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, either coupled with an on-site PV system or as a standalone system if the building does not have on-site PV due to an exception or being part of a CEC approved community solar program. Battery storage is also a criterion of Exception 5 of the prescriptive PV requirements in section 150.1(c). 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.
A PV size can be specified with the performance approach based on a user-defined target energy design rating (EDR) and a coupled battery storage system with an appropriate battery control strategy. This is a cost-effective strategy for meeting lower target EDRs, that may be required by reach codes, with a smaller, grid harmonized PV system. Various battery control strategies are described in Section 7.5.3 below.
The list of qualified JA12 products can be found here:
https://solarequipment.energy.ca.gov/Home/Index
JA12 specifies that the battery storage system must meet or exceed the following specifications for both the prescriptive and performance approaches:
1. Usable capacity of at least 5 kWh
2. 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
In addition, if using the prescriptive approach, the single AC-to-AC charge-discharge cycle (round-trip) efficiency of the battery storage system must be at least 80 percent.
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 to receive the latest firmware, software, control strategy, and other important updates.
The following requirements apply to all control strategies, including Basic Control, Time-of-Use (TOU) Control, and Advanced Demand Flexibility 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 flexibility 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 Section 7.5.3 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 feature 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. At the time of inspection, the battery storage system shall be installed to meet one of the following control strategies. The battery storage system also shall have the capability to remotely switch to the other control strategies.
JA12 includes four 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 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.
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. 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.
Advanced Demand Flexibility 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 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). 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
Controls for Separate Battery Storage Systems: 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:
1. 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
2. Meet all the demand flexibility control requirements specified in Section 110.12(a) 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.
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 those strategies listed in JA12. 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 in JA12.2.3. This alternative control option shall be accompanied with clear and easy to implement algorithms for incorporation into the compliance software for compliance credit calculations.
Other Requirements
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 UL 1973 and UL 9540. Inverters used with battery storage systems shall be tested in accordance with the applicable requirements in UL 1741 and UL 1741 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 controls listed in Section 7.5.3 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 a capacity of at least 5 kWh, programmed for basic, time-of-use, or advanced demand flexibility control, and is coupled with a PV system; a standalone battery storage system separate from an on-site PV system with control requirements meeting JA12.2.3.4. The PV/storage credit may be used to lower the total EDR score towards a more stringent EDR goal set by a reach code such as a local ordinance. However, the software will only 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 are marginally out of compliance.
The manufacturers must self-certify to the Commission that the battery storage systems meet the requirements of JA12. These include 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 energy associated with round trip charging and discharging, 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 power in the middle of the day when the solar resources are generally plentiful and electricity prices are low. The systems discharge the stored power later in the day, during the peak hours when solar resources are diminished, and electricity prices are high. Battery storage systems have a charge-discharge (round trip efficiency) loss of 5 to 15 percent, depending on the type of battery and the inverter efficiencies. A compliance credit is available because the electricity price differential between the mid-day rate and the peak-hours rate is greater than the battery charge-discharge losses. This means that even with the relatively small loss of energy, it is still cost effective for a consumer to store power generated on-site around mid-day 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 an 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.
Only battery storage systems complying with JA12 requirements are eligible for compliance credit. The requirements ensure the battery storage system remains in a dynamic mode allowing 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 want to be in Basic Control?
Answer:
If the local utility does not have a 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.