New research has shown that commonly available solar PV technology used indoors can power building IoT devices.
The research from the US National Institute of Standards and Technology (NIST) was aimed to test the ability of solar PV cells to absorb indoor light and opens the way for harvesting some of this light for low power devices with low capacity batteries such as smoke alarms, security cameras and temperature sensors.
The researchers tested three different materials, gallium indium phosphide (GaInP) and gallium arsenide (GaAs), which are geared toward white LED light, and silicon, a less efficient but more affordable and commonplace material.
The modules were tested with white LED light with a fixed intensity comparable to light levels in a well-lit room. For the silicon and GaAs PV modules, the indoor light proved less efficient than sunshine, but the GaInP module performed far better under the LED than sunlight.
Further, both the GaInP and GaAs modules significantly outpaced the silicon indoors, converting 23.1% and 14.1% of the LED light into electrical power respectively, compared with silicon’s 9.3% power conversion efficiency.
When hooked up to a temperature sensor, even the silicon module, absorbing only light from the LED, was found to supply more power than the sensor consumed in operation. With the light switch off, the sensor continued to run, its battery depleting at half the rate it took to charge.
“People in the field have assumed it’s possible to power IoT devices with PV modules in the long term, but we haven’t really seen the data to support that before now, so this is kind of a first step to say that we can pull it off,” commented Andrew Shore, a NIST mechanical engineer and lead author of the study.
“Even with a less efficient mini module, we found that we could still supply more power than the wireless sensor consumed.”
The researchers consider that the results are particularly applicable to commercial buildings where lights are on, often around the clock.
Outstanding questions are how well PV-powered devices run in spaces that are only lit intermittently throughout the day or shut off at night and the contributory impact of the external ambient light.
These are due to be tested in NIST’s net zero energy residential test facility and in-lab simulation of a residential scenario. Modelling to determine the power output for different light levels also is planned.