Multiple solar panels

I currently use the Particle Power Shield with its 2000 mAh LiPo and a 9V 150mA (1.35W) solar panel. When running my project, I notice that only under the very brightest sun, (I’m even seeing a measurement of 160mA (~1.4W) from the panel at this point) will the panel power the project and charge the battery (slightly). Most of the time, however, the board is drawing from the the battery.

This surprises me, because my project only requires about 110mA @ 3.7 V or about 0.4W. Where’s the rest of the power going, if not in the battery? Its almost as though I’m still only getting the 150-160mA even after it is scaled down to 3.7V by the power shield. Is this what is happening?

Anyway, clearly the panel is not large enough. I realize I could probably get a larger panel, but I’d like to explore connecting multiple panels in a circuit. The idea would be that each would be permanently mounted facing a different direction around a 4"X4" wood post so that one points directly North, one East, one West and one South. In this way, I don’t really require any consideration to how the application is installed.

I seem to recall reading somewhere that if I connect panels in a series, they’ll only perform as well as the worst one in the series. Is this true? Also, is the same thing true if they’re connected in parallel?

Any experience shared here would be great, thanks!

Hi @mkoistinen,

Although the power is the same for series or parallel, since W = V * I, if you wire them in series your current is the same, but voltage doubles. In parallel, voltage is the same, but current doubles (doubling juice for your project). Keep in mind also that power shield maximum input voltage is 20 V.

Thanks for your reply, but this much I know =) In my 4 panel setup described earlier, I’d likely have them as 2 strings in parallel of 2 panels in series each. In this configuration, I’d see 18V @ 300mA (max).

What I’m not clear on is if the 4 would only perform as well as the panel getting the least amount of light.