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1 Email: monika.freunek@gmx.de

Monika Freunek (Müller)

BKW AG, Bern, Switzerland

AbstractIndoor photovoltaics (IPV) is one of the most promising technologies to power IoT and consumer devices in indoor environments. Theoretical efficiency limits exceeding 50%, an established technology, and power densities among the highest of all indoor energy harvesting technologies available, make IPV attractive and an upcoming technology in an expected trillion-dollar market. However, the typical indoor spectral conditions, the optimization goals and processes during design and manufacturing, and the ideal materials differ significantly from the well-established outdoor applications. Thus, IPV devices require specific engineering and characterization. This chapter introduces IPV with its spectra, irradiance levels and operating conditions. Theoretical and demonstrated efficiencies, their modeling, and characterization methods are discussed. Issues such as total energy balance, recycling and lifetime are outlined. With properly adapted design, IPV might be the enabler of many IoT applications in the near future. This chapter provides the state-of-the-art, challenges and solutions for IPV products, and gives an outlook on future products.

Keywords:Indoor photovoltaics, micro energy harvesting, internet of things, wireless sensor nodes, edge nodes, indoor photovoltaic efficiencies, indoor photovoltaic materials

Indoor photovoltaics (IPV) started in the seventies following the invention of microprocessors [1, 2]. In the following decades, IPV was mostly limited to applications such as kitchen scales, solar calculators, and some consumer fun articles [3, 4]. Those devices were designed far beyond their theoretical potential and often suffered from lack of user acceptance, as users most often had to actively place the device close to a window for a proper functioning. In many applications, it was easier and more reliable to power indoor products with batteries or power cords. The introduction of narrow-banded artificial light and ultra-low power electronics, such as the Phoenix Processor with a power consumption in the picowatt range [5], are the technology enabler for IPV, enhancing their applications far beyond those listed above. Recent studies expected IoT systems to become a multi-trillion-dollar market within the next few years [6]. In many applications, IPV will be the ideal technology to supply the power for the IoT devices.