Ford estimates that motorists could save approximately $500 (about £300) per year in energy bills if the company’s conceptual solar-powered C-Max was ever made viable for production.

The Ford C-Max Solar Energi Concept, unveiled at the International CES technology expo in Las Vegas this week, is based on the plug-in hybrid version of the Blue Oval’s medium-sized people carrier currently on sale in the US.

The roof features a 1.5-square-metre array of 275W photovoltaic cells supplied by Ford’s solar technology partner, SunPower.

To recharge, the car sits under a canopy of approximately 15-20 square metres in size – slightly larger than the average parking space. It acts as a Fresnel lens, concentrating more of the sun’s rays onto the Ford’s solar panels.

Ford says the car uses existing autonomous driving technologies, such as the auto-park function that is already a feature of the C-Max, to move a few metres during the day to track the sun’s movement through the sky.

Using this method, Ford says the C-Max’s lithium ion batteries can be recharged in about eight hours, based on the average amount of sunlight received by US cities.

Besides the roof-mounted solar array, the concept has not required significant mechanical tweaking from the existing C-Max PHEV. The solar array weighs about 2kg in total, so does not add significant weight to the vehicle.

David McCreadie, Ford Manager of Electric Vehicle Infrastructure and Smart Grid, explained that the software controlling the lithium ion battery management might need to be reconfigured to optimise recharging. Ford’s boffins will delve more deeply into the technology later this year.

“Ford has not come out and said ‘we’re going to turn this into a production vehicle’, but after CES has ended we’re going to start a testing phase to look at some of the finer details that we’re still working on," said McCreadie. "We’re moving in the direction of getting this to be fully viable.

“We’re really excited about it because it is essentially taking a car off the grid entirely. Our data suggests up to 75 per cent of journeys could be undertaken using energy sourced from solar. That’s the percentage of journeys that our current plug-in hybrid customers are undertaking in electric mode.”

McCreadie also said it was too early to consider the cost of a production version of the solar-powered C-Max and the Fresnel lens canopy, but he believed the vehicle could provide an attractive financial benefit.

“If you were to plug your car into the mains electricity supply during daytime hours instead of using the sun, you’d end up paying between one and three dollars per day to do that," McCreadie added. "You could avoid spending that by charging using the sun, and you can start to envisage a value proposition where it is worth maybe $500 per year in electricity costs.”

McCreadie explained how several factors had combined to make it feasible to explore solar energy as a potential power source at this point in time.

“The first factor is the ongoing proliferation of electric vehicles on our roads, specifically the storage batteries which those vehicles have on them, because storage is essential for solar energy to be working at its optimum.

“The second factor is that the price of solar panels has started to come down, which is making it viable to take them off the roofs of homes and put them on the roofs of cars.

“The third aspect is the technology we have on our car which enables it to autonomously move and therefore reposition itself to always keep the sun on the roof,” he said.