MPPT - Series of Parallel ???

Re: MPPT - Series of Parallel ???

If the panels are mounted on the same surface (both face the sun at the same time at the same angle) and the electrical wire length is relatively short (10 feet or so of 14 awg wire from panels to charge controller)--then, in your case, you could wire the panels in series or parallel and get optimum charging current.

If the panels are not on the same surface when facing the sun (such as one on "left" other facing "right") and/or they will be subjected to shadows from rigging/etc., then you would probably be better off wiring them in parallel. This is because the output of the panels (current) is porportional to the amount of sun hitting the entire surface of the panel. If there is a difference in the level of light and/or shadows on one panel and not the other, the current will be reduced in one panel (the one in shade). When the panels are in series, the one panel will limit the current of both panels.

Panels will only work well for you if they are in full sun. Any shadows from a line/mast/fitting/etc. (or when the panels are not directly facing the sun--such as happens on a boat) will dramatically reduce their outputl. Panels will be helpful in keeping your battery(ies) charged--but if you need a fair amount of power (running lights, anchore light, transmitter, GPS, etc.)--you probably will still need a fuel driven generator (and for backup in cloudy weather).

Things that will help--get LED navigation lights, cockpit lighting, low power radios (at least for primary use), and such... Conserve your power usage.

The Morning Star MPPT charge controller is 100% the best one for its size out there... However, it absolutely needs the Remote Battery Temperature Sensor (PDF Spec.) for charging your battery bank. The controller tends to error on the "hot side" if you use its internal temperature sensor and significantly leaves the battery with less than full charge.

MPPT (Maximum Power Point Tracking) will basically allow your controller to take anything from 17-75 volts (Vmp/Voc solar panel voltage range) and efficiently convert this into the ~14-15 volts DC that your battery needs for charging.

If you where in a very hot area and/or you had a long distance to run your PV panel wires to the charge controller (always keep the wire run short between charge controller and battery bank) then MPPT would be a help to run at a higher voltage (your panels in series). This reduces the voltage drop in your PV wiring run (and/or you can use smaller gauge wire to save money--a big issue for larger arrays used large systems >1,000 watts). And because Vmp (panel output voltage) falls with increasing temperature, if you have hot panels and very cold batteries (which require higher voltage for proper charging) you can run into an issue with Vmp+Controller/wiring voltage drop is less than the optimum voltage required to charge your battery bank (should not be a problem with your panels as their Vmp is over 17 volts at standard temperature).

Remember, never under estimate how much shading will reduce your solar panel output... With two panels in parallel (or even in series), just one rope across one panel may reduce your system's output by 50%.

Also, I would highly suggest that you install a battery monitor in your system if battery power is critical for your safety (and to help prevent battery damage from over discharging and/or deficit charging). They are not cheap--but it is the only way you will know the state of charge of your battery bank at any time (without using a hydrometer to measure the specific gravity of the electrolyte in your battery--which is impossible if you have an AGM/Sealed battery bank).

-Bill

Re: MPPT - Series of Parallel ???

Paul,

Sounds like you have it all taken care of.

Have a fun and safe voyage!

-Bill