New Sodium Ion Battery May Be Best Battery for Utility Grid

Whitacre's sodium-ion cells are similar in some ways to lithium-ion cells--the type used in portable electronics and in some electric vehicles. In both types of cell, ions are shuttled between the battery's positive and negative electrodes during charging and discharging, with an electrolyte serving as the medium for moving those ions. But because sodium is orders of magnitude more abundant than lithium, it is cheaper to use. To make the cells cheaper still, Whitacre plans to operate them at lower voltages, so that water-based electrolytes can be used instead of organic electrolytes. This should further decrease manufacturing costs, since water-based electrolytes are easier to work with.

The change to water-based electrolytes could also make it possible to eliminate much of the supporting material needed in conventional lithium-ion cells, again reducing costs. This is because increasing the ionic conductivity makes it possible to use thicker electrodes with fewer layers of separating and current-collecting materials inside the cell.

"In principle, a sodium-ion system can be low-cost, and with aqueous electrolytes, it could be really low-cost," says Jeff Dahn, a professor of physics and chemistry at Dalhousie University in Nova Scotia, Canada. _TechnologyReview

Jay Whitacre, a professor of Materials Science and Engineering at Carnegie Mellon University, is perfecting a sodium ion battery meant for use at utility-scale. It will contain no toxic materials, cost 1/3 as much as lithium ion cells per kwh stored, and will last longer through more charge-discharge cycles than conventional cells.

Aquion's battery uses an activated carbon anode and a sodium- and manganese-based cathode. A water-based electrolyte carries sodium ions between the two electrodes while charging and discharging. The principle is similar to lithium-ion, but sodium ions are more abundant and hence cheaper to use. Compared to solvent-based electrolytes, the aqueous electrolyte is also easier to work with and cheaper. Even better, the materials are nontoxic and the battery is 100 percent recyclable, Whitacre says.

Grid-scale trials of the technology are next. Aquion has started shipping pre-production battery prototypes to off-grid solar power companies. Next month, a 1,000-volt module will go to KEMA, a Dutch energy consulting and testing outfit, which has a facility outside Philadelphia.

...John Miller, an electrochemical capacitor expert and president of consulting firm JME in Shaker Heights, Ohio, says Aquion's battery could be the cheapest of the various battery technologies vying to provide grid storage. He compares it to today's most common grid storage technology, pumped hydro, which accounts for 95 percent of utility-scale energy storage. Pumped hydro involves moving water to an elevation when electricity demand is low, and releasing that water through turbines during peak periods. It is, however, limited by geology and space, and pumped hydro systems take many years and millions of dollars to build. Utilities are now starting to look at batteries because they can be delivered in months and, in principle, can be sited anywhere.

"Lead-acid is even too expensive," Miller says. "Aquion's technology is getting to the range of pumped hydro in cost, which is two cents per kilowatt-hour [over the system's lifetime]. They're unique. I would say it's very promising for grid storage."

So far, no available technology meets all grid energy storage requirements, says Haresh Kamath, a program manager for energy storage at the Electric Power Research Institute. "Each technology has a different sweet spot" in terms of cost, safety, reliability, lifespan, and efficiency, he says. _TechnologyReview

Here is more information about the new battery from Aquion:

Safe

The core Aquion technology contains zero toxic or otherwise hazardous materials. This facilitates battery installation and manufacturing facilities by preventing delays associated with hazardous material zoning issues. The technology was designed such that harvesting and recycling both the packaging and the active materials is easy. The batteries are also much more efficient than traditional batteries at both a cell and systems level; the end result is an energy storage system that makes better use of the energy it stores.

Reliable

The centerpiece of the technology is an innovative hybrid energy storage chemistry. Over the last two years, the chemistry has been rigorously proven in a laboratory environment and certified by independent third party testing. The electrochemical couple that has emerged from this process is one that combines a high capacity carbon anode with a sodium intercalation cathode capable of thousands of complete discharge cycles over extended periods of time. The materials couple can deliver over 30 Wh/l as packaged. The device functions in a broad range of ambient temperatures and can be repeatedly cycled with little to no loss in delivered capacity. Rapid cycle testing indicates at least 5000 cycles with no fade in delivered capacity, while ongoing calendar life testing shows stable performance for over a year of continuous deep cycle use.

