they can use the phase-change characteristics of the ice to keep the food cold without buying expensive electricity.

Next: Wrapping up energy storage

© Jan TenBruggencate 2013

Hawai`i Energy Storage 7: Beyond chemical batteries

Chemical batteries are the first energy storage technologies that leap to mind, but they are far from being the only show in town.

Heat storage is a big player too.

In our seventh installment on the issue of energy storage for intermittent renewable  energy resources, we will look at the little-used but increasingly important issue of storing energy as heat.

One cool concept actively in research is heat batteries for cars. As you run the heater or air conditioned in the car, the car's fuel efficiency can suffer as much as 30% in some high fuel efficiency cars.

That that makes it hard to meet stringent fuel efficiency standards, which are soon going to be measured with the A/C running—so you’ll see automobile fuel efficiency numbers dropping.

Manufacturers are quietly looking at a separate system for cooling and heating in automobiles—a system not tied to the engine, and thus a system that won’t reduce a car’s fuel economy.

The idea is a heat battery. The stored heat can go to a condenser or an evaporator, depending on whether you want heating or cooling in the vehicle.

You could charge up your heat battery by plugging it in. Where today you might look for a shady parking spot to keep a car cool, this could change the approach entirely. You could power up your air conditioner energy system by parking your car in the hot sun and charging your heat battery.

Heat has other applications, including utility scale energy storage.

There are numerous variants of systems that use mirrors to transfer the sun's heat into a storage medium, and then from there into steam that turns a turbine and makes electricity.  This normally goes by the generic name solar thermal as opposed to solar photovoltaic.

A lot of the current research is on storage media—when the mirror focuses the sun’s energy on a target, what’s that storage target made of? Some ideas include using liquids for lower temperatures, ceramics at super high temperatures, but also molten glass, molten aluminum, plain gravel, concrete, even metal and ceramic-encapsulated phase change materials. (More on those in a later installment.)

 A German researcher suggests you could use nitrate salts, which don’t degrade, and when you dismantle the plant after 30 years, you can use the stuff for fertilizer.

The scientists at the Massive Energy Storage conference referenced in earlier stories in this series spent considerable time on the subject of heat storage. They conceded that the big price drop in photovoltaic panels, driven in part by lots of capital investment and tax credits, have left heat storage the high-priced alternative, but they are convinced that research will bring down prices and make them competitive again.

One of the selling points for solar thermal, compared to solar photovoltaic, is that the storage is built into the system. Concentrated solar heating projects are likely to benefit from economies of scale. Indeed, they are anticipated to be players in the energy world only in a pretty large format.

In the most common application, the heated storage medium is used to make steam, which can then turn a turbine to make electricity.

There is also work underway in converting high temperature solar heat to storable liquid fuel, which could then be used for either utility or transportation purposes. You can use the heat to make hydrogen, or if you have a source of carbon dioxide, you can make syngas, which then can be made into a number of fuels.

Liquid fuels are extremely versatile. They can be used in cars and trucks, in aircraft, in stationary power plants and in fuel cells.

“Numerous storage solutions are being pursued, but the chemical storage of solar energy as a (liquid) fuel is a superior concept due to the high energy density and the existing global infrastructure for fuel transport and storage,” said James Klausner, of ARPA-E and an engineering professor at the University of Florida.

Next: phase change materials.

© Jan TenBruggencate 2013

Hawai`i Energy Storage 6: Some of the chemical batteries

There is no shortage of announcements of a new, cheap, powerful battery technology that will transform the energy industry.

Indeed,  when it comes to chemical battery, the number of variations seems endless.

In this, our sixth installment in Hawai`i Energy Storage, we’ll look at some of the options.

Just to consider the media hype around the issue, there’s this MIT promise of  cheap, power-dense flow battery. 

Here is a cool-sounding technology from Valence Technology, which it promises “can result in significantly lower operating costs when compared with lead-acid batteries.”

It’s easy to find news of research that is improving current technologies, like lead-acid and lithium-ion, as well as entirely new chemical battery formulations.

The cost of energy numbers below come from the Sandia-EPRI-NRECA 2013 EnergyStorage Handbook.

A sodium-sulfur battery is much-talked-about. It needs to operate at high temperature: more than 300degrees C. It has a long discharge time, which is good, and has a number of high-value utility applications. Levelized cost of energy is in the $275/megawatt hour range.

Sodium nickel chloride is another high-temperature battery with utility applications. It’s just coming onto the market this year. The levelized cost of energy is high and ranges widely, from $300 to $900 per megawatt hour, according to the handbook.

You’ll hear a lot about vanadium redox flow batteries. They being made for large scale storage applications now, but they are also not cheap, and they likely will never be cheap, because the vanadium is and is likely to remain expensive. And there are other problems, like power fade as compounds from one of its two electrolytes migrate into the other.

That said, vanadium redox batteries have a very long life, and “are capable of stepping from zero output to full output within a few milliseconds.” There’s value in that quickness. But you pay for it with a levelized cost of energy running from $400 to more than $800 per megawatt hour.

A company called EOS reports it is getting ready to ship in 2014 a Zinc-Air battery that is a fraction of the cost of lead-acid.  Properly it is a zinc-potassium hydroxide-oxygen battery. It is much more energy-dense than lithium-ion battery technology, meaning it’s smaller. They’re already working with ConEdison on prototypes. The handbook puts the levelized cost of zinc-air  at $150 to $200.

