MEMBERS-ONLY FACT SHEET
NEM/NBT Paired Storage
April 30, 2026
To install solar and storage under net energy metering (NEM) or the net billing tariff (NBT), customers need to ensure either that the storage is only charged by solar or that the storage will never export to the grid. In the case of solar-only charging you can export from the battery to the grid for NEM/NBT credit. In the case of no storage export you can interconnect as a NEM/NBT system and export from solar, but can only use the battery to reduce on-site load.
Batteries smaller than 10 kW do not need to install additional metering or controls. Performance is verified using meter data and estimated solar production.
For batteries larger than 10 kW, customers must install either an additional meter or an inverter or charge controller that is a certified power control system (PCS).
The standard for PCS is known as the certification requirements decision (CRD) for power control systems, an optional component of UL 1741. The CRD can certify two operating modes. Solar-Only Charging mode (also known as Export Only Mode) guarantees that a battery cannot charge from the grid. In No Grid Exports mode (also known as Import Only Mode), the battery can charge from the grid but can only discharge for on-site load.
Solar-Only Charging
In this option, the battery can export to the grid for NEM/NBT credit because it only contains clean energy. The utility does not need to track where exports come from. Any exports get NEM/NBT credits. From a billing perspective it is treated the same as solar without storage. Solar and storage providers have long programmed systems to charge the battery only from solar for purposes of ITC eligibility, but the utilities need to verify this performance with a certified PCS set to Export Only Mode.
The California Energy Commission maintains a list of equipment that has achieved certification under the CRD. Go to this page. Click on the small link on the right labeled “Download Excel file.” To qualify for use as NEM/NBT paired storage, the equipment must have a “Max Open Loop Response Time” of 10 seconds or less.
No Storage Export
In this option, the battery can charge from the grid but can only be discharged to power on-site load. This enables interconnection of solar plus storage under NEM/NBT but does not allow the battery to export for NEM/NBT credit. Customers can use storage to avoid
purchasing energy at peak TOU rates.
There are three ways to verify this functionality.
Install a traditional non-export relay. This can cost around $50,000.
Install a net generation output meter (NGOM) in front of the solar inverter to measure solar output.
Install a certified power control system set to Import Only mode.
In the metering option, utilities use NGOM data together with readings from the main service meter to make sure solar generation is always higher than exports to the grid. If exports are higher than solar output, the energy is coming from the battery and is not eligible for export credits. That quantity of exports is deducted from total exports before applying credits.
NGOMs increase cost and cause delay. A timeline standard was recently established in Rule 21 giving utilities 20 business days for NGOM design and 20 days for construction. However, utilities routinely fail to comply with Rule 21 timelines. Delays of nine months are common. Metering can also be expensive, ranging from $400-$600 for a simple bubble meter to $15,000 for complex metering at an interconnection on a primary line.
The NGOM option is not possible for DC-coupled systems because the utilities have not recognized any revenue-grade DC meters. Solar production with DC-coupled storage cannot be measured to compare with exports at the main service meter. DC-coupled systems larger than 10 kW are allowed only if they have certified power control systems.
Below 10 kW
For systems smaller than 10 kW, the utilities use an “estimation methodology” to determine solar production. The goal is still to compare exports with solar production, but the solar production is estimated. The estimate is done on a monthly basis because you cannot accurately predict solar output on an hourly basis due to changing weather conditions. Monthly export credits are capped at the expected monthly output of the solar system. That is, you cannot export over the course of a month more than the estimated generation in that month.
The utilities have agreed to generous assumptions for the production estimate. Therefore, export credits will only be reduced if the customer is intentionally doing storage arbitrage with grid power. The exception is if a customer has an extremely productive system and negligible load, but that would not be an intentional design.
The 10 kW threshold is judged by the storage inverter size in an AC-coupled system. In a DC-coupled system, the storage size is the “maximum continuous discharge rate” of the battery if that value is listed on the battery data sheet. If the battery data sheet does not have a value with that label or a label that is substantially equivalent, the utility uses the inverter size.