Royal Dutch Shell Plc (NYSE: RDS.A) has agreed to buy German residential solar battery maker sonnen, as the oil and gas major expands its electricity business in its bid for a bigger role in the global transition to low-carbon energy.

Sonnen, which has 40,000 battery systems worldwide and in 2017 had sales of 65 million euros (US$73 million), is the German market leader in home storage batteries and has expanded into electric vehicle charging systems.

Regulatory approval and completion of the transaction, involving Shell New Energies, was expected in the first quarter of 2019, a sonnen spokesman said, without giving a value.

Sonnen would continue to operate from the Bavarian town of Wildpoldsried and its top management would stay on, he said.

Germany has 1.5 million solar systems whose subsidized sales tariffs are due to be phased out in coming years. By acquiring batteries, householders can store home-produced power and use it for themselves or sell it to the grid.

Shell, the world's second-largest listed oil and gas producer, has accelerated investment in renewable energy and power markets, betting on a rapid rise in electricity demand due to electric vehicle use and a switch to cleaner energy sources.

It has acquired vehicle charging technologies, solar power producers and retail energy supplier First Utility. Shell injected cash into sonnen last year to help it grow.

Sonnen's existing investors, including GE Ventures and European private equity investors, will be bought out. (US$1 = 0.8870 euros)