Summary: Vehicle-Integrated Photovoltaics Request for Information

State of the Industry and Key Domestic Markets

Market Segments Most Promising for Vehicle PV Systems

In addressing what market segments or subsegments are most promising for vehicle PV systems, respondents identified three primary factors: the available area for PV, the curvature of vehicle surfaces, and the size of the segment (e.g., size of fleets and frequency of use). The market segments most frequently cited by respondents as promising for VIPV/VAPV are:

• Medium- and heavy-duty utility vehicles
• Transport refrigeration units (TRUs)
• Recreational vehicles (RVs)
• Buses
• Local delivery fleet vehicles

Two primary use cases were identified for the role of PV in vehicles: (1) propulsion in electric vehicles, and (2) supporting auxiliary loads. When used in conjunction with electric vehicles (EVs), PV systems could provide additional energy to the battery to increase vehicle range. Respondents noted that this could increase the autonomy of EVs and reduce the risk of stranded vehicles due to lack of charge. Solar charging of EVs could also enable use of EVs as emergency responses vehicles. The role of PV systems in active battery thermal management in EVs was also mentioned.

Vehicle PV systems could also support auxiliary loads in vehicles, such as refrigeration, heating/cooling, or electronics expanding the market opportunity for VIPV/VAPV beyond EVs. Multiple respondents identified transport refrigeration units (TRUs) as a promising market segment for PV integration. PV integration into TRUs was identified as particularly attractive because of the need to replace diesel fuel in TRUs. Further, TRUs have a duty cycle amenable to solar charging. Recreational vehicles (RVs) were also frequently identified as an opportunity to use VIPV/VAPV to support auxiliary loads – in this case, to reduce generator use associated with RVs.

Respondents expressed divergent views about the potential for PV integration into light-duty passenger vehicles. Some suggested that passenger vehicles represent a promising market for PV, citing that passenger vehicles are the most mature EV market and that the efficacy of VIPV reduces significantly as vehicle weight increases. Consumer interest in solar passenger vehicles may help drive this market. However, others noted that the curved surfaces in passenger vehicles creates an integration challenge and that the first markets to address are vehicles offering large, flat surfaces.

Respondents also expressed divergent views about the opportunity for PV integration into trucks and truck trailers. Generally, medium- and heavy-duty trucks were viewed as attractive for VIPV/VAPV because of the high potential for space utilization and flat surfaces amenable to PV integration. However, respondents also noted the need to differentiate between single-unit and combination trucks when evaluating VIPV/VAPV opportunities. They expressed concerns about the feasibility of applying PV systems on the truck trailers or shipping containers of combination trucks, despite the benefit of a large, flat surface, and suggested that single-unit trucks are better suited to VIPV/VAPV.

Other markets that were mentioned to be promising for VIPV/VAPV include:

• Off-road, low speed vehicles (e.g., golf carts)
• Recreational boating
• School buses
• Marine unmanned surface vehicles

Largest Market Opportunity for VIPV/VAPV

Most respondents suggested that commercial trucks and trailers present the largest market opportunity for VIPV/VAPV. The respondents’ decision factors and views of use cases for VIPV/VAPV are similar to those noted above. Commercial vehicles are used frequently and are exposed to ample sunlight (e.g., not parked in garages); therefore, commercial vehicles, particularly those that move high-value products, are most likely to adopt VIPV in the near term. Commercial trucks offer high utilization of VIPV since they are part of large fleets driven during daylight hours. Commercial trucks or trailers typically consist of large, flat surfaces, making them compatible with PV integration. They also have more standardized vehicle designs and shapes than passenger vehicles. The grocer market and long-haul transport in the southern United States were referenced as specific VIPV/VAPV market opportunities.

Several market opportunities in addition to commercial trucks were also mentioned by respondents:

• Bus fleets are also of interest for reasons similar to truck fleets, namely that there are large fleets often driven during daylight.
• The passenger vehicle segment was viewed as the most promising market opportunity by some respondents because it is largest segment by number of vehicles, accounts for the largest share of greenhouse gas emissions in transportation and has the most mature EV technology.
• Solar powered boating is directly aligned with the use case for recreational boating, which is often done on clear, sunny days.

Domestic Manufacturing Opportunities

Respondents expressed strong interest in achieving domestic manufacturing of vehicle PV systems. Domestic manufacturing of VIPV/VAPV products could help quickly meet future domestic demand, particularly given the high number of TRUs in the United States. Respondents also referenced the importance of both manufacturing and installation of vehicle PV systems for domestic job support. Overall, lightweight modules for VIPV/VAPV applications were considered a better match to domestic manufacturing capabilities than stationary modules in terms of both the PV technology and manufacturing volume required. Further, lightweight modules were considered less price sensitive than the stationary PV market which could bolster domestic manufacturing.

