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SETO presented on the current challenges and opportunities of VIPV. Download the slides. 
PV in Motion 2023 – VIPV Presentation
On July 14, 2022, the U.S. Department of Energy (DOE) Solar Energy Technologies Office (SETO) and Vehicle Technologies Office (VTO) released a request for information (RFI) on technical and commercial challenges and opportunities for vehicle-integrated photovoltaics (VIPV) or vehicle-added (or attached) PV (VAPV) systems. DOE has supported research, development, demonstration, and commercialization (RDD&C) efforts on vehicle photovoltaics (PV) via a variety of programs. The purpose of this RFI was to solicit feedback from various stakeholders, such as industry, research laboratories, academia, government agencies, regulators, and other experts, on issues related to VIPV/VAPV technologies and markets. 
The RFI received responses from organizations representing VIPV/VAPV stakeholders including product manufacturers, vehicle fleet operators, research institutions, national laboratories, consultants, and individuals.
Respondents addressed questions in five different categories, spanning the current state of the industry, product requirements, key barriers, RDD&C needs and opportunities, and stakeholder engagement. Respondents framed their responses based on specific questions in each category, though some of them outlined their answers differently around themes of interest spanning various categories and providing more general comments. This summary document is organized around the categories identified in the RFI and the individual questions.
The market segments most frequently cited as promising for VIPV/VAPV are:
 
Two primary use cases were identified for the role of PVs in vehicles:
(1) propulsion in electric vehicles
(2) supporting auxiliary loads
 
Commercial trucks and trailers were generally viewed as the largest market opportunity because they:
 
Other respondents viewed the passenger vehicles market segment as the largest market opportunity, due to the large fleet size and relative maturity of EV technology.
 
 
Use cases and value propositions of VIPV/VAPV 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:
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:
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:
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:
Similar to prior questions, respondents emphasized several use cases and value propositions of VIPV/VAPV systems:
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.
Vehicle PV products: Focus on VAPV products today, applied via adhesives or bracket-mounted
 
Customer market segments:
 
The primary list of key products requirements for VAPV/VIPV applications was identified as:
 
 
 
 
 
 
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:
Respondents also noted that some additional VIPV/VAPV products were listed in the RFI document.
The primary list of key products requirements for VAPV/VIPV applications was identified as:
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:
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.
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.
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:
Five key integration challenges with respect to structural integration and electrical systems integration were identified:
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.
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.
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 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:
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.
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.
 
 
 
 
 
 
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.
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.
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:
Other suggested research topics include:
Respondents discussed several challenges to demonstrating and validating the durability and performance of vehicle PV technologies and systems.
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.
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.
Other challenges noted include:
 
 
 
 
Respondents focused on five major themes when identifying vehicle PV information and knowledge gaps:
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:
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:
Finally, specific avenues for stakeholder engagement were suggested, which could provide platforms for discussion and enable collaboration:
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