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As solar energy becomes a larger share of the energy mix, there is a problem with the dominance of silicon in panel production. Silicon accounts for 95% of the 14 GV of solar module manufacturing capacity installed in the UK. That solar fleet provides just 4% of the UK’s energy demand. The government’s energy strategy for 2022 calls for a fivefold increase in solar capacity, to 70 GV, by 2035. However, seeking an additional 56 GV of silicon solar power presents significant ethical, economic and security implications, and that prospect is driving research into alternatives, which is where perovskites come in.
Manufacturing silicon panels is expensive and complicated, and as the UK does not have significant silicon solar manufacturing capacity, we will continue to rely on imports. As the world has recently learned, the geographic concentration of global supply chains presents energy security and logistics challenges. The production of solar panels has a high carbon footprint and the average carbon payback period for silicon solar panels – the length of time the panel will need to produce electricity before it offsets the carbon emissions embodied in its production – is 300 to 350 days.
Also, the stiffness and mass of silicon solar panels usually limits their application to ground-mounted solar farms and installation on load-bearing roofs. For example, a gigawatt of solar generation capacity requires about 2.5 million panels. Achieving the 70 GW needed by 2035 will require a massive land grab. It is no wonder that the International Energy Agency calls for the diversification of solar photovoltaic production.
Are perovskites the answer?
There has long been interest in the potential use of perovskite for solar power generation, thanks to the superconducting and electronic properties observed in the crystal, which is abundant in the Earth’s mantle. The fact that cheaply available perovskites have outstanding properties for absorbing light photons to create a flow of electrons and generate electricity, makes the material an ideal candidate to replace silicon in solar production.
With so much interest in perovskites, enterprising manufacturers are looking for innovative ways to incorporate them into PV production and my company, Power Roll, is no exception. We have patented a technique that applies perovskites to a flexible, lightweight substrate: polyethylene terephthalate (PET) – an industrial thermoplastic sheet. The PET substrate is embossed with tiny V-shaped channels or “microgrooves” that are no more than one or two microns wide.
Roll-to-roll
The microgrooves are printed with high precision on heat-stabilized PET using a roll-to-roll process. They form conductive paths that are designed to optimize the flow of electrons and “tune” the electrical output of the solar module. The walls of the microgrooves are coated with metals, as electrodes, and then with an oxide layer that acts as an electron transport layer (ETL) and a hole transport layer (HTL). Perovskite ink is printed in grooves over ETL/HTL layers to produce an ultra-thin, flexible solar cell or “solar film” that is 100 times thinner than silicon solar panels.
Roll-to-roll production is a simple and scalable process used in other low-cost sectors, such as packaging, and is key to the low cost of solar film. Importantly, it skips several manufacturing steps involved in other flexible photovoltaic technologies.
After coating and annealing with perovskite ink – the latter a heating process to improve bendability – a barrier film is applied on top under pressure in a continuous process to protect the crystallized perovskite. Further barrier films and a back film can be applied using pressure or vacuum lamination.
To investigate the relationship between price and durability, Power Roll conducted weekly tests on different barriers and lamination types exposed to outdoor conditions over the past six months. This showed that films with high cost barriers and vacuum lamination showed no performance degradation, while films with low cost barriers and pressure lamination were affected at the edges. Further testing is underway.
Power Roll’s methodology produces a perovskite photovoltaic panel with manufacturing costs five times cheaper – and a carbon payback period up to ten times shorter – than traditional silicon solar panels.
Wide range application
The combination of microgrooves and perovskite produces a flexible, lightweight, efficient solar film at a fraction of the cost of silicon solar panels. The flexible nature and simple installation process means that perovskite solar film can be installed in situations where silicon solar panels cannot be installed. For example, it can be integrated with windows, shutters, vehicles, low load roofs and vertical surfaces. While solar panel farms occupy significant amounts of green space, perovskite PV can take advantage of areas already developed for commercial or domestic use.
The largest market for solar foil is on commercial and industrial roofs. Just a quarter of the UK’s 2.5 billion square meters of south facing roofs could generate 30% of the UK’s energy needs. Perovskite PV solar film can be installed on non-structural roof space cheaply and at scale, helping the UK meet its energy security and net zero targets.
And the opportunities for lightweight solar film extend beyond the UK. The manufacturing process is easy to replicate and can be licensed globally to accelerate the use of solar energy. With less than 2% of global rooftops hosting solar installations, there is a huge opportunity for lightweight, low-cost perovskite photovoltaics. Solar film is versatile and has the potential to be integrated onto roofs and onto a wide range of surfaces. It will help improve the availability of clean energy generation in parts of the world that currently lack significant renewable energy infrastructure. Perovskite PV is expected to hit the market next year, with wider adoption by 2025, and promises to revolutionize the solar sector.
Author: NEIL SPANN
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