After a few conversations with Scott Shepard about PV systems in EVs, I began to come around to his view that solar is too expensive and the roof space too limited to make a solar-equipped EV work at the mass market scale. But then I read about another PV in transport project that made economic sense: Indian Railways’ newly launched solar diesel multiple unit (DEMU) trains. A total of 16 300W solar modules are installed on each coach on the train for ₹9 lakh ($13,950 or $2.9/W). The Indian Institute of Science estimates that the annual energy yield in a solar rail coach will be between 6,820 kWh and 7,452 kWh. This could displace 1,862 liters of diesel, saving around $1,650 per year at $0.88/liter diesel.
I see two key elements that make the project work. The first lesson from India is that solar in transport makes more sense when it is displacing liquid fuels rather than electrons. Going back to the Prius example from the first blog in this series, if the solar roof was available in Toyota’s non-plug-in version of the car, its economic effect would be significantly better. If a non-plug-in version of the Prius could run for 2,190 km per year on only solar, it could save about 150 liters per year, which would have a value of around $180 per year (using Japan’s gasoline price in July 2017). The investment in a solar roof could break even within the lifetime of the car, so the current cost of the add-on could be justified.
The second lesson is the use of off-the-shelf modules. In this way, the project benefits from the economies of scale that PV systems are famous for. It would be difficult to use off-the-shelf modules in cars, but if Toyota introduced the solar roof in all its Prius cars (for example), it could increase the production rate of solar roofs for the Prius from a couple of thousand per year to about 350,000 per year (global Prius sales in 2016). Modules with similar high efficiency cells in the wholesale market sell for about $0.50/W (i.e., $90 for the 180W used in the Prius).
Most of the costs arise from integrating the PV cells into the roof of the car. These costs could decline significantly due to economies of scale as well. If Toyota could cut costs to those of the train company ($540 for 180W already installed in the car, including inverters and other costs), the breakeven period would be about 2.5 years. Slashing costs would make a solar roof a no-brainer (especially for consumers like me who would be able to drive the car without ever using a charging point or stopping at a gas station).
This would open an interesting niche for solar companies. If all the EV and hybrid EV cars sold globally in 2017 (expected to be between 3 million and 4 million) had a 180W roof, an additional 840 MW (an extra 1%) could be added to global solar PV demand. But solar roofs need a champion to push them into the mass market in the same way Tesla pushed EVs away from the margins. My last blog discussed two startups that are exploring this niche. However, traditional manufacturers could do the same to differentiate their brand and cars from the competition. Toyota is an obvious choice given its brand association with hybrid cars, but other manufacturers could step in. For example, Volvo could be a great candidate since it is hybridizing all its models.