Equation 9-4
kWbatt = kWPVdc x C
WHERE:
kWbatt = Power capacity of the battery storage system in kWdc
kWPVdc = PV system capacity required as discussed in section 9.2 in kWdc
C = Battery =power capacity factor specified in Table 9.1 for the building type
Where the building includes more than one of the space types listed in Table 9-6, the total PV system capacity for the building shall be determined by applying Equations 9-3 and 9-4 to each of the listed space types and summing the capacities determined for each.
Table 9-6: Battery Storage Capacity Factors
|
|
Factor B-Energy Capacity |
Factor C-Power Capacity |
|
Storage to PV Ratio |
Wh/W |
W/W |
|
Grocery |
1.03 |
0.26 |
|
High Rise Multifamily |
1.03 |
0.26 |
|
Office, Financial Institutions, Unleased Tenant Space |
1.68 |
0.42 |
|
Retail |
1.03 |
0.26 |
|
School |
1.87 |
0.46 |
|
Warehouse |
0.93 |
0.23 |
|
Auditorium, Convention Center, Hotel/Motel, Library, Medical Office Building/Clinic, Restaurant, Theater |
0.93 |
0.23 |
Source: California Energy Commission
There are five allowable exceptions to the prescriptive PV requirements as listed below.
•Exception 1: No battery storage system is required if the installed PV system size is less than 15 percent of the size determined by Equation 9-1.
•Exception 2: No battery storage system is required in buildings with battery storage system requirements with less than 10 kWh rated capacity.
•Exception 3: For multitenant nonresidential or hotel/motel buildings, the energy capacity and power capacity of the battery storage system must 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 battery storage system is required.
•Exception 4: In Climate Zone 1, no battery storage system is required for offices, schools, and warehouses.
Example 9-10: Battery Exceptions
Question:
I am designing a high-rise multifamily building with 20,000 square feet of conditioned floor area in Climate Zone 3. Is PV or battery storage required for my building?
Answer:
First determine the PV requirement by using Equations 9-1 and 9-2. The PV requirement is the smaller of the results from Equations 9-1 and 9-2.
Using equation 9-1 and Table 9-1. A high-rise multifamily building in Climate Zone 3 has a PV capacity factor of 1.82.
kWPV required = (CFA x A)/1000 = (20,000 x 1.82) / 1000 = 36.4 kW
Using Equation 9-2, the kWPV required = (SARA x 14)/1000 = (650 x 14 /1000 = 9.1 kW
The PV requirement is the smaller of the two numbers, therefore this building is required to have a minimum of 9.1 kW PV system. Now we can determine the battery requirement with equation 9-3.Using equation 9-3 and a battery storage system with 90 percent roundtrip efficiency, kWhbatt = kWPVdc x B / D0.5 = 9.1 x 1.03 / (0.9)^0.5 = 9.88 kWh.
Since the required battery storage is less than 10 kWh, this building qualifies for Exception 2 and do not need a battery storage system.
JA12|topic=Appendix JA12 – Qualification Requirements for Battery Storage System specifies that the battery storage system must meet or exceed the following performance specifications:
•Usable capacity of at least 5 kWh.
•For prescriptive compliance, single charge-discharge cycle AC to AC (round-trip) efficiency of at least 80 percent
•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 10-year warranty
Battery storage systems that remain in backup mode indefinitely bring no grid benefits. The JA12|topic=Appendix JA12 – Qualification Requirements for Battery Storage System requirements are designed to ensure that the battery storage system remains in an active control mode and prevent the battery storage system from remaining in the backup mode indefinitely. These requirements also enable the battery storage system to receive the latest firmware, software, control strategy, and other important updates.
The following JA12|topic=Appendix JA12 – Qualification Requirements for Battery Storage System requirements apply to all control strategies, including Basic Control, Time-of-Use (TOU) Control, and Advanced Demand Response Control, described in Section 9.6.5 below:
1. The battery storage system must have the capability of being remotely programmed to change the charge and discharge periods.
