Title 24 · California Energy Code
How to calculate the minimum rated power capacity (kW) for a BESS
For code compliance in California: first compute the **required BESS usable energy (kWh)** using Equation 140.10‑B (or 170.2‑E for tall multifamily) with the CFA and the table B value, then size the BESS power by dividing that kWh number by **4** (Equations 140.10‑D / 170.2‑G). Confirm the PV and kWh exceptions (e.g., no BESS if required kWh < 10 kWh or PV is below the 15% threshold).
Last reviewed: July 6, 2026
What the code requires — plain English
The California Energy Code requires that when a building must install PV, it must also meet minimum BESS size requirements: first compute the Minimum Rated Usable Energy Capacity (kWh) (Equation 140.10‑B or 140.10‑C; or 170.2‑E / 170.2‑F for multifamily >3 stories), then size the Minimum Rated Power Capacity (kW) by dividing that energy capacity by 4. This requirement appears in § 140.10(b) for the general prescriptive path and in § 170.2(h) for multifamily buildings more than three habitable stories.
The single most important rule: size the BESS power (kW) = the required BESS usable energy (kWh) ÷ 4 (see § 140.10 and § 170.2(h)).
Requirements in detail
Key defined terms (first mention)
- BESS — Battery Energy Storage System (must meet JA12 qualification). § 140.10(b).
- Minimum Rated Usable Energy Capacity (kWh batt) — the required energy capacity calculated by Equation 140.10‑B / 140.10‑C (or 170.2‑E / 170.2‑F for >3‑story multifamily). § 140.10(b) and § 170.2(h).
- Minimum Rated Power Capacity (kW batt) — the required power rating; code prescribes dividing the kWh value by 4. § 140.10(b) and § 170.2(h).
What you must calculate (decision‑relevant dimensions)
| Dimension / value | What you use it for | Formula / threshold | Code reference |
|---|---|---|---|
| Minimum Rated Usable Energy Capacity (kWh batt) | Starting point — how many kWh the code requires | Use Equation 140.10‑B (or 140.10‑C if SARA-adjusted); for >3‑story multifamily use 170.2‑E / 170.2‑F. | § 140.10(b); § 170.2(h) — Equations 140.10‑B/C and 170.2‑E/F. |
| Minimum Rated Power Capacity (kW batt) | Final required inverter/PCS or nameplate power | kW batt = kWh batt ÷ 4 (Equation 140.10‑D / 170.2‑G) | § 140.10(b) Equation 140.10‑D; § 170.2(h) Equation 170.2‑G. |
| BESS capacity factor (B, Wh/ft2) | Used to compute kWh batt from conditioned floor area | From Table 140.10‑B or Table 170.2‑V (building type specific). Example: Multifamily >3 stories: 1.82 Wh/ft2. | See Table 140.10‑B or Table 170.2‑V in § 140.10 / § 170.2(h). |
| BESS round‑trip efficiency (C) | Used in the kWh calculation denominator | Use the rated single charge‑discharge AC‑to‑AC efficiency per the equation (Equation 140.10‑B / 170.2‑E). | § 140.10(b); § 170.2(h). |
Notes on the usable‑energy equation:
- Equation 140.10‑B (and 170.2‑E) compute kWh batt from conditioned floor area (CFA) × B divided by 1,000 × C (see the equations for exact placement of variables). Use the building type B value from the appropriate table.
How to apply Equation 140.10‑D and 170.2‑G
- Once you have kWh batt from Equation 140.10‑B/C (or 170.2‑E/F), apply:
- kW batt = kWh batt ÷ 4 per Equation 140.10‑D (general prescriptive) and per Equation 170.2‑G (multifamily >3 stories).
Exceptions & special cases
- No BESS required if the installed PV system capacity is less than 15% of the PV capacity determined by the applicable PV equation. See Exception 1 to § 140.10(b) and Exception 1 to § 170.2(h).
- No BESS required if the computed Minimum Rated Usable Energy Capacity (kWh batt) is less than 10 kWh — Exception 2 to § 140.10(b) and to § 170.2(h).
- Multifamily >3 stories: PV/BESS rules are in the 170.2(g)/(h) grouping; some multifamily PV exceptions apply (e.g., where load‑serving entity programs change applicability). See § 170.2(g) exceptions.
- Mixed occupancy: compute energy capacity per listed building types and sum the required kWh capacities, then convert to kW using the divide‑by‑4 rule (apply per‑building‑type kWh then sum or sum then divide — the code requires summing the energy capacities first). § 140.10(b) and § 170.2(h) explain mixed occupancy aggregation.
If the file excerpts above do not show a default value for C (round‑trip efficiency) or an explicit procedural example for a particular building type beyond the table entries, the code text must be followed directly (use the stated C for your specified equipment) — do not assume a value.
Common mistakes
- Applying the divide‑by‑4 rule to the PV kW instead of the computed BESS kWh. The code requires kW batt = (required kWh batt) ÷ 4, not PV ÷ 4. See Equations 140.10‑D and 170.2‑G.
