PV Energy Harvesting Solution For Powering IoT World

We live in a connected world: It is only a matter of time before hundreds of billions of connected IoT devices and sensors provide mankind with ubiquitous information… or is it really? What is certain is that key issues remain to be solved for these optimistic projections to be realised, and energy supply is one of them: how can these billions or even trillions of devices be powered, sustainably and cost-effectively asks Mathieu Bellanger, CTO of Lightricity?

There are typically three options being considered for powering IoT sensors:

Mains powered: historically, this has been the most straight-forward and reliable way of supplying energy to a device. However, for both economical and practical reasons, cabling is not a viable solution for the large number of devices involved.

Battery powered: this allows more freedom when deploying wireless devices in the field. However, there is significant environmental and practical concern of manually replacing or recharging these batteries when an empty state-of-charge is reached. Many of these individual devices will indeed be placed in remote locations that are difficult to identify or access. Importantly, the consequence of device failure due to a fully-discharged battery could be significant if the device is used for safety-related applications such as condition monitoring or in medical applications.

Powered using energy harvesting: this has been widely considered the only logical and sustainable solution in the medium to long term. New energy harvesting and sensor technologies are now making a viable, practical option in the short term, too. It is also in-line with current trends of device miniaturisation and low-power consumption. There are various ways of harvesting ambient energy depending on what form of energy (thermal, kinetic, light) is available. Light being available almost everywhere and most of the time (either outdoors or indoors), photovoltaic energy harvesters (converting ambient light into electricity) are expected to hold the largest market size within the next 5 years.

On average, people typically spend 90% of their time indoors. Hence one can also imagine that a considerable fraction of current and future IoT devices are to be located in an indoor environment: homes, offices, supermarkets, factories, warehouses, hospitals, to name a few. However, most of existing light energy harvesting solutions, based on silicon active materials, have been designed principally for outdoor use and show a drastic drop of performance in low-light level indoor environments. Other alternatives based on dye-sensitised solar cells (DSSC) and organic photovoltaics (OPV) offer a small power density increase but are larger in size (tens of cm²) and frequently suffer from material degradation and limited lifetime (a few years only). As a consequence, this means none of the commercially available solutions can provide enough “juice” or power for a wide range of wireless applications (including wearables), where there is a clear limitation in the size of the final device or product. So is this the end of it?

Lightricity Ltd¹ is a high-tech company which recently span-out from Sharp Laboratories of Europe, Sharp's European R&D laboratory. After over 4 years of intense research to develop the perfect indoor solar cell, Lightricity has been set-up in 2017 to further develop and commercialise its unique technology based on an inorganic material. With efficiencies up to 35% achieved under standard artificial lighting conditions (200 lux white LED or Fluorescent/FL light), Lightricity currently offers the world's most efficient photovoltaic (PV) energy harvesting components (ExCellLight) for IoT devices. This high conversion efficiency enables now up to six times more power to be delivered to a sensor or IoT device (Figure 1), avoiding the multiple replacements of coin cells, AAA-AA types of batteries.

Figure 1: Comparison of indoor Photovoltaic (PV) Energy Harvesting technologie

This power boost can be used to provide more device functionality or to reduce the footprint of the complete system (to a few cm²). For example, Lightricity's energy harvesting component can provide a perpetual source of energy for more power-hungry air-quality gas sensors, such as CO₂ sensors. The Lightricity team, in collaboration with Gas Sensing Solutions (CO₂ sensor manufacturer) has previously demonstrated an autonomous wireless CO₂, temperature, light, humidity sensor that can perpetually perform and transmit all environmental measurements every 2min 30s at 200 lux, only using a 10 cm² Lightricity PV cell². Over 10 years typical product lifetime, up to 150 battery replacements can be avoided, assuming 1000 lux average illumination (e.g. retail environment) - thereby saving €100's in maintenance and battery costs to the end-users (Figure 2).

Figure 2: Lightricity battery equivalent under indoor conditions

In a project funded by Innovate UK, and in partnership with Ilika (solid-state battery storage) and E-peas (power management chipsets), Lightricity is currently developing a second generation of compact everlasting power supply that can connect to any IoT sensor or wireless tracking devices and beacons (Figure 3).

Figure 3: Energy harvesting power pack (Lightricity, Ilika)

Some environments can be particularly harsh: Lightricity's energy harvesting component has been designed to withstand temperatures of up to 150 °C continuously, and up to 250 °C intermittently. The temperature coefficient of Lightricity's device is twice better than that of silicon, translating into up to 8x performance improvement at elevated temperatures. This opens new applications in automotive and industrial environments, and also new use cases in health monitoring for worker safety, emergency responder safety and sports applications.

These developments demonstrate that powering IoT devices and sensors by energy harvesting is both practical and beneficial for lowering cost of ownership. This opens the way to large scale deployment of connected IoT devices in the short term.