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Battery Powered Data Centers Redux - Part 2

Jun 24, 2015

Batteries may be ready for home applications, but are they ready for the big time: Data Centers?


In the first part of this two part look at battery powered data centers we found that Tesla recently entered the battery electrical storage market for home applications such as emergency backup and metered energy cost savings. Companies like EnerDel that have active data center projects have been supplying industrial as well as transportation power options while Tesla up to recently has concentrated on the automobile market.


Along with the Powerwall option for households Tesla is also making a play for commercial and business applications. Tesla’s announcement provides examples of commercial customers, one being Target. Select stores are conducting pilot studies incorporating Tesla Energy Storage batteries. “David Hughes, senior group manager, Energy Management, Target. “Tesla’s cutting-edge technology offers unique benefits to powering these stores, most importantly relieving stress from the electrical grid at peak times furthering Target’s investment in designing and operating energy-efficient and sustainable buildings.” (Link to Announcement) Here again, managing peak load demand is the goal and savings for large electrical energy users like Target can be substantial.



Figure 1 (Left) shows an artist’s concept of an array of Tesla’s Powerpack Battery System on the roof of a retailer such as Target. Link to Image  Figure 2 (Right) shows the home market Powerwall (left) and the commercial Powerpack (right) for comparison. Link to Image


Each Tesla Powerpack module is rated for 100 kWh. These batteries act like very efficient generators and can supplement the grid when needed as well as take advantage of storing power when rates are the lowest, overnight for example. The Return on Investment (RoI) for the Powerpack would be a function of the difference between peak and off-peak rates in any given location. Alternately, linking the battery array to a solar array would result in “free” electricity for storage, but the cost of the solar array would need to be added to the total RoI. In such cases, the DC output of the solar array could be used directly to charge the batteries, negating the cost of an inverter for the solar piece. Only the battery to AC inverter would be needed.


Still, since companies like Target offer large opportunities for power suppliers, their cost both for grid power as well as battery and solar will likely be significantly lower than smaller enterprises. Someone surely has done the math, but there is no update of the test installation by Portland General Electric’s 5 MW EnerDel battery demonstration project in South Salem, OR. Because this is a public project there may be some economics forthcoming, but a search has turned up empty for this two-year old, $178-million project. (Link to Project Website http://www.pnwsmartgrid.org/)


So what about data centers? Amazon Web Services may shed some light here. According to The Verge, “Amazon is using (Tesla) Powerpacks as part of a 4.8 mWh pilot program in Northern California to assist in running its Amazon Web Services platform. That’s 480 - 100 kWh Powerpacks. James Hamilton, an AWS engineer, said the technology would make it easier for the company to rely on renewable energy sources. Batteries, he said, would "bridge the gap between intermittent production, from sources like wind, and the data center's constant power demands." Amazon has been working with Tesla for the last year, viewing Musk's new Powerpacks as a way to reach its ultimate goal of "reducing the technical barriers limiting widespread adoption of renewables in the grid."


One thought is lithium-ion battery technology is not without limitations. Looking at the artist’s concept drawing (Figure 1) what comes to mind for this New Englander is what that roof would have looked like this past winter when Boston had a record snowfall. Such installations would need to have additional support for the significant battery weight; add to that the weight of 9-feet of snow and there could be real concerns. The second is that lithium-ion batteries don’t like hot and cold weather. The graphs below demonstrate the issue of installations in cold and hot climates.



Figure 3 (Left) Li-ion discharge times fall off dramatically at colder temperatures. Link to Source

Figure 4 (Right) Li-ion battery capacity decreases markedly with increasing temperature, as is witnessed by Tesla car owners in Phoenix.  Link to Image



Two thoughts come to mind here. First, data centers use large battery arrays as UPSs to bridge the time until the generators kick in. Enabling these UPS arrays to provide additional benefit such as renewable energy storage and smart metering savings can have real benefit to data centers with the right economics. In a power market like Northern California where the grid is stretched to the limit during hot summer days, such an approach could bridge the gap of a brownout voltage cut, reducing any electrical strain on data center electronics. Again, cost vs benefit is needed, but for high risk locations these calculations may look more like life insurance than not.



Figures 5, 6. Amazon data centers in Virginia (Left) and Oregon (Right) may be candidates for battery storage.  Left Image Source   Right Image Source


While there is hope for some light to be shed publicly on the Portland demonstration project, AWS and its competitors keep their costs and benefits close, so meaningful analysis will be difficult. According to Forbes, the Powerpack cost is $250/kWh which is below the $350/kWh calculated by a Texas power supplier as break even compared to the cost of a new power generator. (Link to Source) For the Amazon project that translates to $1.2 million in cost for the Powerpacks, plus installation and supporting hardware. Future announcements may help data center managers and owners make a meaningful estimate for RoI. Tesla is reportedly sold out on all products, a good sign that this technology offers real benefit. Stay tuned for updates as this story continues.


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