- Forgetting exceptions: if PV is too small (<15% of calculated PV) or the computed kWh batt < 10 kWh, a BESS may not be required. Check the exceptions in § 140.10(b) or § 170.2(h) before sizing.
- Using an assumed round‑trip efficiency C without documenting it. The energy equation explicitly uses C; record the equipment rating and citation.
- Mixing units (Wh/ft2 vs W/ft2) when using the tables — use the correct table for B (Wh/ft2) or A (W/ft2) depending on the equation. See Table 140.10‑B / 140.10‑A / 170.2‑V / 170.2‑U.
Worked example — step‑by‑step (concrete numbers)
Scenario: New multifamily building >3 stories. The design/calculation yields a required BESS usable energy of 40 kWh per Equation 170.2‑E (you computed that separately from CFA, B and C). Apply Equation 170.2‑G to get required power:
- Required usable energy (from Equation 170.2‑E): kWh batt = 40 kWh.
- Apply Equation 170.2‑G: kW batt = kWh batt ÷ 4 = 40 ÷ 4 = 10 kW. This means the BESS must have at least a 10 kW rated power capacity (dc).
- Verify exceptions: since 40 kWh ≥ 10 kWh, the Exception 2 "less than 10 kWh" does not apply. Also confirm the PV sizing thresholds (e.g., PV not <15% of required) so a BESS is required.
(If you need the upstream step: to compute the 40 kWh you would use Equation 170.2‑E: kWh batt = (CFA × B)/(1000 × C) — obtaining CFA, pick the B value from Table 170.2‑V for your building type, and use the BESS round‑trip efficiency C as rated. )
Related provisions (direct code pointers)
- § 140.10(b) — Prescriptive BESS requirements (Equations 140.10‑B, 140.10‑C, 140.10‑D).
- § 140.10(a) — Photovoltaic prerequisites and PV exceptions that affect BESS applicability.
- § 170.2(h) — Multifamily >3 stories BESS requirements (Equations 170.2‑E/170.2‑F/170.2‑G).
- § 170.2(g) / 170.2‑D — PV sizing rules for >3‑story multifamily that feed into whether a BESS is required.
- Tables: Table 140.10‑B / Table 170.2‑V — building‑type B (Wh/ft2) capacity factors used to compute kWh batt.
Code references
Grounded in the retrieved California Energy Code — click a citation to read the verbatim passage:
§ 170.2 High relevance — show source text
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where:
kWh batt = Minimum Rated Usable Energy Capacity of the BESS in kWh.
kW PVdc = Minimum Rated PV System Capacity in kW from Equation 170.2D. kW PVdc, SARA = Minimum Rated PV System Capacity in kW from the SARA calculation. CFA = Conditioned floor area that is subject to the PV system requirements of Section 170.2(g) in square feet.
B = BESS Capacity Factor in Wh/square foot as specified in Table 170.2-V for the building type.
C = Rated single charge-discharge cycle AC to AC (round-trip) efficiency of the BESS.
EQUATION 170.2-G—BATTERY ENERGY STORAGE SYSTEM MINIMUM RATED POWER CAPACITY
kW batt = kW batt /4
where:
kW batt = Minimum Rated Power Capacity of the BESS in kW dc .
kWh batt = Minimum Rated Usable Energy Capacity of the BESS in kWh.
Exception 1 to Section 170.2(h): No BESS is required if the installed PV system capacity is less than 15 percent of the capacity determined by Equation 170.2-D.
Exception 2 to Section 170.2(h): No BESS is required in buildings with BESS requirements with less than 10 kWh minimum rated usable energy capacity.
TABLE 170.2-V—BESS CAPACITY FACTORS (Wh/ft2 of conditioned floor area) Col2 Col3 Col4 Col5 Col6 Col7 Col8 Col9 Col10 Col11 Col12 Col13 Col14 Col15 Col16 Col17 BUILDING TYPE CZ 1 CZ 2 CZ 3 CZ 4 CZ 5 CZ 6 CZ 7 CZ 8 CZ 9 CZ 10 CZ 11 CZ 12 CZ 13 CZ 14 CZ 15 CZ 16 Event & Exhibit 1.82 1.95 1.74 2.12 1.91 2.13 2.24 2.30 2.36 2.47 2.62 2.16 2.64 2.68 3.22 1.89 Library 0.37 7.17 5.97 6.75 5.64 6.08 6.19 7.13 7.18 7.56 7.17 6.93 6.88 6.81 7.93 6.40 Hotel/Motel 0.86 0.84 0.77 0.92 0.81 0.89 0.90 1.01 1.00 1.11 1.14 0.96 1.18 1.18 1.49 0.85 Office, Financial Institution, § 140.10 High relevance — show source text
(b) Battery energy storage system (BESS) requirements. All buildings that are required by Section 140.10(a) to have a PV system shall also have a BESS meeting the minimum qualification requirements of Reference Joint Appendix JA12. The rated energy capacity shall be not less than the Minimum Rated Useable Energy Capacity determined using Equation 140.10-B or 140.10-C if SARA was used to determine the PV capacity in Section 140.10(a). The rated power capacity shall be not less than the Minimum Power Capacity determined using Equation 140.10-D. In mixed occupancy buildings, the total battery system capacity for the building shall be determined by applying the Minimum Rated Usable Energy Capacity to each of the listed building types and summing the capacities determined for each.