2. During discharge, the battery storage system must be programmed to first meet the electrical load of the dwelling unit(s). If during the discharge period the electrical load of the dwelling unit(s) is less than the maximum discharge rate, the battery storage system shall have the capability to discharge electricity into the grid upon receipt of a demand-flexibility signal from the local utility or a third-party aggregator.
3. The battery storage system must operate in one of the control strategies listed in JA12.2.3.1, JA12.2.3.2, and JA12.2.3.3 except during a power interruption, when it may switch to backup mode. If the battery system switches to backup power mode during a power interruption, upon restoration of power, the battery system shall immediately revert to the previously programmed JA12|topic=Appendix JA12 – Qualification Requirements for Battery Storage System control strategy.
4. The battery storage system must perform a system check on the following dates, to ensure the battery is operating in one of the control strategies listed in Section 9.6.5 below:
a. Within 10 calendar days before the onset of summer TOU schedule
b. Within 10 calendar days before the onset of winter TOU schedule
If the local utility does not offer TOU rate schedule, the default system check dates should be May 1 and 1 November 1.
Designed as a simple control that can be employed as the default control in the absence of TOU or Advanced Demand Flexibility Controls, or where communication between batteries and outside parties are not possible. When combined with an on-site solar PV system, to qualify for the Basic Control, the battery storage system shall be installed in the default operation mode to allow charging only from an on-site PV system when the PV system production is greater than the on-site electrical load. The battery storage system shall discharge only when the PV system production is less than the on-site electrical load.
This control strategy is designed to take advantage of TOU rates where they are available. This control strategy generally results in a greater energy design rating (EDR) impact than the basic control. When combined with an on-site PV system, to qualify for the TOU Control, the battery storage system shall be installed in the default operation mode to allow charging only from an on-site PV system. The battery storage system shall discharge during the highest priced TOU hours of the day. The operation schedule shall be preprogrammed from factory, updated remotely, or programmed during the installation/commissioning of the system. At a minimum, the system shall be capable of programming three separate seasonal TOU schedules, such as spring, summer, and winter.
This control strategy is designed to bring the maximum value to the PV system generations by placing the charge/discharge functions of the battery storage system under the control of a utility or a third-party aggregator. This control strategy allows discharging into the gird upon receiving a demand response signal from a grid operator. This option requires robust communication capabilities between the battery storage system and the local utility or the third-party aggregator. When combined with an on-site solar PV system, to qualify for the advanced demand flexibility control, the battery storage system shall be programmed by default as basic control or TOU control as described above. The battery storage control shall meet the demand flexibility control requirements specified in Section 110.12(a)|topic=(a) Demand responsive controls.. Furthermore, the battery storage system shall have the capability to change the charging and discharging periods in response to signals from the local utility or a third-party aggregator.
When installed separate from (not in combination with) an on-site solar photovoltaic system, including when the building is served by a community solar PV system, to qualify for the compliance credit, the battery storage system shall be programmed by default to start charging from the grid at the onset of lowest priced TOU hours of the day and start discharging at the onset of highest priced TOU hours of the day, or meet all the demand flexibility control requirements specified in Section 110.12(a)|topic=(a) Demand responsive controls. and shall have the capability to change the charging and discharging periods in response to signals from the local utility or a third-party aggregator.
The Commission recognizes that there may be other control strategies that bring equal or greater benefits than the ones listed above. Therefore, the executive director may approve alternative control strategies that demonstrate equal or greater benefits to those strategies listed in JA12|topic=Appendix JA12 – Qualification Requirements for Battery Storage System. To qualify for alternative control, the battery storage system shall be operated in a manner that increases self-utilization of the PV array output, responds to utility rates, responds to demand response signals, minimizes greenhouse gas emissions from buildings, and/or implements other strategies that achieve equal or greater benefits than those specified above. This alternative control option shall be accompanied with clear and easy to implement algorithms for incorporation into the compliance software for compliance credit calculations.
