SuperCaps for UPS

Author:
Michael Adams, Global Vice President, Data & IT, at AEG Power Solutions

Date
09/27/2010

Categories:
Capacitors, Power Supplies

 PDF
Fast, Compact, Long Life, Green Storage Alternative to Batteries

The need to protect IT equipment from the effects of power transients, as well as to provide assured operation during power outages is evidenced by the steady growth in sales of uninterruptible power supplies (UPS) up to the global downturn of 2008/9. As markets start to bounce back post-downturn, the sales of UPS equipment has started to recover and are predicted to return to real growth during the coming 2-3 years. With IT central to the successful operations of most modern organisations, the UPS has a central position in the critical physical infrastructure which supports servers, storage and communications equipment, and which ensures continuity of services during all local mains conditions. Recently, escalating energy costs and increasing concern about the carbon footprint of organisational power requirements, has driven the need to consider alternative back-up technologies and evaluate their effectiveness to ensure business as usual' has become pressing. Pressure on IT and facility managers to utilise green technologies, especially in Western Europe, continues to grow. In addition to the environmental benefits associated with lower carbon footprint, green technologies bring with them lower operating expenses by virtue of their more efficient operation and ability to deliver more with less', i.e., more compute cycles from less energy. As a discipline, energy storage technology has acquired new levels of prominence as methods are sought to overcome intermittency issues associated with solar and wind power generation. Smart grid concepts are being tested which are likely to promote an increasing trend towards distributed power generation combining traditional power sources with renewable or green power sources. The eco-friendly storage industry is currently small, but solutions are either on the verge of commercialisation, or are starting to experience mainstream uptake. But another wrinkle is posed by the fact that the choice of energy storage solutions is highly application-specific, as it varies as per application and requirement of the end-user.

Supercapacitors, or SuperCaps, are not a new concept and their effects were first noted in the late 1950's. Consequently, the technology is well established; has experienced significant advances over the last 10 to 15 years and has also seen recent reductions in cost. At the moment, supercapacitors have been successfully adopted in three different sectors; transportation, industrial and consumer electronics. Why should we consider SuperCaps in UPS applications? SuperCaps core technology is environmentally friendly and offers a high power density (4000W/kg). They have low internal resistance (ESR) and can operate in a wide temperature range which is very useful for data centres. They also offer a low total cost of ownership (TCO) and are capable of over 1 million cycles and offer instant recharging. There is no doubt that there have been significant developments with battery technology over the years, but despite all these advances, they all suffer from the same basic problem in that they utilise a chemical reaction. This means they suffer from a limited life, and can only operate in a limited temperature range. In addition, traditional batteries that experience constant high demands for current, have a shortened operational lifespan. Therefore in order to ensure reliability and long lasting cover, facility managers are forced to deal with higher maintenance costs. It is well known that batteries die after a period of time, and need replacing on average, every two, five or seven years. Any technology that can offer a longer lifetime, so that users do not have to spend their precious budget repeatedly on replacement batteries, will prove to be a big incentive. The SuperCap UPS provides a useful alternative solution in this context as it is ideally suited to provide a short-term "bridge" power until standby power generation equipment kicks in. As the SuperCap industry continues to experience a lot of R&D and maturation, SuperCap UPS are now becoming highly competitive with, and in many cases superior to, older bridge technologies. TCO Considerations Offering a wide temperature range, long life, and flexible voltage range, SuperCaps provide an extremely reliable solution for bridge power. The very high cycle life of a SuperCaps UPS means that unlike lead acid batteries, there will likely be little or no need for constant replacement. The facility to repeatedly charge and discharge for up to a million cycles without disintegrating, means that the lifetime cost of the SuperCap is expected to break even with lead acid batteries. Longevity is helped by the fact that their high power density results in reduced strain on the battery in times of need. Another major consideration is the fact that the SuperCap also has the ability to recharge instantaneously, in a few seconds. This is really useful in data centres, to help cut power costs associated with keeping batteries charged. Another important factor is the ability of SuperCaps to offer versatile functioning in a wide temperature range, dramatically reducing cooling costs. This is because the function of a SuperCap does not require a chemical reaction, and therefore, does not involve an optimal temperature range for best performance or longevity. It has been estimated that the SuperCap can be used from -40°C to +70°C, without degradation in its performance characteristics. This is in stark contrast to the lead-acid battery, which when used in industrial applications, almost always requires a mechanically cooled environment. Pros and Cons The SuperCap is green in two ways. Firstly, it reduces waste because it has a very high cycle life, and therefore decreases disposal issues. Secondly, the materials and substances used in the SuperCap UPS are toxin free and biodegradable, e.g., nano carbon particles are commonly used. They can operate in a wide temperature range without any degradation of performance characteristics, and it also has the ability to recharge instantaneously in a few seconds. SuperCaps are ideal energy storage devices for fast and short-term peak power delivery, which is why they are so suited for UPS systems. They are also more efficient than conventional batteries as they do not release any thermal heat during discharge, and various figures have shown that they operate at around 80% - 95% efficiency in most applications. SuperCaps also take up much less room compared to lead-acid batteries, and indeed weigh less as well, which can be an important factor in certain situations or locations. The following table contrasts the pros and cons of SuperCaps with traditional UPS technology. Pros and Cons of the SuperCap UPS (Maxwell Technologies) Pros