EQUATION 140.10-B—BATTERY ENERGY STORAGE SYSTEM MINIMUM RATED USABLE ENERGY CAPACITY kWh batt = [(CFA × B)/(1,000 × C [0.5] )]
EQUATION 140.10-C—BATTERY ENERGY STORAGE SYSTEM MINIMUM RATED USABLE ENERGY CAPACITY, SARA-ADJUSTED kWh batt = [(CFA × B)/(1,000 × C [0.5] )] x (kW PVdc,SARA /kW PVdc )
where:
kWh batt = Minimum Rated Usable Energy Capacity of the BESS in kWh.
CFA = Conditioned floor area that is subject to the PV system requirements of Section 140.10(a) in square feet.
kW PVdc = Minimum Rated PV System Capacity in kW from Equation 140.10-A. kW PVdc, SARA = Minimum Rated PV System Capacity in kW from the SARA calculation. B = BESS Capacity Factor in Wh/square foot as specified in Table 140.10-B for the building type. C = Rated single charge-discharge cycle AC to AC (round-trip) efficiency of the BESS.
EQUATION 140.10-D—BESS MINIMUM RATED POWER CAPACITY
kW batt = kW batt /4
where:
kW batt = Minimum Rated Power Capacity of the BESS in kWdc. kW PVdc = Minimum Rated Useable Energy Capacity of the BESS in kWh. Exception 1 to Section 140.10(b): No BESS is required if the installed PV system capacity is less than 15 percent of the capacity determined by Equation 140.10-A.
Exception 2 to Section 140.10(b): No BESS is required if the rated usable energy capacity determined by Equation 140.10-B or Equation 140.10-C is less than 10 kWh.
Exception 3 to Section 140.10(b): For multitenant buildings, the energy capacity of the BESS shall be based on the tenant spaces with more than 5,000 square feet of conditioned floor area. For single-tenant buildings with less than 5,000 square feet of conditioned floor area, no BESS is required.
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|TABLE 140.
§ 170.2 High relevance — show source text
The rated energy capacity shall be not less than the Minimum Rated Useable Energy Capacity determined by Equation 170.2-E, or by Equation 170.2-F if SARA was used to determine the PV capacity in Section 170.2-D, and the rated power capacity shall be not less than the Minimum Power Capacity determined by Equation 170.2-G. In mixed occupancy buildings, the total battery system capacity for the building shall be determined by applying the Minimum Rated Usable Energy Capacity to each of the listed building types and summing the capacities determined for each.
EQUATION 170.2-E—BATTERY ENERGY STORAGE SYSTEM MINIMUM RATED USABLE ENERGY CAPACITY kWh batt = k((CFA × B)/(1000 × C [0.5] ))
— EQUATION 170.2-F BATTERY ENERGY STORAGE SYSTEM MINIMUM RATED USABLE ENERGY CAPACITY, SARA-ADJUSTED kWh batt = k((CFA × B)/(1000 × C [0.5] )) × (kWP Vdc,SARA /kWP Vdc )
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where:
kWh batt = Minimum Rated Usable Energy Capacity of the BESS in kWh.
kW PVdc = Minimum Rated PV System Capacity in kW from Equation 170.2D. kW PVdc, SARA = Minimum Rated PV System Capacity in kW from the SARA calculation. CFA = Conditioned floor area that is subject to the PV system requirements of Section 170.2(g) in square feet.
B = BESS Capacity Factor in Wh/square foot as specified in Table 170.2-V for the building type.
C = Rated single charge-discharge cycle AC to AC (round-trip) efficiency of the BESS.
EQUATION 170.2-G—BATTERY ENERGY STORAGE SYSTEM MINIMUM RATED POWER CAPACITY
kW batt = kW batt /4
where:
kW batt = Minimum Rated Power Capacity of the BESS in kW dc .
kWh batt = Minimum Rated Usable Energy Capacity of the BESS in kWh.
Exception 1 to Section 170.2(h): No BESS is required if the installed PV system capacity is less than 15 percent of the capacity determined by Equation 170.2-D.
Exception 2 to Section 170.2(h): No BESS is required in buildings with BESS requirements with less than 10 kWh minimum rated usable energy capacity.
|TABLE 170.
