Solar Power Plus Off-Grid Battery System: Putting It All Together

Readers familiar with my Off-Grid Mobile Battery cart will remember my writing about my plans to use solar panels to recharge the batteries. Reference Off-Grid Mobile Power Supply and Mobile Battery Cart Update for full background information. Over the past few months I have obtained a pair of brand new 100 watt solar panels from a supplier on eBay. I recently ordered the second panel and got it in the mail this week. I took advantage of the sunny weather and a breather from work today to test the panel "live" with the battery cart.

These 100 Watt panels each come with a pair of 10-15 foot long 14 mm cables and a charge controller. That is NOT a bad deal for $140 apiece!! Even ignoring the cost of the cables and controller, that comes to $1.40 per watt. Additional panels can be purchased without the controller for closer to $125. That said, any solar power system needs a charge controller to ensure the batteries aren't overcharged during full sun.

I figured I'd need about 300 - 400 Watts worth of solar panel capacity to really handle these 220 ampere hour batteries. As of now I have a pair of 100 Watt solar panels, though I'm just testing the one I got this week.

To run a quick test, I temporarily connected the whole mess up to the battery cart with some alligator clips, then arranged the panel on my front porch with the cables running through the front doorway back into my living room. I believe the charge controller may have issues, as it was only allowing about 2.5 amperes through even with a heavy load connected to the battery and a terminal voltage of 12.58 volts. I disconnected the charge controller and just connected the panel straight and got plenty of current, as the meters in the photo reveal. The orange meter is reading the current in amperes; the gray one is reading the voltage. At one point I did see the rated 5 amps these panels produce. Clearly, I need to address the charge controller issue, because at 4+ amps for ONE panel with a battery voltage of 15 volts, I'd quickly cook these batteries if I ran without one for long!

Stay tuned for future testing of the system with both panels : )