A common theme in response to this question was the opportunity for domestic manufacturing of thin-film PV modules for vehicle integration, particularly high efficiency, conformal modules. Thin-film PV technologies offer flexibility, light weight, and less capital-intensive manufacturing processes which makes them amenable to vehicle integration. Keeping in mind that responses were received prior to passage of the Inflation Reduction Act of 2022, some respondents expressed doubt about vehicle-integrated silicon PV in domestic manufacturing, commenting that VIPV/VAPV will not create enough of a new market opportunity in silicon PV compared to stationary PV to drive domestic manufacturing.

Stakeholders also discussed components required for VIPV/VAPV systems where the United States could lead manufacturing:

• Power electronics, like inverters and maximum power point trackers (MPPTs), designed for VIPV/VAPV applications
• Specialized balance of systems components for PV integration with vehicles, such as smart max power tracking, charge controllers, integration into vehicle electrical systems, etc.

Establish Ways in Which Solar-generated Electricity Could Be Used in a Vehicle System

Similar to prior questions, respondents emphasized several use cases and value propositions of VIPV/VAPV systems:

• Range Extension: In EVs or hybrid vehicles, VIPV/VAPV systems can be used to extend the range of the battery, reducing wear on the battery and emissions from a fossil-fuel-dominant grid. Vehicle PV systems allow vehicles to produce solar-generated electricity both on the road and when stationary during sun hours. Power not used could be stored in the vehicle batteries for later use. To supplement the energy provided by VIPV/VAPV and completely power EVs by solar energy, VIPV/VAPV systems could be coupled with stationary solar canopies augmented with batteries, allowing the vehicle PV system to extend vehicle range between charging stations and then charge from batteries instead of grid energy.
• Auxiliary Power: VIPV/VAPV can provide power to auxiliary loads such as climate control systems and other electronic loads. This use case is particularly compelling for diesel, gas, and natural gas vehicles, such as many trucks and marine vehicles, where VIPV/VAPV can reduce fuel consumption by supporting auxiliary loads. Doing so also reduces wear and tear on equipment and therefore maintenance expenses. Commercial vehicle applications such as tractor trailers, buses, and rail are viewed to be of particular interest for such non-propulsion loads.
• Improved Safety: VIPV/VAPV could enable safer vehicle operation by minimizing or eliminating the usage of fuels and thus reducing the possibility of hazardous fuel spills.
• Backup Power: EVs with VIPV/VAPV could provide backup power to buildings or other vehicles.

Other respondents approached this question by considering what information is needed to determine the most effective use of vehicle PV systems. A reliable source is needed to define system requirements, considering both vehicle performance and cost. VIPV/VAPV applications face a challenge distinct from grid-tied PV that the value of VIPV/VAPV is more than simply the energy generation provided; however, no common assessment exists to determine and communicate this value and examine the different product designs that will be most beneficial to different markets.

Available Vehicle PV Products

Some respondents approached this question from the market segment perspective and others focused on the type of VIPV/VAPV technology. Respondents commented that most vehicle PV products available today are VAPV products, such as rigid, flexible, or semi-flexible modules added to vehicles, rather than solar products integrated into the body of vehicles. These VAPV products are typically applied to vehicles via adhesives, in the case of flexible or semi-flexible mat-style systems, or bracket mounted systems in the case of rigid framed glass panels. Flexible modules typically consist of crystalline silicon (c-Si) or copper indium gallium diselenide (CIGS), and rigid, flat modules are commonly made of c-Si and encased in glass.

Available vehicle PV products were also discussed in terms of market segments:

• Passenger vehicles: EVs with rooftop solar panels are available, though still in an early stage and have not yet realized significant benefit to either range or auxiliary functions. Examples of vehicles commercially available, according to respondents, include the Hyundai Sonata hybrid and the Toyota Prius. Others are under development and not yet commercially available.
• Other on-road vehicles: Respondents reported that several companies are developing trucks (including on cab roofs), tractors, and trailers with PV roofs. Limited examples of commercially available vehicles were reported, including golf carts and PV modules for RVs.
• Marinevehicles: VAPV technologies for boats, yachts, and ferries are available to provide additional power.

Respondents also noted that some additional VIPV/VAPV products were listed in the RFI document.

