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 : )

Mobile Battery Cart - Update

Those of you who have read my June 2015 post about the mobile battery cart will remember the Deka marine battery and the unpainted plywood lid. Since then I have painted the lid to match the rest of the unit and have replaced the Deka battery with two new 6 volt/220 ampere-hour golf cart batteries, purchased from the battery company I work for part-time. The batteries are both contained in ABS battery boxes so they are out of sight and any leakage that might occur will be contained. Having the batteries NOT readily visible is important, lest my landlord or, in the event of some emergency - firemen or EMTs, see them and get upset. Given the way this unit is constructed, it looks clean, organized and purposeful. One would NOT walk up to this and say "why do you have car batteries in your house?" Yes, it's clearly some sort of electrical device, BUT it's NOT scary looking.

Note that since the golf cart type batteries are taller than a marine or car type battery, they will not fit inside the standard ABS battery boxes available at big-box stores like Wal-Mart or at auto parts places - you'll probably need to get them at a battery company as I did. Mine cost me between $7 and $8 apiece. The batteries - made by USA battery - will run between $130-$170 apiece, typically. USA battery uses really hokey "quick release" type battery caps that inevitably leak; since I bought my batteries at a battery shop I was able to get GOOD LEGITIMATE screw-type retrofit battery caps at nominal cost. They're well worth the investment.

This system can provide about 2400 watt-hours of electrical storage - PLENTY for operating lights, amateur and shortwave radios, etc. in an emergency. Given about 300 watts of solar panel capacity, it could provide sustainable "off grid" operation.