REP Storage and Grids 5 — Questions and Answers
Question 1: Which US grid interconnection region covers the largest geographic footprint, spanning 15 states across the Midwest and Mid-Atlantic?
- MISO
- PJM Interconnection (Correct answer)
- WECC
- SPP
Correct answer: PJM Interconnection
PJM Interconnection operates the transmission system across 13 states plus DC and manages the largest centrally dispatched electricity market in North America by load served.
Question 2: What NFPA standard governs the installation of stationary energy storage systems, addressing fire protection, ventilation, and spacing requirements?
- NFPA 70 (NEC)
- NFPA 855 (Correct answer)
- NFPA 110
- NFPA 13
Correct answer: NFPA 855
NFPA 855 (Standard for the Installation of Stationary Energy Storage Systems) provides requirements for the safe design, construction, and installation of battery storage systems.
Question 3: In power systems, what does the term 'black start capability' refer to?
- The ability of a storage system to operate at zero state of charge
- The capability of a generator or storage resource to restart without drawing power from the grid after a blackout (Correct answer)
- The process of disconnecting a microgrid from the utility during a fault
- Dark fiber communication backup for SCADA systems
Correct answer: The capability of a generator or storage resource to restart without drawing power from the grid after a blackout
Black start resources can self-energize and then supply power to restart other generators during grid restoration following a widespread outage, without requiring external grid power.
Question 4: Which strategy allows distributed behind-the-meter storage systems to be aggregated and dispatched as a single virtual resource in wholesale electricity markets?
- Net energy metering (NEM)
- Virtual power plant (VPP) (Correct answer)
- Demand charge management
- Interconnection clustering
Correct answer: Virtual power plant (VPP)
A virtual power plant aggregates behind-the-meter DERs including storage, solar, and controllable loads into a coordinated dispatchable resource that can participate in wholesale markets.
Question 5: What electrochemical phenomenon causes irreversible capacity loss in lithium-ion batteries when they are repeatedly charged to 100% state of charge?
- Sulfation of the anode
- Lithium plating and solid electrolyte interphase (SEI) growth (Correct answer)
- Vanadium crossover through the membrane
- Hydrogen evolution at the cathode
Correct answer: Lithium plating and solid electrolyte interphase (SEI) growth
Lithium plating on the anode and continued SEI layer growth at full charge permanently consume active lithium and increase internal resistance, degrading capacity over time.
Question 6: Under the US FERC Order 2222 framework, which entities are required to revise their tariffs to allow distributed energy resource aggregators to participate in wholesale markets?
- Municipal utilities and rural electric cooperatives only
- All registered RTOs and ISOs under FERC jurisdiction (Correct answer)
- Vertically integrated investor-owned utilities
- State public utility commissions
Correct answer: All registered RTOs and ISOs under FERC jurisdiction
FERC Order 2222 (2020) directed all FERC-jurisdictional RTOs and ISOs to revise their tariffs to permit DER aggregations, including storage, to compete in wholesale capacity, energy, and ancillary services markets.
Question 7: What is the primary advantage of a liquid-cooled thermal management system over an air-cooled system in a large-scale lithium-ion battery installation?
- Lower upfront installation cost
- More uniform cell temperature distribution and higher heat removal capacity (Correct answer)
- Elimination of fire suppression requirements
- Simpler BMS integration with fewer sensors
Correct answer: More uniform cell temperature distribution and higher heat removal capacity
Liquid cooling maintains tighter cell temperature uniformity (often within ±2°C) and removes heat more efficiently than air, extending battery life and enabling higher charge/discharge rates.
REP Storage and Grids 5
Which US grid interconnection region covers the largest geographic footprint, spanning 15 states across the Midwest and Mid-Atlantic?