Key Product Requirements for Given Markets

The primary list of key products requirements for VAPV/VIPV applications was identified as:

• Weight
• Size
• Flexibility
• Resistance to vibration
• Aesthetics (includes smoothness and continuity between cells)
• Cell performance
• Reliability
• Lifetime/durability
• Supply chain integration
• Maintenance requirements
• Safety (human and environmental)

While most of these factors are important to some extent in each VIPV/VAPV market segment, the prioritization of these product requirements changes based on the market segment. For passenger vehicles, aesthetics is considered a high priority, and a low VIPV/VAPV system weight is also critical to avoid negating the additional driving range provided. Alternatively, factors such as reliability and supply chain integration are viewed as a higher priority in medium- and heavy-duty vehicles. In commercial vehicles, SAE and International Organization for Standardization (ISO) standards for environmental and electrical applications are often included in validation testing, so VIPV/VAPV products for this segment need to be compliant with those standards.

For some of the product requirements listed above, respondents provided detail on how to define these requirements and optimize them for VIPV applications. For example, silicon cells could be cut in half to better fit the limited available area of a vehicle and increase voltage. Respondents emphasized the importance of cell performance in various lighting conditions and suggested that integration of bypass diodes between cells could mitigate power loss under partial shade. Panel cleaning should also be a key component of maintenance requirements to maintain cell efficiencies. With regard to reliability and product lifetime, VIPV/VAPV product lifetime may be hindered by the weathering and motion deterioration innate to the vehicle environment. Safety of VIPV/VAPV systems should include secure installation to prevent systems from detaching while in motion, potentially causing injury and property damage. Environmental safety was also referenced, with respondents suggesting the use of non-toxic materials for VIPV/VAPV systems and establishing safeguards to prevent environmental contamination.

Other product requirements mentioned by respondents include:

• Resistance to scratches, crashes, and mechanical shocks
• Form factor
• Temperature gradients
• Maximum temperature tolerance
• Walkability (particularly for the marine market)
• Ease of install
• Standards compliance
• MPPT controllers specified different vehicles

PV Cell Technologies for VIPV

When evaluating the best PV cell technologies for VIPV applications, respondents commented on a variety of factors and trade-offs that informed their decisions. The most frequent factor cited was the limited area available on vehicle surfaces and resultant importance of high efficiency PV cells, leading several respondents to favor silicon cell technology. However, flexibility could also be an important factor, depending on the form factor of the vehicle, and it may be worth trading off some efficiency gains for increased flexibility. The flexibility offered by thin-film absorbers (e.g., CIGS, OPV, perovskites) could be attractive for VIPV, but respondents expressed the need to address challenges such as lower efficiency, poor shade tolerance, and electrical hysteresis impacting some thin-film PV technologies. Other important factors were lightweight, aesthetics, and transparency. Cadmium telluride was not specifically mentioned by respondents as a promising technology for VIPV.

• Silicon: Favored for its high efficiency, silicon was the most frequently mentioned PV cell material for suitability in VIPV applications. Efficiencies of 20% or higher were specifically preferred. Rigid, high-efficiency silicon absorbers are well-aligned with the needs of large, rectangular fleet vehicles. Several respondents mentioned that they currently use monocrystalline Si with integrated back contacts (IBC) for existing VIPV applications. Small-format silicon cells were mentioned as an attractive option to provide both high efficiency and flexibility. Further, thin crystalline silicon cells were proposed as an option more compatible with VIPV than thicker, rigid, silicon panels. Thin silicon cells enable flexibility without flexing-induced reliability issues, offer improved high-temperature performance, and can provide off-angle collection capabilities.
• CIGS:  CIGS modules are attractive for VIPV due to their flexibility, allowing easy integration into existing vehicles and are currently available, particularly outside the United States.
• Perovskites: Perovskites were noted to potentially offer comparable or improved efficiency, weight, flexibility, and price over silicon solar cells. However, commercialization of perovskite technology has been hindered by issues such as sensitivity to oxygen, moisture, and heat which need to be addressed.
• Organic PV: Organic PV (OPV) was viewed as advantageous for VIPV for several reasons, including that it is lightweight and flexible; the necessary materials can be sourced domestically, mitigating supply chain risks; and its low toxicity could be particularly attractive after a vehicle crash and at end-of-life. However, to date, efficiencies of OPV are less than half those of silicon PV.
• Gallium Arsenide: Commonly employed in the aerospace industry, gallium arsenide (GaAs) is attractive for VIPV applications due to its high efficiency and power-to-weight ratio. However, cost challenges may make it more suitable to heavy-duty market segments, where a cost premium might be more easily absorbed, rather than passenger vehicles.

As the VIPV sector matures, stakeholders will develop an improved understanding of use conditions of vehicles, standards, testing, costs, manufacturing processes, and other factors that can help inform which PV cell technologies are best suited to VIPV.

