https://en.wikipedia.org/wiki/Nuclear_power_in_Germany

In 2002, under the Red-Green government of Gerhard Schröder, the "Act on the structured phase-out of the utilization of nuclear energy for the commercial generation of electricity" took effect, following a drawn-out political debate and lengthy negotiations with nuclear power plant operators. The act legislated for the shut-down of all German nuclear plants by 2021.

So when the Greens first came to power in the Schröder administration of 1998 they achieved their major political goal for which they had fought for 20 years: abandoning nuclear energy in Germany.

The Greens wanted swift abandoning of nuclear energy in Germany already in the 2000s, but the government would have to compensate the nuclear power plant owners for the costs of building the nuclear power plants (multiple bilion DM in the 2000s, most of the nuclear power plants were still new and the costs of construction were still not payed by the electricity). Therefor the Government negotiated with each electric utility company a rest quota of nuclear produced electricity and as a result nuclear electricity production would continue until 2021 (with a planned decrease in production every year).

In 2007 amid fears that Russian energy supplies to western Europe might not be reliable, conservative politicians, including Chancellor Angela Merkel and Economics Minister Michael Glos, continue to question the decision to phase out nuclear power in Germany.

In September 2010, German government policy shifted back toward nuclear energy and the government wanted to extend the use of nuclear energy in Germany.

After the 2011 Fukushima nuclear disaster, the conservative German government reversed it's nuclear position and returned back the original 2002 Red-Green nuclear phase-out time table.

The current conservative German government under Merz again reversed it's nuclear position towards a more pro-nuclear stance, but decided that it's too expensive to revive the nuclear industry.

I would not say that the current German Green party are environmentalists, currently they are mostly renewable industry lobbyists. CDU has connections to German heavy industry. SPD had strong connection to coal mining regions and coal unions. FDP connections to German car manufacturing.

Germany had enough power to close down all nuclear power plants, because older coal power plants when taken offline have been carefully mothballed (preserved for later restart, when necessary).

In contrast the 2002 German nuclear law (deutsche Atomgesetz (AtG)) requires that nuclear power plants have to be started to be dismantled immidiately after shutting down. There are no technical reasons why nuclear power plant after shutting down, taking out nuclear fuel and decontamination (as is done regularly during maintanance) could not be preserved for 10, 20 or 50 year (you have to mostly periodicaly repair the roof, repair the paint and guard the buildings, e.g. it can be done without large costs).