Affordable

To minimize cost, only the cheapest raw materials were considered in the basic R&D phase. As a result, sodium interactive materials and water based electrolytes are used instead of the traditional lithium-based materials and organic solvents. We are also vertically integrated, with manufacturing that incorporates in-house electrode active materials production. Processes borrowed from the food and pharmaceutical industries are then used to create freestanding electrodes that are then packaged into large units. _Aquion

It is likely to take years more to perfect the technology for industrial and utility scale use and production. But this technology would seem to be the most promising battery technology seen recently, besides flow cell batteries -- which will take up to 10 more years to perfect.

In the meantime, the cryogenic storage technology being developed in the UK is felt to be the most promising non-battery utility storage technology.

A Fascinating Look at Possible Utility-Scale Thermal Storage

Efficient and economical utility-scale energy storage would provide power grids much greater stability and versatility. Here are excerpts from an intriguing look at future prospects for thermal grid storage from Intelligent Utility:

The molten-salt heat-of-fusion thermal storage initiative has potential in the nuclear power industry. Nuclear power stations operate optimally when the reactors and steam lines remain at constant temperature, with steam lines also operating at near constant pressure. To achieve such an objective, owners of nuclear power stations may sell off-peak power at bargain-basement prices or even pay outside utilities to take the excess off-peak nuclear-electric power. Such operation also enhances prospects for cost-competitive and viable energy storage.

At geographic locations where pumped hydraulic or compressed air storage is unavailable, thermal storage may become a potentially attractive option. Steam lines may carry off-peak thermal energy from nuclear reactors to molten salt-based thermal energy storage installations. The useful life expectancy of thermal energy storage technology greatly exceeds that of various chemical battery storage technologies that offer 4,500 to 5,000-deep-cycle recharges and discharges. Over the long-term, thermal energy storage may be cost-competitive against grid-scale chemical battery storage.

High Temperature Storage:

While older generation, heavy-water nuclear reactors operate at temperatures that are comparable to molten-salt heat-of-fusion stored thermal energy installations, modern light-water nuclear power station operate at higher temperature. The reactors are cooled by helium that transfers the heat to boilers at a temperature near the melting point of aluminum. At such temperatures, boilers may raise super-critical steam capable of producing power at over 40% thermal efficiency.

Instead of using molten aluminum for thermal storage, there may be scope to use molten mixtures of naturally occurring metallic oxide ores that melt near the same temperature. The mineral ore cryolite (Na3AlF6) melts at 900°C to 1000°C and may be mixed with bauxite hydrate (Al2O3.H2O) to reduce melting temperature to near that of a helium-cooled nuclear reactor. Other variations of aluminum fluoride contain potassium (NaK2AlF6) or lithium (Li3AlF6) and may used in thermal storage material.

Some naturally occurring bauxite ores such as diaspore and bhoemite contain hydrogen [AlO (OH)] while other variations contain sodium (NaAlO2) or lithium (LiAlO2). There are numerous possible mixtures of bauxites and cryolite ores that can melt at temperatures that are near the operating temperature of newer generation, light water nuclear technology. Alternative thermal energy storage systems may be based on alternative a compound between the heat of decomposition and heat of formation.

When heated, several metallic carbonates such as calcium carbonate (CaCO3) will decompose and release carbon dioxide (CO2), leaving the metallic oxide calcium oxide (CaO). Unglazed calcium oxide may be reacted under pressure with carbon dioxide to produce the metallic carbonate and release massive amounts of heat. The temperature of the heat of formation of some metallic carbonates is sufficiently high to raise super-heated steam and/or super-critical steam. At some locations, it may be possible to storage massive volumes of compressed carbon dioxide in subterranean caverns and the metallic oxides in above ground silos.

Several compounds that are hydrates release water vapor (H2O) when heated. When some dehydrated compounds encounter water and/or steam, there is either a heat of reaction or a heat of formation as a hydrate is formed. The heat of reaction/formation may occur at a sufficiently high temperature to generate steam that may drive turbines and electrical generating machinery. Banks of insulated and pressurized accumulators may hold saturated water to produce the steam needed to sustain the heat of formation operations.

