DER Grid Integration & Operational Considerations

Grid Benefits: Flexibility, Resilience, and Decarbonization

DERs significantly enhance grid operations in several ways:

• Peak Load Reduction: Solar, DR, and storage help shave peak demand, deferring peaker plants or infrastructure upgrades.
• Ramping Support: DERs mitigate steep evening ramps caused by solar drop-off (the "duck curve") by shifting load or discharging storage during critical hours (e.g., 5-9 PM).
• Ancillary Services: Fast-responding DER (batteries, smart inverters) provide essential grid services like frequency regulation and spinning reserve.
• Voltage Regulation: Smart inverters actively manage local voltage by adjusting reactive power (Volt/VAR control), mitigating issues caused by high solar penetration on feeders.
• Resilience and Reliability: DERs diversify supply and can provide backup power during outages (especially microgrids). They can contain outages via islanding and support quicker recovery. Reducing reliance on long transmission lines also lessens outage impacts.
• Decarbonization: Many DER are carbon-free (solar) or enable lower emissions (storage offsetting gas peakers, EVs displacing gasoline). They allow deeper renewable penetration by providing flexibility and electrifying end-uses like transport and heating.

Operational Tools: DERMS and Virtual Power Plants (VPPs)

Managing numerous DER requires sophisticated control systems:

DERMS (Distributed Energy Resource Management Systems)

• Utility control center software to monitor and manage DER on the distribution network.
• Functions include:
  • Visibility: Real-time data on DER status and output.
  • Dispatch and Control: Sending control signals to DER/aggregations for grid needs (e.g., curtailment, discharge commands, setting adjustments).
  • Optimization: Calculating optimal DER dispatch to meet economic or reliability goals, potentially increasing feeder hosting capacity.
  • Coordination with ISO: Managing DER dispatch requests from the wholesale market while respecting distribution constraints (evolving area).
• DERMS deployments are becoming more common as DER grows.

Virtual Power Plants (VPPs)

• Aggregation of diverse DER operated as a unified resource.
• Operational aspects:
  • Pooling: Combining heterogeneous DER (solar, batteries, DR, EVs) via a control platform.
  • Aggregation Logic: Forecasting aggregate capability and bidding/scheduling into markets or for grid services.
  • Dispatch: Sending signals to individual DERs within the VPP to meet the aggregate commitment.
• Example: PG&E/Tesla VPP delivered 16.5 MW from ~2,500 Powerwalls during a 2022 CAISO emergency.
• VPPs offer meaningful scale and are seen as alternatives to traditional power plants.
• DERMS and VPPs are complementary: DERMS often manage grid reliability, while VPPs deliver aggregated services, ideally interoperating.

Technical Integration Challenges

Integrating DER introduces technical complexities:

• Bidirectional Power Flow & Protection:
  • Backfeed: Power flowing from DER back towards the substation when generation exceeds local load.
  • Protection Coordination: Legacy protection (fuses, reclosers) may misoperate with bidirectional flow. Requires updates (bidirectional relays, setting adjustments).
  • Anti-Islanding: Critical safety function; DER must rapidly disconnect during grid outages to prevent energizing faulted lines.
• Voltage Control:
  • High DER penetration can cause voltage issues (midday high voltage, evening low voltage).
  • Requires active voltage management using smart inverters and legacy devices coordinated by advanced software (ADMS/DERMS).
  • Hosting Capacity Analysis: Used to determine how much DER a feeder can handle before upgrades are needed. Maps guide interconnection.
• Thermal Overloads:
  • High DER export can exceed thermal limits of feeders or transformers, potentially requiring upgrades.
  • Storage or targeted load control can mitigate overloads (Non-Wires Alternatives).
• Short-Circuit Currents:
  • Inverter-based DER contribute little fault current.
  • Synchronous DER (CHP, generators) do contribute and may require re-evaluating protection equipment ratings.
• Cybersecurity and Communication:
  • Networked DER increases the cyber attack surface. Coordinated attacks could destabilize the grid.
  • Requires robust cybersecurity standards (encryption, authentication), secure DERMS/aggregator platforms, and potentially new technologies like blockchain for secure coordination.
  • Physical security of DER assets is also a concern.