Integration Requirements and Challenges

Respondents highlighted two main themes when considering vehicle PV integration requirements and challenges: (1) the importance of designing systems to enable vehicle maintenance and repair, and (2) the safety of occupants and first responders in the event of a crash. If these two items are not sufficiently addressed, the adoption risk of VAPV/VIPV will likely be too high to justify the investment. Several key integration requirements and considerations were identified by respondents, including:

• Panels must be correctly mounted based on the vehicle structure and expected driving conditions.
• Connections and components should be water-resistant.
• The power conversion modules must be properly sized with protections provided against electrical shorts if conversion of power supply to another voltage is required.
• From an operations and maintenance (O&M) perspective, a safe but quick-to-disconnect architecture for individual components is desirable.
• Wiring should be hidden for safety and aesthetics.
• Internet of Things telematics stacks can be used to monitor solar loading and battery capacity.
• Front cover materials selection should consider supply chain management, ultraviolet (UV) tolerance, and impact resistance.

Five key integration challenges with respect to structural integration and electrical systems integration were identified:

• PV module curvature: Curving PV modules may be necessary to integrate PV into the body of the vehicle, particularly for passenger vehicles. This curvature could introduce current mismatch, reduce performance, and affect reliability.
• Designing access for repairs: PV panels should be easily accessible for repairs for the system to retain value. However, this can be challenging for VAPV/VIPV systems since the panels must be secured to avoid unintentionally detaching from the vehicle at high (e.g., highway) speeds.
• UV resistance: Most current semi-flexible PV modules consist of fluoropolymer-coated polyethylene terephthalate (PET) sheets, which have poor UV resistance. A cost-effective, UV resistant cover sheet is needed to enable VIPV/VAPV applications.
• Vibration and impact resistance: Vibrations ubiquitous in the vehicle environment may present durability challenges for VIPV/VAPV. Energy absorption materials can be used to prevent damage from vibration and impacts, such as by surrounding the panels with energy absorbing, anti-impact materials.
• Impact of driving patterns: Advanced solar predictions and charging controls could help reduce transformation losses due to driving patterns. PV modules on a moving vehicle will experience rapid fluctuations in irradiance; current MPPT technology, designed for stationary arrays, therefore may not work as intended under these conditions. This challenge could be mitigated through novel cell interconnection topologies and smart max power tracking.

Challenges to Vehicle Material Performance Requirements and Rating Metrics

Respondents commented that some existing metrics and standards should be modified for vehicle PV integration while other metrics and standards should not change. In the case of PV performance and reliability, existing standards may require adjustment for vehicle PV systems because of the different operating conditions of the vehicle environment compared to stationary solar. Further, safety standards may need to address the vehicle environment specifically to ensure passenger safety and prevent risk of shock. Respondents commented that components such as cables, wires, and charge controllers should follow the codes or standards of the auto parts industry. Respondents also noted that VIPV/VAPV systems will be subject to a wide variety of operating conditions and that comprehensive metrics do not yet exist that account for these conditions. Further, metrics such as durability and lifetime will be more challenging to predict for vehicle PV systems than for stationary PV due to variable road and climate conditions.

Multiple respondents commented on the importance of considering end-of-life opportunities, challenges, and regulations, potentially through future research, development, and demonstration (RD&D). While VIPV/VAPV system lifetime will likely differ from stationary PV lifetime based on the environment and PV materials used, stationary PV modules today have estimated useful lifetimes longer that those of most vehicles, potentially presenting opportunities for reuse of modules on multiple vehicles. No regulations currently exist for recycling of PV modules or waste materials recovery. Further, integrating PV modules into vehicles may complicate the established vehicle waste stream processing; depending on how VIPV recycling and disposal processes are designed, integrating PV into vehicles may introduce hazardous materials (e.g., lead and cadmium) into vehicle waste streams.

Finally, respondents commented on the end user expectations surrounding vehicle PV system cost. If end users base their expectations for system cost on the relatively lower-cost stationary PV modules, customer adoption of VIPV/VAPV systems may be low since VIPV/VAPV may not be cost-competitive with utility-scale PV.

Alignment of Performance Requirements with Vehicle PV Applications

Respondents noted that existing standards and performance requirements are tailored to stationary systems and not aligned with vehicle PV applications. For example, irradiance variability on a moving vehicle differs significantly from that of a stationary PV module, necessitating alternative performance metrics. Further, current characterization standards are designed for flat panels and not curved PV modules. New standards for vehicle PV systems are needed to ensure quality and safety and encourage adoption. Lessons from space solar could be used to establish new performance requirements, such as the ability of space solar to resist g-forces and impacts. A few respondents mentioned that they are directly developing or aware of others developing standards for specific vehicle PV segments or technologies.

Other Considerations for Vehicle O&M and Insurance

Respondents stressed the importance of being able to inspect, diagnose, and safely repair system components, especially considering the long lifetimes of commercial vehicles. VIPV/VAPV systems should be removable and replaceable in the event a car is damaged, such as via thin films applied to vehicles with an adhesive. Respondents also noted that VIPV/VAPV systems should be designed to allow for recyclability or simple disposal at end of life. Repair of individual cells in VIPV/VAPV systems – rather than replacement of an entire module – was viewed as highly beneficial for simplifying operations and maintenance (O&M) and reducing maintenance costs.

