Tesla has started building its next-generation Megapack 3 grid battery, with the first units rolling off the line at the company’s new Megafactory in Brookshire, Texas.

The plant went from groundbreaking to production in 16 months and is designed to build 50 GWh of Megapack 3 a year. That’s the version Tesla says packs roughly 28% more energy into the same footprint as the Megapack it replaces.

Tesla and independent energy firm NatPower have reached a deal to build 25 gigawatt-hours of battery storage in Italy and Britain, the first phase of a program worth up to $5 billion.

Under the multiyear agreement, NatPower will deploy Tesla’s Megapack systems and use Tesla’s trading software to decide when to buy and sell electricity — extending Tesla’s reach deeper into Europe’s fast-growing grid storage market.