Frequently asked questions
Q. Is there a limit to the run time of compressed air batteries?
A. The run time of Pnu Power batteries is only limited by the capacity of the air supply when operating from cylinders: however, cylinders can be recharged automatically using an optional air compressor, which is fully integrated with the Pnu Power’s control electronics. There is no practical run time limit when operating from plant mains compressed air supplies. Compressed air of at least 15 bar is required to operate our smallest systems.
Q. How much electrical energy is available from each compressed air cylinder?
A. A standard 89 litre cylinder contains 0.3 kWh of extractable energy. Total energy availability is easily increased by using multiple and/or larger cylinders.
Q. How are compressed air batteries more reliable than conventional batteries?
A. Compressed air batteries have no moving parts and suffer no loss of stored energy over time in standby mode, so they are ‘always ready’. Every Pnu Power unit includes a screen which confirms state of readiness and run time availability – something difficult to achieve accurately with conventional batteries, even if such a display is provided. Pnu Power batteries are also able to operate reliably in harsh environmental conditions, where conventional batteries require environmentally controlled housings.
Q. How are compressed air batteries more energy efficient than rotary/flywheel UPS solutions?
A. Pnu Power compressed air batteries have no moving parts, so minimal energy consumption, in standby mode. The only standby losses are a few Watts used by the units’ control electronics. Rotary/flywheel solutions consume significant power in standby, because they are always moving.
Q. How do you substantiate your claim that Pnu Power compressed air batteries are proven technology, as they are relatively new?
A. All Pnu Power products use proven components. The heart of Pnu Power compressed air batteries power train is a scroll generator. This is effectively a scroll pump (aka compressor) running in reverse. Scroll pumps/compressors have been used reliably for decades in millions of products, including refrigerators, air conditioning units and superchargers. The air supply control valve uses technology widely employed in submarines. Pnu Power compressed air batteries are already operating reliably with companies including National Grid, Harris Corporation, Abertis Telecom and Telecom Italia (see Case Studies).
Q. Are compressed air batteries suitable for energy storage where generation is intermittent, say to balance load in a wind farm application?
A. This is technically possible but its practicality depends on the efficiency of the compressor used to create the air store, and the size of the air store that would be needed to ensure a suitable run time at reasonable load. Most compressors are relatively inefficient. However, Pnu Power units can certainly be used to generate electricity where a supply surplus compressed is available. Aerospace company ATK (see Case Studies) uses a Pnu Power ReGen 20 in this way to shave peak electricity load at one of its plants.
Q. Can compressed air batteries run on gases other than air?
A. Standard Pnu Power units are not hermetically sealed, so there will be some loss of gases during operation, which may be unacceptable. However, hermetically sealed and ATEX approved scroll expanders can be utilised for gases other than air, which need to be contained.