The primary function of the battery storage system is to grid harmonize the onsite PV system with the grid, to bring maximum benefits to the grid, environment, and the occupants.
Grid Harmonization: For the purpose of Building Standards, grid harmonization is defined as strategies and measures that harmonize customer owned distributed energy resources assets with the grid to maximize self-utilization of PV array output, and limit grid exports to periods beneficial to the grid and the ratepayer. This is done by charging the battery from the PV system when there is limited electrical load at the building and the cost of electricity is low in midday, and discharging when the cost of electricity is high, usually in the late afternoon and early evening hours.
Battery storage system is available as a compliance credit in the performance compliance method and also as Exception 6 to the prescriptive PV requirements in section 150.1. In all cases, the battery storage system must meet all applicable requirements in Joint Appendix JA12 and be self-certified to CEC by the manufacturer as a qualified product.
Coupling a PV system with a battery storage system and appropriate control strategy described in Section 7.5.2 below, allow reaching specific target Energy Design Rating Targets (EDR) with a smaller PV system than otherwise would have been possible. This is a useful and cost effective strategy for meeting lower target EDRs that may be required by reach codes, with a smaller and grid harmonized PV system.
The list of qualified JA12 product list can be found here:
http://www.energy.ca.gov/title24/equipment_cert/
JA12 specifies that the battery storage system must meet or exceed the following performance specifications:
a. Usable capacity of at least 5 kWh.
b. Single Charge-discharge cycle AC to AC (round-trip) efficiency of at least 80 percent.
c. 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 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 receive the latest firmware, software, control strategy, and other important updates.
The following JA12 requirements apply to all control strategies, including Basic Control, Time-of-Use (TOU) Control, and Advanced Demand Response Control, described in section 7.5.3 below:
1. The battery storage system shall have the capability of being remotely programmed to change the charge and discharge periods.
2. During discharge, the battery storage system shall 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 response signal from the local utility or a third-party aggregator.
3. The battery storage system shall 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 control strategy. The device must have the algorithm that would enable export to be built in at the time of installation. It can be in the off mode and be turned on later with a remote signal.
4. The battery storage system shall perform a system check on the following dates, to ensure the battery is operating in one of the control strategies listed section 7.5.3 below:
a. Within 10 calendar days before the onset of summer TOU schedule, and
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 1 May and 1 November.
JA12 includes three control strategies that are designed to encourage charging the batteries when electricity prices are low, generally in the middle of the day when solar resources are plentiful and demand is low, and discharge the batteries later in the day when demand is high and solar resources are diminished:
Basic Control: Designed as a simple control that can be employed as the default control in the absence of TOU or Advanced Demand Response Controls, or where communication between batteries and outside parties are not possible. This control strategy does not allow discharging into the grid. 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 photovoltaic system when the photovoltaic system production is greater than the on-site electrical load. The battery storage system shall discharge only when the photovoltaic system production is less than the on-site electrical load.
Time-of-Use (TOU) Control: 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. This control strategy does not allow discharging into the grid. To qualify for the TOU Control, the battery storage system shall be installed in the default operation mode to allow charging from an on-site photovoltaic system. The battery storage system shall begin discharging 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.
Advanced Demand Response Control: 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 is the only control strategy that 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. To qualify for the Advanced Demand Response 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 responsive control requirements specified in Section 110.12(a). Additionally, 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
Alternative Control Approved by the Executive Director: 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 ones listed above in Section 7.5.2. 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, and/or other strategies that achieve equal or greater. 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:
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).
Enforcement Agency: The local enforcement agency shall verify that all Certificate of Installations are valid. The battery storage systems shall be verified as a model certified to the Energy Commission 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 control listed in Section 7.5.2 above. The programmed control strategy at system final inspection and commissioning shall be the strategy that was used in the Certificate of Compliance.
Example 7-10 Battery Storage Credit
Question:
Can you explain the battery storage credit requirements and how to comply with them?
Answer:
The performance path allows a compliance credit for a battery storage system with at least a 5 kWh capacity that is coupled with a PV system; standalone battery storage systems are ineligible for a compliance credit. The PV/storage credit may be used to lower the EDR score towards a more stringent EDR goal set by a reach code such as a local ordinance; however, the software will allow a portion of the available credit to be used for efficiency measures tradeoff; this is a modest credit that can be used to achieve compliance in buildings that have marginal difficulty achieving compliance.
The manufacturers must self-certify to the Commission that the battery storage systems meet the requirements of JA12. 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 Commission. The self-certification form may be downloaded from the Commission’s website:
Example 7-11 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 Commission provide a compliance credit for 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. A compliance credit is available because 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 compliance credit of a battery storage system coupled with a PV system, the Energy Commission’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 JA12 (JA12). 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 homeowner, the grid, or the environment.
Example 7-12 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 1 May and 1 November 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.