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Using solar to charge 18v batteries?


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I recently purchased a Ryobi jobsite battery charger, as I have a good amount of batteries to charge. One of the main reasons I have these batteries, besides using them with my current tools, is so I will have an option for power (light, charger for phones, radio, fan, ect) if our electricity was to go out due to storms or any other reason.


As it is impossible to know how long power can be out, I am thinking about possibly setting up a back up solar system to continue charging the batteries if necessary. Does anyone here have any experience for the basic requirements for a system like that would be? Thank you in advance!



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You can do it. We have solar farms in NC (second only to California in solar) that are hundreds of acres. But realistically it’s not usually worth the money to do more than trickle charging to maintain. But for instance at a local mine we put up portable wi fi hot spots which were a couple car batteries, a solar panel, an inverter, and the radio. Trouble is the wind are up the solar panels with blown sand and dirt (scratched them up) in a year.

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It could be a lot more size and complexity than you may want to commit to. But you’d probably really like what you end up with if you do it right. I’d recommend going with a 12V RV-style system to reduce the complexity, cost, and inefficiency of inverters, especially if you do in fact intend to move the thing between job sites. The panels will retain the charge of however many deep-cycle lead acid batteries, which depending on how you do things can loosely be thought of as doing much of the actual charging for your tool batteries. You’ll have to buy Ryobi’s automotive charger, but that isn’t terribly expensive and in Ryobi’s case charges just as fast as their plug-in chargers.


You’d want to do the math for how quickly you burn through battery charges, based on that decide how many deep cycle lead acid batteries you want, and then how many panels you’d need to keep them charged. Like a lot of things, overbuilding is better than falling short. I would shoot for a system where the lead acid batteries are never going to get below 50% charged (deep cycle or not). Be aware panel ratings are generally very close to “best-case” estimates and they’ll spend most of their time making quite a bit less power than their rating. Angle of the sun, cloudy days, etc. There will also be efficiency losses all over the place. So shoot for generously overbuilt.

I have a small system (100W) that I use at Burning Man (a week-long festival out in the middle of a desert in Nevada). It powers lighting, ventilation, and I will use it to charge some of my lithium batteries for tools and other things as they die...which at my rate of usage out there isn’t very fast. Maybe a battery every few days. It’s plenty for that. But beginning next year it may have to power more for general camp operations so it will likely have to be expanded. But it’s very likable. Set it, forget it, no noise, refueling or fuss like with a generator. When something needs power just plug it in. But if your power needs are very large, you’d need a correspondingly large system. That may be a lot of hassle to build up and tear down constantly depending on how often you have to move it. A friend did a 400W system that he installed on his fifth wheel, panels permanently installed on the roof which has been serving him nicely. You have to protect the panels from wind. It’s not a trivial project to do right. But it’s awesome.

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  • 2 weeks later...

You don't want to use 12v to charge, you can certainly use the 12v panel and convert it to 18v. You'll lose charge current but you won't destroy the battery by under-volting.




Should be able to connect directly to 100-200watt panel.

Should use a voltage regulator.


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