Compressed air battery

A compressed air battery stores energy in the form of compressed air and uses it to generate electricity.. A compressed air battery uses air to drive a scroll expander or other device, which in turn drives a conventional generator, to produce electricity. They are used for standby and UPS applications by several industries, including data centers, and have been proposed for use in automobiles.^{[citation needed]}

History

UK company Energetix Pnu Power was granted patents in Europe(2006), China (2008) and the USA (2010), for the principle of using compressed air to turn a scroll expander , which drives a conventional electricity generator to produce AC or DC current.

The first commercially available compressed air batteries were developed and launched under the Pnu Power brand in 2009 as alternatives to traditional batteries, for industrial applications including standby and Uninterruptible Power Supply (UPS). In 2008/9 these batteries were adopted by companies including National Grid (UK), Telecom Italia (Italy), Eskom (South Africa), ATK (USA) and Harris (USA)^[1] Applications include an installation at ATK, which uses surplus compressed air to generate electricity and feed it into the site’s power grid.

There are also available standardised plug-and-play compressed air batteries, in capacities of 3, 5, 10, 20, 100 and 200 kW, and containerised 1MVA Compressed Air Diesel Rotary UPS Systems Air-DRUPS,^[2] as a direct competitor for larger traditional battery and large rotary (DRUPS / Flywheel) solutions.^[3] As these systems have no moving parts in standby mode, it offers significantly greater energy efficiency^[4] which increases reliability and reduces standby losses leading to an overall higher efficiency system and lower carbon emissions than flywheel UPS solutions.^[5]

Design

Compressed air batteries are often supplied as complete "plug and play" installations, in weatherproof enclosures. The principal components are:

• Compressed air supply: either from cylinders or a plant’s compressed air mains
• Air flow controller to ensure precise metering of air supplied to the power train
• Power train comprising: a scroll expander (ref scroll expander), generator and rectifier/converter. As a scroll expander is effectively the same as a scroll compressor (or scroll pump), the technology is well proven and understood.
• Auto compressor to top up the air supply after it is depleted
• Control electronics

Features

• Maintenance of compressed air batteries is confined to an annual inspection
• There are no moving parts in standby mode
• Standby losses are confined to the running of the control electronics (<100W)

References

1. ^ (see Pnu Power case studies and user links).
2. ^ Air-DRUPS - Wikipedia
3. ^ Air-DRUPS Article. Air-DRUPS.
4. ^ Article on Pnu Power - T and D World
5. ^ Article Independent Power Asia - Page 13

• Article from Power Engineering International, September 2009.
• Announcement of US Patents, from RNS London Stock Exhange company news service, March 2010.
• Article on Pnu Power product range
• Pnu Power Home page
• 1MVA Product Description
• Glossery of terms Describing meaning of Air-DRUPS]
• Article Data Centre efficiency