As third-wave technologies are rapidly bringing us into a future once thought only possible in science-fiction, the burden of powering these emerging innovations is perhaps the greatest hurdle to overcome. Although there are incredible advancements being made in battery technology, this staple practice does not completely mesh with a future of ubiquitous sensing and continuous human-technology interaction. The encumbrance of monitoring and replacing batteries or utilizing cable charging for billions of new devices, including time/monetary cost and waste, is demanding alternative solutions to enable mass-market deployment of new technologies.
But finding sources of power isn’t a problem. Heat, vibration, friction, sunlight, wind, kinetic energy – our everyday lives are teeming with unused or wasted energy. What is needed are ways to convert the energy that already exists all around us into usable electrical energy. That is what the newest developments in energy harvesting technologies are accomplishing.
Energy harvesting technologies are finding innovative ways to capture the unused energy in our environment (ambient energy) to power our multitude of electronic devices, including small wireless ones such as those used in wearables and IoT. While to ultimate goal is to advance this technology to achieve reliable power self-sufficiency for devices, the power demands of many devices are still greater than what can be supplied by energy harvesting alone. For some low-powered devices, the power generating capabilities of energy harvesting technology are sufficient, but at this stage, harvesters are likely to serve in more of an adjunct capacity, helping to extend battery life. Still, the benefits of realizing this technology in terms of cost savings, waste saving (green technology), and the spawning of new applications is motivating increasing investment and interest.
The ways in which innovators are designing energy harvesters and their capabilities are quite impressive. Current technologies are exploring many different energy sources (thermoelectric, light, vibration, etc.) in a variety of form factors, creating the possibility of converting our environment into a reliable and perpetual power source. We will examine some of the latest energy harvesting technologies presented at IDTechEx 2016 and discuss what future developments are expected.
With the ability to convert light from more parts of the spectrum into usable electric energy, newer photovoltaic energy harvesters can now supply power for both indoor and outdoor lighting conditions, even when sub-optimal. Far from bulky grid solar arrays, the latest technologies are seeing good performance from small or thin-film form factors for low-power devices.
As covered in The 10 Most Futuristic and Innovative Startups at IDTechEx USA 2016 (Cont.), Ubiquitous Energy has developed the first transparent solar cell that can be applied as a thin film to any surface. Their ClearView Power™ technology absorbs light from outside the visible spectrum (ultraviolet and infrared) enabling transparency and has the potential to transform a wide selection of unused light-exposed surfaces to energy harvesting surfaces.
Alta Devices manufactures their solar cells from gallium arsenide, a design responsible for the world-record in efficiency for single (28.8%) and dual junction (31.6%) energy conversion. Their thin and flexible cells can be used for energy harvesting purposes to extend battery life and are especially ideal for wearable, IoT, and energy vehicle applications. The form factor allows for custom sizes to be produced for integration into a final product.
Dye-sensitized solar cells (DSSC) from Fujikura are efficient converters even in low lighting environments (both indoors and outdoors) or for light reflected off other surfaces. DSSC has been called ‘artificial photosynthesis’ because it works akin to the process of photosynthesis. Just as pigments in plants absorb sunlight energy to power operations, the specialized dyes used in the solar cells convert light energy into usable electricity. The cells are well-suited for small devices, such as sensor nodes for IoT applications.
While still in the early stages of commercialization, perovskite photovoltaics are an exciting advancement in solar technology. Perovskite is a calcium titanium oxide mineral. The material is garnering a great amount of interest for its incredible efficiency improvement (from 2% in 2006 to 20.1% in 2015), but it is unclear if it will pass conventional (silicon) solar cell performance. However, the technology has value as far as lowering manufacturing costs and it carries the beneficial properties of other 3rd generation photovoltaics: thin-film, flexible, customizable form factors. Analysis from IDTechEx projects the market for this still-emerging technology to be over $200 million in ten years, and it will be interesting to see if further development yields greater efficiencies in the future.
Harvesters of this variety generate electricity from a temperature differential between two materials. Given that much of our machinery, our bodies, and the materials in our environment give off heat, there is huge potential for harvesting wasted heat if efficient systems can be designed. Thermoelectric (TE) harvesters are focused on several applications: waste heat recovery from vehicles (or machinery), and the powering of wireless sensor networks and consumer electronics, including wearable tech. Success in powering sensor networks and consumer applications depends on providing high energy conversion efficiency in a convenient or suitable form factor.
In a presentation titled ‘High-Performance and Low-Cost Thermoelectric Energy Harvesting: Advanced materials, Manufacturing and Systems’, Dr. Yanliang Zhang, Director of the Advanced Energy Lab at Boise State University, discussed two remarkable developments in TE energy harvesting. The first is a printed flexible TE energy harvester. The devices are made by synthesizing nano TE ink which is directly converted into a flexible film through screen printing process. By using printing technology, the harvesters can be made at a significantly reduced cost compared with bulk materials. These high-performance harvesters have promising applications in powering sensors, flexible electronics, and wearable devices.
The second great development out of the Advanced Energy Lab is a high-temperature and high-power density thermoelectric generator (TEG) that was measured as producing 1 kW of electricity by harvesting automotive waste heat. As with the printed TE harvesters, the TEG is fabricated from nanostructured particles, which are built up into larger components. The system can be used to harvest energy from automobiles, industrial equipment, aerospace, etc. This technology will go a long way in recovering and making useable the massive amount of waste heat produced by large mechanical devices.
Figure 2. Advanced Energy Lab’s high-performance printed thin film energy harvester using nano TE ink.
Otego’s sugar-cube-sized TE generators are a great example of achieving the two main qualities required for successful deployment in IoT: small size and cost efficient. The generators are produced by printing electrically conductive plastics on ultra-thin foils with 3D printing technology, allowing for mass production at a lower cost. The conveniently small harvesters are durable, flexible, and heat resistant.
Figure 3. Example application of TEG by Otego. A circular wireless temperature sensor on the left transforms heat to electricity when there is temperature difference (the heat from the water circulation in this example) to power itself.
For use in sensor networks and other low-powered IoT devices, TE energy harvesting solutions will likely continue to incorporate low-cost materials and manufacturing processes, and thin and flexible form factors. As more and more options emerge, gains in efficiency will provide added value.