Common solar technology can power smart devices indoors
Every time you turn on a light at home or in the office, you are expending energy. But what if flipping the switch also meant producing energy?
“People in the field assumed that it was possible to power IoT devices with long-term PV modules, but we haven’t really seen the data to back it up before, so it’s kind of first step to say we can pull it off, “ said Andrew Shore, NIST mechanical engineer and lead author of the study.
Most buildings are illuminated by a mixture of sunlight and artificial light sources during the day. At dusk, these could continue to supply power to devices. However, light from common indoor sources, such as LEDs, covers a narrower spectrum of light than the wider bands emitted by the sun, and some solar cell materials capture these wavelengths better than others.
To find out exactly how a few different materials would stack up, Shore and his colleagues tested mini-photovoltaic modules made of gallium indium phosphide (GaInP), gallium arsenide (GaAs) – two materials geared towards white LED light. – and silicon, a less efficient material. but more affordable and commonplace material.
The researchers placed the modules a few inches wide under a white LED, housed inside an opaque black box to block out external light sources. The LED produced light at a fixed intensity of 1000 lux, comparable to light levels in a well-lit room, for the duration of the experiments. For silicon and GaAs PV modules, soaking in indoor light was found to be less effective than sunlight, but GaInP module performed much better under LED than sunlight. Both GaInP and GaAs modules have far surpassed the silicon inside, converting 23.1% and 14.1% of LED light into electrical energy, respectively, compared to the power conversion efficiency of 9.3. % of silicon.
Unsurprisingly to the researchers, the ranking was the same for a load test in which they timed the time it took for the modules to fill a half-charged 4.18-volt battery, with silicon coming in last with a margin of more than a day and a half. The team wanted to know if the silicon module, despite its poor performance compared to its high-end competitors, could generate enough power to run an IoT device on low demand, Shore said.
Their IoT device of choice for the next experiment was a temperature sensor that they connected to the silicon PV module, once again placed under an LED. By turning on the sensor, the researchers found that it was able to wirelessly transmit temperature readings to a nearby computer powered by the only silicon module. After two hours, they turned off the light in the black box and the sensor continued to work, its battery draining at half the charging speed.
“Even with a less efficient mini module, we found that we could still deliver more power than the wireless sensor consumed,” Shore said.
The team plans to tackle both issues, first by installing light meters at NIST’s residential net zero energy test facility to understand what light is available throughout the day in an average residence, Shore said. Then, they’ll replicate the net zero home lighting conditions in the lab to find out how PV-powered IoT devices work in a residential scenario.
Feeding their data into computer models will also be important in predicting how much energy PV modules would produce indoors with a certain level of light, a key capability for cost-effective implementation of the technology.
“We turn on our lights all the time and as we move more and more to commercial buildings and computerized homes, photovoltaics could be a way to reclaim some of the wasted light energy and improve our efficiency. energy “, Shore said.
Source and top image: National Institute of Science and Technology (NIST)