Dutch startup Lightyear plans to launch an electric car powered by a combination of solar panels and batteries. That car isn't quite ready for production yet, but Lightyear is testing its solar tech on modified Tesla Model 3 sedans.

Lightyear has two of these Tesla research vehicles, numbered 005 and 006, as well as a solar-equipped Volkswagen Crafter van. These vehicles started testing this week on public roads around Lightyear's hometown of Helmond, The Netherlands, the company said in a press release.

As the cars are driven, they will measure solar yield to find out how much usable energy the roof-mounted panels are generating. Tests will also provide real-world data on vibration, shock absorption, and waterproofness, according to Lightyear.

By the end of 2020, Lightyear plans to complete a validation prototype of its Lightyear One production model. Dubbed 007, it will marry the solar roof with a production-spec powertrain and battery pack.

Tesla Model 3 modified by Lightyear for solar roof testing

The startup recently signed an agreement with Royal DSM to produce the solar roof for the One, which is scheduled to launch in 2021.

Lightyear was formed by former members of a World Solar Challenge team and aims to bring some of that expertise to a production vehicle.

Use of solar power aims to "leapfrog the grid" by emphasizing efficiency and solar and easing requirements on plugging in and high-power DC charging. Lightyear previously said the solar roof could account for 70% to 90% of annual mileage, minimizing the need for plugging in—a claim that sounds like a serious engineering challenge even given improved solar efficiencies.

While other automakers have experimented with solar roofs, Lightyear claims its car is optimized for that. The startup also claims the Lightyear One will be the most aerodynamic car on the market, with a drag coefficient (Cd) below 0.20.