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

Hawai`i Energy Storage 4: Running the battery numbers--prepare to be confused

There are all kinds of ways to store energy.

First thing to come to mind is a chemical battery, and there are all kinds of chemical batteries. We'll look at some of those in detail in the next installment of this series on energy storage.

You can also store energy in the form of heat. If we can make electricity out of hot rocks using natural geothermal resources, we can make electricity out of hot materials that we heat—perhaps using mirrors to focus the sun’s energy.

If we pump water to a high place, and then run it through a turbine as it flows to a low place, we have what’s called pumped storage. It has been built across the world for most of the last century.

People have pumped air into deep underground chambers, and then collected energy when it is released, a technology called Compressed Air Energy Storage or CAES.

Some folks are fascinated by big fast-spinning flywheels as a storage medium.

If you use energy to make a liquid fuel, like hydrogen, which later can be used to generate power—that’s a form of energy storage, too.

So with all these alternatives, how can we distinguish between them? That’s a complex problem. Some of the factors to be considered:

How much does it cost to build the system, and how much power will it store? This might be called installation cost—how many dollars per megawatt stored.

How much energy is lost in charging and then discharging? In a calculation called round-trip efficiency, if you need to deliver two megawatts to the battery but there’s only one megawatt that can be drawn from it, that’s a 50% round-trip efficiency. There’s some loss in every system, and one standard chemical battery folks shoot for is 80%.

How fast will it deliver its charge, and how fast will it recharge?

How many such charge/discharge cycles will it take before the power storage system--or part of it--needs to be replaced?

One calculation that seeks to answer a lot of those questions is levelized cost of energy, or LCOE. The National Renewable Energy Laboratory defines it here.

It is a calculation that combines the “capital costs, operations and maintenance, performance, and fuel costs.” It is often delivered as units of money divided by units of energy, such as dollars per megawatt-hour.

As an example, the 2013 Electricity Storage Handbook estimates the LCOE at 2012 prices of pumped hydro at $150 to $220 per megawatt hour. Lead-acid battery storage can come in anywhere from $250 to $1,700 per megawatt hour.  Flywheels turn in at about $375 per megawatt hour.

But even this calculation isn’t the whole story. The numbers can change dramatically depending on how you use the storage medium.

A lithium-ion battery used in frequency regulation—meaning it is responding quickly to sharp jumps and drops on the grid—can come in at $100 to $350 per megawatt hour. Use such a technology to help out in transmission and distribution applications and it can run from $700 to nearly $1,200 per megawatt hour. In some commercial and industrial applications, the Energy Storage Handbook puts the LCOE at from $700 to more than $2,500 per megawatt hour.

All those numbers are useful for one type of comparison between different storage types.

But sometimes when you’re looking at references, you’ll see similar dollar numbers attached to similar energy numbers, but this time energy is listed as kilowatt hours.That's because you're looking at a different thing entirely.

Example:  Last year Scientific American reported on a new kind of lithium-ion battery that could be produced for $125 per kilowatt hour. That’s what it costs to buy the system divided by how much energy it can hold at full charge.

The number doesn’t tell you a lot about the cost to operate that battery system. If it is cheap and will operate satisfactorily for 20 years, that’s one thing. If it’s cheap but needs to be replaced after 3 years, then maybe it’s not cheap.

To look at this a different way, consider that electricity in Hawai`i sells to consumers for roughly 35 to 40 cents per kilowatt hour, and maybe 20 cents of that is the cost to generate the electricity. If the LCOE for your storage system is $300 per megawatt hour, that’s 30 cents per kilowatt hour.

So if your solar photovoltaic system in the daytime delivers energy at 20 cents, and you store it for 30 cents—your energy cost is already 50 cents and you haven’t yet paid the cost to deliver it to a customer.

Thirty-cent storage may make a lot of sense for one application, such as stabilizing the grid, where a little storage goes a long way. But it does not make so much sense for bulk storage of daytime solar energy for delivery at night. For that, you might need a better, far cheaper alternative.

Selecting a storage system, then, is a little like buying a car. How much money do you have to spend and what are you going to use the car for? Is your limit $15,000 or $50,000? A little convertible roadster might get you a date, but won’t take six kids to soccer practice, and a passenger van won’t get you down a muddy road to a hunting spot like an SUV or four-wheel pickup might. A golf-cart looking neighborhood electric car does your local shopping duties, but might not get you to a North Shore beach and back for a weekend outing.

Next, we’ll look at some specific non-chemical batteries.

© Jan TenBruggencate 2013

Hawai`i Energy Storage 3: Energy experts review the future of storage

A small group of highly educated geeks got together recently to talk about the current state of research in utility-scale energy storage systems.

This was a small conference of about 50 people, mainly chemical and mechanical engineers, but also physicists, and others. A handful were students. Twenty percent were women. The nationality list was enormous: Australia, China, Czech Republic, Germany, Holland, India, Japan, South Africa, Spain, Sweden, Thailand, and, of course, the U.S. 