Vehicle use patterns and unique elements of the vehicle environment and value chain necessitate consideration of factors for VIPV/VAPV systems that may not be relevant for traditional PV systems. For instance, maintenance and repairs are often avoided or deferred in vehicles, so one respondent suggested that vehicle PV systems be designed to accommodate a similar repair schedule (or lack thereof) and offer long-term reliability and durability. Also, vehicle drivers and operators will require education about any VIPV system operation or maintenance that they will be responsible for. Cell technology selection should consider possibilities such as vehicle collisions or fires, where hazardous materials could be released. Further, hazardous cell materials could present new challenges for vehicle repair shops not trained or equipped to handle them.

Regarding considerations for vehicle insurance, respondents noted that VIPV/VAPV systems may necessitate special collision insurance options. Additionally, insurance companies should recognize the value of and offer specialized rates for vehicle PV systems.

Barriers to the Adoption and Commercialization of VIPV/VAPV

Barriers to adoption and commercialization of VIPV/VAPV technologies were addressed from the technical and market perspectives. These barriers include manufacturing-line integration, immature supply chains, uncertain reliability, maintenance concerns, and aesthetics. Respondents focused on four major themes in their discussion of these barriers:

• Cost: Several respondents commented that cost was a major barrier to VIPV/VAPV adoption. Cost is particularly a barrier when considering the performance of vehicle PV systems currently on the market, resulting in payback periods longer than passenger car lifetimes according to one respondent.
• Performance: Some respondents believe that the performance of VIPV/VAPV products improvements are needed before widespread adoption can be realized. Respondents particularly emphasized the need for improved vehicle PV system efficiency and, relatedly, benefits to vehicle range. However, it is challenging to achieve impactful PV power density in the limited surface area of vehicles. PV products also need to be better designed for the specific conditions of the vehicle environment, particularly through increased durability, and to enable seamless integration with vehicles. Respondents also commented that increased availability of funding is needed to drive forward these performance improvements and the development of new VIPV/VAPV technologies. Finally, the performance of retrofit VIPV/VAPV products was specifically commented on; retrofitting was identified as typically less aesthetically pleasing, expensive, and less efficient than integrating PV into new vehicle designs.
• Perception of Vehicle PV: The perceptions of the public, industry, and private investors about vehicle PV were viewed as a barrier to adoption. There is an overall lack of public interest in and awareness of vehicle PV systems, despite their varied use cases as previously described. Many in the solar, vehicles, and clean tech fields, including private capital, do not view vehicle PV as a large and valuable enough market for major investments. Respondents attributed this lack of interest to several causes. Several respondents proposed that clear communication of the VIPV/VAPV value proposition was needed to drive stakeholder engagement. They suggested strategies such as marketing VIPV/VAPV products as vehicle components that also can produce energy, therefore providing longer range and/or ancillary benefits. The lack of industry and investor interest may also be due to the view that technology advancements are no longer needed in solar, making industry and investors less interested in investing in low technology readiness level (TRL) technologies.
• Uncertainty: In addition to communicating the overall value proposition of vehicle PV to stakeholders, there is a need to communicate more effectively about the return on investment of VIPV/VAPV systems. The return on investment should be tailored to various segments and use cases to reduce performance uncertainty and to show the significance of the benefits and how they ultimately outweigh the costs. End users need a better understanding of how their duty cycle might impact PV power production so they can appropriately plan for these changes. For example, vehicles driving north/south routes should generally expect less power production in the northern portion of the route. Reliability was also cited as a concern and barrier to adoption, particularly with respect to risk of collision and resulting repairs. 

Barriers to Collaboration between Solar and Vehicle Industries

Barriers to collaboration and partnering between the solar and vehicle industries on vehicle PV technologies and businesses range from unfamiliarity and risk aversion to lack of important data. Respondents generally agreed that cross-sector partnering via technology and manufacturing integration will be critical to the success of vehicle PV. It is particularly important for PV and vehicle manufacturers to partner to integrate VIPV/VAPV products into the vehicle design and supply chains, rather than focusing largely on retrofit vehicle PV systems as is done today.

Several respondents commented that one or both industries may be resistant to entering the vehicle PV market or with working with the other industry. In particular, traditional solar manufacturers may not be eager to enter the VIPV/VAPV market while it remains relatively unproven. Trust between the two industries, particularly when players of different sizes are involved and power dynamics come into play, was also viewed as a barrier to sharing ideas and technology. Further, validated system data and tools need to be readily available to demonstrate the value of vehicle PV systems, particularly when attempting to partner with those in another industry.

