Tahina has seven 80-watt solar panels on top of our bimini roof. This has always given us a nice way to compensate for some of our electrical energy use each day (primarily our freezer and refrigerator). We recently upgraded our battery bank to new Lithium-based batteries (read about the upgrade here). The batteries are working great, and we are thrilled with the decision to get them. But, we had an issue with our old solar system.
The solar charge controller that came with the boat seemed to be fine for traditional boat batteries (Lead, Gel, or AGM), but the new batteries run at a higher voltage and need to be charged up to 15.2 Volts regularly. Solar panels actually run at 17-18 Volts, so it should have been a simple matter of adjusting the controller settings. But, the unit we had could not be adjusted to high enough voltages. As it turns out, I’m glad.
The new controller recommended to me by the outfit that sold me the new batteries is a Morningstar Tristar MPPT controller. The new controller not only has the ability to charge to the higher levels, but the MPPT part is important. It stands for Multiple Point Power Tracking and gets more power efficiency out of a solar system. I’ve been surprised at the results. They claim it will gain 10% efficiency, but we are seeing much better performance with our system. This is probably because of the higher voltage the batteries use (less voltage drop).
During the first few days with the new system, it not only smoothly topped off the batteries to the higher voltages, it also completely re-filled the batteries for 4 days straight with no engine use. The only reason it didn’t on the 5th day was that we had a cloudy day. This was far better than we were getting with our previous controller.
Thanks to the new batteries, which can charge at a much faster rate, we can use the engine alternators, or the generator, to charge up at bulk amperages to fill the deep cycles. Then use the solar to top off to the absorption voltage until it settles to float. We did that before, but the new system will do it even better. Nice!