The May sales figures for plug-in electric cars continued steady, with the Chevrolet Volt leading the pack at 1,680 deliveries--15 percent up on the April figure of 1,462, but below its all-time March high of 2,289.

The Nissan Leaf logged sales of just 510 units in May, barely starting a recovery from its April low of 370. June Leaf sales remained well below last May's level of 1,142.

Global Leaf production is constrained by limits on fabrication of the car's lithium-ion battery pack, cells for which are shared with an increasing number of Renault models as well. That problem is expected to ease later this year as lithium-ion cell plants in both the U.K. and Tennessee come on line.

As for the for the Toyota Prius Plug-In Hybrid, which outsold both the Volt and the Leaf last month, 1,086 were delivered, for a year-to-date total of 3,638.

For the first five months of the year, Chevy has sold 7,057 Volts and Nissan delivered 2,613 Leafs--giving overall U.S. totals since December 2010 of 15,054 and 12,287 respectively.

2012 Chevrolet Volt

2012 Chevrolet Volt

As for the third plug-in volume car to go on sale in the U.S., 85 copies of the Mitsubishi i electric minicar were sold last month--its best-ever monthly performance, bringing the total sold since last November's launch to an even 300--putting it in the second tier of plug-in sales.

Notably, Ford is expected to record its first Focus Electric sales since January when it releases its hybrid and plug-in sales breakdown on Monday.

The company confirmed that it has sold at least a few electric Focus conversions, though it couldn't confirm that Saturday's unpublicized delivery on Long Island was the very first Focus Electric sold to a retail buyer.

Plug-in carmakers Coda, Fisker, Tesla, and Wheego refuse to report monthly sales--the practice among conventional automakers--and so are not included in our monthly total.

2012 Ford Focus Electric, New York City, April 2012

2012 Ford Focus Electric, New York City, April 2012

There are now approximately 30,000 plug-in vehicles on U.S. roads, four or five times as many as there were a year ago at this time.

And we firmly expect that the electric-car sales rate will continue rise, though it will be slow.

Later this year, a handful of so-called compliance cars from Chevrolet, Fiat, Honda, and Toyota will add to the total, but their numbers will be low.

The Volt, Leaf, and Prius Plug-In will continue to be the top sellers among plug-in electric cars, with 2012 Tesla Model S deliveries starting this month as well.

And the numbers roll silently on.


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