Aluminum to the rescue

When it comes ot fuel cells , the challenge of storing the hydrogen has been vexing. Lightweight interstitial hydrides -- compounds in which hydrogen atoms occupy the interstices (spaces) between metal atoms -- have now been proposed as a safe and efficient means for storing hydrogen for fuel cell vehicles. And fuel cells are what many see as the future.

Hydrides using magnesium, sodium and boron have been manufactured, but so far, none have proven practical as a hydrogen repository. An aluminum-based alloy hydride offers a more viable candidate because it has the desired traits of light weight, no toxicity to plants and animals, and absence of volatile gas products except for hydrogen.

Until now, however, only complex aluminum hydrides -- unsuitable for use as a hydrogen storage system -- have been created. In a recent paper in the AIP Publishing journal APL Materials, a joint research group with members from the Japan Atomic Energy Agency (Hyogo, Japan) and Tohoku University (Sendai, Japan) announced that it had achieved the long-sought goal of a simple-structured, aluminum-based interstitial alloy.

“Although its synthesis requires very extreme conditions and its hydrogen content is low, our new compound showed that an aluminum-based alloy hydride is achievable," said Hiroyuki Saitoh, lead author of the APL Materials paper. "Based on what we've learned from this first step, we plan to synthesize similar materials at more moderate conditions -- products that hopefully will prove to be very effective at storing hydrogen."

Rdeox flow batteries show the way

As more power gets generated from intermittent sources of power, such as solar and wind energy, the need for energy storage devices that level out corresponding irregularities in the power supply becomes crucial. Fraunhofer scientists have recently made an important breakthrough with their development of a redox flow battery that reaches stack power up to 25 kW, with a cell size of 0.5 square meters. This is eight times larger than the previous A4-sized systems.

The German Federal Government has set itself the objective of generating total electricity the country needs from sun, wind, biomass, by 2050. For this, increasing amounts of solar and wind energy have to be stored for use during the night, or for times when there is less wind. Electric batteries are an option. Redox flow batteries offer an effective way to balance out fluctuations in the supply of renewable energy and thus guarantee its constant availability.

The batteries store electrical energy in chemical compounds, the liquid electrolytes. The electrolytes are charged and discharged in small reaction chambers. Several of these cells are lined up in stacks. However, the batteries that are currently available on the market, which are roughly the size of A4 paper (1/16 square meters), can only generate 2.3 kilowatts (kW) of power.

Scientists at the Fraunhofer Institute for Environmental, Safety and Energy Technology UMSICHT in Oberhausen, Germany, have succeeded in significantly increasing the size of the stack and, with it, its capacity. A new design has allowed them to produce stacks up to 0.5 square meters in size. This is eight times larger than the cells in previous systems, and results in power up to 25 kW. Successfully redesigning the battery stacks was an important step in developing redox flow batteries that could, for example, supply 2000 households with electricity. Redox flow batteries offer several advantages; they are cost-effective, robust, durable, and can be individually customized.

Building storage costly, says study

A key problem to wind energy development in the US is that the electrical grid has virtually no storage capacity, so grid operators can't stockpile surplus clean energy and deliver it at night, or when the wind isn't blowing. To provide more flexibility in managing the grid, researchers have begun developing new batteries and other large-scale storage devices. But the fossil fuel required to build these technologies could negate some of the environmental benefits of installing new solar and wind farms, according to Stanford University scientists.

"We calculated how much energy it will cost society to build storage on future power grids that are heavily supplied by renewable resources," said Charles Barnhart, a postdoctoral fellow at Stanford's Global Climate and Energy Project (GCEP) and lead author of the study. "It turns out that that grid storage is energetically expensive, and some technologies, like lead-acid batteries, will require more energy to build and maintain than others."

The results are published in a recent online edition of the journal Energy & Environmental Science.

Most of the electricity produced in the United States comes from coal- and natural gas-fired power plants. Only about 3 percent is generated from wind, solar, hydroelectric and other renewable sources. The Stanford study considers a future U.S. grid where up to 80 percent of the electricity comes from renewables.

Wind and solar power show great potential as low-carbon sources of electricity, but they depend on the weather, said co-author Sally Benson, a research professor of energy resource engineering at Stanford and the director of GCEP.

The total storage capacity of the U.S. grid is less than 1 percent, according to Barnhart. What little capacity there is comes from pumped hydroelectric storage, a clean, renewable technology. Here's how it works: When demand is low, surplus electricity is used to pump water to a reservoir behind a dam. When demand is high, the water is released through turbines that generate electricity.