 The June conference, “Massive Energy Storage for the Broader Use of Renewable Energy Sources,” was chaired by Sudhakar Neti of Lehigh University. and Trung Van Nguyen of University of Kansas. Convener Engineering Conferences International ’s technical co-sponsor was MEMC/SunEdison.

The world of energy storage is amazingly complex. The conference dealt mainly with chemical storage systems and heat storage systems, but also pumped hydroelectric power, and issues like converting solar heat into liquid fuels.

Why is storage important? Eighty-five percent of the world’s energy still comes from fossil fuels, 6 percent from hydro, 5 percent from nuclear and only 1.9 percent from renewables.

But renewables are the fastest growing category at 7 percent annually, and a lot of renewables are intermittent. Thus they need storage to be able to play a significantly larger role.

Hawai`i is on the radar for these energy folks. They know about the Hawai`i Clean Energy Initiative. They recognize that Hawai`i’s high electricity costs and dependence on oil create a special demand for renewable energy storage.

Babu Chalamala of Sun Edison, a major national solar contracting firm, said grid-scale storage was not likely to be a big player on the U.S. Mainland. Rather, it would be more likely to play a role in places with smaller, unreliable grids, and in high-cost places like Alaska, California and Hawai`i.

It’s not just Islanders who are aware of the high cost of power here. Hawai`i’s costs were mentioned more than once by the Massive Energy Storage researchers.

I would guess that when most folks think storage, they think battery, and most of those batteries are chemical batteries.  Perhaps the most common example of a standard chemical battery is lead acid—the battery in your car, and the battery most folks use who have off-grid home power systems. Or lithium-ion, the battery that's in your phone and your laptop/

But these kinds of chemical batteries aren’t the only kind of energy storage. Not by a long shot.

Another class of chemical battery is the flow battery, which differs from familiar batteries in that a liquid electrolyte doesn't just sit there like in your car battery, but is pumped through the battery. It is also different in that the energy is stored in the electrolyte, while in a standard battery the charge is stored on the electrodes.

At this conference, there was also discussion of capacitors, an energy storage device that takes a charge very quickly and discharges very quickly. These cannot normally be used to deliver energy over time like a lead-acid battery.

But there is work on hybrid capacitor systems, which use capacitors to charge an electrolyte, which then can be used for long term energy delivery. The title of a talk on this was “The Electrochemical Flow Capacitor: Grid Scale Capacitive Energy Storage.” They’re being studied at Drexel University.

And, of course, there are many kinds of energy storage that have nothing to do with chemical batteries, like compressed air, pumped hydro, solar thermal, flywheels and lots more.

The Department of Energy’s Advanced Research Projects Agency-Energy (ARPA-E) grants cash to researchers that are developing entirely new ways to generate, store, and use energy.”

ARPA-E doesn’t just fund anything—it’s not a vehicle for pure basic research. Its projects are designed to have ready application. The projects need to have a “road to market.”

ARPA-E is looking for projects that develop storage at $100 per kilowatt hour, can charge and discharge at least 5,000 times, have an 80 percent roundtrip energy efficiency, are made of abundant raw materials and are recyclable.  (http://arpa-e.energy.gov)

There's nothing out there right now that meets all those requirements, but there's lots of work underway on the subject.

As this series progresses, we will doubtless be called out for not listing one or another kind of storage. We’ll plead guilty right here. The list of energy storage research areas is pages long and we won't get to all of them.

In our next section, we’ll look at a few of prominent ones that came up at the Massive Energy Storage conference.

© Jan TenBruggencate 2013

Hawai`i Energy Storage 2: Time travel and stacked services

The numbers generally don’t add up for a homeowner with a solar array to put in a big battery system and go off-grid—it’s too costly.

But it CAN make sense for utilities—largely because they can make those batteries perform far more tasks, each of which has a payback value. Stacking those services a battery performs can make a compelling argument for them.

For this second piece in a series on Hawai`i energy storage , we are relying primarily on a new industry/government report, the DOE/EPRI/NRECA Electricity Storage Handbook for 2013, which was released earlier this summer. It is available without cost here. 

The report makes the point that one of the most critical functions of a battery system is to make energy travel through time. That is, they let you collect energy at one time, and hold it for delivery at another time.

That is particularly valuable if there are times when you don’t have enough generating capacity to meet the load, or if (think solar, wind) there are energy sources whose production doesn’t coincide with when you need the power.

We won’t go into lots of detail here. You can find a much broader discussion in the 340-page report. But briefly, some of the services include:

TIME SHIFTING, LOAD SHIFTING. The energy time-travel service discussed above.

COST CONTROL. A good storage system may not only be able to shift energy from periods of periods of excess to periods of shortage, but may also be able to shift energy from periods when it’s cheap to periods when it’s expensive. (Often, these may be the same.)

COST DEFERRAL. Meeting peaks in demand with stored energy may allow you to hold off on spending new money for generation to meet those peaks. The construction of transmission and distribution equipment can also be deferred through energy storage.

