Power Engineering International

Welcome to the online version of our Power Engineering International (Pei) print publication. This is where to find archive magazine articles as well as our present edition. For any feedback on the content contact us here or discuss on PEi LinkedIn Group

Pnu tricks: compressed air energy storage

PEi visits the headquarters of Energetix, a UK firm specializing in low cost energy efficiency products, to find out more about Pnu Power – a pneumatic battery that is set to challenge lead acid batteries as the energy storage medium of choice for uninterruptible power supplies for high ambient temperatures.

Tim Probert, Deputy Editor

Adrian Hutchings thinks his company’s technology is old hat. He is happy to tell you that his new products do not utilize the latest cutting-edge, state-of-the-art technology. That they are more Ford than Ferrari. In fact, he is rather proud of it.

Energetix, a UK manufacturer of energy efficiency products, specializes in the ingenious modification of existing technologies to create low-cost energy efficiency products. Pnu Power, pronounced ‘new power’, is one such product. Pnu Power is a pneumatic battery that provides an uninterruptible power supply (UPS) solution and back-up power using compressed air.


The Pnu Power energy storage system represents an ingenious modification of an existing technology
Click here to enlarge image

Energetix engineers have taken the standard scroll compressor, first patented in 1905, and operated it in reverse – as an expander. On detecting a mains outage, the system opens a fast-acting solenoid valve to allow air from the cylinders to pressurize downstream air regulators. The air then passes into the scroll expander, the heart of the Pnu Power system, where the expansion process turns a generator, which provides power to the DC bus that can then be converted for any voltage requirements.

The philosophy of Energetix is not to spend vast fortunes developing unproven technology, but to take a low-risk approach using mass-produced, easily available components. Not only does this approach bring down costs – being able to negotiate between different manufacturers of the same components is a huge plus – but using well-proven technology also leads to a more robust final product, says Hutchings, Energetix’s chief executive.

Intellectual property

Given the lack of cutting edge technology in Pnu Power, one could be forgiven for believing, at least at first glance, that anyone could come along and offer the same product. Not so, says Hutchings. He said: “Whilst I talk about robust engineering rather than esoteric science, we do a lot of patenting and building intellectual property as well. We have granted system patents, we have minefield patents around that, but the most important strand is the development of intellectual property derived from our own knowledge of the components.

“There are millions of scroll compressors out there, but no one else has ever developed or designed a scroll expander before. But it’s not as simple as just running the compressor in reverse.

“You can just roll a scroll compressor in reverse, and we do that with our first generation product, but with our next generation products, because we’ve learned so much about the process – upping efficiency, reducing component counts and so on – we are actually building our own intellectual property and patents into the component design. Manufacturers can now produce scrolls to our own designs.”

Hutchings had looked at flywheels, something he knew a great deal about from his time as managing director of International Energy Systems – a subsidy of British Nuclear Fuels Limited (BNFL), as an energy storage solution for the UPS and distributed generation markets. It was not until Energetix developed Genlec, a domestic boiler that first used the reverse scroll compressor concept to generate both heat and power from natural gas, that he realized that compressed air could provide an alternative to valve regulated lead acid batteries (VRLA).

Energetix has targeted three main areas for Pnu Power – telecommunications firms that require battery-free bridging power for a short duration (1-8 hours), while at the same time providing cool air – thus eliminating 90 per cent of generator start. Pnu Power can also provide standby power for utility circuit breaker and protection relay applications in the transmission and distribution industries. It also has a use for industrial firms that need a reliable and consistent UPS system in harsh environments.

Energetix sees great potential for Pnu Power in the southern United States. Indeed, it has set up a business – Energetix Technologies Incorporated – in Fort Lauderdale, Florida. Hurricane-prone Florida and other states in America’s deep south are an ideal markets for Pnu Power – power outages are relatively frequent and despite only lasting for a second or two, they are a big hit on lead acid batteries.