For the Stanford study, Barnhart and Benson compared the amount of energy required to build a pumped hydro facility with the energetic cost of producing five promising battery technologies: lead-acid, lithium-ion, sodium-sulfur, vanadium-redox and zinc-bromine. The data revealed that all five batteries have high embodied-energy costs compared with pumped hydroelectric storage.

After determining the embodied energy required to build each storage technology, the next step was to calculate the energetic cost of maintaining the technology over a 30-year timescale. To quantify the long-term energetic costs, the team came up with a new mathematical formula they dubbed ESOI, or energy stored on investment. The higher the ESOI value, the better the storage technology is energetically.

A pumped hydro facility has an ESOI value of 210. It can store 210 times more energy over its lifetime than the amount of energy that was required to build it. The five battery technologies fared much worse. Lithium-ion batteries were the best performers, with an ESOI value of 10. Lead-acid batteries had an ESOI value of 2, the lowest in the study.

To reduce a battery's long-term energetic costs, one way is to improve its cycle life -- that is, increase the number of times the battery can charge and discharge energy over its lifetime. None of the conventional battery technologies featured in the study has reached that level. Lithium-ion is the best at 6,000 cycles, while lead-acid technology is at the bottom, achieving a mere 700 cycles.

They also calculated the material costs of building these grid-scale storage technologies. And found that the material constraints aren't as limiting as the energetic constraints. It appears that there are plenty of materials in the Earth to build energy storage. There are exceptions, such as cobalt, which is used in some lithium-ion technologies, and vanadium, the key component of vanadium-redox flow batteries.

Storage holds the key for meaningful transition

Science Daily reports on a study from the University of Delaware and Delaware Technical Community College suggests that wind and solar could power the grid 99.9% of the time if combined with a certain amount of energy storage and fossil fuel backups for the rare occasion that clean energy alone was not enough.

Using computer modeling, the researchers explored 28 billion combinations of renewables and storage mechanisms, each tested with four years of weather and energy demand data. The results were encouraging, and because the study focused not just on matching supply with demand, but rather achieving the most cost effective solutions, it revealed some rather useful findings. For one, that it is cheaper to over-build generation capacity to a point where there is excess supply on sunny or windy days, and still an adequate direct supply when demand is high but wind or sun are in short supply.

During the hours when there was not enough renewable electricity to meet power needs, the model drew from storage and, on the rare hours with neither renewable electricity or stored power, then fossil fuel. When there was more renewable energy generated than needed, the model would first fill storage, use the remaining to replace natural gas for heating homes and businesses and only after those, let the excess go to waste.

The study used cost estimates for renewables in 2030, that showed wind and solar at roughly half the installation price they are today, with maintenance costs remaining roughly constant. Add energy conservation and sustainable resource use and what have you?!

Liquid batteries are the key

There is plenty of wind and plenty of sunshine to provide energy for the world many times over. But the wind does not blow always nor sun shine at night! That intermittency has been the bane of renewable energy. And bateries to store the energy when available have proven to be expensive and bulky.

Needn' be, says MIT. According to MIT, liquid batteries are inexpensive and last longer than traditional batteries. The three materials contained in the liquid batteries each settle in separate layers due to the difference in their densities, which, in this case, is a good thing. They need to be separate.

The negative electrode (anode) is in the top layer and is made of magnesium; the middle layer, the electrolyte, consists of a salt mixture containing magnesium chloride; and the bottom layer, which is the positive electrode (cathode), is made of antimony. This battery operates at a temperature of 700 °C.

The battery generates an electric current as each magnesium atom (this is in the negative electrode) loses two electrons, then becoming magnesium ions which travel to the other antimony electrode. The magnesium ions then reacquire two more electrons and become magnesium again because of this. This causes an alloy to form with the antimony.

When the battery is supplied with an electric current, this process is reversed and the electrons are driven out of the antimony electrode, and back to the magnesium electrode.

Not only does the battery act as storage but actually generates electricity through the chemical reaction! Liquid batteries could be used by utilities too, notes MIT.

Central storage with batteries

Is storage capability the holy grail of renewable energy, or is there more to it? In the US, grid operators believe the challenge is not so much in storing energy where generated but building energy storage centrally.

There is a system of regulation service purchased by independent system operators in a specialised marketplace. For instance, an additional twenty megawatts of regulation service could support the adoption of the more than 4,000 megawatts of wind power in the New York queue.

Grid operators use regulation services to handle unplanned drops in supply or spikes in demand, like when air conditioning use goes sharply up on a hot afternoon or a power line goes down. Regulation services must be instantly dispatchable. System operators do this by throttling power plants up or down. They believe batteries could do this too, and betteries could do this too, and better, as storage is faster and more flexible than the plants.