CUTTING GENERATOR WEAR AND TEAR. Since many generators wear more quickly if their output needs to vary, a storage option can reduce wear by taking up the variable load while the generator operates at stable output.

SPINNING RESERVE, SUPPLEMENTAL RESERVE. This refers to using a battery as a source for quick power delivery in case of a generator failure or transmission problem. Spinning reserve is defined as that which can be delivered within 10 minutes, while supplemental reserve is electricity that can be available within an hour. Utilities often meet this need now by burning oil to keep generators hot and running without load—so they can be quickly called into service.

BLACK START. This is a term for starting up a system that has shut down entirely. Many generators need power (think pumps, blowers, etc.) to start up. You can fire up a diesel generator to power the startup of a big steam generator, or you can use stored energy to deliver that power immediately.

VOLTAGE SUPPORT, FREQUENCY RESPONSE. In being able to respond quickly to add power or remove power from the grid, some kinds of storage can provide reliability, stability and better power quality.

As discussed earlier, it might not make sense to pay for a storage system for just one of these things, but it might if you consider all the potential uses. Example: having a massive battery just to provide black start capacity might be cost prohibitive, but if that battery also allows you to shift energy through time, reduce generator wear and create spinning reserve—then it might make economic sense.

It is clear that not every storage technology is appropriate for every one of these energy services. Example: pumped hydro and compressed air energy storage are great for bulk power management, but may not be much use for frequency response. And while high-energy supercapacitors might be wonderful for maintaining power quality, they’re not so good for load shifting.

In our next segments, we’ll begin looking at some of the energy storage options that are available now, or may soon be ready.

© Jan TenBruggencate 2013

Hawai`i Energy Storage: Many storage technologies compete to back up intermittent renewables

You can’t run a 24/7 power system on intermittent renewables like wind and solar.

They won’t keep the lights on.

But the Islands are building intermittent renewables like mad, and leaving legacy fossil fuel plants to back them up. Ultimately, that’s neither sustainable nor in line with state policy.

The next few RaisingIslands posts will review how the paradigm is changing. The key to the change is the fast-moving new world of energy storage.

With appropriate storage, intermittent power becomes firm power. Oil and coal plants can go away.

Our primary sources for this series are a four-day conference on utility-scale energy storage research and a new industry/government report, the DOE/EPRI/NRECAElectricity Storage Handbook for 2013, which was released earlier this summer.

If you’re interested, you should read the report, as we’re only going to summarize pieces of it here.

As little as 10 years ago, there was very little choice available in terms of energy storage—most folks were getting by with lead-acid batteries, although there was a lot of “potential” out there for different storage technologies.

That has changed.

“Storage for frequency regulation has become fully commercial and facilities are being built to explore renewable integration, PV smoothing, peak shifting, load following and the use of storage for emergency preparedness,” wrote Imre Gyuk, of the U.S. Department of Energy’s Energy Storage Program, in the foreword to the report.

The Hawai`i Clean Energy Initiative plays a role in the story, and is cited in the report.

What quickly becomes clear when you pay attention to energy storage is that this field is dense, complex and difficult to summarize, other than to say there’s a lot going on.

Most folks think about storage and think batteries, and indeed, batteries are a key piece—perhaps the biggest piece. But they’re certainly not all of it. There is also, flywheel energy storage, compressed air energy storage (CAES), pumped hydropower, thermal storage, and hydrogen.

Each of these technologies has strengths and most also have significant weaknesses. Some are appropriate for certain applications but not for others. Balancing those features is both difficult and necessary to move forward.

There are many issues in deciding whether a new system is ready for prime time. Here are some of them, which I drew from my participation in a June conference in Newport Beach, “Massive Energy Storage for the Broader Use of Renewable Energy Sources.”

This list is largely designed to rank battery storage systems, but much of it can be applied to any storage technology.

The dream energy storage system of the future needs to be:

Made of cheap materials;

Efficient, in that you get nearly as much energy out as you put in—preferably 80 percent round-trip efficiency or better;

Safe, in that it won’t explode, leak, or otherwise endanger those in the immediate vicinity;

Have charge-discharge capacities of approaching 10,000 times;

Energy dense, so it is compact (although this is more important for mobile systems like electric car batteries than stationary utility-scale storage, it can't take up too much acreage);

Made of non-toxic compounds;

Recyclable at the end of its useful life;

Able to operate at ambient temperatures.

Oh, and it needs to be far cheaper than anything available today. The U.S. Department of Energy’s ARPA-E program is looking for batteries in the $100 per kilowatt-hour range. Most of the cheapest technologies available today are in the range of 5 to 10 times that...or more.

Can we get there? In this series we’ll take a look.

(ARPA-E stands for Advanced Research Projects Agency-Energy. It is a Department of Energy program modeled on the Department of Defense's DARPA, the Defense Advanced Research Projects Agency.)

© Jan TenBruggencate 2013