  • A SuperCaps UPS is green and does not contain toxic materials
  • Can operate in a wide temperature range, without a degradation in its performance characteristics
  • A SuperCaps UPS is much more efficient than a conventional battery
  • Ideal energy storage device for fast and short-term peak power delivery, for indefinite cycles.
  • Up to 20 years lifespan
  • Reduced footprint compared to lead-acid batteries, and also weighs less
  • Scalable-modular nature that make it well suited for many applications
  • A SuperCaps UPS, used strictly as a bridge, has high power density that is well suited to supply high power for short periods of say around 30-100 seconds
  • Flexible voltage range
  • A SuperCaps UPS is inherently reliable because of its composition and construction. There are no mechanical moving parts, eliminating maintenance
  • Capable of sitting on a charge voltage for extended periods without any loss of capacity, unlike a battery
  • Development of the technology is being pushed by massive industry heavyweights in the transportation sector. Honda for example has developed its own SuperCaps for its vehicles Cons
    • Despite their indefinite life cycle, SuperCaps have the ability to provide only very short-term power
    • High initial cost of ownership. SuperCaps are more expensive than flywheel, as it is still in its nascent stage of commercialisation
    • End users are unable to perceive or experience the true advantages of this technology due to early stages of take-up and lack of awareness
    • Lack of industry standards to regulate and stimulate full commercialisation of the technology. Design time is longer, which results in a longer lead time to get a product ready for the end user
    • The SuperCaps UPS is unable currently to store as much energy as a battery because there are no chemical reactions taking place that can sustain the slow discharge of current to power equipment
    Conclusion There is no doubt that the industrial market needs an energy storage solution that is both reliable, and can offer a quality service. SuperCaps offer high power density, cycle life, and thermal susceptibility, and the increasing adoption of renewable energy expands the possibilities of using SuperCap-based technology. Frost and Sullivan reported the total world ultracapacitor (SuperCap) market had generated revenues of $113.1 million in 2008 and is likely to reach $381.9 million by 2015. It feels that this market has witnessed growth (despite the economic situation) due to the great interest in propelling alternative energy storage mechanisms by governments. Indeed, Europe has given the highest priority to any environmentally friendly technology and has a proud tradition of being one of the first global markets to accept new technology and consider its applicability in various solutions. The high price of oil, coupled with high electricity costs, the need for devices that can reduce the power burden of a data centre represents a significant opportunity. The increasing use of SuperCap technology within the transportation industry will also serve to spur new developments and help drive down the initial cost of ownership. www.aegps.com

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