The technology to store energy for regulation services is a new tool but is not just theory. It has been deployed in places like Chile where power variability is high. As more renewable energy is added to grid, more such regulation services will be needed to address the variability. Excess renewable energy can be used to charge batteries and balance system variability

This is why the focus has shifted from merely storage to storage centrally. That is where batteries like lithium ion are very efficient.

Making good use of gravel

Electricity cannot be stored easily, and that has been the hurdle of intermittent renewable energy. But a new technique that uses gravel and argon gas may hold the answer.

So far the only economically viable way of storing large amounts of energy is through pumped hydro – where excess electricity is used to pump water up a hill. The water is held back by a dam until the energy is needed, when it is released down the hill, turning turbines and generating electricity on the way. The problem is that this needs a water source nearby as also the expenses.

The company Isentopic claims its gravel-based battery would be able to store equivalent amounts of energy but use less space and be cheaper to set up. Its system consists of two silos filled with a pulverized rock such as gravel. Electricity would be used to heat and pressurize argon gas that is then fed into one of the silos. By the time the gas leaves the chamber, it has cooled to ambient temperature but the gravel itself is heated to 500C.

After leaving the silo, the argon is then fed into the second silo, where it expands back to normal atmospheric pressure. This process acts like a giant refrigerator, causing the gas (and rock) temperature inside the second chamber to drop to minus160C. The electrical energy generated originally by the wind turbines originally is stored as a temperature difference between the two rock-filled silos. To release the energy, the cycle is reversed, and as the energy passes from hot to cold it powers a generator that makes electricity.

Isentropic claims a round-trip energy efficiency of up to 80% and, because gravel is cheap, the cost of a system per kilowatt-hour of storage would be between $10 and $55. The energy in the hot silo (which is insulated) can easily be stored for extended periods of time – as long as three years.

Sounds perfect? Goes to show how all it needs is some elementary thinking and some waste material to achieve big things.

Search for storage

A new agency in the US called Advanced Research Projects Agency-Energy has mechanical engineer Arun Majumdar, in charge. The agency awarded $400 million in stimulus-act funding to 37 projects. More is expected. In an interview, Arun spoke, among other things, about what excited him most in energy tech. Storage. ‘Let’s say we create battery technology that improves hybrid electric vehicles. You can then use electricity to run our cars, and that becomes part of our energy security. Storage in general is a huge missing piece in the grid today. If you can get it cost effectively, that’s a game-changer.

For those interested in the technical details, Sandia National Lab has just published a study of energy storage applications for the electric grid: “Energy Storage for the Electricity Grid: Benefits and Market Potential Assessment Guide”. The technologies, the opportunities and challenges are all there.

‘The other part is carbon-capture technology for coal.’

Storage has long been seen as the missing link in the energy transformation plan. But coal? In the US (and elsewhere) one of the unresolved burdens haunting the coal sector, in addition to the emissions of CO2, is what to do with the coal ash—the remnant of burning coal—that is accumulating in 194 landfills and 161 holding ponds in 47 states. This ash is not an easy material to dispose of since it is laced with arsenic, lead, mercury, and many other toxic materials.

Yet, governments cannot let go of coal. It is after all cheap and abundant (so far) and the technology is tried, tested. Perhaps, we can place a ban on coal once other cleaner technologies start spinning energy to demand. Or is that a chicken-egg fix? Will clean tech really take off as long as coal is burning bright?

That aside, what advanced research in energy is happening in developing countries? Is it tailored to the need and resource availability? Should multiple agencies work together on this rather than leaving it to technocrats alone?

No such thing as waste

A breakthrough in battery technology, which combines waste carbon dioxide with tiny microbes, could be the next best thing for wind and solar energy. Scientists at Pennsylvania State University are using a combination of tiny microbes and CO2. Placed under an electrical current – for example from an off-grid renewable power source such as wind or solar – the microbes convert the CO2 into methane.

The initial carbon dioxide needed for the chemical reaction could even come from industrial sources. CO2 is soluble in water, so the gas stream could be bubbled or transferred in pipes from factories, for example. The ‘battery’ is designed to work as a closed loop, capturing and reusing the CO2 that’s released when the methane is burned.

The energy conversion is about 80%, but scaling up will need to be worked on. Not only is carbon used up but more energy generated in the form of methane, and a storage unit created for intermittent energy.

Meanwhile, there is hope from what’s unwanted, dirty and a nuisance – waste. According to a recent study by the university of Singapore, fuel from processed waste biomass, such as paper and cardboard, is a promising clean energy solution.