OPERATION IN HARSH CONDITIONS

Energetix says the reliability of Pnu Power is not compromised by temperatures between -20 ºC and 40 ºC irrespective of the load profile. Every degree above 25 ºC halves a VRLA battery’s life, says Hutchings. So with a five-year battery in Florida at an ambient temperature of between 30 ºC and 32 ºC, a VRLA will barely last six months. Pnu Power is unaffected at such temperatures: using an ISO freight environmental testing chamber at the Capenhurst testing facility in the UK, Energetix was able to demonstrate Pnu Power operation at 40 ºC and at 95 per cent relative humidity, replicating the most challenging conditions in Florida.

The ability to operate in high ambient temperatures eliminates the need for expensive environment control systems. The known level of stored energy, which can be monitored locally or remotely, will also provide confidence of operation and accurate run time remaining. For example, in South Africa, Eskom operates Pnu Power via a remote monitoring system.

Energetix has conducted 30 000 stop starts – equivalent to 700 years of operations. Hutchings says that Pnu Power has ten times the lifecycle of a lead acid battery. Of course, Pnu Power has higher upfront costs than VRLAs, but Hutchings is confident that the advantages of compressed air outweigh any short-term factors. He said: “Pnu Power has ten times the life of a lead acid battery. You need licenses for lead acid batteries, plus with VRLA systems you need to change and dispose of the toxic batteries.”

Neil Bright, Energetix’ group operations directors, who joined the firm from Exide Technologies, one of the world’s largest producers of lead-acid batteries, says that Pnu Power eliminates the need for batteries. He says that Pnu Power is unique in being completely battery free.

The Pnu Power system is modular; it consists of the power conversion module (PCM), the energy store and a recharge compressor. Being modular, many PCMs can be connected to a common energy store to meet increased power requirements.

The unit is scaleable and additional duration can be provided simply by adding more compressed air cylinders. Typically, ten air cylinders would provide a 20 kW system with ten minutes of back-up power.

The light inertia of the scroll, combined with an ultra-fast response time of the electro-pneumatic regulator, enables Pnu Power to respond to step changes in power instantaneously by varying the control signal. As well as light inertia, the scroll has a very low component count, which improves reliability. The scrolls are also designed to be operate lubricate-free, which greatly reduces the need for maintenance – it also means no exhaust filtering is required.

From standby mode, Pnu Power takes less than 300 milliseconds to get up to full power. The compressed air is stored at 300 bar, a similar level to a diving tank. The noise emissions from the system, with silencers, have been recorded at 70 decibels at a distance of one metre.

ORDER, ORDER

Pnu Power was initially launched in 2007 and after successful trials Energetix has recently bagged its first large order – a $380 000 deal from US aerospace and defence firm P&E Automation – to be installed at a site in the state of Utah. Pnu Power also has won orders from a telecommunications firm in Florida and Telecom Italia in Italy, plus South Africa’s state-owned utility Eskom. It is also used to back-up Energetix’ computers at Capenhurst!


Florida’s M/A-COM is testing a 5 kW Pnu Power system for a State Law Enforcement Radio System site in Brooksville
Click here to enlarge image

In April, Energetix received an order to supply a 5 kW Pnu Power compressed air back-up energy system to M/A-COM Incorporated for a trial installation at a State Law Enforcement Radio System (SLERS) site in Brooksville, Florida, USA. M/A-COM has indicated that the performance of the Pnu Power product will be evaluated to assess its ability to provide a high-reliability DC power back-up system in an application that requires 99.999 per cent uptime and which is subject to the disruption of extreme lightning strikes.

A successful trial that validates the Pnu Power technology is likely to lead M/A-COM to consider Pnu Power for the expansion of the SLERS network. On 19 August, Energetix announced that it would supply a unit for National Grid’s 275 kV switchyard in Capenhurst, Cheshire. The trial system will evaluate the performance of Pnu Power in providing back-up power in a real-life application on relay and circuit breaker switching, which requires high levels of system integrity.

FURTHER USES OF PNU POWER?

