Sensing an opportunity for indoor PV

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Scientists at Massachusetts Institute of Technology (MIT) have outlined what could be a significant opportunity for new solar manufacturers, in the form of ‘indoor PV.’

According to MIT, the market for indoor PV cells, such as those used to power watches and calculators, was worth just US $140 million in 2017. But price reductions in solar are beginning to line up with decreasing energy requirements for technologies such as wireless sensors, RFID tags, and Bluetooth beacons. MIT predicts billions of these sensors will be installed in the coming years, while also stating that their current reliance on battery power is a major constraining factor, leading to sacrificed performance for increased battery life, and additional operations and maintenance costs associated with replacing these batteries.

Integrating PV cells into the devices could solve a lot of these problems, leading the university to predict a boom in the indoor PV market, surpassing $1 billion annually in 2024. Around half of the sensors are expected to be placed indoors, with little or no access to sunlight, meaning the PV cells would have to rely artificial light, typically at intensities three orders of magnitude lower than sunlight.

Material matters

MIT’s analysis, explained in the paper Technology and Market Perspective for Indoor Photovoltaic Cells, published in the journal Joule, suggests that the poor low light performance of silicon would not make it a good candidate for indoor PV applications, opening the door for various thin film technologies.

Emerging technologies including organic PV and perovskites have exhibited the kind of low light performance needed for indoor PV, and their well-documented stability issues would be less of a problem in an indoor setting. The type of sensor being powered may have a lifetime much shorter than the 20 years plus which has become the industry standard.

For perovskites in particular, MIT theorizes that the indoor PV market could provide an opportunity to mitigate many of the risks associated with commercial introduction: “Our market analysis in this paper makes it clear that the rapid growth of the indoor IoT market could provide an ideal jumping-off point for perovskite products, allowing a new PV company to establish customers, revenue, and credibility before establishing larger-scale solar panel manufacturing facilities,” state the authors.

Volume down

The impressive cost reductions achieved by solar so far have resulted from achieving economies of scale, something which will have to be discounted entirely when it comes to indoor PV – meaning that low capex for production equipment and processes is a key consideration. MIT’s analysis predicts that for established thin film materials, as well as perovskites and other new entrants, it should be possible for manufacturing costs to be brought low enough, while acknowledging more work is needed to understand the impact of initial capex investment on lower volume manufacturing.

While predicting a 70% annual market growth rate for PV devices powering IoT sensors, the researchers note three things required to ensure this market development – a set of universal standards for measuring indoor PV’s performance, the development of devices specially tuned to this environment, and the development of cost and business models for low volume manufacturing.