Data from the United Nation’s Human Development Index and the Earth Trends database was used to arrive at an estimate of how much waste is produced in 173 countries and how much fuel the same countries annually require.

The research team has calculated that 82.93 billion liters of cellulosic ethanol can be produced by the available landfill waste in the world and the resulting biofuel can reduce global carbon emissions in the range of 29.2% to 86.1% for every unit of energy produced.

With improvements in technology the numbers will increase. And make cellulosic ethanol an important component of our renewable energy future.

Not that there is reason enough to keep wasting! But waste for sure need not be waste, whether it be carbon dioxide or organic waste!

Flywheels to be deployed

A Massachusetts utility is planning to build a 20 MW flywheel plant in New York. Spinning flywheels that found use in pottery to running steam engines now will be deployed to smooth out the electricity flow, and do it fast and clean.

Beacon Power's flywheels - each weighing one ton, levitating in a sealed chamber and spinning up to 16,000 times per minute - will make the electric grid more efficient and green, the company says. Beacon's flywheel plant will act as a short-term energy storage system for New York's electrical distribution system, sucking excess energy off the grid when supply is high, storing it in the flywheels' spinning cores, then returning it when demand surges.

The job is done now mainly by fossil-fuel powered generators that are one-tenth the speed of flywheels and create double the carbon emissions. The carbon emissions saved over the 20-year life of a single 20-megawatt flywheel plant are equal to the carbon reduction achieved by planting 660,000 trees, says the company.

Flywheels also figure into the emerging renewable energy market, where intermittent energy sources such as wind and solar provide power at wildly varying intensities.

Flywheels are rotating discs or cylinders that store energy as motion, like the bicycle wheel that keeps rotating long after a pedal's been turned. They still have technological hurdles like friction to surmount. A one-ton flywheel has to be durable enough to spin smoothly at exceptionally high speeds. To avoid losing stored energy to friction, the flywheel levitates between magnets in a vacuum chamber.

Despite their potential, flywheels have not taken off as expected. Is it simply a case of not exploring all avenues under the illusion of ‘plentiful’?

Up or down, does it matter?

Pumped hydro storage is a simple technology already in wide use. Pump water up a hill when you have available energy, let it fall when you need its power.

But Riverbank Power; a new start-up is trying out a new idea. Instead of using hills for the height, it will go the other way. Down into the ground.

Their Aquabank would let gravity drop water underground to turn turbines and make hydro electricity. That electricity would be sent from underground to the grid day time. At night, when excess wind is available; wind powered electricity would gently push the water back up to replenish its surface source.

Each project would use a source of water at ground level, an excavated cavern approximately 2,000 feet below ground and four 250-MW generators in a below-ground powerhouse.

The surface footprint would be only 5 to 10 acres, mainly for the water diversion structure and transmission infrastructure. The underground footprint would be about 100 acres.

It would use about 1 billion gallons of water for six hours of electricity production. It would take eight hours to pump out the cavern. The remaining sixteen hours each day the water supply would not be diverted.

To avoid sucking up fish inadvertently, the initial intake from the river is extremely slow and filtered so that the natural flow of the river remains unaltered, unlike conventional hydro power.

Given that the water is stored underground only for a short time, the pumping does not change the quality or temperature of the water before it is returned to the river.

So is this simply a tweaking of what was already done? Down instead of up? What are the advantages of going down? For one, you don’t need hills around. What else? Write in to us.

Boys' Toys?

Energy storage is an area that will probably see a lot of research as clean energy gathers steam. In fact it will have to be developed alongside new energy source technologies. Are we doing enough?

Most renewable sources are infirm and not available when the demand is at its peak. It makes sense to look at storage. Storage means a good energy density, storage capacity and speed of discharge.

Energy densities of batteries and capacitors are much lower than that of fossil fuels. From lead acid to lithium ion to silicon based, the density rises but is still limited. Combining the storage capacity of batteries and discharge speed of capacitors will yield the perfect energy storage. Nanotech capacitors are promising but will take time. That is where simple technologies like flywheels and compressed air could come in.

Where flywheels work on the inertia principle and keep spinning when small amount of electricity is supplied, when the power is gone they keep spinning. But not for too long. At most they can provide power for a few minutes. But innovation is at work in reducing friction, using lighter materials, etc.

Perhaps compressed air can provide a longer period of stored power? Compressed air energy storage technology basically takes excess energy from a power plant or renewable energy and is used to run air compressors, which pump air into an underground cave where it is stored under pressure. When the air is released, it powers a turbine, creating electricity.

The problem here is finding the right place underground. Read more.

As is clear, these are all simple concepts, and work like toys that most boys like. Right?