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On March 4, 2011 the Pacific Northwest National Laboratory published a comprehensive review of "Electrochemical Energy Storage Technologies for Green Grid" that is a must-read for serious investors who want to understand the technical and economic intricacies of the energy storage sector. It explains why storage is a key enabling technology for wind and solar power, the smart grid, efficient transportation and a legion of high-technology manufacturing and service enterprises that can't survive without reliable power. It also explains why energy storage is an investment mega-trend that will endure for decades. While I normally try to provide links to materials that are available for free, this particular review is only available from the American Chemical Society website and their charge for non-members is $35. If you own stock in a battery company or are thinking about investing in one, it's the best $35 you'll ever spend.

Conceptually, a battery is nothing more than a bottle that stores electricity. The term "energy" describes the total amount of electricity you can put into the bottle. The term "power" describes how quickly you can empty or fill the bottle. The basic problem with energy storage is that batteries are thousands of times more expensive than the electricity they store. You may be able to buy a kilowatt-hour (kWh) of electricity for a dime, but a battery to store that much electricity will set you back $150 to $1,000. Once you include battery depreciation in the equation, the cost of electricity from a battery is always higher than the cost of electricity from a wall-socket. If you only need to store a few watt-hours of energy for a cell phone or laptop computer, convenience will usually outweigh battery cost. If you need five, ten or twenty thousand watt-hours of battery capacity so that you can use electricity from solar panels at night or drive a plug-in vehicle 40 to 80 miles, battery cost quickly becomes a major issue, if not an insurmountable obstacle.

In its report, the PNNL explains that capital cost and life-cycle cost are the most important and fundamental issues in the energy storage sector. Capital costs are usually expressed in terms of dollars per kilowatt ($/kW) for power applications and dollars per kilowatt-hour ($/kWh) for energy applications. Cycle-life cost is calculated by dividing the sum of the capital cost and expected maintenance costs by the number of cycles a battery can deliver over its useful life. In general, the authors of the PNNL report believe the following attributes are essential for grid storage applications:

  • Capital cost of $250 per kWh or less;
  • Long calendar life (e.g. > 15 years);
  • Long cycle-life (e.g. > 4,000 deep cycles);
  • High safety standards; and
  • Low maintenance costs.

It's a tall order and most energy storage technologies fall short of the mark. The following graph from the PNNL report shows the estimated capital cost per cycle of various storage technologies before project financing costs, operation and maintenance costs, and replacement costs.

3.8.11 Storage Costs.jpg

After studying the PNNL report in detail, I believe flow battery and lead-carbon battery technologies have the best shot at meeting these high standards in the short term. Others will no doubt disagree. The only way for a serious investor to make an informed decision is to download the report, study the PNNL observations and draw his own conclusions.

There is one publicly-held pure-play energy storage company in the flow battery space. ZBB Energy (NYSEMKT:ZBB) is the owner of a zinc-bromine technology that was invented by Exxon, developed by Johnson Controls and ultimately sold to ZBB. Over the last few years, ZBB has developed a modular system architecture for its technology and successfully completed a three-year validation test by Australia's Commonwealth Scientific and Industrial Research Organisation (CSIRO). ZBB has also devoted considerable resources to an open-platform power management system that facilitates the integration of diverse power sources and diverse energy storage device types to meet the needs of a particular customer. ZBB has been a poor market performer since its IPO in 2007 and currently trades at one-fifth of the IPO price. Its market capitalization of $33 million is the lowest of the 18 pure-play energy storage companies I follow. ZBB hasn't had a particularly strong balance sheet for several years and it will need to raise additional capital. Given the proven status of its technology and its low market capitalization, I believe ZBB has limited downside risk and attractive upside potential.

The section of the PNNL report that I found most illuminating was their discussion of lead-acid batteries in general and lead-carbon batteries in particular. While I've been writing about lead-carbon battery technologies for a couple of years, the PNNL review is the first major report from a national laboratory that does not require A to B to C analysis to integrate information from several sources. The following schematic from Furukawa Battery shows the three primary lead-acid battery electrode configurations that are presently being developed.