Pnu Power’s ability to generate cold air – effectively the exhaust gas from the generation of electricity – has a potentially very important use for data centres, which are energy intensive and generate a great deal of heat. Hutchings claims that up to 1 kWth of cooling is generated for every 1 kW of electrical power produced. To this end, Energetix is developing a 50 kW prototype for use in data centres. In the long term, Hutchings expects to sell a number of units “in the low hundreds” of Pnu Power in 2010 and then shift to what he calls “real volume” in 2011.

More Powe Engineerimg International Issue Articles

Recommend this article Recommend this article () Yo recommended this article Yo recommended this article ()
Follow Power Engineering International on Twitter

Editor's Picks

Fallon says ‘get ready for shale’ but warns of wind cuts

The UK’s Energy and Business Minister Michael Fallon today said it was time for Britain “to get ready for shale” after a r...
GE Alstom

GE’s $13bn takeover of Alstom could be finalised next week

General Electric (GE) is on the verge of pulling off what would be the company’s biggest acquisition ever, as it emerged t...

UK unveils eight renewable projects under new market regime

The UK government today unveiled eight renewable energy projects which it is backing under its new Electricity Market Refo...
Borwind

Siemens to lead major grid connection project

Siemens has been chosen to lead a consortium responsible for constructing and installing an offshore wind connection in th...
Rajendra Pachauri

UN advocates tripling of renewables and nuclear energy

A report from the United Nations Intergovernmental Panel on Climate Change (IPCC) has warned that the world needs to drast...

PEI Magazine Issues



>> Current Issue           >> Past Issues

Latest Wire News

Vantage Drilling Company Schedules First Quarter 2014 Earnings Release Date and Conference Call

Vantage Drilling Company Schedules First Quarter 2014 Earnings Release Date and Conference C...

XR Energy, Inc. Enters Completion Phase of Acquisition of Producing Oil Assets

XR Energy, Inc. Enters Completion Phase of Acquisition of Producing Oil Assets

SEACOR Holdings Announces Results for Its First Quarter Ended March 31, 2014

SEACOR Holdings Announces Results for Its First Quarter Ended March 31, 2014

Smart Ventures Announces Analyst Report Coverage

Smart Ventures Announces Analyst Report Coverage

Cornerstone Participates in City of Glasgow, KY Project Converting Landfill Methane Gas Into Electrical Power

Cornerstone Participates in City of Glasgow, KY Project Converting Landfill Methane Gas Into...

Editorial Guides

How to cut your OPEX

How to cut your OPEX In a constantly evolving electricity market, factors such as over capacity and low coal costs can pu...

Alstom Editorial Guide: Thailand to showcase latest upgrade of Alstom's GT26 in combined-cycle

Read all about Alstom's new advanced GT26 gas turbine in the North Bangkok CCPP expansion project online with the Power En...

PLEXOS® Integrated Energy Model – Leading the Field in Energy Market Modelling

PLEXOS® Integrated Energy Modelling is an advanced software tool that employs the latest mathematical programming methods ...

Power Engineering International

Whitepapers

Evaluating cogeneration for your facility: A look at the potential energy-efficiency, economic and environmental benefits

The energy-efficiency, economic and environmental benefits of cogeneration are the subject of this in-depth white paper. The paper argues that producing electricity and heat/cooling from the same f...

The Effect of Moisture on the Breakdown Voltage of Transformer Oil

Power transformers utilize oil as a heat transfer medium and a dielectric material, together with cellulose. Breakdown voltage (dielectric strength) is one of the most important parameters of trans...

Improving Mission Critical Cooling Systems With More Reliable Level Sensing

The choice of coolant level sensor may seem like an insignificant detail when designing complex machinery such as emergency generators and cranes, but if this sensor fails, the operator has no warn...

Steps Towards a Low Carbon Future: Solutions and Technologies That Will Support the Global Revolution Required

A smart grid is becoming more and more essential as clean energy becomes more dominant. In addition, the demand for electricity is expected to treble the ability to supply it over the next decade. ...

Latest Digital Edition

  Power
  Engineering
  International
Look Inside >
Cover
Current Issue

Article Archives for Power Engineering International Magazine

Latest Energy Jobs