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I’m not familiar with your particular application, so I can’t speak to what is normal. I’m going to assume your 300W panels are 12VDC. Also don’t know if your controller is MPPT or pulse width modulation. An MPPT controller isn’t 100% efficient. 80-90% efficiency should be expected.
If you made your own panel, what is the rating for each pv cell? You can wire more cells in series to increase voltage. Your current panel is probably delivering about 25 amps with good sunlight, direction, and a clean surface. Remember anytime you double voltage, your amperage is inversely affected. At 24 volts, your amperage will be 12.5 (W/V=A). Your amperage is limited by wire size and controller output.
My personal opinion is that’s a lot of work to charge some lead acid batteries. I can offer a couple different solutions to get the same thing done. Obviously a traditional charger is a suggestion. Size an inverter that can work with your pv cells, or just buy a small generator. The other option, if space allows, is to wire in another set of batteries using a DPDT switch. When one set gets low, flip the sw to use the others while set 1 is charging.
That being said adding another panel, if yours is store bought, might be easier if the controller can handle it.
(Short story to illustrate)
When I had another water well dug I was overseas, so it was done over the phone. I wanted a strong pump and a freq drive. When I got home, I saw the traditional contacts and a big pressure tank. Looking at the invoice I notify the pump installed was only .5 hp. Obviously things were not to spec and the pump had to come out, but so was the wiring since it was good for 1/5 hp @ 110VAC, but not adequate for 2hp. Since a VFD was going in anyway, wiring the breaker to 240v cut the amperage in half, allowing it to be sufficient.
Last edited by Jjorgis5569; 09-17-2019 at 03:08 AM.