During off-peak hours, special piping systems may transfer heat from the reactors to thermal storage. During peak periods, stored heat would raise steam to drive turbines and electrical machinery to meet market demand for electric power. During off-peak periods, it may be possible to flow minimal amounts of steam through the piping system to maintain constant temperature and pressure in steam lines connected to the thermal storage system. Such operation may reduce thermal stress problems caused by thermal cycling of thermodynamic components.

...There is scope to combine ultra-high-temperature thermal energy storage with compressed air energy storage. Compressed air may be super heated to over 1000°C (1800°F) and drive a multi-stage turbine engine system that include reheat capability and exhaust heat recovery, along with preheating of the incoming compressed air. The super heated compressed air may energize turbines that drive electrical machinery during peak demand periods, while diverting the power normally allocated to driving turbo-compressors to instead drive electrical generating equipment.

Depending on final exhaust temperature, there may be scope to use the exhaust heat to sustain the preheating requirements for a Rankin-cycle engine or to sustain the operation of thermal seawater desalination during peak periods. As with steam-based power systems, there may be scope during off-peak periods to flow a small amount of super heated compressed air through the piping systems, to minimize problems related to cyclic thermal stresses in the thermal components.

Conclusions:

Future thermal energy storage would likely cover the temperature range from the sub-freezing point of water to ultra-high temperatures of some 1000°C. Heat-of-fusion technologies offer greatly extended useful service lives and cost-competitive long-term costs. While compact thermal energy storage systems are possible, most such systems would likely be built on a large scale that involve massive volume. Most future research into thermal energy storage may involve high-temperature systems that generate steam and energize air turbine engines. _IntelligentUtility

The excellent article by Harry Valentine should be read in full at the link above.

One omission from the fine overview of future thermal storage methods, is the cryogen method being developed at the University of Leeds. Such cryogenic energy storage methods extend the temperature range considerably on the low end, with concomitant potential for greater efficiencies.

Complementary Uses for Waste Heat and Cryogenic Storage

Leeds Engineering
The scheme pictured above is from the University of Leeds Engineering. The process involves using low cost off-peak power to cool air to liquid cryogen. During peak load hours, the cryogen is combined with waste industrial heat to generate peak load power in a turbine.

Oregon State Engineering
The above schema comes from Oregon State University Engineering, depicting a process for turning waste heat into mechanical power for cooling. Heat-to-cooling efficiencies of up to 80% are claimed. The OSU process combines micro-channel heat exchange with an organic rankine cycle turbine to drive the refrigerant compressor. If used to generate electric power from waste heat, efficiencies of only 15% to 20% are claimed.

Leeds Engineering
The schema above is from the University of Leeds Engineering. It depicts a combined use of waste heat from power production for either cooling -- using absorption refrigeration -- or for assisting in the generation of electric power using cryogenic storage.

It is easy to see how the OSU micro-channel / organic rankine cycle process might be used in such a trigeneration scheme, substituting for the absorption cooling in the scheme above.

The purpose of combining different processes together -- as in either CHP or IGCC etc -- is to achieve higher efficiencies and more economical production.

While the above waste heat retrieval processes are more efficient than thermoelectric conversion, they are less suited for mobile uses due to their greater complexity. But for use on industrial and utility scales, such processes are likely to prove as useful for integration into total power schemes as the emerging flow cell batteries.

An advantage of the cryogenic storage approach is that whenever a relative excess of electricity persists over an extended time, the cryogen can be separated into liquid N2 and liquid O2 and sold for a profit.

Cryogenic Utility-Scale Power Storage for Load Leveling 50% Efficient

Charge/Store: The system operates by using electrical energy to drive an air liquefier (effectively the charging system) and storing the resultant liquid air in an insulated tank (effectively the energy store) at atmospheric pressure.
Power recovery: When the stored energy is required, the liquid air is released from the storage tank, pumped in its liquid form to high pressure, vapourised and heated to ambient temperature (using either ambient heat or waste heat); the resultant high pressure gaseous air is used to drive an expansion turbine which in turn powers a generator (collectively the power recovery system). The exhaust is cold air.
Cold recapture: As the cryogen is evaporated and returned to ambient temperature in the power recovery unit, we capture the cold exergy and store it. It is then used back into the liquefaction process. Harnessing and ‘recylcing’ the cold broadly halves the energy cost of liquefaction, increasing the round-trip efficiency of the system to ~ 50%. This can be increased further by adding in waste heat, including low grade heat to the power recovery process. _Highview

POThis approach to utility-scale power storage comes from the UK, where it has been used at a Scotland power plant for 9 months. It involves cooling air to liquid temperatures (-196 C) with excess power, and storing the cryogen in an insulated tank. When power is needed, the cryogen is released into a sealed space and allowed to warm and expand -- driving a turbine to generate power.