In addition to the requirements above, the battery storage system must also meet the following requirements in JA12|topic=Appendix JA12 – Qualification Requirements for Battery Storage System:
Safety Requirements: The battery storage system shall be tested in accordance with the applicable requirements given in UL1973 and UL9540. Inverters used with battery storage systems shall be tested in accordance with the applicable requirements in UL1741 and UL1741 Supplement A.
Interconnection and Net-Energy-Metering Requirements: The battery storage system and the associated components, including inverters, shall comply with all applicable requirements specified in Rule 21 and net-energy-metering (NEM) rules as adopted by the California Public Utilities Commission (CPUC).
Electric Rule 21 Tariff provides customers, wishing to install generating or storage facilities on their premises, with access to the electric grid while protecting the safety and reliability of the distribution and transmission systems at the local and system levels.
Enforcement Agency: The local enforcement agency shall verify that all certificates of installations are valid. The battery storage systems shall be verified as a model certified to the CEC as qualified for credit as a battery storage system. In addition, the enforcement agency shall verify that the battery storage system is programmed and operational with one of the controls listed in Section 9.5.2 above. The programmed control strategy at system final inspection and commissioning shall be the strategy that was used in the certificate of compliance.
Example 9-11: Battery Storage Credit
Question:
Can you get compliance credit for battery storage and how to comply with them?
Answer:
Battery storage is a prescriptive requirement for certain nonresidential building types. (See Table 9-6.) Additional compliance credit is available under the performance path allows a compliance credit for a battery storage system larger than the prescriptive requirement. It can be used for compliance tradeoff for a smaller PV system and source energy.
The manufacturers must self-certify to CEC that the battery storage systems meet the requirements of JA12|topic=Appendix JA12 – Qualification Requirements for Battery Storage System. JA12 lists minimum performance requirements, communication requirements, control requirements, safety requirements, and interconnection requirements, among others, that must be complied with and certified to the CEC. The self-certification form may be downloaded from the Commission’s website.
Example 9-12: Battery Storage Credit
Question:
When batteries are used there is a loss of electricity associated with the roundtrip charge and discharge resulting in fewer generated kWh. Why does the CEC require a battery storage system that is coupled with a PV system if there is a loss of energy?
Answer:
Battery storage systems store the PV generated electricity in the middle of the day when the solar resources are generally plentiful and electricity prices are low. The systems discharge the stored electricity later in the day, during the peak hours when solar resources are diminished and electricity prices are high. Battery storage systems have a roundtrip charge and discharge loss of 5 to 15 percent, depending on the type of battery technology and the inverter efficiencies. The electricity price differential between the middle of the day and the peak hours is greater than the battery charge and discharge losses. This means that even with the relatively small loss of electricity, it is still cost-effective for a consumer to store electricity generated onsite around midday and use it later on instead of purchasing additional electricity from the grid.
To calculate the performance of a battery storage system coupled with a PV system, the CEC’s compliance software on hourly basis accounts for the PV generation, losses, storage capacity remaining, charge and discharge rates, cost of electricity, house loads, and hourly exports. Similar calculations are also performed to calculate the benefits of storage for CO2 emissions.
Not any battery storage system is eligible for compliance credit; it must comply with the requirements of Reference Joint Appendix 12 (JA12|topic=Appendix JA12 – Qualification Requirements for Battery Storage System). The requirements ensure that the battery storage system remains in a dynamic mode that allows residents to take advantage of variable electricity costs associated with charge and discharge periods throughout the day. Static batteries that remain mostly in backup mode have little to no value to the building owner, the grid, or the environment.
Example 9-13: Battery Storage TOU Schedule
Question:
How will control requirement be enforced for customers that are not on a TOU schedule? How about customers on TOU rate but wants to be in basic control?
Answer:
If the local utility does not have TOU schedule, to comply with JA12.2.3 the battery storage system should perform a system check on May 1 and November 1 by default. A customer can set the control strategy to Basic Control, regardless of whether a TOU rate is available for the customer; however, this strategy will reduce the benefits of the battery storage for both the customer and the grid and, therefore, is not recommended.