§ 140.10 High relevance — show source text
EQUATION 140.10-D—BESS MINIMUM RATED POWER CAPACITY
kW batt = kW batt /4
where:
kW batt = Minimum Rated Power Capacity of the BESS in kWdc. kW PVdc = Minimum Rated Useable Energy Capacity of the BESS in kWh. Exception 1 to Section 140.10(b): No BESS is required if the installed PV system capacity is less than 15 percent of the capacity determined by Equation 140.10-A.
Exception 2 to Section 140.10(b): No BESS is required if the rated usable energy capacity determined by Equation 140.10-B or Equation 140.10-C is less than 10 kWh.
Exception 3 to Section 140.10(b): For multitenant buildings, the energy capacity of the BESS shall be based on the tenant spaces with more than 5,000 square feet of conditioned floor area. For single-tenant buildings with less than 5,000 square feet of conditioned floor area, no BESS is required.
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TABLE 140.10-A—PV CAPACITY FACTORS (W/ft2 of conditioned floor area) Col2 Col3 Col4 Col5 Col6 Col7 Col8 Col9 Col10 Col11 Col12 Col13 Col14 Col15 Col16 Col17 BUILDING TYPE CZ 1 CZ 2 CZ 3 CZ 4 CZ 5 CZ 6 CZ 7 CZ 8 CZ 9 CZ 10 CZ 11 CZ 12 CZ 13 ** CZ 14** ** CZ 15** ** CZ 16** Events & Exhibits 3.48 4.28 3.66 4.32 3.77 4.05 4.28 4.83 4.63 4.80 5.04 4.44 4.95 4.36 5.48 3.38 Library 0.39 3.23 2.59 3.25 2.48 2.74 3.04 3.49 3.32 3.69 3.79 3.32 3.79 3.37 4.49 2.84 Hotel/Motel 1.69 1.90 1.66 1.97 1.69 1.87 1.94 2.22 2.09 2.20 2.30 2.05 2.30 2.02 2.72 1.73 Office, Financial
Institution, Unleased
Tenant Space, Medical
Office Building/Clinic2.59 3.13 2.59 3.13 2.59 3.13 3.13 3. § 140.10 High relevance — show source text
Exception 1 to Section 140.10(a): No PV system is required where the total of all available SARA is less than 3 percent of the conditioned floor area.
Exception 2 to Section 140.10(a): No PV system is required where the required PV system capacity is less than 4 kW dc .
Exception 3 to Section 140.10(a): No PV system is required if the SARA contains less than 80 contiguous square feet.
Exception 4 to Section 140.10(a): Buildings with enforcement-authority-approved roof designs, where the enforcement authority determines it is not possible for the PV system, including panels, modules, components, supports and attachments to the roof structure, to meet ASCE 7-16, Chapter 7, Snow Loads.
Exception 5 to Section 140.10(a): For nonresidential and hotel/motel multitenant buildings, the PV capacity determined by Equation 140.10-A shall be calculated without including tenant spaces meeting all of the following: i. The tenant space is less than or equal to 2,000 square feet of conditioned space; ii. The tenant space is served by an HVAC system that does not serve other tenant spaces in the building; and iii. The tenant space has an individual utility meter to track electricity consumption that does not include the electricity consumption of other tenant spaces in the building.
This exception does not apply where the Commission has approved a community solar program for showing compliance as specified in Title 24, Part 1, Section 10-115, or where a load-serving entity provides a program where PV generation is compensated through virtual energy bill credits for occupants of nonresidential and hotel/motel tenant spaces to receive energy bill benefits from netting of energy generation and consumption.
(b) Battery energy storage system (BESS) requirements. All buildings that are required by Section 140.10(a) to have a PV system shall also have a BESS meeting the minimum qualification requirements of Reference Joint Appendix JA12. The rated energy capacity shall be not less than the Minimum Rated Useable Energy Capacity determined using Equation 140.10-B or 140.10-C if SARA was used to determine the PV capacity in Section 140.10(a). The rated power capacity shall be not less than the Minimum Power Capacity determined using Equation 140.10-D. In mixed occupancy buildings, the total battery system capacity for the building shall be determined by applying the Minimum Rated Usable Energy Capacity to each of the listed building types and summing the capacities determined for each.
EQUATION 140.10-B—BATTERY ENERGY STORAGE SYSTEM MINIMUM RATED USABLE ENERGY CAPACITY kWh batt = [(CFA × B)/(1,000 × C [0.5] )]
EQUATION 140.10-C—BATTERY ENERGY STORAGE SYSTEM MINIMUM RATED USABLE ENERGY CAPACITY, SARA-ADJUSTED kWh batt = [(CFA × B)/(1,000 × C [0.5] )] x (kW PVdc,SARA /kW PVdc )
where:
kWh batt = Minimum Rated Usable Energy Capacity of the BESS in kWh.
CFA = Conditioned floor area that is subject to the PV system requirements of Section 140.10(a) in square feet.
