outdoor-related applications include solar fans for camping or solar power LED lamps. The module sizes for these applications already come close to the range of square meters.
3.5 Degradation and Lifetime Issues
Degradation effects decrease the efficiency over time, thus limit the lifetime among other effects. As most degradation effects are related to energy and intensity levels, indoor conditions are again in favor of the photovoltaic materials. The Stabler-Wronski-Effect in a:Si:H is related to intensity [38], so a:Si:H can expect a longer lifetime indoors than in outdoor operation. As the first generations of outdoor systems start to report lifetimes above three decades, for most materials the photovoltaic module will not be the limiting device for the total device lifetime in IoT edge nodes.
However, so far, few studies have been reported investigating the lifetime for IPV products. In a study from 2013, photodiodes from GaAsP and organic solar cells (P3HT:PCBM) were irradiated by fluorescent light for 3900 hours [39]. This would be approximately 2.3 years of use in an office with 222 working days per year and 8 hours of artificial irradiance per day. The organic cells degraded about 15% from their initial efficiency, the GaAsP about 10%. As these devices might be installed for a long time, degradation issues need to be addressed during design.
A second topic in product design is recycling and toxicity. As IoT devices are small, they might be forgotten in their installations or be integrated into building structure and furniture. Easy removal and recycling and avoidance or handling of toxicity is thus important during early design. Finally, the total cost of ownership and the CO2 footprint of those devices need to be addressed over the whole production chain and life cycle. Reinders and Apostolou provided an overview of product integrated PV, including IPV and outdoor applications, such as in cars [40]. Chapter 8 introduces current IPV product integration.
3.6 Conclusions and Outlook
The recent takeoff of the IoT could enable the takeoff of IPV. This chapter showed its large potential, and issues to be solved on the way to a safe and secure mass production enabling the full efficiency and reliability of IPV-powered products. The time when we might start to wonder why devices were not powered by IPV might not be so far away.
References
1 1. Hyatt, G.P., Single chip integrated circuit computer architecture. US Patent 4942516A, 28, Dec. 1970.
2 2. Faggin, F., Hoff, M., Mazor, S., Memory system for a multi chip digital computer, vol. 22, Intel Corp, US Patent 3821715A, Jan. 1973.
3 3. Conti, J.A., Electronic postage weighing scale, vol. 10, Pitney-Bowes Inc, US Patent 4084242A, Nov. 1976.
4 4. Roen, S.A., Solar powered portable calculator, vol. 03, Litton Business Systems Inc, US Patent 4017725A, Jan. 1975.
5 5. Hanson, S. et al., IEEE J. Solid-State Circuits., 44, 1145–1155, 2009.
6 6. Atluri, V. et al., The trillion-dollar opportunity for the industrial sector. McKinsey Digital, November 2018. Article https://www.mckinsey.com/business-functions/mckinsey-digital/our-insights/the-trillion-dollar-opportunity-for-the-industrial-sector, accessed 2020-01-24.
7 7. IEC 60904-3:2019, Photovoltaic devices - Part 3: Measurement principles for terrestrial photovoltaic (PV) solar devices with reference spectral irradiance data, 2019.
8 8. Randall, J.F. and Jacot, J., Is AM1.5 applicable in practice? Modelling eight photovoltaic materials with respect to light intensity and two spectra. Ren. Energy, 28, 12, 1851–1864, 2003.
9 9. Hirata, Y. et al., Variation of output with environmental factors, in: Photovoltaic Modeling Handbook, M. Freunek Müller (Ed.), Wiley Scrivener, Hoboken NJ, USA, 2018.
10 10. Freunek, M. et al., Maximum efficiencies of indoor photovoltaic devices. IEE J. Photovol., 3, 1, 59–64, 2013.
11 11. Roth, W., Photovoltaische Energieversorgung für Geräte im kleinen und mittleren Leistungsbereich, report, Fraunhofer-Institut für Solare Energiesysteme, Freiburg, Germany, 1991.