Additional Barriers Impeding Adoption

In addition to barriers previously discussed, several adoption barriers were commented or expanded on in response to this question. Repair and replacement of the vehicle PV systems or components were considered a large barrier given the likelihood of general wear and tear, damage from the environment or inclement weather (e.g., hail or tree branch damage), vehicle crashes, and potentially vandalism and theft. Warranty and insurance processes and costs to consumers should be designed to be straightforward and analogous to common vehicle repairs and replacements.

Regarding VIPV/VAPV installation, respondents expressed concern that the upfront cost of installation could be an adoption barrier without subsidies or other financing mechanisms. Further, challenges with available installation options, such as methods to safely adhere panels to vehicle roofs, need to be addressed. Additionally, PV installation could cause problems with vehicle warranties if holes are drilled in the vehicle roof, making it preferable to integrate PV into directly into vehicle design and manufacturing.

Finally, a comprehensive market assessment was suggested to better understand and overcome existing market barriers and demonstrate the role of vehicle PV in commercial and general consumer markets as a value-added product.

Limitations in current modeling tools for vehicle PV systems

Respondents reported that limitations exist in current modeling of energy yields, installed system costs, and system integration, including understanding of ancillary benefits, for vehicle PV technologies and systems.

• Energy yields: Current models can predict PV energy yields in specific locations, but it is not yet understood how to model PV energy yields for a PV in motion. Models should eventually be able to output energy yield based on specific routes and parking schedules. Limitations also exist in energy yield models of curved PV modules.            
• Installed system cost: The costs of installed VIPV/VAPV systems are not well understood since few exist today and the methodology is still being developed. Retrofitted vehicle PV systems further complicate cost analysis and add to installation costs.
• System integration: Vehicle energy requirements and emissions have historically focused on fuel economy, particularly the efficiency of the propulsion system. As addressed in response to prior questions, VIPV/VAPV could offer ancillary benefits to vehicles such as power climate control, low-voltage applications, parked-car ventilation, and battery maintenance; these benefits should be captured by models. Respondents noted that more understanding is needed on the process of integrating PV into vehicle manufacturing and that modeling is not currently standardized to provide useful estimates of VIPV/VAPV production. Additionally, a detailed understanding is needed of many VIPV/VAPV system components, such as inverters, chips, and wiring.

Limitations in current evaluations of vehicle PV systems

The majority of respondents focused on current evaluations and standardized calculations for vehicle PV energy production in response to this question. Suggested inputs to vehicle PV energy production calculations include local weather tables across the year, to provide monthly energy production estimates, and energy required to cool vehicles. One respondent suggested that current calculations do not consider that solar car roofs may cause vehicles to heat up when parked in the sun more than traditional car roofs, though data supporting this claim was not cited. Respondents again noted the limitation of existing calculations to determine PV yield for a given driving route and the importance of predictability for realizing the value propositions of VIPV/VAPV (e.g., extended battery range).

Limitations in energy production data collection and monitoring were also addressed by several respondents. Access to vehicle PV system energy production data is important for troubleshooting issues and learning how the panels are charging; however, access to this data is currently not possible with all VIPV/VAPV systems. Respondents also noted a lack of standardization and ownership for measuring parasitic power consumption (e.g., telematics, controller, etc.), which is critical to accurately model the energy needed from a PV system to offset that load and maintain battery health.

Several respondents discussed the need for performance evaluations and standardized calculations to consider the variable angles of incidence likely in VIPV/VAPV systems. Calculations would need to consider how PV is integrated into the vehicle and the integrated energy throughout the day based on the changing angle of the PV modules to the sun. An integrated software tool was specifically suggested that included the PV performance across 90 degrees of incident sunlight along with a computer aided design of the vehicle. Respondents also cautioned that calculations based on current solar technologies may not provide accurate efficiency data if applied to VAPV/VIPV systems; new solar technologies may exhibit improved performance at wide angles of incidence. Thin-film PV technologies were particularly mentioned as resilient to off-angle performance degradation.

Finally, it is important to understand how to accurately calculate factors in addition to energy production, including the impact of VIPV on range, power electronics, and peak power tracking. A data-driven analysis based on information from private industry could enable standardized calculations for the impact of VIPV/VAPV systems on vehicle performance, energy production, and carbon emission reduction.

