RTF analysts developed estimates of per unit technical potential for demand response for Connected level 2 Electric Vehicle (EV) Chargers. Connected level 2 chargers may reduce charging output power in response to a DR signal with a typical range of ~3-7kW per unit maximum Demand Response potential during steady state charging. Chargers can be throttled between 100%-0% output power. Chargers currently predominantly communicate via Wi-Fi or cellular service.
The primary components influencing this per unit potential are the vehicle itself, specifically the vehicle maximum power acceptance (kW), above which the vehicle will not accept a higher rate of charge. Potential impact is also affected by the charger's maximum output capacity (kW), the typical range of residential level 2 AC 240V charger output power is 3-7 kW, and finally by the charger throttled output capacity (%). A charger's throttled output capacity will reduce the per unit DR potential below 100% of 3-7kW.
Data sources used for this analysis include publicly available regional electric vehicle registration and vehicle maximum power acceptance datasets paired with literature reviews of electric vehicle charger studies, and interviews with electric vehicle charger subject matter experts and programs.
The per unit potential is calculated with the following governing equation:
Residential Level 2 AC Charger Per Unit DR Potential=Steady State Charger Output Capacity (kW)*Charger Throttled Output Capacity (%)
Level 2 EV Charger DR Workbook RTF Presentation DR Subcommittee Presentation DR Subcommittee Notes
Key Assumptions
The governing equation for estimating demand response impact is:
Residential Level 2 AC Charger per Unit DR Potential=Steady State Charger Output Capacity (kW)*Charger Throttled Output Capacity (%)
Due to lack of data, the RTF made the following assumptions:
- Steady State Charger Output Capacity: This depends on vehicle type and charger sizing practices. The RTF used registration weighted vehicle maximum power acceptance to estimate this value. Additional information about end-user charger sizing practices would help improve this assumption.
- Charger Throttled Output Capacity: This depends on how programs intend to administer demand response to customers. As the RTF does not have insight on the regionally preferred program approach, the RTF modeled ranges from 0% to 100%, in 25% increments.
Expert opinion:
To support the research, RTF analysts discussed this DR mechanism with regional DR and EV experts on the RTF's Demand Response Subcommittee. The group went over data limitations, vetted the analysts approach for calculating potential and provided additional references and contacts to further support this work. A number of important clarifications about the scope and context of this estimate came out of this conversation. The potential DR impact that the analyst arrived at through this work is a maximum per unit potential estimate predicated on the assumption that the energy technology is installed first and then the DR is added on top. The specificity of this number is due to the constraints of the RTF's scope when exploring DR. This analysis will eventually be passed to the Council's Demand Response Advisory Committee and used as the develop supply curves for the 2021 plan. This feedback was integrated into the analysis and the eventual presentation to the whole RTF.
Limitations:
There remain some outstanding questions about this analysis primarily due to unavailable data. RTF analysts brought these questions to the Demand Response Subcommittee for their expert take but there are still challenges with the data currently available. There is persistent uncertainty surrounding the existing fleet, more data to inform a broader more granular view of Pacific Northwest vehicle registrations would benefit this estimate. There are also questions about charger sizing practices, whether customers typically under, match, or oversize their EV chargers relative to their vehicles, and about connected charger equipment and installation costs.
RTF Decision:
At the February meeting the RTF approved the per unit demand response savings estimates for Networked Residential Level 2 AC EV Chargers. Acknowledging that these per unit savings estimates are intended to reflect the maximum per unit potential for Residential Level 2 AC EV Chargers, assuming the energy efficient option is already installed. They recognize that additional factors will need to be applied to these estimates for them to represent utility or regional potential of demand response.