Tesla Signs Deal for 90% of Arizona Solar-Plus-Storage Project Output

Tesla signed a long-term agreement on July 28 to purchase about 90% of the electricity produced by Project Sterling, a utility-scale solar and battery-storage development in Arizona, giving the company access to approximately 1 terawatt-hour of power annually as its electricity requirements continue to grow.

The Tesla Arizona solar storage deal covers output from a planned facility combining 509 megawatts-peak of solar generation with a 360 MW, 1.4 GWh battery system capable of operating at full rated output for four hours. Construction is scheduled to begin in the third quarter of 2026, with commercial operation targeted for early 2028.

ContourGlobal describes Project Sterling as a 450 MWac hybrid renewable-energy facility with expected annual production exceeding 1.1 TWh. The agreement would leave the developer with approximately 10% of the plant’s output available for other transactions or market sales.

The agreement combines a large solar plant with four-hour storage

Project Sterling’s battery system is designed for 360 MW of discharge capacity and 1.4 GWh of stored energy. Dividing the energy capacity by the power rating gives the system a duration of approximately four hours at full output.

That duration could allow the project to continue delivering electricity after solar production falls in the evening, shift generation away from low-value daytime periods, and reduce short-term fluctuations in the facility’s grid deliveries.

The battery does not make the project a continuously available 24-hour power source. Its ability to meet a buyer’s demand will depend on solar conditions, charging strategy, contractual delivery requirements, transmission availability, and the amount of stored energy retained for later periods.

Investor’s Business Daily reported that the contracted volume represents roughly 90% of Project Sterling’s expected annual output. Financial terms and the length of the power purchase agreement were not publicly disclosed.

Project Sterling will connect through the Western grid

The project is expected to interconnect with the Western Area Power Administration system and hold point-to-point transmission rights providing access to the California Independent System Operator market.

That structure may allow the project’s output to support electricity demand beyond the immediate location of the generating facility. Actual delivery will depend on the terms of the transmission rights, scheduling arrangements, grid congestion, and the point at which Tesla takes contractual delivery.

The agreement does not necessarily mean that every electron generated at the Arizona site will physically serve a specific Tesla factory or computing facility. Corporate power purchase agreements can combine physical electricity deliveries, renewable-energy attributes, financial settlements, or several of those elements.

Neither ContourGlobal nor Tesla identified the specific operations that the agreement will support.

The purchase adds to Tesla’s utility-scale energy procurement

The Sterling transaction was announced alongside a separate agreement under which Tesla will purchase the full output of Zelestra’s planned 140 MWac Lumen Farm solar project in northeast Texas.

Business Insider reported that the two agreements cover approximately 600 MW of planned utility-scale solar capacity. The contracts indicate that Tesla is becoming a significant buyer of renewable electricity in addition to manufacturing solar and battery products.

Tesla has not publicly assigned Project Sterling’s output to a particular vehicle plant, battery factory, artificial-intelligence computing system, or other operating site. It would therefore be speculative to claim that the agreement directly powers any one facility.

Why the battery component matters

A solar-only agreement can provide substantial annual energy but may not align with a buyer’s hourly demand. Solar production is concentrated during daylight hours, while factories and computing facilities may operate continuously.

Four-hour storage can improve the match by shifting part of the daytime output into evening hours. It can also reduce abrupt changes in the project’s output and potentially provide grid services, depending on the interconnection agreement and market participation structure.

The battery’s full role remains unclear. ContourGlobal has not publicly disclosed how much storage capacity will be reserved for Tesla, how frequently the system is expected to cycle, or whether part of the battery will participate independently in wholesale markets.

What remains uncertain

Project Sterling remains under development. Its construction and 2028 operating targets are subject to permitting, equipment procurement, interconnection work, financing, construction performance, and other development risks.

The parties have not disclosed the contract price, duration, settlement structure, delivery point, escalation provisions, or remedies if the project is delayed.

The announcement also does not establish that the agreement will directly reduce Tesla’s electricity costs. The financial effect will depend on the contracted price compared with future market rates and the value of any associated environmental attributes.

What happens next

ContourGlobal plans to begin on-site construction during the third quarter of 2026. Development milestones to watch include final financing, equipment procurement, interconnection construction, transmission arrangements, and confirmation of the project’s commercial operation date.

Additional disclosures may clarify which Tesla operations are associated with the purchase and how the battery will be dispatched relative to the solar facility and the wider Western electricity market.

Microgrid Media Editorial Desk

The Microgrid Media Editorial Desk reports on microgrids, energy storage, grid modernization, data center power demand, distributed energy resources, and energy policy. Reporting published under the Editorial Desk byline is developed from primary regulatory records, utility filings, government documents, company disclosures, and independently verifiable sources, and is reviewed under Microgrid Media’s editorial standards.

Editorial oversight: Jonas Muthoni, Editor-in-Chief