The Highview Cryo Energy System uses liquefied air or liquid nitrogen (78% of air) which can be stored in large volumes at atmospheric pressure. Liquid nitrogen is a very common commercial product, transported daily from liquefaction plant to customer; or, for larger users, produced on site.

Liquefied air has a high expansion ratio between its liquid state (-196º Celsius) and, more common, gaseous state; expanding about 700 times when regasified. As with a traditional steam engine, a cryogenic engine relies on phase-change (liquid to gas) and expansion within a confined space e.g. engine cylinder or turbine.

Since liquid air boils at -196º Celsius, ambient temperature will superheat it, creating regasification and expansion. An engine can therefore use freely available environmental heat as the heat source.

The energy density of cryogenic fluids, such as liquid nitrogen compares favourably with alternative energy storage fluids such as compressed air. Cryogenic storage also has the advantage over compressed gases in that it can be bulk stored above ground in low pressure tanks. _Highview_via_PO

More:

Energy storage offers the opportunity to store, or ‘bank’ ‘wrong time’ energy and time-shift it to periods of peak demand or hold it in reserve. This is critical to enable the use of intermittent renewable power (e.g. wind or solar) when the customer needs it, not just when it is available. It can equally “provide shape” to must-run generation (i.e. nuclear or Energy from Waste/biomass), moving excess off-peak energy to the peak demand and pinch points. It also reduces both the capital cost and carbon footprint of electricity networks by making them more efficient; with stored reserves – not over-capacity of generation in reserve – to manage supply and demand.

Electricity supply and demand have to match on a second by second basis. Historically, the balance is achieved by significantly overbuilding generation, transmission, and distribution assets, and specifically keeping enough quick response generation in reserve. This is unlike any other commodity market, where storage/reserves are used to manage supply and demand, including unexpected imbalances.

Currently, quick response reserve generation includes (i) ‘spinning reserve’: generation plants burning coal or other hydrocarbons, but producing reduced power so as to be in a state of readiness; or (ii) gas and diesel generators: quick to start but environmentally poor.

Emission and environmental legislation, plus the simple cost of building over-capacity into the network is driving the need for a zero emission solution.

Market Potential for energy storage: ~ $600 billion over the next 10 -12 years

According to the US Dept of Energy, “big energy storage is an effective tool to improve the reliability, stability, and efficiency of the envisioned electrical grid of the future. This grid will be significantly impacted by new demands, such as plug-in electrical vehicles, increased use of renewable energies, and smart grid controls. Large scale storage technology could shave the peaks from a user or utility load profile, increase asset utilization and delay utility upgrades, decrease fossil fuel use and provide high levels of power quality, while increasing grid stability. In addition, distributed energy storage near load centers can reduce congestion on both the distribution and transmission systems.”
_Highview

This technology can also be used for "waste heat to power" and for commercial cooling.This approach is almost an "off the shelf" design, requiring no new technology development. It appears to be easily scalable. Efficiencies of 50% are somewhat below that of flow cells (65%) and pumped storage hydroelectric (75%), but cryogenic storage does not require nearby mountain reservoirs (as with pumped storage hydro) or significant technology improvements (as with flow cells).

More: An optimist hopes that large scale energy storage will allow a small arid country like Israel to generate 90% of its power needs from solar. He is looking at pumped storage hydro and redox flow cell batteries, but the principle is the same when using cryogenic storage. Unfortunately for the Israeli solar champion quoted at the link, following his prescription would assure an even speedier death of the micro-state than is already in the cards due to demographics. The expense of building and maintaining such a huge photovoltaic array, compared to likely costs for small modular nuclear reactors, would be exorbitant -- without even taking into account the cost of necessary storage. The result of relying on big wind or big solar is economic devastation and energy starvation. Israel, like most advanced nations, cannot afford more of either.