Power Control System (PCS) Features for the Lunar System
Application Note | lunarenergy.com
Introduction to PCS
Power Control System (PCS) features are a set of on-grid controls that apply multiple independent limits by controlling the outputs of the Lunar ESS. PCS can reduce expensive electrical upgrades, reduce complicated load relocation, and ensure safe, compliant operation per NEC and utility regulations.
The Lunar System has been certified to both UL 1741 PCS CRD and UL 3141. Maximum Open Loop Response Time (OLRT) is less than two seconds. PCS is relevant to Articles 705, 750, and 220 of the 2020 NEC, 2023 NEC, and 2022 CEC.
Available PCS features: Bridge Limit | MSA Limit | Panel Limit at Rogowski Coils | PCS Modes | Export Limit
Compliance Information
A busbar limit label is factory applied on the Lunar Bridge dead front. An additional busbar limit label is applied to the panelboard when Rogowski Coils are installed. Installers must write the User Set Limit on each label. PCS settings can only be configured by qualified personnel in the Lunar Installer App during commissioning.
Bridge Limit
By setting a PCS Busbar Limit at the Lunar Bridge, Lunar Inverter AC current will curtail so that current on the Bridge busbar does not exceed the user-set limit. Battery charge, discharge, and PV output may all curtail as needed.
Use Case – Install 200A Breaker for Lunar Bridge: Set Bridge Limit to 200A in Installer App → PCS Limits. The Bridge has built-in CTs; no additional Rogowski Coils are required.
MSA Limit
Similar to Bridge Limit, a PCS Busbar Limit at the Meter Socket Adapter (MSA) curtails Lunar Inverter AC current so that current at the MSA does not exceed the user-set limit.
Use Case – Connect Lunar ESS to undersized 100A main panel: Install ConnectDER IslanDER MSA and Lunar MSA Controller → Set MSA Limit to 100A in Installer App → PCS Limits.
Panel Limit at Rogowski Coils
By setting a PCS Panel Limit at Rogowski Coils (CTs), Lunar Inverter AC current curtails so that current on the Coil-measured busbar does not exceed the User Set Limit.
Use Case – Avoid Main Panel Upgrade for 100A Service Homes: Install Rogowski Coils at the service disconnect → Set Busbar Limit at Rogowski Coils to 100A in Installer App → Apply busbar limit and CT label at main panel.
PCS Modes
PCS Mode | Battery Export to Grid | Battery Import from Grid | PV Export to Grid |
No Restriction | Yes | Yes | Yes |
Export Only | Yes | No (only charge from PV)* | Yes |
Import Only | No (only discharge to offset load) | Yes | Yes |
No Exchange | No (only discharge to offset load) | No (only charge from PV)* | Yes |
*For Export Only and No Exchange modes, battery may temporarily charge from grid for critical maintenance or ahead of extreme weather events.
Use Case – CA Net Billing Tariff (NBT): Export Only mode is recommended for battery + PV (battery charges from PV, exports when NEM credits are most valuable). Import Only is recommended for standalone battery with no PV.
Export Limit from Lunar System
The Export Limit caps the maximum power the Lunar System can export to the grid. Applied at Rogowski Coils (or Bridge CTs if no Rogowski Coils are installed). Note: Export power limit applies to L1 and L2 combined. Setting 0W may prevent VPP export credits.
Use Case – Undersized Distribution Transformer: Set Export Limit at remaining transformer capacity (e.g. 10kW - 7.6kW = 2.4kW) or 0W based on utility guidance.
AC-Coupled PV Use Cases
AC-Coupled PV in Backup (100A panel): Use Eaton AbleEdge smart breakers for AC-coupled PV → Install ConnectDER IslanDER MSA → Set MSA Limit to 80A. Note: AC PV is uncontrolled; set PCS limit to account for PV at peak output.
AC-Coupled PV not in Backup: Install Rogowski Coils at main panel → Set Panel Limit to 100A minus AC PV max current (e.g. 100A - 16A = 84A).
NEM-2 Compliance with AC-Coupled PV: Set Export Limit to 0W at Bridge CTs (do not install Rogowski Coils) — existing AC PV can still export independently to the grid.
FAQs
Does PCS work if there's a communication failure? Yes — PCS settings continue to work without internet. If the Lunar ESS loses communication to the Bridge, the ESS limits all output per PCS certifications.
Can I set multiple PCS settings? Yes — any combination of Bridge Limit, Panel Limit at Rogowski Coils, PCS Mode, and Export Limit can be used together.
Can I permanently derate inverter output? No, this is not allowed.
How to demonstrate PCS to AHJs? Present the commissioning report produced by the Installer App, which includes all PCS settings.
Can I set a grid import limit? Site import limits are not user-accessible in the Installer App. Contact Lunar if needed for a specific site. Use Bridge/MSA/Panel Limits to curtail battery grid charging.
Source document: https://documents.lunarenergy.com/power-control-system-pcs-features