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Load Management System with Intermittent Power on the Grid
Ruth KemsleyCEng MIMechE MIEE
Econnect Ventures Ltd
• Econnect’s long experience with demand-side management – distributed load control devices– providing system (frequency) control on small islanded
networks with intermittent and limited generation sources
• Desire to develop these devices and associated system design techniques to assist grid integration of renewables using DSM
• Need to evaluate potential markets and target technology development accordingly
Project background
• Identify contractual requirements and commercial benefits of different load management systems – under the Renewables Obligation and electricity trading
arrangements
• Model economic benefits of load management to customers with intermittent generation on site
• Develop low cost load management system– incorporating communication technologies and switching
devices – to maximise renewable energy use on a demonstration site
• Identify associated social and psychological aspects
Project objectives
Project tasks
• Identified and evaluated four potential control strategies for a load management system on the distribution network – A solution to voltage rise problems caused by distributed generation– Ensuring zero export from a site with renewable generation– Avoiding load demand discrepancies– Creating an additional market for renewable energy
• Selected one strategy suitable for application at the test site• Demonstrated technical aspects of load management
equipment• Investigated the social aspects of the load management
strategy
Project partners
• Econnect– analysed potential DSM strategies– carried out computer modelling work– designed, developed, installed and tested load
management equipment
• Findhorn Foundation Community– provided a test site and assisted with implementation
• De Montfort University– carried out social impact studies
• Mitigating voltage rise from embedded generation– technically achievable– benefits of avoiding voltage-related constraints ~ 4 x implementation cost in case study
• Maximising on-site usage of renewables on a site with embedded generation and loads– technically possible to ensure close to zero power export to the grid– quick payback of implementation cost possible
• Avoiding demand discrepancies between actual and contractual volumes of load– possible only to reduce, rather than avoid, demand discrepancies– savings ~ 5 x installation cost over 20 years in case study
• Creation of additional demand for renewable energy– complex system with high capital cost of duplicated heating equipment– possible to reduce energy bills and increase generation / supply companies’ revenues– benefits less marked
Conclusions from preliminary evaluation
• Technique selected for demonstration at Findhorn Foundation Community
• 75kW wind turbine with plans for ~600kW more wind capacity (at time of project inception)
• Extensive low voltage distribution network, administered by FFC
• Power export from site rare, but will increase significantly when new wind turbines added
• Installation aimed to demonstrate load management technology
Minimising energy export from embedded generation
System tasks
DECIDE WHETHER
TO INCREASE SITE LOAD
MEASURE POWER EXPORT
SEND SIGNAL TO LOAD CONTROLLERS
SWITCH LOADON OR OFF
SWITCH LOADON OR OFF
SWITCH LOADON OR OFF
System components
POWER MEASUREMENT
UNIT
COMMUNICATIONSUNIT
LC
LC
ADD LOAD OR REMOVE LOAD
1
2
3
SEND“ON” OR “OFF” SIGNAL
GRID SUPPLYPOWER IMPORT OR EXPORT
FINDHORN DISTRIBUTION NETWORK
CURRENT AND VOLTAGE MEASUREMENT
IMMERSIONHEATER
SPACEHEATER
SPACEHEATER
“TRAFFICLIGHT”
LC
LC
CONTROL UNIT
LOAD CONTROLLERS ANDCONTROLLABLE LOADS
(SMALL PERCENTAGE OF TOTAL SITE LOAD)
POWER IMPORT OR EXPORT, kW
4
Engineering challenges
• Measurement of imported / exported power• Signal communications – needs to be robust
– powerline carrier demonstrated here via overhead line and underground cable
– low power radio– communications cables– internet
• Control algorithm for deciding when to switch devices– need to avoid increasing import from grid!– need to avoid switching large blocks of load simultaneously
Social challenges
• Selecting suitable loads for automatic management• Identifying and communicating benefits to consumers
of surrendering control over their loads– “traffic light” idea popular with the community – voluntary
load switching– test loads were mostly in central community buildings
• Ensuring no loss of quality or reliability of supply• Integrating system with tariff structure to incentivise
take-up
System designPrototype equipment
GRID SUPPLYPOWER IMPORT OR EXPORT
POWER MEASUREMENT
UNIT
COMMUNICATIONSUNIT
LOAD CONTROLLER
LOAD CONTROLLER
SUBSTATION – CENTRAL CONTROLLER LOAD CONTROLLER / TRAFFIC LIGHT
Simulation results
• Key to developing control algorithms and identifying benefits
• Example results:– assume 72kWh per day provided by 40kW of deferrable
load– without control – timeswitch controls 40kW just before
midnight– with control – 40kW switched on and off throughout the
day depending on wind availability– saving in this instance = 19kWh – depends on wind
profile and switching speed
Test results
• Demonstrated:– low-cost power measurement system– simple PIC-based control algorithm– powerline carrier communications over three phase low
voltage network around test site (including cable and overhead lines)
Conclusions
• Identified several beneficial applications of load management in context of renewable energy
• Extended application of Econnect’s load controllers from off-grid systems to grid-connected operation
• Developed a load management system for implementation
• Demonstrated successful technical operation of component parts
• Identified issues which will make a system practicable and successful