Project Sterling Breaks Ground With 509 MW of Solar and 1.4 GWh of Batteries for Tesla

ContourGlobal broke ground on Project Sterling in Mohave County, Arizona, a 509-megawatt solar plant with a 1.4-gigawatt-hour battery that will sell about 90 percent of its output to Tesla.

Construction Review dates the ceremony Oct. 7 in Topock; Electrek's account says Oct. 6. The Tesla power purchase agreement was announced in July. ESS News reported on July 29 that ContourGlobal chief executive Antonio Cammisecra called it "our biggest PPA ever." None of the three reports gives a price or a contract term.

What the plant is made of

The project sits on more than 2,000 acres about 20 miles north of Lake Havasu City. Construction Review lists more than 760,000 solar modules and more than 300 battery containers; the batteries are lithium iron phosphate, per the same report.

Item	Figure
Solar	509 MW DC, 450 MW AC
Battery	360 MW, 1.4 GWh (about 3.9 hours)
Expected output	More than 1.1 TWh a year
Tesla's share	About 1 TWh a year, roughly 90%

The 3.9 hours is arithmetic, 1,400 megawatt-hours divided by 360 megawatts, and none of the reports states it.

The battery is smaller than the output it has to move

The number that matters here is not the 1.4 GWh but what fraction of a day's generation it can hold. An output of 1.1 TWh a year is about 3.0 GWh a day on average, or about 126 megawatts averaged over every hour, which is a 28 percent capacity factor against the plant's 450 megawatts AC. The battery can therefore shift about 46 percent of an average day's output.

That is useful for evening delivery, but it is not firm round-the-clock supply. Electrek says the project will deliver up to 16 hours of clean electricity a day; the other two reports do not state that. It would depend on the battery covering the hours the sun is down, and 3.9 hours at full power is the limit.

Tesla's 1 TWh is about 114 megawatts if it were taken evenly all year. ESS News says the power goes to Tesla's California operations as bundled electricity and renewable energy certificates, delivered through firm transmission rights from Arizona's Western Area Power Administration grid into the California ISO market. None of the reports says how Tesla will use it.

Dates, workforce and money

Off-site work began in June 2025, according to Construction Review, and ContourGlobal acquired the project in December 2024. The access road, the 5.2-mile Polaris Road from historic Route 66, began construction in July 2026.

The report gives September 2026 as the start of construction, first energization in the third quarter of 2027 and commercial operation in the first quarter of 2028, with an average workforce of about 400. ESS News gave only "2028" in July.

ContourGlobal is financing the build privately and has an equity bridge loan from a syndicate of international banks. The amount and the lenders are not disclosed.

How 360 MW compares

For scale, Vermont's home-battery fleet is rated at 110 MW, against 360 MW of batteries at this one site. At the household end, Tesla's 11.52 kW home-backup mode for the Model 3 and Model Y needs a Powerwall 3 and a new order.

What would change my read is the contract term and the shape of the delivery schedule. ESS News describes the 90 percent as as-generated output, which leaves open who controls the battery and when it discharges.

The next milestone is first energization, targeted for the third quarter of 2027, followed by commercial operation in the first quarter of 2028.