Back in June, I wrote about the Volkswagen Golf Twin Drive concept, a plug-in diesel hybrid that VW had planned to test as part of a 20-car fleet in Berlin, ahead of a 2011 model year release. Motor Trend reports that the basic proof-of-concept version using the diesel engine is now officially in testing. But VW engineers now say the production version will be gasoline-powered because emission controls will soon get too expensive for a diesel.

The Golf Twin Drive's electric-only range is expected to be 30 miles, or 10 miles less than the Chevy Volt. "Although VW engineers talk of the Twin Drive's gas engine as a range extender, the gasoline motor is clutched to the wheels. That's quite unlike GM's Volt, where the combustion engine never drives the wheels mechanically."

Some more details: the 350-lb battery pack is by Sanyo, with lithium-ion cells. Capacity is 12 KWh, though it is normally depleted only by 8 KWh in regular driving. The car can accelerate to about 30 mph before the gas engine kicks in, and there's 40 hp of regenerative braking. Reverse is electric-only. An interesting take on the whole concept, even though it's a bit disappointing that the diesel hybrid didn't work out (could you imagine the fuel economy?)