§ 1.27 High relevance — show source text
63|1.27|1.63|1.27|1.63|1.63|1.63|1.63|1.63|1.63|1.63|1.63|1.63|2.46|1.27| |Warehouse|0.39|0.44|0.39|0.44|0.39|0.44|0.44|0.44|0.44|0.44|0.44|0.44|0.44|0.44|0.58|0.39| |Religious Worship|4.25|4.65|3.49|4.52|3.72|4.29|4.64|5.89|5.30|5.67|5.89|4.99|5.78|4.63|7.57|3.90| |Sports & Recreation|2.47|1.97|1.54|2.03|1.60|1.84|1.98|2.63|2.47|2.60|2.75|2.20|2.72|2.15|4.03|1.81| |Multifamily > 3 stories|1.82|2.21|1.82|2.21|1.82|2.21|2.21|2.21|2.21|2.21|2.21|2.21|2.21|2.21|2.77|1.82|
(h) Battery energy storage system (BESS) requirements—more than three habitable stories. All buildings that are required by Section 170.2(g) to have a PV system shall also have a BESS meeting the minimum qualification requirements of Reference Joint Appendix JA12. The rated energy capacity shall be not less than the Minimum Rated Useable Energy Capacity determined by Equation 170.2-E, or by Equation 170.2-F if SARA was used to determine the PV capacity in Section 170.2-D, and the rated power capacity shall be not less than the Minimum Power Capacity determined by Equation 170.2-G. In mixed occupancy buildings, the total battery system capacity for the building shall be determined by applying the Minimum Rated Usable Energy Capacity to each of the listed building types and summing the capacities determined for each.
EQUATION 170.2-E—BATTERY ENERGY STORAGE SYSTEM MINIMUM RATED USABLE ENERGY CAPACITY kWh batt = k((CFA × B)/(1000 × C [0.5] ))
— EQUATION 170.2-F BATTERY ENERGY STORAGE SYSTEM MINIMUM RATED USABLE ENERGY CAPACITY, SARA-ADJUSTED kWh batt = k((CFA × B)/(1000 × C [0.5] )) × (kWP Vdc,SARA /kWP Vdc )
268 2025 CALIFORNIA ENERGY CODE
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where:
kWh batt = Minimum Rated Usable Energy Capacity of the BESS in kWh.
kW PVdc = Minimum Rated PV System Capacity in kW from Equation 170.2D. kW PVdc, SARA = Minimum Rated PV System Capacity in kW from the SARA calculation. CFA = Conditioned floor area that is subject to the PV system requirements of Section 170.2(g) in square feet.
§ 170.2 Medium relevance — show source text
The PV capacity in kW dc shall not be less than the smaller of the minimum rated PV system capacity determined by Equation 170.2-D, or the total of all available solar access roof areas (SARA) multiplied by 18 for steep-sloped roofs or multiplied by 14 for low-sloped roofs. In mixed occupancy buildings, the minimum rated PV system capacity for the building shall be determined by applying Equation 170.2-D to the conditioned floor area of each of the listed building types and summing the capacities determined for each.
SARA include the area of the building’s roof space capable of structurally supporting a PV system, and the area of all roof space on covered parking areas, carports and all other newly constructed structures on the site that are compatible with supporting a PV system per Title 24, Part 2, Section 1511.10.
SARA does not include:
A. Any area that has less than 70 percent annual solar access. Annual solar access is determined by dividing the total annual solar insolation (accounting for shading obstructions) by the total annual solar insolation if the same areas were unshaded by those obstructions. For all roofs, all obstructions including those that are external to the building,
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and obstructions that are part of the building design and elevation features, may be considered for the annual solar access calculations.
B. Occupied roofs as specified by CBC Section 503.1.4. C. Roof area that is otherwise not available due to compliance with: i. Other state building code requirements, or ii. Local building code requirements if the local building code requirements are confirmed by the Executive Director.
EQUATION 170.2-D—PHOTOVOLTAIC DIRECT CURRENT CAPACITY
kW PVdc = (CFA × A)/1000
where:
kW PVdc = Minimum rated PV system capacity in kW.
CFA = Conditioned floor area in square feet.
A = PV capacity factor in W/square foot as specified in Table 170.2-U for the building type.
Exception 1 to Section 170.2(g): No PV system is required where the total of all available SARA is less than 3 percent of the conditioned floor area.
Exception 2 to Section 170.2(g): No PV system is required where the required PV system capacity is less than 4 kW dc .
Exception 3 to Section 170.2(g): No PV system is required if the SARA contains less than 80 contiguous square feet.
Exception 4 to Section 170.2(g): Buildings with enforcement-authority-approved roof designs, where the enforcement authority determines it is not possible for the PV system, including panels, modules, components, supports and attachments to the roof structure, to meet ASCE 7-16, Chapter 7, Snow Loads.
§ 503.1.4. Medium relevance — show source text
on Jul 18, 2025 11:14 AM (CDT) THEREUNDER.
MULTIFAMILY BUILDINGS—PERFORMANCE AND PRESCRIPTIVE COMPLIANCE APPROACHES
and obstructions that are part of the building design and elevation features, may be considered for the annual solar access calculations.
