Hi
I am in the process of ordering IXOLAR solar cells for a smoke detector project that will utilise ambient light indoors. Your website has datasheets for IXOLAR solar panels at STC, while the IXOLAR solar cells are for both indoor and outdoor application. Is there any datasheets available for indoor application for these products? I have a daily load consumption of 24mAh and a charging current of 2.4mA over a 10 hour period when the ambient/natural light inside is approximately 1500lux-2000lux. I am considering using SM641K10TF (6.91V) or SM811K08TF (5.53V) IXOLAR solar panels. The charge controller is a BQ25504. From the existing datasheets I am having difficulty in approximating the voltage and current for indoor application.
Greetings,
One can get a rough grasp on the question from basic principles, starting with an estimate of the energy available.
2000 lux is 2000 lumens per square meter. Lux/lumens are units calibrated to human visual sensitivity and thus crummy for things not related to human vision, so we’d want to convert that to radiometric units. One would need to define the light source to do that properly, but a loose guesstimate figure might be on the order of 400 lumens/watt.
That means (loosely) that the available light energy amounts to about 5 watts/square meter of panel area, before conversion efficiencies.
Going to the datasheet for the '641, we can check the O.C. voltage vs irradiance curve.
5 Watts/square meter is at the extreme left end of the business where the curve is falling precipitously. That chart’s drawn on a per-cell basis and they spec the O.C. voltage as~6.9v @ 1000w/m2, so it can be inferred that the product in question has 10 cells in series. So, open-circuit voltage with 2000 lux might end up in the ballpark of 4 to 4.5v.
Current at max power point with 1000w/m2 irradiance is said to be 252 mA. As a loose guesstimate one could assume that’s proportional to irradiance, so with only 5w/m2 (2000 lux) one probably shouldn’t hope for more than about 1.3mA of current at MPP.
Depending on conversion efficiency and the voltage you want that 2.4mA to be delivered at, I’d guess that the '641 panel would end up on the borderline of being feasible for your intended use. Ultimately, it’s a thing you’d have to to prove out for yourself.