The Internet of Things (IoT) is bringing the benefits of wireless communication to devices everywhere. Whether it’s adding connectivity to devices in your home, tracking the location of your keys, or adding sensors in an industrial plant, low-power wireless connectivity has become a must-have for the IoT.
However, adding connectivity requires a power source in all these devices, which sometimes means using a battery, creating an environmental issue as billions of batteries are added to the waste stream every year. Making the IoT revolution sustainable means we need to drastically reduce our reliance on batteries.
Here is where harvesting light energy offers a potential solution. Because communication in many IoT applications generally consumes very little power and is only intermittently used, reliably power
ing devices with harvested light energy is feasible. But for photovoltaic energy harvesting to be a more common feature in IoT, we first need to overcome some stubborn misconceptions.
Misconception #1: All Usable Photovoltaic Energy Comes from Solar
When most people think about photovoltaic energy today and consider its role in a sustainable energy future, the images that tend to come to mind are often related to things like utility-scale solar arrays or residential solar panel microgrids. This is perfectly understandable given solar energy’s critical role in our collective, clean energy future. Nearly 3% of US electricity comes from solar PV, representing about 13% of total US renewable energy generation. Globally, the International Energy Agency (IEA) projects an average annual rate of generation growth of 24% between 2020 and 2030.
As we all know, solar energy technology converts sunlight (electromagnetic radiation) into useful electrical energy using photovoltaic cells for immediate use or to be stored in batteries for use later. But if you stop and think about it, not all usable photovoltaic energy is solar, and not all our energy needs must be met via the electricity distribution grid. What if a major step forward in global sustainability could be achieved in microwatts in addition to megawatts?
As it turns out, low-power, wireless applications targeting the IoT can rely on photovoltaic cells for some or all their energy needs by harvesting ambient indoor light energy inside the home or commercial/industrial buildings. There are many options for low-cost photovoltaic cells designed specifically to harvest energy at indoor lighting levels, as opposed to the bright sunshine required for outdoor PV cells. Modern PV technology even allows for non-visible light sources to be used in harvesting energy. For example, infrared light can be harnessed in a variety of implementations including when the light source is an LED.
As many industrial or consumer applications consume only tens of microwatts of average power and only need higher power for brief intervals on an occasional basis, an integrated solution combining energy harvesting, power management, and flexible storage can meet the requirements of these low-power applications. Harvested PV energy, when used with a suitable storage element like a supercapacitor or rechargeable battery, can operate and power a device for its entire lifetime. Examining the output
power curves for PV cells at indoor light levels, along with daily ambient light profiles and the energy usage model for the application, it is possible to design a system with the correct operating behavior using a PV cell, and a storage element to meet the demands of a specified IoT application. As the number of options for PV cells, storage elements, and low-power wireless devices continues to grow, more and more IoT applications have the potential to shift to renewable, harvested photovoltaic energy. Consider all the batteries that could be saved in the billions of new devices that will be deployed over the coming years.
Misconception #2: Products that Use Energy Harvesting Require Large, Unappealing Glass PV Cells
Another closely related misconception about photovoltaics has to do with the characteristics of the PV cells that we associate with solar technology. Photovoltaic technology has advanced well beyond the rigid, flat glass panels we see on rooftops or associate with battery-less calculators from our school days. Newer organic polymer and dye-sensitized PV cell technologies offer the potential of highly customizable cells built on flexible substrates, with the efficiency, stability, and price point comparable to the more traditional silicon-on glass cells. It is even possible to create a device with the PV cell integrated into the molded plastic, making the PV cell virtually invisible to the casual observer.
Today, a new generation of eco-designed products incorporating flexible photovoltaics are available for several consumer applications. These products are sustainable, stylish, and convenient to use. For example, PV cells from Exeger, a Swedish manufacturer, have been integrated into the headbands of wireless headphones and the shells of bicycle helmets to keep these devices continuously charged. It doesn’t take much imagination to see how consumers are going to feel about aesthetically pleasing products that don’t have to be plugged in or set aside for charging.
Misconception #3: It is Impractical to Develop IoT-Enabled Products that Harvest Photovoltaic Energy
The third misconception conce
rns the implementation difficulty or additional cost of adding energy harvesting to a device, leading one to believe it just isn’t practical. The good news is that more and more component manufacturers are incorporating features that directly support energy harvesting into system-on-chip (SoC) solutions. These integrated SoCs include more advanced power management with the ability to manage a variety of energy harvesting and energy storage devices intelligently. Combined with a modern low-power wireless design, it is possible to provide everything required to add PV harvesting to a low-power wireless IoT application in a single integrated circuit or module. Besides reducing the cost to add energy harvesting to a product, these integrated solutions can also take advantage of the close coupling between the Power Management Unit (PMU) and application software running on the device. For example, being able to use harvested energy directly to power the device increases efficiency when compared with more expensive solutions that implement the PMU and wireless SoC separately. Furthermore, application software can adjust for the performance of the PV cell as light levels change and modify device behavior based on the current energy storage level and the amount of energy being harvested. For example, an environmental sensor in an office conference room may change its measurement and reporting interval based on the amount of energy harvested.
To enter the market for IoT-enabled photovoltaic products, companies need to overcome the misconception that photovoltaic energy harvesting cannot be feasibly harnessed to develop a cost-effective product. Wireless application platforms that support energy harvesting with integrated power management and flexible energy storage options can meet heightened customer expectations and enhance eco-brand identification.
As sustainability becomes a more important criterion for products in both consumer and commercial market segments, we’ll see a growing demand for manufacturers to integrate the latest advancements in PV cell technology and wireless SoCs to bring energy harvesting to connected devices. These devices will run the gamut from keyboards
to sensors to eBadge readers to industrial applications, and beyond. We look forward to witnessing this next era of sustainability-focused innovation and the exciting new opportunities it will unleash for the IoT.