Early adopters test-drive markets, and if the curbside view in San Francisco is any indication, electric vehicles could soon be ready to shift to the next gear.

Mark Mendenhall is the general manager of SunEdison North America and he’s seen a notable shift in the number of EVs on the city’s streets since the beginning of the summer. The question now from a national and global perspective is how to turn an uptick in a place known for environmental consumerism into a mainstream market.

SunEdison is one of the companies making headway in tying solar directly into the EV equation. Mendenhall calls it the virtuous cycle, and he defines it as the interplay between electric vehicles, distributed generation power such as solar and emerging storage technologies.

“That combination is another thing that will continue to extend the market for solar well past the time when the utility projects have reached a stable state as opposed to the growing state we’re in today," he said.

Mendenhall sees the growing marriage of EV and distributed solar energy as a "mega-trend" that he says is inevitable. "[The trend] gives us confidence of long-term viability and desirability of solar as an integral solution in energy production,” he added.

Getting there could take a while, though there have been some developments that are sure to strengthen the relationship between solar companies and carmakers. According to Mendenhall, there is a three-pronged approach to getting the virtuous cycle from a conceptual possibility to a market reality.

First, companies producing EVs need to offer as part of their solution a home charging station as well as solar and storage solutions. The next step is for companies that have a sustainability program to encourage their employees to charge plug-in vehicles at work by installing charging stations in the ofifce parking lots. Then for consumers themselves, there needs to be a residential solution that does not shift the cost of their electricity from the pump to the meter. This last part is the time-of-use solution that allows solar generation to feed into the grid during the day at receive peak rates while the vehicle recharges from the grid at night when the cost of the electricity is cheaper. The cars themselves could also act as a storage system.

Many of these individual solutions are coming together in Austin, Texas, as part of the Pecan Street smart-grid demonstration project built around home appliances, consumer devices and electric vehicles. SunEdison recently announced it was joining the project to lead the development of home PV charging systems for the Chevy Volt.

SunPower is another of the leading solar companies that have forged an alliance with a carmaker. In August, Ford announced it had partnered with SunPower for a “Drive Green for Life” program that will use a 2.5-kilowatt rooftop array to charge the new Ford Focus electric vehicle due to hit the streets in 2012.