Rooftop

A new market emerges: Retrofitting batteries to existing residential solar

A new market emerges: Retrofitting batteries to existing residential solar
(Courtesy: sonnen)

Peanut butter and jelly. Football and fall. Solar and batteries.

Some things just go well together.

Yet if a customer doesn’t purchase that clean energy combo outright (sadly, this site doesn’t cater much to sandwiches or sports) is there hope for pairing up down the road? A residential solar and battery installer and a virtual power plant (VPP) company have announced the initial results of a new program indicating that the answer is an emphatic “yes”.

ES Solar and sonnen say they’ve already sold more than 18 MWh of sonnen retrofit energy storage systems through their “Go Back” initiative, an innovative VPP business model enabled by Rocky Mountain Power (RMP) which targets existing residential solar customers. The program allows Utah homeowners with existing solar installations to upgrade their system to include a grid-interactive smart sonnen battery, designed to harness solar and harmonize it with greater grid operation. Customer benefits include a substantially higher upfront Wattsmart Battery incentive from RMP, an annual bill credit for grid services, proactive backup power, and lower CO2 emissions, the companies say. RMP customers who have installed solar before September 1, 2021 may qualify for an upfront incentive of $600/kW on their battery system by enrolling in Wattsmart. Wattsmart customers installing both new solar and a new battery may qualify for $400/kW.

“Existing solar customers are very interested in adding an intelligent energy storage system to their solar array, not just for backup power, but for the other benefits that a storage system can provide,” said Zach Randall, VP of sales at ES Solar. “The Go Back initiative has become a game changer for us, as it continues to drive the majority of ES Solar’s monthly battery sales.”

The Go Back initiative is a part of Rocky Mountain Power’s Wattsmart Program, one of the most robust VPPs in the country. Launched in 2020, WattSmart utilizes 3,200 customer-owned batteries with approximately 20 MW of load available for real-time dispatch. Rocky Mountain Power expects to onboard 2,000 additional batteries with 10 MW of capacity in 2024. The batteries are autonomously managed by the energy management system used by Rocky Mountain Power’s parent company, PacifiCorp, and are used daily to reduce overall system demand. The RMP Wattsmart Distributed Battery Grid Management System (DBGMS) VPP has now grown to over 40MWh of energy capacity, a substantial portion of which was sold by ES Solar. RMP is the only vertically integrated utility in the U.S. that has directly integrated a specialized behind-the-meter battery VPP into its grid operating system (without a distributed energy resources management system (DERMS) solution) while dispatching a battery fleet every day.

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The Go Back program is a sharp contrast to the standard “new solar new battery” Wattsmart business model, but it appears to have tapped into an eager market. ES Solar estimates that more than 75% of its 2024 sales are via the Go Back Program, resulting in 200-500 sonnen battery installations in Utah each month – unprecedented growth for a specific use case that has rarely been focused on by major solar contractors, the companies contend. ES Solar says it is seeing a 95% battery attachment rate for new solar sales, and more than 90% of these customers enroll in the Wattsmart VPP.

Rocky Mountain Power has approximately 80,000 solar customers across its service territory that do not have smart grid interactive batteries. Over the next five years, ES Solar intends to “firm up” 40% of all residential solar arrays in Utah with retrofit sonnen VPP batteries, an estimated 32,000 homes. This would effectively convert a rooftop solar fleet from intermittent generation to a firm, dispatchable grid asset.

“Through their Wattsmart Go Back expansion, ES Solar has established a new, replicable business model and sales marketing strategy designed to inspire the revolution away from solar alone and into grid-interactive and responsive solar that supports, rather than becomes a nuisance to, society’s energy grid,” said Blake Richetta, chairman and CEO of sonnen USA. “ES Solar’s work in the RMP service area to date is an ideal case study which illustrates the potential national impact and scalability of a grid harmonizing, as opposed to a grid defecting business model. Using batteries to firm existing solar and enable the implementation of flexible DER systems and VPPs is the key to supporting genuine energy transition for humanity.”

ES Solar believes its VPP-focused business model can be scaled and applied in other markets, like California, where smart grid interactive batteries can firm solar and support a reliable and sustainable grid infrastructure alongside California’s Net Billing Tariff (NBT). At its current growth rate, ES Solar’s VPP business model innovations are likely to expand into regions across the U.S. over the coming years, the company says.