The extent to which solar-powered vehicles reduce carbon dioxide emissions depends on variables such as the carbon intensity of the local grid, driving patterns and solar radiation. Entering the market requires the technical optimization of solar electricity, but also of vehicles.
To some extent, solar-powered vehicles replace grid or charging station electricity with their own solar electricity. This offers users benefits in terms of reduced CO2 emissions (in most countries), cost savings and reduced grid charging frequency, as well as “subtle” benefits in terms of autonomy and independence.
The majority of PV vehicle development is passenger car-based projects, particularly short-distance commuting vehicles, ultra-lightweight vehicles and high-performance vehicles, where silicon-based cells are the most common technology used. However, PV power can also be considered for auxiliary components such as air conditioning systems, refrigerators and heating systems in heavier commercial vehicles such as truck trailers, delivery vans and buses. In these latter applications, solar power often helps reduce fuel consumption, which seems like a compelling proposition economically.
Case studies on the reduction of CO2 emissions from solar-powered passenger cars have been conducted in Japan and the Netherlands, and have shown that the benefits of solar-powered vehicles depend on variables such as driving style, the amount of solar radiation available to the vehicle, the vehicle. efficiency, battery size, installed PV capacity and use of the PV resource. A reduction in emissions of about 220 kg CO2-eq/year has been observed especially during long driving trips in Japan; However, the reduction of CO2 emissions depends on the carbon intensity of the local network and varies from country to country. To highlight these differences, IEA PVPS Task 17 researchers have assessed the expected environmental benefits of solar-powered vehicles in different cities (see Figure 1).
Figure 1: Comparison of CO2 emissions in each location with and without solar power
In most cases, CO2 emissions are reduced during vehicle operation with built-in solar power. However, in countries with low-carbon grid energy (see Bern (Switzerland) and Paris (France) in Figure 1), embedded CO2 based on PV module manufacturing may lead to slightly higher lifetime emissions. State-of-the-art well-integrated PV technologies, such as curved, flexible and lightweight PV modules, in addition to more efficient PV technologies and longer PV component life, increase PV production and reduce embedded emissions. The expected higher solar power efficiency in the future will enable even more efficient solar power vehicles.
The total and relative decrease in charging frequency in different locations is directly proportional to the amount of solar energy produced (see Figure 2).
Figure 2: Comparison of total long-distance vehicle charging frequency (left axis) and relative reduction in charging frequency (right axis) for a simple 15 km commuting profile
As shown in Figure 2, without PV the charging frequency is very similar in all cities. With PV, places with higher radiation power – Canberra, Madrid and Rabat – see the greatest reduction in charging frequency, as solar power adds more of the required driving energy.
Current issues in the implementation of solar-powered vehicles
PV modules integrated in vehicles are tested and classified according to two standards: as a photovoltaic system and as an external electrical component of the vehicle. Compared to standard home solar systems, which are installed in such a way as to avoid shading in the installation, car roof solar modules are often shaded and not oriented to optimize the use of solar energy.
PV-powered vehicles can be optimized by taking into account solar radiation, vehicle efficiency, battery capacity and PV system efficiency. The surplus electricity produced could be fed into the grid or used in buildings connected to it.
In order to exploit the market potential of PV-powered vehicles, the expected benefits should be further validated and evaluated in terms of energy and environmental aspects as well as the user perspective. The results form a solid basis for discussions with stakeholders, such as car companies and decision-makers.
This article is part of the IEA’s PVPS program monthly column. It was facilitated by IEA PVPS Task 17 – PV & Transport. More information can be found in the Task 17 report: PV Powered Electric Vehicle Charging Stations – Preliminary Requirements and Feasibility Conditions.
Keiichi Komoto and Bettina Sauer