Toyota is trial-testing a Prius Prime equipped with high-efficiency solar batteries

Working with NEDO (New Energy and Industrial Technology Development Organization) and Sharp, and aiming to create an onboard solar battery panel that can increase efficiency and range in its electrified vehicles, Toyota has been road-trialing a Prius Prime PHV equipped with a solar charging system using modularized Sharp batteries. The new system increases solar conversion efficiency by 34%.   

By John Coulter, CMO, Current EV / September 2019   

The Sharp high-efficiency solar batteries in the Prius Prime have achieved a power generation output of around 860 W, which is approximately 4.8-times higher in comparison with the commercial model Prius PHV. In addition to substantially boosting its power generation output, the demo car employs a system that charges the driving battery while the vehicle is parked and also while it's being driven, a development that is expected to lead to considerable improvements in electric-powered cruising range and fuel efficiency.   

Translated into battery range, Toyota’s demo vehicle can drive for up to 27.6 miles, versus a current version of the Prius Prime that offers a small solar panel as an option, which generates only 3.8 miles before converting to gas. That model is only available in Japan. In addition to a significantly increased range, Toyota’s new solar-powered Prius Prime will be able to recharge its batteries while driving, as well as charging while parked.   

Increasing BEV range makes sense for Toyota, a car manufacturer which has sold millions of plug-ins. As indicated by the National Household Travel Survey (hts.ornl.gov), cars in the USA are driven 30 miles a day on average. If it reaches production, Toyota’s new solar-powered Prius Prime could provide significant savings for daily commutes. With BEV electric-only ranges currently averaging around 26 miles, the solar-powered Prime would have major consumer appeal. If the car is driven four days a week for around 27 miles a day, there will be very little need to plug it into an outlet; a great selling point for consumers who don't normally drive far from home.  

From a Toyota press release: “Toyota plans to conduct the trials under various driving conditions in Toyota City, Aichi Prefecture, Tokyo, and other areas. Various data, including the power generation output of the solar battery panel and the amount the drive battery is charged, will be obtained and verified, and then used in the development of an onboard solar recharging system. Toyota plans to share a selection of trial data results with NEDO and Sharp. The PV-powered Vehicle Strategy Committee (PV: photovoltaic), sponsored by NEDO and other entities will evaluate the benefits based on improvements in CO2 emissions reductions and convenience, such as the number of times a vehicle requires recharging. The goal is to contribute to the creation of a new solar battery panel market, including the transport sector, and find solutions for energy and environmental issues.”   

Meaning: Toyota is still considering it’s options. The car's greatest potentials will be, of course, in markets with sunny climes, such as California and Western China. Toyota and NEDO are evaluating whether or not the car is suitable for other cities, such as Tokyo, as well, where the Prius Prime is a big seller.   

Other solar-powered cars: Toyota's Prius Prime equipped with Sharp’s world-class, high-efficiency solar battery cells is being developed in the wake of two European solar models with long-range solar capabilities; the Dutch Lightyear One and Germany’s Sion. Lightyear One was unveiled in the Netherlands on June 35, 2019. It’s fitted with a solar roof and battery system which provides a 450-mile range. The Sion is a solar-powered, fully electric car with a 35kWh battery that can be charged by the electric grid or the car’s own solar cells. The 5-door, 5-seat car has a 158-mile range. Its solar panels add 21 additional miles of range per day. (See articles about both these cars on the CURRENT EV blog).

Hyundai's 2020 Sonata will have a solar roof that adds approximately 800 extra miles per year. (See the article on Page 2 of the CURRENT EV blog).   In July 2018, Chinese solar panel manufacturer Hanergy signed a strategic cooperation agreement with Bolloré to design, manufacture and produce solar electric vehicles equipped with lithium-ion batteries to consumers in China. Hanergy also operates as an original equipment manufacturer, manufacturing thin-film components for various companies in the automotive industry. It cooperates with Audi, FAW-Volkswagen, Guangqi Honda, Tesla, and Bolloré, as well as domestic car companies like BAIC. All these companies have heavily invested in creating solar panels to add to their automotive lines. Hanergy says that five to six hours of sunlight should allow the thin-film solar cells on the cars it's designing to generate between 8-10 kWh of power a day, allowing the car to travel about 80 km (50 mi) on solar power alone. Maximum range is expected to be about 350 km (217 mi).   

Solar cars combine technology typically used in the aerospace, bicycle, alternative energy and automotive industries. Most solar cars have been built for the purpose of solar car races. Unlike solar thermal energy which converts solar energy to heat, the photovoltaic cells used in cars directly convert sunlight into electricity. When sunlight (photons) strike PV cells, they excite electrons and allow them to flow, creating an electric current. PV cells are made of semiconductor materials such as silicon and alloys of indium, gallium and nitrogen. Crystalline silicon is the most common material used and has an efficiency rate of 15-20%. Solar arrays on solar cars are mounted and encapsulated very differently from stationary solar arrays. Solar arrays on solar cars are usually mounted using industrial grade double-sided adhesive tape right onto the car's body. The arrays are encapsulated using thin layers of Tedlar.   

Because the Sharp solar cells being used by the Toyota Prius Prime are only about 0.03 millimeters thick, they can be placed and wrapped around many curvy parts of the roof, hood and hatchback. The final production model will not look like the prototype shown in this article. The cells will be be laminated into the car's body in a way which will make them far less visible. This is an aspect of the car's design that Toyota is still working on.   

The list of solar-powered cars that have been developed is extensive, though only a few of them have been designed with mass production in mind: https://en.wikipedia.org/wiki/List_of_prototype_solar-powered_cars   

Toyota has released no details of their timeline to commercialization yet for their solar-paneled car, but the test findings will be shared with NEDO and Sharp in order to help bring this technology to market.  https://global.toyota/en/newsroom/corporate/28787347.html https://nhts.ornl.gov/