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The Tierra team worked with Sonoma Clean Power, a community choice aggregator (CCA) in California, to develop a grid-interactive heat pump water heater pilot program for residential customers.  This use of distributed energy resources (DERS) is more energy efficient than other baseline water heating technologies. This results in substantial energy savings and reductions in greenhouse gas (GHG) emissions.  Installing grid-connected controls enables these units to be used as a grid resource.  Water heating is a movable load that can be dispatched instantly; such that the HPWHs can be involved in peak-shaving and demand response events.

Tierra’s work with SCP includes the following key components: 

  • Technology Assessment – Evaluate heat pump water heaters from leading manufacturers to identify best-in-class systems.
  • Market Assessment – Profiled water heating market in Sonoma County via interviews and market research to ensure the availability of systems.
  • Potential Quantification – Quantified the estimated energy savings, GHG emissions reduction, and cost savings for the pilot program for three different use case scenarios.
  • Load Shifting and Grid Resource Analysis – Analyzed the load shifting capability and potential benefits to the grid of controlled heat pump water heating. This analysis includes cost savings for customers on standard, time-of-use, and EV-specific rate structures.
  • Implementation Plan Development – Develop a guidance document to assist Sonoma through program implementation, including incentive design, customer segmentation and marketing, delivery strategy, administration, and verification and reporting.


Tierra will deliver the implementation plan and a final report to SCP including the market assessment, technology assessment, and estimated impact potential. Figure 4 shows the annual estimated energy savings per water heater for various fuel types.

Annual Energy Savings per Water Heater over Various Baselines

Annual Cost to Operate Savings

Figure 5 shows the annual cost to operate savings over three baselines:  50-gallon natural gas, 50-gallon electric resistance, and 50-gallon propane, while

Figure 6 summarizes the load shifting analysis per water heater for baseline water heating and three different heat pump water heaters use cases. 

Load Shape Analysis (per water heater)

Strategic EV Pilot Projects, APS

Strategic EV Pilot Projects, APS

A senior staff member is currently leading program design, new program development and implementation support for new strategic electric vehicle (EV) pilots and other electrification projects for Arizona Public Service Company (APS or the Company).  These projects are...

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