3.8.11 LAB Configurations.jpg

In its discussion of conventional lead-acid batteries the PNNL report noted that lead-acid has historically suffered from limited cycle life (e.g. 1,000 cycles), limited depth of discharge (e.g. less than 30%), low round-trip energy efficiency (e.g. 50% to 75%) and low charge acceptance capacity (e.g. 7% of the one hour discharge rate). In combination, these technical factors have made large-scale applications problematic from an economic perspective.

The first innovation PNNL discussed in the field of advanced lead-acid batteries involves the use of carbon additives to improve cyclability while inhibiting the formation of hard lead sulfate crystals on the negative electrodes. In the graphic, a carbon additive design will replicate the conventional lead-acid battery configuration shown on the upper left. Johnson Controls (NYSE:JCI) and Exide Technologies (XIDE) are both actively developing carbon enhanced lead-acid batteries in both flooded and absorbed glass mat, or AGM, form factors. Both companies claim performance improvements of 100% or more, which can reduce the capital cost per cycle by 50% or more.

The second innovation PNNL discussed is an asymmetric lead-carbon capacitor that uses a carbon electrode assembly to replace conventional lead-based negative electrodes. In the graphic, an asymmetric lead-carbon capacitor is shown on the upper right. The key advantages noted by PNNL include a higher operating voltage for the cell as a whole, greater utilization of negative electrode capacitance, the elimination of negative electrode sulfation and reduced swings in acid concentration. The asymmetric lead-carbon capacitor was patented in 2001 and is owned by Axion Power International (OTCQB:AXPW) which has trademarked the name PbC® and filed a suite of protective patents around the core technology. In exhaustive performance tests over the last three years, Axion has demonstated that the PbC battery:

  • Offers a depth of discharge of up to 70%, as compared to 30% for conventional lead-acid;
  • Offers stable round-trip energy efficiency of 85%, as compared to 50% to 75% for conventional lead-acid;
  • Offers cycle life improvements of 400% or more; and
  • Offers dynamic charge acceptance rates that are a 10x improvement over conventional lead-acid.

In combination, these unique features of the PbC battery can reduce capital cost per cycle by an order of magnitude and make the PbC the most cost-effective electrochemical storage system in the industry. Axion's PbC battery is almost ready for commercial roll-out. The company has taken delivery of its second generation electrode fabrication line and expects to commission the line by the end of this month. Once the line is commissioned, potential customers who have been testing first generation products for over a year will need to conduct extensive process and equipment validation evaluations before placing orders. Barring unforeseen difficulties, that process should be completed this year. Axion has enough capital to finance its activities over the next year, but will need additional capital to build new electrode production capacity if demand for its product develops. Given the unique attributes of the PbC technology and Axion's relatively low market capitalization of $70 million, I believe Axion has limited downside risk and attractive upside potential.

The last innovation PNNL discussed in the field of advanced lead-acid batteries was the Ultrabattery, a half-measure developed by CSIRO that represents an improvement over conventional lead-acid batteries but does not offer all the performance advantages of the PbC. In the graphic, Ultrabattery is shown on the bottom. The PNNL report was the first detailed discussion I've seen of the Ultrabattery technology and it highlights a couple of issues that strike me as potentially problematic. During a discharge cycle the Ultrabattery does not begin to access the capacitance of its carbon electrode until the lead electrode has been depleted. Likewise during a charge cycle, the carbon electrode charges first which results in significant hydrogen production at the lead electrode.

Several lithium ion battery companies including A123 Systems (AONE), Ener1 (NASDAQ:HEV) and Altair Nanotechnologies (NASDAQ:ALTI) have sold high profile demonstrations of their technologies in grid- connected applications. After reading the PNNL report I'm more convinced than ever that these demonstrations will not turn into sustainable businesses until those manufacturers are able to overcome a variety of hurdles relating to system cost, safety, durability and cycle life. They may be successful, but when I compare their market capitalizations with the market capitalizations of ZBB and Axion, I have to believe that the greater upside potential lies in the companies with the lower current market capitalizations.

Disclosure: Author is a former director of Axion Power International and owns a substantial long position in its common stock.

Source: Two Stocks for Grid Storage: ZBB Energy and Axion Power