Additional research, development, and demonstration needs

Most respondents addressed research and development needs; however, it was noted that field demonstrations are key to identify changes needed and that the marine market is advanced enough to begin demonstrations and start uncovering issues. Research and development in several areas was highlighted:

• Impact resistance: Similar to discussion in prior sections, respondents emphasized the importance of PV module impact resistance for VIPV/VAPV applications. Research could focus on protecting cells from impact while maintaining other attractive attributes like light weight and flexibility. This would increase the power production over time by minimizing impact damage to PV systems.
• Durability and lifetime: Due to the harsh operating conditions of vehicles, vehicle PV systems need to be more durable than other PV systems, necessitating that new PV products are designed with high flexibility and durability. However, one respondent cautioned that setting unrealistic target VIPV/VAPV system lifetimes could result in unnecessarily limiting materials selection. Specifically, if VIPV/VAPV systems will be damaged within a 20-year lifetime, the expected system lifetimes should be less than 20 years, which would open the door for using new types of polymeric encapsulant materials in vehicle PV systems.
• Safety and electronics access: Several respondents commented on the unique considerations of safety with vehicle PV systems, since the panels will be readily accessible to consumers, and the need for research and demonstrations to help design safe systems. Also, VIPV/VAPV system designs should consider easy access to electronics and other system parts for easy repair and replacement.

Other suggested research topics include:

• Flexible form factors
• Increased PV efficiency
• End of life strategies
• VIPV/VAPV performance models
• New MPPT hardware for VIPV/VAPV
• Identifying new encapsulation materials
• Product development for energy storage in RVs
• Supply chain constraints
• Tandem PV architectures
• Cost analysis
• Design of curved modules with multiple shading zones
• Impact on insulation materials lifetime (if any)

Challenges to demonstrating and validating the durability and performance of VIPV systems

Respondents discussed several challenges to demonstrating and validating the durability and performance of vehicle PV technologies and systems.

• Lack of established standards and testing procedures: Several respondents cited the lack of established standards and testing procedures for vehicle PV as a challenge to demonstrating performance and durability. Specifically, vehicle testing suites are not designed for VIPV/VAPV, and data collection methods and tools are not yet established. Respondents also cited the lack of standards to validate VIPV/VAPV performance, though did note that industry groups have published recommended practices for VIPV/VAPV technology evaluation. Similar to previous responses, the importance of developing specific metrics for VIPV/VAPV were also discussed, such as oblique-angle energy production, aesthetics, and geographic orientation.
• Data collection: Data collection of vehicle PV system performance could prove challenging due to varying angles of irradiance, causing solar power collection to be dependent on the many factors affecting irradiance in the road environment. Further, cost effective approaches to integrate VIPV/VAPV performance data during established vehicle test cycles need to be explored.
• Durability and lifetime testing: Vehicle PV system demonstration could pose the challenge of requiring collaboration among multiple stakeholders, including PV and vehicle manufacturers, particularly to test the lifetime of VIPV/VAPV systems. Durability testing will require consideration of both vehicle vibrations and direct impact. In the case of mounting PV modules via adhesives, thermal and moisture testing would also be required.
• Funding: Respondents also expressed the need for additional funding to demonstrate and validate VIPV/VAPV systems, particularly including support in developing automated assembly and shipping systems and funding to develop engineering design guides.  

Several strategies to mitigate these challenges were also discussed. Overall, broad market acceptance and adoption of VIPV/VAPV will drive understanding of the benefits of vehicle PV systems. Further, lessons learned from other material changes in vehicles, such as the use of aluminum and composite vehicle bodies, can inform how the vehicle industry can successfully shift from established products to more complex technologies.

Challenges in mobile solar + energy storage systems

Respondents addressed the challenges in mobile solar combined with energy storage systems from the perspectives of both specific mobile solar-as-storage challenges and general vehicle-as-storage challenges.

• Mobile solar-as-storage challenges: In addressing mobile solar-as-storage, respondents focused more on the challenges of solar vehicles as standalone storage option, rather than potential value of VIPV systems to augment stationary PV + storage solutions utilizing the battery in an EV. Respondents noted several challenges specific to mobile solar-as-storage uses, including that energy yield from vehicle PV is not typically high enough to serve as a reliable storage solution alone and that the energy conversion efficiency would need to be improved. Further, the vehicle would need to be located in an area with high insolation to be most effective. Finally, low use applications (e.g., seldom used RVs or boats) would require a rugged grid-tie inverter to allow the PV system to supply energy to buildings when the vehicle is not in use – a necessary element to realize the full benefit of the VIPV/VAPV system.
• General vehicle-as-storage challenges: Respondents expressed differing views about the potential of vehicle-as-storage uses. Existing charging standards include well-established standards for vehicle-to-vehicle and vehicle-to-grid uses, and equipment is available for these uses as well. However, concerns were expressed that vehicle-as-storage would not be widely adopted in the absence of rapid charging technology and that costs need to be improved. Knowing how energy is produced and safely stored in vehicle-as-storage systems was considered important. Respondents also expressed the need for improvements to the specific energy of batteries.

