I've got a cabin that I visit on weekends and because I need to charge my computer and tools there, I decided to bring an old car battery and bought a solar panel to charge it. Right now I use a cheap regulator and there's enough energy to power the lights and charge a laptop twice a week but I'm planning to expand the setup to achieve greater input and battery capacity and more effective charging. I'll probably have multiple solar cells and multiple batteries.

Starting from the solar panel, I'll probably need a MPPT regulator to harvest the maximum power available from the cell. I think that I'll have to use just one regulator even if I buy more solar cells, since most regulators aren't waterproof, I guess, and I've got only two wires to the roof. Does this mean that I'll have to buy solar panels with similar V-I curve and connect them in parallel?

I'm not really sure about the next part. If my understanding is correct, I get some power from the MPPT and I need to convert it to a form that is best suited to charging the battery using some kind of an intelligent step-up convertor. How does that work exactly? I guess it's not enough to use this thing set to 14.4 V output, or is it? What exactly do I need to do with the voltage?

  • \$\begingroup\$ There are a lot of questions there covering a bunch of issues. Try breaking your post down into individual questions and do a search for answers to each of the individual questions. As it stands this is going to get closed for being to broad. \$\endgroup\$ – RoyC Dec 11 '18 at 9:57
  • \$\begingroup\$ I removed the trivial sub-questions and only left the things that I don't understand. Is this better? Do you have any other recommendations? \$\endgroup\$ – m93a Dec 11 '18 at 10:10
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    \$\begingroup\$ what you want is a battery charger (for the correct chemistry), with MPPT input capability (for the range of input voltages you want to cover). Job done. An 'MPPT regulator' is like the sound of one hand clapping. What's its output? You could choose a random voltage and do the job in two stages, but so much easier to choose a battery charger output. \$\endgroup\$ – Neil_UK Dec 11 '18 at 10:10

I would recommend sourcing a proper MPPT battery charger, designed for the job. You don't want to over-charge the battery when it's not being used.

If you connect panels in parallel, ensure they are protected by diodes, to prevent one panel forcing current backwards through the others. Some panels may have diodes already built in.

Or use a charger designed to handle a larger input voltage and wire the panels in series. But if wiring in series, the current is limited by the weakest panel. Beware of issues with shading of the panels by nearby trees.

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