by Stephanie Bond-Hutkin, Australian PV Institute (APVI)
The rapid uptake of electric vehicles around the world has enormous potential for reduction of CO2 emissions and driver benefits, but when renewable fuel sources are not available, EVs still consume electricity from coal-fired sources. This has the potential to change with a new fleet of solar vehicles that create their own clean energy.
With built-in PV panels, solar vehicles are able to generate their own solar energy, resulting in less or no dependency on grid electricity, and lower CO2 emissions. The reduced need for external charging also provides drivers with more convenience and autonomy.
The introduction of PV-powered vehicles can be important for the uptake of electric transport and creates opportunities for other PV applications in the transport sector.
Finding the right solar cells
Pioneer manufacturers are using vehicle integrated photovoltaics (VIPV) with curved, flexible and lightweight solar modules built-in to the materials of the vehicle. Silicon-based cells are the most common technology for PV-powered vehicles, showing the best compromise between performance, price, and reliability. Their weakness is the lack of flexibility for two-directional bending.
The more expensive III-V multi-junctional solar cells are also being used, which have higher power conversion efficiency but spectrum mismatching loss compared with crystalline Si solar cells. Four-terminal III-V on Si multi-junction solar cells have demonstrated improvements in these disadvantages.
Other thin-film solar cells, such as amorphous silicon and chalcogenide are less efficient than other PV technology, but they can be deposited onto glass or metal foil, providing the potential fabricate curved vehicle body parts (perhaps more cheaply).
Perovskite cells have the potential of combining high efficiency, low cost, and flexibility, but this technology is not currently manufactured at a large scale, due to a lack of reliability and durability, and at present, lower efficiency than c-Si-based PV at scale.
Charging autonomy
Currently, low-carbon options for EV charging include: from the existing grid network with PV, other sustainable electricity sources, or charging from a dedicated charge point with local PV electricity generation.
VIPV provides the driver with greater autonomy and convenience as the vehicle is charged directly and independently with on-board PV.
Optimising CO2 efficiencies
Undoubtedly, one of the key benefits of PV-powered passenger vehicles is the reduction in CO2 emissions compared with fuel-powered passenger vehicles. Efficiencies can be further improved by reducing the embedded emissions from PV manufacturing, and continued improvements in curved, flexible, and lightweight PV module technology.
Driving patterns also impact the way solar power is utilised. For long-distance driving patterns, relying solely on PV electricity can be difficult and will often require grid charging.
For short-distance driving patterns however, the vehicle can be powered solely by PV electricity and the excess PV electricity generated can be used for other purposes. These patterns also impact the effectiveness of CO2 emission reductions.
For all driving patterns, with the exception of low suburban use (up to 5km per day), the PV-powered vehicle will realise CO2 reductions.
Regarding the application of solar vehicles in Australia where road travel requirements can be lengthy, Australian VIPV expert, Ned Ekins-Daukes, said, “The point is not to achieve fully self-sufficient operation over long-distances – for that, fast-charge stations will still be necessary – but the daily errands conducted around town can substantially be covered by direct solar charging of the vehicles.”
Stationary Mode
One of the most promising approaches of PV-powered vehicles will be to provide PV electricity to surroundings when the vehicle is parked (V2X), both excess solar stored in the car’s battery that was generated while the car was in motion, and the real-time production of the PV system integrated in the car while parking in a public place or at home.
These additional opportunities while in stationary mode include V2H (vehicle to home), V2G (vehicle to grid), V2V (vehicle to vehicle) and other surrounding options V2X (vehicle to everything). Another way to maximise PV utilisation is managing the battery’s State Of Charge (SOC) to ensure that enough capacity is available for storing on-board PV electricity.
When the reserved capacity for PV is well-managed, demand for grid electricity is reduced and less PV electricity generated on-board will go to waste.
How willing are consumers to pay for VIPV?
To evaluate consumer attitudes to EVs equipped with on-board solar charging, a survey of over 2,000 individuals from all socioeconomic backgrounds was carried out in eight cities in Australia.
The questionnaire was designed to determine the desire of the consumer towards a solar electric vehicle and by presenting them with a choice between vehicles that they might wish to purchase, as well as their willingness to pay for the technology.
The study showed that the appeal of VIPV is highest among young adults with a willingness to pay for a solar electric range of up to $50 per km among wealthy young adults, and an average of $25 per km for all participants.
A further premium of $1,415 was determined for colour coordination of the photovoltaic module with the vehicle bodywork and styling. This places the viable VIPV module cost in the region of a few USD/Wp.
Commercial applications
VIPV also presents opportunities for light commercial vehicles and long-distance trucks. “Even when fitted to existing diesel trucks, a 5 per cent reduction in fuel consumption has been achieved, with solar power offsetting some of the electrical loads,” Mr Ekins-Daukes said.
“For heavier commercial vehicles such as truck trailers, delivery vehicles, and buses, on-board PV can also make significant contributions to auxiliary systems such as air-conditioning, heating and refrigeration.”
As the market introduces more commercially-available solar vehicles, there will also be a flow-on effect to the EV market as a whole, with more uptake of electric transport and other PV applications in the transport sector.
Small market, big potential
The most realistic applications for PV-power are short-driving range commuter vehicles, ultra-lightweight vehicles, and high-efficiency EVs.
A bridging technology to PV-powered vehicles may be the use of PV power for auxiliary components such as air conditioning systems, refrigerators, and heating systems, as can already be seen in some passenger vehicles.
For heavier commercial vehicles such as truck trailers, goods delivery vehicles, and buses, on-board PV can make significant contributions to these auxiliary systems and the electric conversion of these systems. According to the IEA PV Power System Programme report, the PV market in the transport sector is still small.
However, the potential impact is large and the electrified transport market will be a key driving force for the further development of PV in the coming years. PV-powered vehicles have the potential to further decrease the CO2 emissions impact of electrified transport (particularly in the short term) and accelerate the adoption of electric vehicles overall due to decreased dependence on the grid.
