California Community Choice Aggregator (CCA) Clean Power Alliance (CPA) last week (8 December 2025) moved one step closer to executing agreements for offtake with two companies developing innovative thermal battery storage projects.
The two separate agreements, which are a result of the CCA’s “Innovation Solicitation,” were discussed during CPA’s most recent Energy Planning and Resources Committee meeting.
CEO of CPA, Ted Bardacke, described the solicitation as a way of finding out what the “next big thing is” within the energy storage space, whilst also enhancing the CCA’s portfolio of assets in the future.
Broad eligibility criteria
First launched in May 2025, CPA received four proposals for the first iteration of its innovation solicitation, with two proposals being long-duration storage projects and two others based around carbon capture technology.
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The eligibility criteria for the solicitation were broad, with CPA looking for emerging renewable technologies capable of providing energy storage capacity, sized between 1MW-200MW in the California Independent System Operator (CAISO) region for a period of 5-20 years.
Although not offering fully fledged power purchase agreements (PPAs), the solicitation provides developers with a letter of support of a conditional shortlist agreement. For developers unsure of pricing and commercial operation dates, they can opt for a letter of support. Under this arrangement, CPA agrees to consider the project in future RFOs once certain criteria are met.
For developers more certain over project specifics, they can opt to execute a conditional shortlist agreement with CPA. Under this arrangement, developers must commit to a firm price and provide collateral to CPA, which, upon receiving this, agrees to shortlist the project for a PPA as part of a future RFO.
At the recent meeting, John McNamara, CPA Director of Structured Contracts, described the technology behind the two long-duration projects as showing great potential. However, with both being at the early stages of commercialisation, McNamara expressed caution due to the uncertainties which still surround the technologies.
Photon Vault
As outlined during the recent meeting, CPA has negotiated a conditional support agreement with San Ramon, California-based startup Photon Vault, for a hybrid thermal energy storage system located in Kettleman City, Kings County.
The project will pair a 25MW solar facility with a 5MW/120MWh battery storage system utilising the company’s patented thermal energy storage system.
Unlike traditional lithium-ion-based batteries, which store energy in chemical form, Photon Vault’s proprietary technology stores solar energy as heat within composite sand bricks.
The firm’s chief commercial officer (CCO) John Langhus gave Energy-Storage.news more details on its tech in May 2024, explaining that it features a hybrid charging process using first electricity then heat. The heat comes from the solar thermal tech, which enables it to make up for lost electricity during its charge-discharge cycle.
Although untested at utility-scale, Photon Vault has built a 10kW prototype model and is targeting an ambitious 90% round-trip efficiency rating.
As reported by Energy-Storage.news, the company last year submitted a proposal for an RFI issued by Microsoft, Google and Nucor utilising its proprietary technology, although it ultimately wasn’t selected.
Despite not revealing the contract price, McNamara revealed that it was similar to that of geothermal resources. If the agreement moves forward, the project will provide resource adequacy (RA), energy and renewable energy credits (RECs) from the second quarter of 2029 for a period of 20 years.
As part of its market entry strategy, Photo Vault hopes the agreement will serve as an opportunity to demonstrate the viability of its technology in California.
Exowatt demonstration
Additionally, as part of the solicitation, Miami-headquartered startup Exowatt sought a letter of support from CPA for a demonstration-scale development utilising its P3 thermal battery storage system.
Located in Calexico, Imperial County, the project will be paired with an existing renewable energy development owned by MN8 Energy and provide 10MW/80MWh of capacity for a period of 20 years.
The P3 system captures solar energy and stores it within a thermal battery, which is then converted into electricity and discharged when needed using a heat engine. It launched a modular configuration of its solution in September 2024 which it said was built for the 24/7 needs of data centres.
As reported by Energy-Storage.news, Exowatt hopes that it will eventually be able to offer electricity from this system for as low as US$0.01/kWh.
In its position as technology provider and systems integrator, Exowatt said the letter of support would hopefully strengthen its position for land expansion negotiations, attract financing partners and increase technology credibility.
MN8 will lead development and site operations, which are also slated for 2029.
During the recent meeting, CPA’s Energy Planning and Resources Committee unanimously approved both the letter of support and conditional support agreement. Following this initial solicitation, CPA is currently receiving proposals for a second round, which closes for submissions in February next year.
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