12 12. Müller, M. et al., Characterization of indoor photovoltaic devices and light, in: Proceedings of the 34th IEEE Photovoltaic Specialists Conference, pp. 738– 743, Philadelphia, USA, 2009.
13 13. Müller, M. et al., Simulations and measurements for indoor photovoltaic devices, Proceedings of the 24th European Photovoltaic Solar Energy Conference, Hamburg, Germany, 2009.
14 14. Müller, M., Energieautarke Mikrosysteme am Beispiel von Photovoltaik in Gebäuden, PhD Thesis, Der Andere Verlag, Osnabrück, Germany, 2010.
15 15. Apostolou, G. et al., Spectral irradiance measurements in a room fit for indoor pv products, Proceedings of the 27th EUPVSEC, pp. 4240–4244, Frankfurt, Germany 2012.
16 16. Queisser, H.J. and Shockley, W., Detailed balance limit of efficiency of p-n junction solar cells. J. Appl. Phys., 32, 510–519, 1961.
17 17. Trupke, T. and Würfel, P., Fundamental limits of solar energy conversion, in: Photovoltaic Modeling Handbook, M. Freunek Müller (Ed.), Wiley Scrivener, Hoboken NJ, USA, 2018.
18 18. Hovel, H.J., Solar cells, in: Semiconductors and Semimetals, vol. 11, R.K. Willardson and A.C. Beer (Eds.), Academic Press, New York, USA, 1975.
19 19. Sze, S.M. and Lee, M.-K., Semiconductor Devices: Physics and Technology, 3rd Ed., Wiley, New York, USA, 2012.
20 20. Gemmer, C. and Schubert, M.B., Solar cell performance under different illumination conditions. MRS Online Proc., 664, 2001.
21 21. Shah, A.V. et al., Basic efficiency limits, recent experimental results and novel light-trapping schemes in a-Si:H, μc-Si:H and ‘micromorph tandem’ solar cells. J. Non-Cryst. Solids, 338–340, 639–645, 2004.
22 22. Thompson, I.R., Modelling of organic photovoltaics, in: Photovoltaic Modeling Handbook, M. Freunek Müller (Ed.), Wiley Scrivener, Hoboken NJ, USA, 2018.
23 23. Freunek Müller, M. (Ed.), Photovoltaic Modeling Handbook, Wiley Scrivener, Hoboken NJ, USA, 2018.
24 24. Gemmer, C.E.M., Analytische und numerische Untersuchungen von Solarzellen unter wechselnden Beleuchtungsbedingungen, PhD Thesis, Der Andere Verlag, Osnabrueck, Germany, 2003.
25 25. Bahrami-Yekta, V. and Tiedje, T., Limiting efficiency of indoor silicon photovoltaic devices. Opt. Express, 26, 28238–28248, 2018.
26 26. NREL, Reference Air Mass 1.5 Spectra, https://www.nrel.gov/grid/solar-resource/spectra-am1.5.html, accessed 28-01-2020.
27 27. Green, M.A., Solar Cells: Operating Principles, Technology and System Applications, Prentice-Hall, Englewood Cliffs, N.J., USA, 1982.
28 28. https://www.enlitechnology.com/indoor-solar-cell-testing-room-light-simulator.html, accessed 28-01-2020.
29 29. Reich, N. et al., Weak light performance and spectral response of different solar cell types, in: 20th European Photovoltaic Solar Energy Conference and Exhibition, vol. 10, pp. 2120–2123, 2005.
30 30. Apostolou, G. et al., Comparison of the indoor performance of 12 commercial PV products by a simple model. Energy Sci. Eng., 4, 69–85, 2016.
31 31. https://www.ikea.com/jp/en/catalog/products/00340306/, accessed 28-01-2020.
32 32. https://www.ixys.com/ProductPortfolio/GreenEnergy.aspx, accessed 28-01-2020.