Nuclear. The Schroeder government initiated the German nuclear phase-out (which was later reverted and re-reverted by Merkel). But rumor has it that the nuclear phase-out wasn't only motivated by the greens being anti-nuke, but also by Schroeder being interested in pushing gas instead.

Btw., after his chancellorship, Schroeder got a post at the Russian state gas supplier Gazprom.

Germany's gas problem wasn't purely about energy, but the availability of feedstock to produce chemicals.

Natural gas, being 90% methane, is a valuable source of hydrogen.

That's just the energy part of it, German heavy industry needs petroleum-derived products as raw materials.