Battery Energy Storage for Enabling Distributed Solar Power Generation
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Advanced Power Systems and Controls Laboratory Battery Energy Storage for Enabling Distributed Solar Power Generation Introduction The rapid growth of wind and solar power is a key driver of the development of grid-scale Battery Energy Storage Systems (BESS). A well implemented BESS co-located with solar photovoltaic (PV) power generation can significantly improve power quality at the point of connection, and even increase the value of energy generated. The control system for the BESS must be coupled to the renewable source for maximum benefit. We present an overview of this technical area, and initial results form a real time BESS test facility developed as part of an ongoing collaboration between the University of Texas at Austin, and Xtreme Power of Kyle, TX. Software was provided by National Instruments of Austin, TX. Solar PV Challenges • Connected to the distribution system • Low Voltage connection • Radial system, not designed for two-way power flow • Intermittency (3 forms): • Seasonal fluctuations • Well understood • Lowers capacity factor in Winter • Daily fluctuations • Can be beneficial: sun typically coincides with peak demand times, reducing net demand and need for inefficient “peaking” generation units • Note that peak summer load coincides with maximum PV output • Short-term fluctuations [cloud cover] • 80% loss of power output in seconds • Ramp Rates >100 MW/min • Poses a threat to grid stability at high penetration rates Battery Energy Storage Systems A BESS consists of a battery bank, a control system, and a power electronics interface for bidirectional four quadrant AC- DC power conversion. The BESS is connected to the power grid in a shunt configuration, often in parallel with a renewable power generating facility or critical load. Control modes for BESS/Solar PV installations include: • Time Shifting / Peak Extension • Solar Smoothing / Ramp Rate Limiting • Solar Leveling • Load Leveling • Reactive Support Methodology A real-time control system test-bed was developed at the Xtreme Power research and development facility for the evaluation of algorithms and components for the XP-DPR, an integrated BESS system developed for wind and solar applications. The test platform can be run with up to four 1.5MVA power converters in Hardware-in-Loop mode, or in a software only mode using mathematical models for the battery and power converters, known as Model-in-the-Loop operation. Using high resolution data from the UT Solar installation and XP customer sites, various algorithms and battery maintenance routines are tested in real time with the XP-DPR pushing and pulling power to the Texas power grid. Results To date, the XP real time test platform has been successfully used in a variety of applications. The system is used to generate stimulus profiles from real renewable energy installations, and allows the BESS to push and pull power from the local utility grid exactly as it would in the field. This capability has been used to test control algorithms including automatic reactive power support and ramp rate limiting. Shown below are screenshots from a full day test of the power smoothing algorithm for a 1.5MVA/1MWh BESS coupled with a 1.2MW photovoltaic generation facility. Solar panel output is in white, and the response of the XP DPR is in red, with the net output in green. The output ramp rate is limited to a user specified value in MW/minute, set low enough to ensure that nearby generators are able to maintain the necessary balance of generation and load. Conclusions As utility scale PV and rooftop solar PV become commonplace on our electric grid, battery energy storage systems are a true “smart grid” solution to the challenges posed by their intermittent output. Through the work presented here, we hope to enable greater penetration of clean renewable power sources, as well as further the state of knowledge regarding energy storage and its effect on the electric power system. Further Work In the future, we plan to investigate the application of smaller networked battery systems deployed on the feeders of the distribution system, to support neighborhoods with integrating rooftop solar PV. There are also many more algorithms and applications to test and quantify for the current setup. Distribution system modeling to examine the effects of intermittent sources plus storage is also planned. We thank the following companies and institutions for their support: Xtreme Power - UT Cockrell School of Engineering - UT School of Mechanical Engineering UT School of Electrical and Computer Engineering - National Instruments Cody Hill, Dongmei Chen Clayton Such University of Texas at Austin Xtreme Power Seasonal average daily load profile One-line of a BESS and Solar PV generator connected to a substation bus. Control systems not shown. Xtreme Power DPR , 1.5MVA/1MWh BESS Power Real Time Control Test-bed block diagram Solar Noon Dawn Dusk Full day ramp rate limiting algorithm test Detailed view of one hour of ramp rate test
Transcript of Battery Energy Storage for Enabling Distributed Solar Power Generation
Advanced Power Systems and Controls Laboratory
Battery Energy Storage for Enabling Distributed Solar Power Generation
Introduction The rapid growth of wind and solar power is a key driver of the development of grid-scale Battery Energy Storage Systems (BESS). A well implemented BESS co-located with solar photovoltaic (PV) power generation can significantly improve power quality at the point of connection, and even increase the value of energy generated. The control system for the BESS must be coupled to the renewable source for maximum benefit. We present an overview of this technical area, and initial results form a real time BESS test facility developed as part of an ongoing collaboration between the University of Texas at Austin, and Xtreme Power of Kyle, TX. Software was provided by National Instruments of Austin, TX.