B. Occupied roofs as specified by CBC Section 503.1.4. C. Roof area that is otherwise not available due to compliance with: i. Other state building code requirements, or ii. Local building code requirements if the local building code requirements are confirmed by the Executive Director.
EQUATION 170.2-D—PHOTOVOLTAIC DIRECT CURRENT CAPACITY
kW PVdc = (CFA × A)/1000
where:
kW PVdc = Minimum rated PV system capacity in kW.
CFA = Conditioned floor area in square feet.
A = PV capacity factor in W/square foot as specified in Table 170.2-U for the building type.
Exception 1 to Section 170.2(g): No PV system is required where the total of all available SARA is less than 3 percent of the conditioned floor area.
Exception 2 to Section 170.2(g): No PV system is required where the required PV system capacity is less than 4 kW dc .
Exception 3 to Section 170.2(g): No PV system is required if the SARA contains less than 80 contiguous square feet.
Exception 4 to Section 170.2(g): Buildings with enforcement-authority-approved roof designs, where the enforcement authority determines it is not possible for the PV system, including panels, modules, components, supports and attachments to the roof structure, to meet ASCE 7-16, Chapter 7, Snow Loads.
Exception 5 to Section 170.2(g): Multifamily buildings with more than three habitable stories in areas where a load-serving entity does not provide a program where PV generation is compensated through virtual energy bill credits. This exception does not apply where the Commission has approved a community solar program for showing compliance as specified in Title 24, Part 1, Section 10-115, or where a load-serving entity provides a program where PV generation is compensated through virtual energy bill credits for occupants of nonresidential and hotel/motel tenant spaces to receive energy bill benefits from netting of energy generation and consumption.
TABLE 170.2-U – PV CAPACITY FACTORS (W/ft2 of conditioned floor area) Col2 Col3 Col4 Col5 Col6 Col7 Col8 Col9 Col10 Col11 Col12 Col13 Col14 Col15 Col16 Col17 BUILDING TYPE CZ 1 CZ 2 CZ 3 CZ 4 CZ 5 CZ 6 CZ 7 CZ 8 CZ 9 CZ 10 CZ 11 CZ 12 CZ 13 CZ 14 CZ 15 CZ 16 Event & Exhibit 3.48 4.28 3.66 4.32 3.77 4.05 4.28 4.83 4.63 4. § 150.1 Medium relevance — show source text
where:
kW PV = kW dc size of the PV system.
CFA = Conditioned floor area.
N DU = Number of dwelling units. A = CFA adjustment factor from Table 150.1-C. B = Dwelling unit adjustment factor from Table 150.1-C. Exception 1 to Section 150.1(c)14: For steep slope roofs, SARA shall not consider roof areas with a northerly azimuth that lies between 300 degrees and 90 degrees from true north. No PV system is required if the SARA is less than 80 contiguous square feet. Exception 2 to Section 150.1(c)14: No PV system is required when the minimum PV system size specified by Section 150.1(c)14 is less than 1.8 kW dc . Exception 3 to Section 150.1(c)14: Buildings with enforcement-authority-approved roof designs, where the enforcement authority determines it is not possible for the PV system, including panels, modules and components and supports and attachments to the roof structure, to meet the requirements of the American Society of Civil Engineers (ASCE), Standard 7-16, Chapter 7, Snow Loads. Exception 4 to Section 150.1(c)14: For buildings that are approved by the local planning department prior to January 1, 2020 with mandatory conditions for approval: a. Shading from roof designs and configurations for steep-sloped roofs, which are required by the mandatory conditions for approval, shall be considered for the annual solar access calculations; and b. Roof areas that are not allowed by the mandatory conditions for approval to have PVs shall not be considered in determining the SARA. Exception 5 to Section 150.1(c)14: PV system sizes determined using Equation 150.1-C may be reduced by 25 percent if installed in conjunction with a BESS. The BESS shall meet the qualification requirements specified in Joint Appendix JA12 and have a minimum cycling capacity of 7.5 kWh as defined in Joint Appendix JA12. 15. Ventilation system fault indicator display (FID): All HRV/ERV systems serving individual dwelling units shall have a fault indicator display (FID) that is ECC-Rater field verified as specified in Joint Appendix JA17.
182 2025 CALIFORNIA ENERGY CODE
on Jul 18, 2025 11:14 AM (CDT) THEREUNDER.
SINGLE-FAMILY RESIDENTIAL BUILDINGS—PERFORMANCE AND PRESCRIPTIVE COMPLIANCE APPROACHES
|TABLE 150.
§ 170.2 Medium relevance — show source text
EQUATION 170.2-C—ANNUAL PHOTOVOLTAIC ELECTRICAL OUTPUT
kW PV = (CFA × A)/1000 + N DU × B)
where:
kW PV = kW dc size of the PV system.
CFA = Conditioned floor area.
266 2025 CALIFORNIA ENERGY CODE
on Jul 18, 2025 11:14 AM (CDT) THEREUNDER.
