FRANKFURT, Nov 19, 2008 (AFP) - German solar power group SolarWorld caught the auto industry by surprise Wednesday when it unveiled what it said were preparations for a takeover of troubled GM's German car division Opel.

SolarWorld said it would offer a billion euros (1.26 billion dollars) for Opel and create the "first green European automotive group" in a move that had analysts reaching for calculators and scratching their heads.

A SolarWorld statement said it would offer 250 million euros in cash and 750 million euros in bank credits for Opel's four auto factories and a research centre in Ruesselsheim, western Germany.

It attached several conditions to the deal however, including a complete split of Opel from GM, which is threatened with bankruptcy, and compensation payments of 40,000 euros per Opel worker, which would total roughly one billion euros.

SolarWorld, which also sought a liquidity guarantee for Opel from the German government, did not say who it expected to pay the compensation.

Opel was not in a position to immediately give a reaction, a spokeswoman told AFP.

A stock trader told Dow Jones Newswires: "At first I checked to see if today is April 1," or April Fool's Day, and Commerzbank analyst Robert Schramm added: "My first reaction to the news was big amazement."

SolarWorld shares plunged by 14.60 percent to 13.75 euros in afternoon trading on Frankfurt's TecDax index of high-technology issues.

The index had fallen by 5.65 percent overall.

But another stock dealer said the bid was not totally out of the question, "because Opel merely needs a white knight in order to get rid of the Americans."

A so-called white knight is an investor that saves a company from dire financial straits or a hostile takeover.

It was not clear how SolarWorld intended to finance its bid however, and an analyst said he did not know who could pay the compensation in question because "General Motors certainly can't."

Another trader added that the deal "would be good for SolarWorld's cashflow, but strategically impossible to assess."

SolarWorld said it would keep making Opel brand cars in the plants and would "offer electric drive and hybrid drive vehicles in the future."

The statement quoted chairman Frank Asbeck as saying: "The group has already been working for some years on the development and testing of electric drive vehicles that are propelled by solar energy and that even participate successfully in motor racing."

SolarWorld employs 2,000 workers, while Opel's German staff numbers about 26,000.

The German automaker has been hit by slumping sales and financial problems at its parent company, and has asked the German government for loan guarantees if it can no longer obtain GM financing.

The Frankfurter Allgemeine Zeitung newspaper quoted Opel directors Wednesday as saying that the company will cut output next year and is mulling a 30-hour work week.

In Washington, GM chairman and chief executive officer Rick Wagoner joined executives from major rivals Ford and Chrysler to plead for 25 billion dollars in US government-backed loans, warning that otherwise the economy will face a "catastrophic collapse."

In Strasbourg, eastern France, EU Industry Commissioner Guenter Verheugen said that the exceptional circumstances in which Opel finds itself justify "exceptional measures," though he was likely referring to the company's request for state loan guarantees rather than to SolarWorld's takeover proposals.