Solar Panel analysis

Hi all!

I hooked up a solar panel and LDR to the sparkCore – not to power it, but to figure out how much power I can really get out of it. I wanted to know if a panel would generate enough power to take on backpacking trips, and also to know if I could use it to power a spark when outside, away from an outlet.

It turns out that panels, at least the Goal Zero Nomad7, are pretty picky when it comes to light. They just shut down when clouds drift over, or even with a little shadow. Here’s my complete analysis:

I’d really like your feedback. Did I do all my math correctly? Any suggestions on how to better analyze the panel?


Hi @bheliker

I liked your write-up–it was very nice! I have a bunch of Goal Zero gear including a Nomad7 from 2 years ago and several Guide 10 and Switch 8 battery packs and I like their stuff quite a bit.

A couple of things in your analysis might be hurting you.

  • You had the panel indoors behind glass, but that cuts the output way down in my experience. Outside is better. I am sure there are practical considerations here, but if want better data, you probably need to measure outside.

  • You analyzed the USB output, not the raw output. It’s an 8-9V panel so the +5V USB port has to have electronics (probably a buck converter) to bring it down to a regulated 5V output. That voltage converter is not 100% efficient so some power is lost, but more importantly it probably has a drop out zone when the input solar power is too low.

  • You might want to mention how you got the data off your Spark and onto those nice graphs.

It takes a really sunny day to fully charge a Guide 10 pack with 4 AA’s for me and so generally it takes one and a half normal days to get it full. The Switch 8’s do charge in a normal day but don’t hold as much. I may get a Switch 10 eventually but I have a lot of batteries right now.

By the way, don’t let anyone with a newer Android phone borrow your Switch 8 battery for charging their phone–I loaned one out last June on a whitewater rafting trip and the battery overheated and shut down in just a few minutes!

Nice job!

1 Like

Thanks for the compliments!

  • Indoors vs outdoors: agreed and I know. But I didn’t have many options, as my setup isn’t waterproof so I’d have to actually baby-sit the device instead of set-and-forget :slight_smile: Good point though: I should include a disclaimer sentence.

  • USB: I thought about using the ‘raw’ output, but what I’m really testing is the ability for the Nomad to charge my phone, so I figured even though it is capped at 5V it is a more legitimate test. Does the Nomad charge the Switch via USB or via the raw? I wasn’t able to figure that out from their online descriptions.

  • I suppose I could reveal some secret sauce, haha!

Thanks again,

I get your point about comparing the panel for phone charging. And the Switch 8 is USB in and out only, so that applies here as well.

The Guide 10 packs take the “raw” 2.5mm connector.

Obligatory Spark content: Both the Switch 8 and Guide 10 work great for powering a Spark core. I often use the Switch 8 to make a firmware testing setup mobile for WiFi range testing or to take the Spark to the sensor for testing.