The ubiquitous nature of energy autonomous microsystems, which are easy to install and simple to connect to a network, make them attractive in the rapidly growing Internet of Things (IoT) ecosystem. The growing energy consumption of the IoT infrastructure is becoming more and more visible. Energy harvesting describes the conversion of ambient into electrical energy, enabling green power supplies of IoT key components, such as autonomous sensor nodes. Energy harvesting methods and devices have reached a credible state-of-art, but only a few devices are commercially available and off-the-shelf harvester solutions often require extensive adaption to the envisaged application. A synopsis of typical energy sources, state-of-the-art materials, and transducer technologies for efficient energy conversion, as well as energy storage devices and power management solutions, depicts a wide range of successful research results. Developing power supplies for actual usage reveals their strong dependence on application-specific installation requirements, power demands, and environmental conditions. The industrial challenges for a massive spread of autonomous sensor systems are manifold and diverse. Reliability issues, obsolescence management, and supply chains need to be analyzed for commercial use in critical applications. The current gap between use-case scenarios and innovative product development is analyzed from the perspective of the user. The white paper then identifies the key advantages of energy autonomy in environmental, reliability, sustainability, and financial terms. Energy harvesting could lead to a lower CO2 footprint of future IoT devices by adopting environmentally friendly materials and reducing cabling and battery usage. Further research and development are needed to achieve technology readiness levels acceptable for the industry. This white paper derives a future research and innovation strategy for industry-ready green microscale IoT devices, providing useful information to the stakeholders involved: scientists, engineers, innovators, the general public, and decision makers in industry as well as in public and venture-funding bodies. This inclusive strategy could bridge the energy harvesting technology frontier and the IoT node power demands to create value
