Quote:
Originally Posted by dave777
Hi Waeshael,
Thanks for that in depth explanation.
Does the same hold true when you have an MPPT charger on the solar cells? My understanding is that the MPPT charger is a DC to DC converter and essentially reduces the charging voltage to the lowest amount which will still charge the battery.
In any case, what do you recommend when motor sailing with a solar charger. Should we turn solar off when motoring and hopefully remember to turn it back on when the motor is off?
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Answer:
Under
power I would switch off the Solar feed to the
regulator. This will allow the alternator to do its job. I presume you are under
power to charge the
batteries? Even a small alternator will charge the
batteries in much less time than either solar or wind.
The MPPT controller attempts to maximize the current output by operating the solar panel at its maximum power setting. Usually this requires the o/c voltage from the panel to be above 18 volts, but the battery of course limits this to whatever is its current battery terminal voltage approx 13 volts. The internal
regulator of the MPPT controller converts the 18Volts at the panel to the 13V of the battery using a DC to DC converter, as you said. There are some losses in this so you won't notice a lot of benefit in a small solar array. Perhaps you might get a 10% net benefit. In any case the same regulation problem remains even with an MPPT controller, so disconnect the solar input to the regulator.
To get the most from the
solar panels you need to orient them so that any shadow that falls affects the least number of
panels. On a sailboat the
panels should be installed along the long axis of the vessel, not across the beam where the shadow of the
mast or
shroud would cross all panels.
If you are at
anchor you could rig a second
anchor rode attached to the main
rode with a rolling hitch that would allow you to pull the
boat around to avoid
mast shadows.
On my
boat I removed the main boom altogether at anchor so the panels can see the sky clearly.
Another thing is to reduce the power
consumption by using LED
lighting for everything, and
low power fans etc. The biggest power consumer is the fridge/freezer and there are some models that consume less than 2.5 Amps average thats about 50 A-Hrs a day. I hope to put about 100 A-Hrs a day into the batteries, that's 120 A-Hrs from the panels, and keep the sum total of my power usage to less than 100 A-hrs a day. I measure current using a clamp on probe.
One way to remind you that the solar needs to be turned on is to have a bright voltage display in the
companionway where you can glance at it every time you go up. If it is reading less than 13V, you need to switch the solar on. A battery not being charged at all will read less than 12.8 volts with a moderate load, such as TV.
cheers