Overview
Under the 2025 Energy Code, a battery energy storage system is defined as stationary equipment that receives electrical energy and then uses batteries to store that energy for later use to supply electrical energy when needed. BESS consists of one or more modules, a power conditioning system, and the balance of plant components.
General Information
Section 170.2(h) - PDF of the 2025 Energy Code has battery energy storage system (BESS) requirements for newly constructed high-rise (4 habitable stories or more) multifamily buildings that require a solar photovoltaic (solar PV) system (2025 High-rise Multifamily Solar FAQs), with two exceptions (see below).
Information regarding the solar PV requirements for high-rise multifamily buildings, see 2025 High-rise Multifamily Solar PV FAQs.
Solar PV and battery energy storage system (BESS) requirements do not apply to additions and alterations.
The required battery energy storage system size is based on the solar PV system size determined for building types listed in Table 170.2-V - PDF, including mixed-occupancy buildings.
Prescriptive Compliance
Section 170.2(h) - PDF of the 2025 Energy Code has three equations to calculate the total minimum battery capacity for building types listed in Table 170.2-V - PDF using the solar PV system capacity from Equation 170.2-D - PDF or solar access roof area (SARA) method.
- Rated usable energy capacity (Equation 170.2-E - PDF), based on:
- Conditioned floor area (CFA) used to calculate PV system size requirements
- BESS capacity factor per Table 170.2-V - PDF
- Round trip efficiency of the BESS
- Rated usable energy capacity SARA-Adjusted (Equation 170.2-F - PDF):
- Conditioned floor area (CFA) used to calculate PV system size requirements
- Rated PV system capacity from Equation 170.2-D - PDF
- Rated PV system capacity from SARA calculation
- BESS capacity factor per Table 170.2-V - PDF
- Round-trip efficiency of the BESS
- Rated power capacity (Equation 170.2-G - PDF):
- Rated usable energy capacity of the BESS (either from Equation 170.2-E or Equation 170.2-F)
The rated energy capacity of a battery energy storage system (BESS) must be no less than the usable energy capacity calculated using either Equation 170.2-E - PDF or Equation 170.2-F – PDF. The rated power capacity of the BESS must be no less than the power capacity calculated using Equation 170.2-G - PDF. For mixed occupancy buildings that contain the building types listed in Table 170.2-V - PDF, apply the minimum rated usable energy capacity equation (either Equation 170.2-E or Equation 170.2 -F) to each of the listed building types, including support areas, then sum the capacities to determine the minimum capacity for the entire mixed-use building.
Table 170.2-V: BESS Capacity Factors
Footnote to Table 170.2-V:
- NR = Not Required
Performance Compliance
The standard design battery energy storage system size is determined using the prescriptive solar PV size requirement for the proposed design, regardless of the fuel type. A battery energy storage system can be installed as a standalone system for additional compliance credit, when not required prescriptively. Also, a battery energy storage system larger than the prescriptive requirement can be used to tradeoff for a smaller solar PV system.
Yes. Two exceptions can exclude high-rise multifamily buildings from the battery energy storage system requirements:
- If the installed solar PV system size is less than 15 percent of the capacity determined by Equation 170.2-D - PDF
- Buildings with battery storage system requirements less than 10 kWh minimum rated usable energy capacity
NOTE: Solar PV requirements still apply when battery energy storage system requirement exceptions apply.
The installed battery must meet or exceed requirements in the 2025 Energy Code Reference Joint Appendix JA12 - PDF and be manufacturer-certified to the California Energy Commission (CEC). A list of certified batteries is available on the CEC website.
The battery energy storage system must meet the safety and minimum system performance requirements specified in Table 1 below, in addition to meeting control requirements.
- Table 1: Minimum Performance Requirements for Battery Energy Storage Systems
| Battery Performance Specification | Prescriptive | Performance |
|---|---|---|
| Usable capacity greater than 5 kWh per building. | X | |
| Single charge-discharge cycle AC to AC (round-trip) efficiency greater than 80 percent. | X | |
| Energy capacity of 70% of nameplate capacity after 4,000 cycles covered by warranty or 70% of nameplate capacity under 10-year warranty. | X | X |
The local enforcement agency shall verify that:
- All Certificate of Installations are valid,
- The BESS is a model certified to the Energy Commission, and
- The BESS is commissioned and operational with the 2025 Energy Code Reference Joint Appendix JA 12 control requirements.
- The control strategy and the compliance cycling capacity at system installation, commissioning, and final inspection by the enforcement agency shall be the control strategy and the compliance cycling capacity that was used in the Certificate of Compliance.
Frequently Asked Questions
Yes. The battery energy storage systems are self-certified to meet the 2025 Energy Code Reference Joint Appendix JA12 - PDF qualifications by the manufacturer to the CEC to comply with the applicable prescriptive and performance requirements in the 2025 Energy Code. For more information, please visit the manufacturer certifications of building equipment Battery Energy Storage Systems.
Yes. The Solar Equipment Lists Program includes equipment that meets established national safety and performance standards. These lists provide information and data that support existing solar incentive programs, utility grid connection services, consumers, and state and local programs. Please note that equipment on the CEC’s Solar Equipment Lists have reportedly undergone tests to achieve minimum safety and performance standards. The CEC makes no claim or warranty on the equipment and its safety, performance, or durability. For more information, please visit the solar equipment lists.
No. For compliance with the 2025 Energy Code the minimum rated usable energy capacity of the battery energy storage system in kWh must be used for Equation 170.2-E or Equation 170.2-F - PDF. The minimum rated usable energy capacity is the battery energy storage system capacity in kWh that a manufacturer allows to be used for charging and discharging. To comply with Section 170.2(h) - PDF a battery energy storage system must meet the minimum qualification requirements of Reference Joint Appendix JA12 - PDF which includes having a round-trip efficiency of at least 80 percent and an energy capacity retention of 70 percent of nameplate capacity after 4,000 cycles covered by a warranty, or 70 percent of nameplate capacity under a ten year warranty.
See the Blueprint for more information, including articles and frequently asked BESS questions, about the 2025 Energy Code.