Other challenges noted include:

• Efficiency
• Availability of chargers
• Battery storage size required
• Grid availability
• Vehicle-to-building transfer efficiency
• Off the grid capability

Areas of Information and Knowledge Gaps in the Industry

Respondents focused on five major themes when identifying vehicle PV information and knowledge gaps:

• Perception of VIPV/VAPV: As discussed in the “Barriers to Adoption and Commercialization” section, respondents noted a lack of interest in VIPV/VAPV products by both the public and industry. This was somewhat attributed to a misunderstanding of the value of vehicle PV systems and a need to more clearly communicate the benefits and comprehensive return on investment of vehicle PV.
• Product awareness and availability: Respondents noted a number of knowledge gaps related to VIPV/VAPV product awareness and availability. Potential buyers lack knowledge about the availability and capability of VIPV/VAPV products and how to acquire them. Increased visibility and exposure of VIPV/VAPV products to industry and the public was suggested. Further, only a handful of VIPV/VAPV products are commercially available and relatively few established solar manufacturers are actively working on vehicle PV systems. Curved solar modules were specifically mentioned as needing advances in equipment and supply chains before they are widely available.
• Performance uncertainty: Uncertainty of the performance of vehicle PV systems, including lifetime and efficiency, was cited as a major knowledge gap. Commercial end users do not have the resources nor data to understand the value of vehicle PV technologies to their segments. Particularly due to the high levels of wear of VIPV/VAPV systems compared to ground-mounted PV, industry needs data demonstrating the performance and economics of VIPV/VAPV systems over time under real-world road conditions from credible sources, including data on carbon reduction potentials and lifetime performance. Vehicle PV adoption could also benefit from a harmonized metric to create a common goal among stakeholders, similar to the solar industry’s cost target per kilowatt hour and the vehicle industry’s miles per gallon metric. Several respondents also discussed the need to understand variables that could impact VIPV/VAPV system performance and impact quality, such as installation practices. The need for testing and certification standards was also noted.
• Collaboration challenges: Respondents noted a lack of communication between solar manufacturers, installers, and the vehicle industry, leading to knowledge gaps around product design and integration.
• Funding opportunities: Respondents also expressed the need for accessible government funding for low TRL technologies to advance VIPV/VAPV products.

Key Stakeholder Groups

In response to which stakeholder groups should be involved in conversations on VIPV/VAPV product requirements, barriers, and RDD&C needs, most respondents named types of stakeholder groups. However, it was also suggested to include stakeholders across the value chain of VIPV/VAPV products, including raw materials and end-of-life stakeholders. Respondents also expressed the need for a U.S.-based consortium with PV expertise that leverages industry-leading automotive consortia to advance the VIPV/VAPV industry. Specific stakeholder group mentioned are:

• End customers
• Vehicles repair shops
• Vehicle dealerships
• Auto manufacturers, including TRU manufacturers
• Existing and new, VIPV/VAPV focused solar panel manufacturers
• Downstream component suppliers
• Certification entities
• Truck and bus fleet owners and managers, ranging in size and resources
• Shippers across the range of loads shipped and received
• Communities who are adjacent to diesel pollution sources and/or where the drivers and freight handlers live (ensuring they also participate fully)
• Ports and rail hubs
• Sustainability professionals
• PV and automotive consortia
• Highway Vehicle Enforcement (Commercial Vehicle Enforcement Officers)
• Academic institutions
• Government

Outreach Mechanisms

Respondents addressed an array of stakeholder engagement needs, ideas, and specific engagement opportunities in response to this question. Three general strategies were suggested for DOE to engage stakeholders:

• Information sharing: Government engagement with vehicle companies was suggested to share information about the latest developments in PV and particularly advancements amenable to VIPV/VAPV systems. Vehicle companies may not be aware of PV designs beyond rigid silicon modules for distributed or utility-scale deployment; engaging with them on the recent advancements could help spur investment in VIPV/VAPV and integration of PV into vehicle design. In engagements with vehicle companies, it was suggested that the focus remain on vehicles with large, flat surfaces before approaching the consumer sector.
• Facilitating collaboration: Government facilitation was suggested to enable collaboration between PV, electronics, and vehicle manufacturers.
• Enabling funding: Enabling more risk-taking and experimentation was also suggested to mature the currently nascent market through increased access to funding mechanisms such as venture capital.

Finally, specific avenues for stakeholder engagement were suggested, which could provide platforms for discussion and enable collaboration:

• Auto shows
• New technology showcases
• Conferences (e.g., PV in Motion)
• Webinars and workshops (e.g., in collaboration with CARB)
• Professional organizations (e.g., SAE, American Trucking Association's Technology & Maintenance Council, Truck Trailer Manufacturer’s Association)
• Direct conversations with stakeholders, including small companies
• LinkedIn News