Solar PV Challenges
• Connected to the distribution system • Low Voltage connection • Radial system, not designed for two-way power flow
• Intermittency (3 forms): • Seasonal fluctuations
• Well understood • Lowers capacity factor in Winter
• Daily fluctuations • Can be beneficial: sun typically coincides with peak
demand times, reducing net demand and need for inefficient “peaking”
generation units • Note that peak summer load coincides with maximum PV output
• Short-term fluctuations [cloud cover] • 80% loss of power output in seconds • Ramp Rates >100 MW/min • Poses a threat to grid stability at high penetration rates
Battery Energy Storage Systems A BESS consists of a battery bank, a control system, and a power electronics interface for bidirectional four quadrant AC-DC power conversion. The BESS is connected to the power grid in a shunt configuration, often in parallel with a renewable power generating facility or critical load. Control modes for BESS/Solar PV installations include:
• Time Shifting / Peak Extension • Solar Smoothing / Ramp Rate Limiting • Solar Leveling • Load Leveling • Reactive Support
Methodology A real-time control system test-bed was developed at the Xtreme Power research and development facility for the evaluation of algorithms and components for the XP-DPR, an integrated BESS system developed for wind and solar applications. The test platform can be run with up to four 1.5MVA power converters in Hardware-in-Loop mode, or in a software only mode using mathematical models for the battery and power converters, known as Model-in-the-Loop operation. Using high resolution data from the UT Solar installation and XP customer sites, various algorithms and battery maintenance routines are tested in real time with the XP-DPR pushing and pulling power to the Texas power grid.
Results To date, the XP real time test platform has been successfully used in a variety of applications. The system is used to generate stimulus profiles from real renewable energy installations, and allows the BESS to push and pull power from the local utility grid exactly as it would in the field. This capability has been used to test control algorithms including automatic reactive power support and ramp rate limiting. Shown below are screenshots from a full day test of the power smoothing algorithm for a 1.5MVA/1MWh BESS coupled with a 1.2MW photovoltaic generation facility. Solar panel output is in white, and the response of the XP DPR is in red, with the net output in green. The output ramp rate is limited to a user specified value in MW/minute, set low enough to ensure that nearby generators are able to maintain the necessary balance of generation and load.
Conclusions As utility scale PV and rooftop solar PV become commonplace on our electric grid, battery energy storage systems are a true “smart grid” solution to the challenges posed by their intermittent output. Through the work presented here, we hope to enable greater penetration of clean renewable power sources, as well as further the state of knowledge regarding energy storage and its effect on the electric power system.
Further Work In the future, we plan to investigate the application of smaller networked battery systems deployed on the feeders of the distribution system, to support neighborhoods with integrating rooftop solar PV. There are also many more algorithms and applications to test and quantify for the current setup. Distribution system modeling to examine the effects of intermittent sources plus storage is also planned.
We thank the following companies and institutions for their support: Xtreme Power - UT Cockrell School of Engineering - UT School of Mechanical Engineering
UT School of Electrical and Computer Engineering - National Instruments
Cody Hill, Dongmei Chen Clayton Such University of Texas at Austin Xtreme Power
Seasonal average daily load profile
One-line of a BESS and Solar PV generator connected to a substation bus. Control systems not shown.
Xtreme Power DPR , 1.5MVA/1MWh BESS
Power
Real Time Control Test-bed block diagram
Solar Noon Dawn Dusk
Full day ramp rate limiting algorithm test Detailed view of one hour of ramp rate test
