Cryogenics for Storing Air
for Electricity Generation
in a UK Policy Context
Dr Tim Fox
Head of Energy and Environment
Institution of Mechanical Engineers
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Fully engaged in public debate
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Introduction
Overview
 Policy landscape and drivers
 Energy storage
 A novel cryogenic approach
 Pilot plant project
 Barriers
 Policy needs
 Conclusions
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UK energy landscape
• Stable demand profile for past three decades
• Need to replace ageing plant and infrastructure
• North Sea gas depleting (by 2020, 80% of gas
demand will need to be met through imports)
• Increasing global competition for limited primary
energy resources, particularly oil and gas
• Decarbonisation aspirations and obligations (targets)
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UK Energy policy
Sustainability
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EU 20 / 20 /20
targets
Climate Change
Act 2008
Increased
renewables
Decarbonisation of
electricity
Decarbonisation of
other sectors
Increased use of
electricity as a clean
energy vector
Energy conservation
Energy efficiency
Distributed
generation
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Security of supply
Economy
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Open markets
deliver competitive
prices
Interconnections
link markets
Avoid price
uncertainty for
consumers
Political intervention
and regulation to
protect consumers
Community and
domestic
stakeholder
participation in
ownership,
production and
trading
Asset
optimisation
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Licence conditions
provide requirements
for supply
Ensure sufficient
peak capacity
(Winter)
Maintain margin with
adequate reserves
Increase
renewables and
nuclear to reduce
reliance on
imported gas and
other fuels
Develop system
flexibility and
community level
resilience
Adopt smart grids
Invest in storage
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Future generation mix
Generation Capacity (GW)
100
OCGT
Oil
Pumped Storage
Interconnectors
Wind
Gas (CCGT+CHP+MGT )
Coal
Hydro
Wave and Tidal
Biomass
Nuclear
80
60
40
20
2025/26
2024/25
2023/24
2022/23
2021/22
2020/21
2019/20
2018/19
2017/18
2016/17
2015/16
2014/15
2013/14
2012/13
2011/12
2010/11
0
Year
Generation under ‘Gone Green’ scenario
Source: National Grid
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Renewables and power system
 Large scale and small scale
 Variability and location
 Surplus and shortfall
 Short and long term
reserves
 Markets/subsidies
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UK power network
Today’s network
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Large scale competitive
generation, regulated
transmission and distribution
Limited embedded generation
(at distribution level)
Wholesale market supplies
retail customers
Limited number of self
suppliers
System planned to meet peak
demand plus reserves – spare
(or under utilised assets)
Low level of interconnections
to other networks
Regulated wires businesses
Facing substantial change
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The future
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Significant shift from
dispatchable generation to time
variable generation
Peaky demands from digital
society, switch to heat pumps,
uncertain effect of electric
vehicles
Distributed community and
domestic level generation and
trading
Average and peak domestic
demand likely to increase
Balancing the system requires
more flexibility
Higher level on continental
interconnection
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Tools for system balancing
Flexible
generation
(reserve)
Storage
Demand
response
Connectors
(import or
export)
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(absorbs and
rejects power)
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Storage – enabling technology
• Intermittent renewable energy sources
 ‘Wrong time’ electricity generation – too much or too little
 Optimises return on investment (ROI) in renewables plant
 Reduces need for idle spare capacity (reduces investment
costs in asset base) and avoids (volatile) fuel costs
• Large base-load electricity generation
 Sweats assets for improved ROI – e.g nuclear and biomass
• Flexibility of scale and location
 Mix of storage technologies analogous to generation mix
 Defers network investments and lowers system costs
 Reduces SMART grid and interconnection risks
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Enablers – electricity storage
• Pumped hydro
• Compressed-air
• Power to gas
• Flywheels
• Thermo processes
• Batteries and capacitors
• Fuels
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Storage application matrix
Application scales and potential users
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Using cryogenic technology
• Principles
 Use liquefied air or liquid nitrogen as storage medium
 Mature technology from air separation industry
 Proven ‘standard’ equipment in daily use with well
established supply chains
 Energy density of cryogen compares well with other
medium
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Highview Power Storage Ltd
• The Company
 Established 2005 to design and develop utility-scale energy
storage and power systems
 $18m equity investment plus $1.8m DECC capital grant
 UK company based London with pilot plant in Slough
 Working with UK Universities to develop technology further
• Pilot Plant
 300kW hosted by SSE at Slough Heat & Power
 Operating since April 2010, fully integrated into local
distribution network
Tim Fox thanks the Directors of Highview Power for
permission to present this work and the engineering staff for
assistance in preparing this talk.
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The storage cycle
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The plant (1)
 300 kW turbine output, 20° (68°) to 60°C (140°F) inlet temp
 30 tonne/day liquefier, 2.5 MWhrs storage
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The plant (2)
• Milestones
 2005 – research begins University of Leeds
 2008 – pilot plant project starts November
 Power recovery and cold recovery ops
Spring 2010
 2010 – STOR service trials begins
 Cold storage, recycle and liquefaction
ops Spring 2011
 2011 - Triad service trials
 2012 – pilot successful – next step
commercialisation
Note: STOR = Short Term Operating Reserve
– balancing duty
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Value of cold recycle
 Available enthalpy for cold cycle ~300kJ/kg of liquid product
 Cycle simulation indicates near term target thermal storage
efficiency of 80% would deliver >50% cycle efficiency
Achieved on pilot plant
Target cold recycle at full scale
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TS diagram for power recovery
Heat addition at
Constant pressure
Four Stage Expansion
With re-heat between
stages
Compression of cryogenic liquid
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The value of waste heat
More work recovered
with use of waste heat
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Commercial service trials
Summary of STOR trials
 Over 2 week period achieved 94.6% availability.
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Results - Power recovery
Power (kW)
Time (minutes)
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Pilot outcome
• Overall
 Highview have successfully demonstrated use of cryogenic
technology for electricity storage at pilot plant scale
 Viability of cold recycle to improve efficiency of cryogen
manufacture
 Use of waste heat for cycle efficiency improvements
 Ability to deliver commercial reserve services
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Possible next steps
• Commercial scale demonstration
 10 MW output with >50% efficiency
 Liquefier sized to suit market application
 100’s MWs output
with GWhs storage
 Capital cost ~$900 to
$1900/kW
 Annual O&M cost
~2% capital cost
 No geographical
constraint and benign
environmentally
 70% efficient with
waste heat at 239°F
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Barriers and challenges
• Classification of storage solutions
 Electricity “consumer” and electricity “generator”
• Electricity market structure
 Competitive generation market and highly regulated
transmission and distribution provider
 Need to be allowed to access multiple income streams
 Lack of incentivisation
• Research, development and demonstration funding
 DECC Energy Storage Technology Demonstration
 £0.5 million for 12 organisations – feasibility of ideas
 DECC Storage Component Research & Feasibility Study
 £1.5 million for 4 companies to improve materials and
explore systems in UK electricity networks
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Policy needs
• Recognise the value of storage
 Strongly dependent on network generating mix and local
market rules
• Separate classification for storage
 Recognise unique roll as both ‘consumer’ and ‘provider’
• Create competitive incentivised environment
 Needs to ensure inclusion and access to multiple streams
• Support demonstration at commercial scale
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Conclusions
• Encourage/support UK companies and
research organisations that are developing and
demonstrating storage technologies
• Create a shop-window for UK electricity
storage technology so innovations can be seen
and sold
• Develop policy frameworks and mechanisms
that reward value of electricity storage in UK
power markets
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Thank you
@TimFox_IMechE
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Storage comparisons
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