MULTIFAMILY BUILDINGS—PERFORMANCE AND PRESCRIPTIVE COMPLIANCE APPROACHES
N DU = Number of dwelling units.
A = CFA adjustment factor from Table 170.2-T.
B = Dwelling unit adjustment factor from Table 170.2-T.
Exception 1 to Section 170.2(f): For steep slope roofs, SARA shall not consider roof areas with a northerly azimuth that lies between 300 degrees and 90 degrees from true north. No PV system is required if the SARA is less than 80 contiguous square feet.
Exception 2 to Section 170.2(f): No PV system is required when the minimum PV system size specified by Section 170.2(f) is less than 4 kW dc .
Exception 3 to Section 170.2(f): Buildings with enforcement-authority-approved roof designs, where the enforcement authority determines it is not possible for the PV system, including panels, modules and components and supports and attachments to the roof structure, to meet the requirements of American Society of Civil Engineers (ASCE) Standard 7-16, Chapter 7, Snow Loads.
Exception 4 to Section 170.2(f): For buildings that are approved by the local planning department prior to January 1, 2020 with mandatory conditions of approval: a. Shading from roof designs and configurations for steep slope roofs shall be considered for the annual solar access calculations; and
b. Roof areas that are not allowed to have PVs by the mandatory conditions of approval shall not be considered in determining the SARA.
Exception 5 to Section 170.2(f): PV system sizes determined using Equation 170.2-C may be reduced by 25 percent if installed in conjunction with a BESS. The BESS shall meet the qualification requirements specified in Joint Appendix JA12 and have a minimum cycling capacity of 7.5 kWh as defined in Joint Appendix JA12.
TABLE 170.2-T—CFA AND DWELLING UNIT ADJUSTMENT FACTORS Col2 Col3 CLIMATE ZONE A—CFA B—DWELLING UNITS 1 0.793 1.27 2 0.621 1.22 3 0.628 1.12 4 0.586 1.21 5 0.585 1.06 6 0.594 1.23 7 0.572 1.15 8 0.586 1.37 9 0.613 1.36 10 0.627 1.41 11 0.836 1.44 12 0.613 1.40 13 0.894 1.51 14 0.741 1.26 15 1.56 1.47 16 0.59 1.22 (g) **Photovoltaic requirements—more than three habitable stories.
§ 150.0 Medium relevance — show source text
(s) Battery Energy Storage Systems (BESS) ready. All single-family residences that include one or two dwelling units, which a load-serving entity provides with electrical service for the dwelling unit that is greater than 125 amps, shall meet the following.
- At least one of the following shall be provided: A. BESS-ready interconnection equipment with a minimum backed-up capacity of 60 amps and a minimum of four BESS-supplied branch circuits specified in Section 150.0(s)2, or B. A dedicated raceway from the main service to a panelboard (subpanel) that supplies the branch circuits in Section 150.0(s)2. All branch circuits are permitted to be supplied by the main service panel prior to the installation of a BESS. The trade size of the raceway shall be not less than 1 inch. The panelboard that supplies the branch circuits (subpanel) must be labeled “Subpanel shall include all backed-up load circuits.”
- A minimum of four branch circuits shall be identified and have their source of supply collocated at a single panelboard suitable to be supplied by the BESS. At least one circuit shall supply the refrigerator, one lighting circuit shall be located near the primary egress and at least one circuit shall supply a sleeping room receptacle outlet.
- The main panelboard shall have a minimum busbar rating of 225 amps.
- Sufficient space shall be reserved to allow future installation of a system isolation equipment/transfer switch within 3 feet of the main panelboard. Raceways shall be installed between the panelboard and the system isolation equipment/transfer switch location to allow the connection of backup power source.
Exception to Section 150.0(s): Buildings which have a BESS installed.
(t) Heat pump space heater ready. Systems using gas or propane furnace to serve individual dwelling units shall include the following:
- A dedicated 240 volt branch circuit wiring shall be installed within 3 feet from the furnace and accessible to the furnace with no obstructions. The branch circuit conductors shall be rated at 30 amps minimum. The blank cover shall be identified as “240V ready.” All electrical components shall be installed in accordance with the California Electrical Code .
- The main electrical service panel shall have a reserved space to allow for the installation of a double pole circuit breaker for a future heat pump space heater installation. The reserved space shall be permanently marked as “For Future 240V use.”
(u) Electric cooktop ready. Systems using gas or propane cooktop to serve individual dwelling units shall include the following:
- A dedicated 240 volt branch circuit wiring shall be installed within 3 feet from the cooktop and accessible to the cooktop with no obstructions. The branch circuit conductors shall be rated at 50 amps minimum. The blank cover shall be identified as “240V ready.” All electrical components shall be installed in accordance with the California Electrical Code .
- The main electrical service panel shall have a reserved space to allow for the installation of a double pole circuit breaker for a future electric cooktop installation. The reserved space shall be permanently marked as “For Future 240V use.”
