▶️2 - Open Session: PGRR124: ESR Maintenance Exception to Modifications
Battery Degradation and Augmentation Approach
Tesla batteries degrade approximately 30% over 20 years (about 1.5% annually), with faster degradation under high cycling.Tesla aims to maintain original clean firm capacity over time through augmentation strategies.
Two proposed augmentation methods:
Low Voltage Augmentation
Medium Voltage Augmentation
Augmentation adds hardware but maintains original electrical performance metrics (MVA, short circuit contribution, ride-through capabilities).
System performance is managed through firmware to match original interconnection agreement.
No physical changes are required to protection settings.
Augmented systems preserve electrical equivalency despite new hardware additions.
Regulatory and Procedural Issues
Tesla submitted Planning Guide Revision Request (PGRR124) to address augmentation as a maintenance method, not a modification.
Tesla argues augmentation should not trigger a full Generator Interconnection Modification (GIM) process.
Instead, proposes proving system equivalency through unit type testing rather than full interconnection restudy.
ERCOT representatives raised concerns about:
Verification and validation of firmware-controlled performance.
Reliability of firmware versus traditional hardware-based configurations.
Whether firmware-based augmentation qualifies as a "replacement in kind."
Compliance with existing ERCOT protocols and aggregation rules.
ERCOT suggested that Tesla might use the existing model review process (PGRR109) instead of proposing a new exception.
Stakeholder Discussion Points
Clarification questions addressed:
Nature and scope of augmentation (hardware and firmware aspects).
Impacts on system performance and interconnection studies.
Concerns raised regarding:
Aggregation at AC level vs. DC level and implications for system modeling.
Potential classification of augmentations as material modifications under current standards.
Use of different-generation equipment and modeling implications.
Discussions touched on Planning Guide sections relevant to interconnection modification processes.
Stakeholders considered the possibility of expediting augmentation alternatives while maintaining reliability.
Participants agreed to:
Continue follow-up discussions before the Planning Working Group meeting.
Explore a middle ground between Tesla’s proposal and current ERCOT processes.
Define appropriate unit type testing requirements for verification.
Expanded Summary
Sarah Dodamead, Tesla's MegaPack 2 Excel Product Manager, presented to ERCOT regarding Tesla's approach to managing battery degradation
The meeting appears to be part of an ERCOT working group discussion about interconnection requirements
The presentation focused on the technical and regulatory aspects of battery augmentation processes
Eric Doss from Tesla also participated in the discussion
Battery Degradation Background
Tesla batteries degrade at approximately 30% over a 20-year period (roughly 1.5% per year)
Degradation is directly related to throughput - more cycling leads to faster degradation
Battery degradation is a fundamental challenge that requires planned management to maintain capacity
Without augmentation, battery energy storage systems would steadily lose duration capabilities over time
Tesla's Technical Augmentation Methods
Tesla presented two specific augmentation approaches:
Low voltage augmentation: Adding Power Pack units that connect to the AC bus bars within existing MegaPack units
Medium voltage augmentation: Adding separate MegaPack units or other medium voltage BESS solutions at the site
Low voltage augmentation involves adding new AC outputs behind the breaker onto the AC bus bars in the existing MegaPack
Medium voltage augmentation can be implemented at the feeder level, transformer level, or by adding a new feeder
Both approaches allow customers to maintain clean, firm capacity as efficiently as possible
Tesla's products are described as "firmware-controlled hardware" unlike traditional mechanical generation technologies
Firmware Control Mechanism
When new hardware is added, Tesla uses firmware to derate the kVA of inverters in the original MegaPack
The firmware limits the total site capability to match the original interconnection agreement
No changes to protection settings are required because aggregate system performance remains identical
Tesla performs extensive validation with third-party engineers to verify firmware performance
The firmware settings control, not increase, the site's capability beyond approved limits
System Performance Parameters
Tesla emphasized that the augmented system maintains identical performance characteristics:
Maintains the same MVA (power rating)
Same short circuit contribution
Same dynamic performance
Same voltage and frequency ride-through capabilities
Same harmonic impedance (validated through lab and field testing)
The only change is increased energy capacity to offset degradation
The original duration of the system is maintained through augmentation
Regulatory Proposal - PGRR124
Tesla submitted PGRR124 to create a clear augmentation process
Tesla proposes that augmentation should not require a GIM process
The proposal suggests augmentation should be treated as routine maintenance during planned outages
The key argument is that since system performance remains identical, there is nothing to restudy
Tesla proposes proving system equivalency through unit type tests rather than full interconnection studies
The proposal aims to create an exception in section 5.2.1 of the planning guide
Unit Type Test Approach
Tesla proposed unit type testing to demonstrate identical performance pre and post augmentation
Tests would verify MVA short circuit rating, dynamic performance, and voltage/frequency ride through
Tests would use the same PSCAD models used in original interconnection studies
Both lab testing and field validation have been performed on Tesla systems