Lithium ion batteries are increasingly common, and there’ s still a lot of work being done to improve them. They are expensive, $500-$600 per kilowatt hour, and although they can take repeated deep discharge.

One concern: You’ve heard of lithium ion batteries overheating, and rarely, exploding. Considerable research is underway on a number of techniques to control this, including cooling systems, so they can’t heat up at all. And many researchers say that the overheating isn’t a problem with lithium-ion, if they’re properly manufactured and properly charged and discharged.

There is a manganese oxide ion battery about to be marketed by a company named Aquion Energy. It’s being built now on a small scale.  http://www.aquionenergy.com/

Its initial indications are impressive, but caution: it’s still early. That said, the Aqueous Hybrid Ion (AHI) chemistry sounds impressive. It is composed of a saltwater electrolyte, manganese oxide cathode, carbon composite anode, and synthetic cotton separator. It operates at room temperature.

The makers say it is 85 percent efficient and can go more than 5000 cycles while maintaining better than 80 percent efficiency. It is now cheaper than lithium-ion and cheaper than lead-acid at $300-$400/kWh, and founder Jay Whitacre, who addressed a June engineering conference on utility-scale energy storage conference, said  they hope to get it down to 100/kWh. They can get half a megawatt into a 20-foot shipping container.

Another promising battery: Michael Aziz of Harvard talked about a super-cheap flow battery using an organic molecule called a quinone, but there are still significant issues to be solved.

Sri Narayan of the Department of Energy’s ARPA-E program said the best looking technology right now is iron-air chloride . They still have some problems to solve, but their preliminary indications are that it could meet all the other requirements, AND come in at less than $100 a kilowatt hour. Iron and air, after all, are both abundant and cheap.

Sodium sulfur batteries, storage conference participants said, have a number of excellent features. They operate at high temperatures—550 degrees F.,--and there have been fires as recently as two years ago in Japan.  The technology is not cheap, at roughly $500/kWh.

Some of the other technologies being studied are sodium-nickel, sodium zinc, nickel-zinc, nickel-hydrogen. Each has strengths and weaknesses.

Nobody is predicting when some of these batteries might become available, and even the ones that promise they’ll get to the ARPA-E $100/kilowatt hour level—well, they’re not there yet.

There is a lot of work going on, and lots of promise, but it will take years before one or more of these technologies prove themselves able to meet all the really important criteria for a utility-scale storage system.

© Jan TenBruggencate 2013

Hawai`i Energy Storage 5: Energy storage solutions without chemical batteries

Chemical batteries are a traditional energy storage medium, but batteries are hardly alone.

In this installment of our energy storage series, we'll be talking about water, air and spinning metal as energy storage media.

Three of the storage sources that are not chemical batteries are pumped hydro, compressed air and flywheels.

Pumped hydro has been used across the United State and the world for the last century. It’s reasonably priced, but currently difficult to get permitted.There are several folks on several islands in Hawai`i discussing pumped storage projects.

In essence, here’s how it works. You have two reservoirs of water, separated by vertical distance.  When power is cheap, you pump water from the lower to the upper reservoir. When you need the power, you run the water downhill through a hydroelectric plant into the lower reservoir. Either reservoir can be man-made or can be a natural reservoir, like a lake or even the ocean.

The Sandia-EPRI-NRECA Electricity Storage Handbook for 2013 estimates a levelized cost of energy for pumped storage in the neighborhood of $200 per megawatt hour. These systems have lifespans in the many decades, so that cost may look low when adjusted over time for inflation.

Compressed Air Energy Storage (CAES) systems in place today are based on pumping air into deep underground caverns. Our Hawaiian geology may be too porous for that application, but there have been suggestions we could install massive bladders in the ocean, and use the weight of the water to maintain compression. 

When you need the power, you open a valve and let the compressed air spin a turbine.

Based on the existing cavern systems, the handbook estimates levelized costs also in the $200 per megawatt hour range , but a different storage mechanism likely would raise the cost.

A lot of folks like the whole concept of flywheel storage. Flywheels have been around for ages in all kinds of applications. Old (and some modern) diesel engines use flywheels to create rotational inertia, translating the periodic firing of the diesel cylinder into a steady force.

You can store solar power, wind power, any kind of power in flywheels, and then later convert it back to electricity. In the words of the handbook: “Flywheels store energy in the form of the angular momentum of a spinning mass, called a rotor. The work done to spin the mass is stored in the form of kinetic energy. A flywheel system transfers kinetic energy into A/C power through the use of controls and power conversion systems.”

The handbook concludes that this form of storage is more useful for short-term grid stabilization applications than bulk energy storage. It puts the levelized cost of energy in the $375 per megawatt hour range.

Learn more about flywheel systems this company’s site.

Pumped storage and CAES tend to be priced for economies of scale. They need to be very big to have good pricing. Flywheels don’t scale up so well—you’re better off building lots of smaller flywheels than one big one, and as we said, they’re not recommended for bulk storage.

NEXT: We’ll discuss some chemical battery storage ideas next.

© Jan TenBruggencate 2013