Seamless integration of solar film in FRP materials

One of the important challenges facing the automotive industry lies in stringent environmental protection requirements and the associated emission laws, which are mainly focused on reducing CO2 emissions. Vehicle- integrated photovoltaics (VIPV) play an important role in achieving these environmental criteria. As part of Audi’s predevelopment project conducted in cooperation with Apollo Power (Israel) and Mubea Carbo Tech (Austria), a new process based on the integration of non-encapsulated flexible solar film in fibre-reinforced plastic parts using HP-RTM was developed and successfully evaluated on Audi’s series rooftop.

This application offers the following benefits:
– Best lightweight design compared to other applications (e.g. integration in glass);
– Class A surface with high aesthetics and design freedom (including complex 3D designs); – Better durability compared to other parts with bonded (glued or laminated) solar film;
– Fibre-reinforced plastic parts with embedded solar film are protected against weather conditions and theft;
– Range extends through applied solar film.

Partners

As part of the pre-development project (started in 2019), Audi is cooperating with Apollo Power and Mubea Carbo Tech as associated partners. Founded in 2014, Apollo Power is an innovative energy company from Israel that created a unique technology for manufacturing flexible, lightweight, durable and high-efficiency energy films that transform surfaces into an energy source and challenge the limitations of legacy solar energy technology.
At only 430 grammes per square metre (bare cells), the company’s solar film does not require any change in the parameters (temperature, pressure, or time) of standard manufacturing processes for composite parts such as autoclave (prepreg) or resin infusion processes (e.g. RTM).
The integration of flexible solar cells using other manufacturing processes (such as injection moulding or thermoforming) was also demonstrated by Apollo Power.

Mubea Carbo Tech (MCT) is a Tier 1 supplier from Austria that develops and produces composite parts, focusing on complete consistency from the project stage through to construction, strength design, model building, mould making and final testing. Integrative lightweight design as achieved in this project plays a key role in MCT’s products. The company provides access to a wide array of conventional and innovative production technologies such as RTM, wet pressing, SMC and fibre placement solutions including automated 2D/3D preforming, TFP or braiding. By continuously increasing efficiency, the output of bio-based and recyclable composites and transitioning the energy sources to renewables, MCT contributes to decreasing the CO2 footprint of production.

Process description

The new process consists of four stages:
– Preparation of a preform (e.g. based on carbon fibres)
– Addition of a layer of flexible solar film on the preform – Resin infusion by HPRTM
– Assembly including painting with a UVresistant coat

The process was developed on small lab-scale samples measuring 50 cm x 50 cm and then successfully transferred to a series carbon fibre-reinforced roof produced by Mubea Carbo Tech in their Zebrak plant (Czech Republic) since 2021. All the trials showed that the HP-RTM high-cycle production (<20 min per part) is feasible for Apollo Power’s flexible solar film without any visual or other damage to the solar film and without any reduction in electrical performance.

The final product shows superior results including best solar efficiency (>200 Wp), lightweight design (minimum 50% lighter than a standard solar glass roof ) and compliance with automotive quality standards, namely class A surfaces with high aesthetics and design freedom.

Additionally, complex 3D shapes with a higher degree of drapeability can be produced as well, so that the technology can be transferred to other components and industries (such as railway or aerospace).

The ability of Apollo Power’s flexible films to conform to very complex 3D shapes was demonstrated in a previous study with Audi. Combining a flexible solar film with natural fibres and bio-resins makes it possible to produce sustainable eco-parts with a lower CO2 footprint (even a negative footprint over their lifetime).

This will be demonstrated during the next development stages with all the associated partners, in 2022/2023.

This article has been published in the JEC Composites Magazine N°148.

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