The Supple Grid Challenges and Opportunities for Integrating Renewable Generation UC Center Sacramento May 9, 2013 Dr. Alexandra Sascha von Meier Co-Director, Electric Grid Research, California Institute for Energy and Environment Adjunct Associate Professor, Dept. of Electrical Engineering and Computer Science, UC Berkeley http://uc-ciee.org vonmeier@uc-ciee.org
Imperatives for a viable energy future: major improvements in energy efficiency some conversion of fuels to electricity fully decarbonized electricity
Pathways to decarbonized electricity $$$ $$$ $$$ Predominant challenges: social-political security defining mission resource adequacy engineering Problems are difficult but solvable
Problems are difficult but solvable 33% by 2020 in CA 12,000 MW in distributed installations 100%?
Pacific Gas & Electric, 1989
Addressing resource intermittence Firming resources: load-following and reserve generation storage demand response whose effective and economical coordination depends on: good forecasts real-time data fast response good algorithms
Addressing resource intermittence Firming resources: load-following and reserve generation storage demand response on different time scales: seasonal day-ahead hour intra-hour minutes seconds cycles frequency regulation
Time scales in electric grid operation
Coordination challenges in time Matching P IN = P OUT on different scales Constrained by ramp rates (dp/dt) of resources Maintaining stability on the scale of seconds, cycles Long-distance a.c. transmission constrained by stability Impact of switch-controlled generators (inverters) on angle stability not yet well understood Requires management at the sub-cycle level: synchrophasors (observe precise local timing of a.c. waveform) ac-dc-ac conversion power flow control devices chopping up waveform with solid-state technology
Coordination challenges in space Transmission capacity to distant resources Protection coordination on distribution circuits Voltage regulation on distribution circuits Optimal siting of DG for grid support Aggregation and recruitment of DER for ancillary services Need more refined observation and control capabilities
Distance scales in electric grid operation
Distribution vs. transmission systems Important differences: architecture diversity time variation vulnerability opacity
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Protection coordination A C
Protection challenges from DG: device coordination fault current contributions relay desensitization
Advances in circuit protection transfer trip schemes adaptive relaying
Islanding IEEE 1547 requires preventing unintentional islands (although many solar enthusiasts don t realize this) power island
power island
Voltage regulation ± 5%
Voltage regulation permissible range violation load tap changers voltage regulators capacitors violation violation
Potential impacts of DG permissible range violation drive equipment out of range mechanical wear from excessive hunting of voltage beneficial contribution from inverters? violation violation
Voltage excursions due to PV intermittence 2 min source: San Diego Gas & Electric courtesy of Bill Torre
Technologies under development for refined observation and control four-quadrant (P,Q) inverters volt-var control advanced inverters harmonic cancellation transient mitigation distributed storage micro-synchrophasors power routers solid-state transformer responsive loads communication networks distributed resources & coordination tools increasingly provide capability to balance power and manage power quality & reliability
The push toward the periphery due to capacity limitations of the core grid aesthetic and philosophical preferences necessity to engage loads drives investment in supple technologies intended to mitigate weaknesses of legacy system, which provide means to observe, communicate and control at higher resolution in time and space enabling new options to configure and operate the grid
Requirements for a manageable power island separation switch generation-load matching frequency regulation load shedding capability voltage regulation power quality assurance management algorithms communication synchronizing (phase matching) upon re-connection smart inverters responsive loads distributed storage micro-synchrophasors power routers solid-state transformer distributed resources and coordination tools could handle this
Today s grid generation storage load
Today s grid bulk generation scheduling frequency regulation voltage regulation load shedding
Supple grid?
storage generation responsive loads intelligent switching: coordination? power conditioning
Supple grid? Balanced resource cluster
A taxonomy of electric grid subsets physically co-located able to disconnect from grid matches generation & load coordinates diverse resources crosses property lines power island ( ) microgrid balanced cluster virtual power plant RESCO
Supple grid? bulk generation scheduling frequency regulation variable connectivity frequency regulation load coordination voltage regulation
Supple grid? bulk power variable connectivity power quality & reliability
Variable connectivity What s in it for the power island? - access to cheap energy from distant sources while connected - remuneration for ancillary services to grid while connected - autonomous power supply for some loads during system outages What s in it for the mainland grid? - power sales while connected - relaxed obligation to maintain power quality & reliability - guilt-free load shedding - less need to build out transmission capacity Why not do this? - illegal in 50 states - redundancy: rare instances where islanding capability is useful - abandon social compact of legacy grid?
Open questions What business case can be made for balanced clusters providing ancillary services? What is the best mechanism for aggregation? What device(s) must be developed to manage clusters with intermittent connectivity? What is the scale dependence of viable clusters? What savings, if any, could be realized by relaxing power quality and reliability constraints in the core grid? What are the implications for social equity of a supple grid?