Tesla plans to have the factory up and running by July 1, 2021 to start building its electric crossover, the Model Y but the process has been slow and complicated by environmental disputes.

A Tesla spokesman confirmed the plant's opening was still scheduled for the summer, adding up to 500,000 Model Y cars could be produced there annually once the factory is completed.

In December, Tesla was told by a court to suspend clearing of a forest at the site of the proposed factory after environmentalists said cutting down more trees could endanger hibernating snakes.

"The German approval framework for industrial and infrastructure projects as well as spatial planning directly contradicts the urgency to plan and realise such projects that is necessary to battle climate change," Tesla said in a letter to a local court seen by Reuters.

Tesla, in the letter dated April 7, said it was "particularly irritating" that there was still no timetable for the final approval of the plant, located in Gruenheide outside Berlin, 16 months after the carmaker applied for it.

It remains unclear when Tesla will receive final approval for the site. A decision by the enviromental agency had been expected months ago.

The letter, first reported by newspaper Frankfurter Allgemeine Zeitung, urges authorities to speed up processes to ensure investors have more transparency about when their investments in climate-friendly technologies pay off.

Red tape in Germany has also been a problem in the area of wind energy expansion, with some projects taking several years from application to realisation.

(Reporting by Nadine Schimroszik and Markus Wacket; Writing by Christoph Steitz; Editing by Bernadette Baum and Jonathan Oatis)