(v) Electric clothes dryer ready. Clothes dryer locations with gas or propane plumbing to serve individual dwelling units shall include the following:
- A dedicated 240 volt branch circuit wiring shall be installed within 3 feet from the clothes dryer location and accessible to the clothes dryer location with no obstructions. The branch circuit conductors shall be rated at 30 amps minimum. The blank cover shall be identified as “240V ready.” All electrical components shall be installed in accordance with the California Electrical Code .
§ 4.44 Medium relevance — show source text
04|4.44|4.95|4.36|5.48|3.38| |Library|0.39|3.23|2.59|3.25|2.48|2.74|3.04|3.49|3.32|3.69|3.79|3.32|3.79|3.37|4.49|2.84| |Hotel/Motel|1.69|1.90|1.66|1.97|1.69|1.87|1.94|2.22|2.09|2.20|2.30|2.05|2.30|2.02|2.72|1.73| |Office, Financial Institution,
Unleased Tenant Space,
Medical Office Building/Clinic|2.59|3.13|2.59|3.13|2.59|3.13|3.13|3.13|3.13|3.13|3.13|3.13|3.13|3.13|3.80|2.59| |Restaurant|8.55|9.32|8.16|9.65|8.21|8.73|9.11|10.18|9.75|10.28|10.85|9.73|10.69|9.73|12.25|8.47| |Retail, Grocery|3.14|3.49|3.01|3.61|3.05|3.27|3.45|3.83|3.65|3.81|4.09|3.64|3.99|3.71|4.60|3.21| |School|1.27|1.63|1.27|1.63|1.27|1.63|1.63|1.63|1.63|1.63|1.63|1.63|1.63|1.63|2.46|1.27| |Warehouse|0.39|0.44|0.39|0.44|0.39|0.44|0.44|0.44|0.44|0.44|0.44|0.44|0.44|0.44|0.58|0.39| |Religious Worship|4.25|4.65|3.49|4.52|3.72|4.29|4.64|5.89|5.30|5.67|5.89|4.99|5.78|4.63|7.57|3.90| |Sports & Recreation|2.47|1.97|1.54|2.03|1.60|1.84|1.98|2.63|2.47|2.60|2.75|2.20|2.72|2.15|4.03|1.81| |Multifamily > 3 stories|1.82|2.21|1.82|2.21|1.82|2.21|2.21|2.21|2.21|2.21|2.21|2.21|2.21|2.21|2.77|1.82|(h) Battery energy storage system (BESS) requirements—more than three habitable stories. All buildings that are required by Section 170.2(g) to have a PV system shall also have a BESS meeting the minimum qualification requirements of Reference Joint Appendix JA12.
Frequently asked questions
How exactly do I get the kWh batt value before dividing by 4?
Compute kWh batt using Equation 140.10‑B (or 140.10‑C if SARA/SARA‑adjusted PV sizing was used) or Equation 170.2‑E/F for >3‑story multifamily: kWh batt = (CFA × B) / (1,000 × C). Use the building‑type B from the correct table and the BESS round‑trip efficiency C.
Do I size kW per inverter nameplate or per battery DC rating?
The code specifies Minimum Rated Power Capacity of the BESS in kW dc (the required kW batt per Equation 140.10‑D / 170.2‑G) — size the battery system power (DC) to meet or exceed that rating and ensure your inverter/PCS and labeling match code requirements.
What if the computed kWh batt is 9 kWh?
If the computed Minimum Rated Usable Energy Capacity is < 10 kWh, the code states no BESS is required under the listed exceptions. Confirm PV thresholds before assuming exemption.
Can PV reduction options change the need for a BESS?
Yes — PV sizing exceptions and SARA adjustments can change the PV required; if PV installed is less than 15% of the calculated PV capacity, a BESS may not be required. Check the PV exceptions in § 140.10(a) and § 170.2(g).
Where do I find the B value (Wh/ft2) for my building type?
Use Table 140.10‑B (nonresidential/hotel) or Table 170.2‑V (multifamily >3 stories) in the code; for example, Table 170.2‑V lists Multifamily >3 stories = 1.82 Wh/ft2 in at least one climate zone entry.
More in California Energy Code
- Compliance paths, energy budgets, performance modeling and forms/software requirements
- Controls, commissioning, demand-response, sensors, and field verification/diagnostic testing
- Domestic hot water systems, efficiency, controls and installation requirements
- Electrical infrastructure, EV charging readiness, load management and demand controls
- Envelope construction, insulation, fenestration and thermal performance
- HVAC systems, ventilation rates, ducting, controls and testing
- Interior and exterior lighting power, controls and daylighting requirements
- Mandatory measures, appliance efficiency and certification requirements
- Photovoltaic requirements, BESS (battery energy storage) sizing and SARA procedures
- Reference appendices, test procedures, product certification and labeling requirements
- Scope, applicability, definitions and administrative requirements
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