Energy harvesting in its different forms has been in place for many years with larger installs like solar fields and wind turbines being the most obvious demonstrations of these in action. However, it is in the industrial and automotive spaces where the next range of devices are set to benefit from harvesting energy from the environment.
As IoT moves more into the industrial space its ability to harvest from vibration, heat and internal light sources will become increasingly important. According to EETimes, the expectation by 2020 is that in automotive 46% of energy harvesters will be based on thermal harvesting and a further 44% will be using vibration as an energy source. Vibration harvesting is expected to see its biggest market coming from Tire Pressure Monitoring systems on vehicles.
>Both automotive and industrial environments have some similarities. They have to cope with variable temperatures, high moisture levels, as well as both often having difficult-to-access measurement points. These environmental elements require the wireless sensor node to be moisture resistant, small in size whilst being able to withstand both high and low temperatures. These demands create challenges not only for the energy harvester and control systems but also for the energy storage solutions vital for enabling the sensor node to function even when the harvested energy source is not available.
Current implementations require either wired solutions or battery/capacitor energy storage in wireless installs. In automotive, the wiring harness has become the third heaviest component of the car and adds considerable time and cost to the assembly and maintenance of vehicles. By being able to remove a proportion of this wiring through the use of wireless sensor nodes reduces costs. However, the energy storage used needs to be small in size, able to withstand higher temperatures as well as required to work in increased ambient moisture. In the industrial context IoT is gaining most traction in providing additional functionality to existing installed equipment. Any additional sensing nodes need to be standalone from the equipment they are monitoring.
Batteries offer a range of energy storage solutions to these markets but come with a series of trade-offs. Standard battery cells can provide an extension to the energy harvested power, however they need additional shielding to make them tolerant to moisture and require replacement maintenance. Capacitor storage results in higher leakage current shortening the amount of time between charges and a larger form factor making it unsuitable for small sensor nodes. Ilika has been working with partners in the automotive space for many years and has gained a greater level of knowledge of the battery requirements for less hospitable environments. This knowledge has been applied to its solid state battery technology, Stereax, which provides improved energy density footprint enabling more energy to be stored in a smaller space. It can support temperatures up to 100Deg C and with no free lithium and it is more suitable for high moisture environments. Battery technology holds one of the keys to the proliferation of wireless sensing in industry and automotive spaces alongside the thermal and vibration energy harvesting.