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post #6 of Old 03-07-2008
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99.1% ? Not according to that PDF file, or other information I've been given. That PDF files says 98% IF you are using a 48VDC battery and array--which isn't going to be on sailboats.

The numbers I'd gotten from one of their competitors said about a 4-6% power loss in pretty much all MPPT controllers, but that is offset by the greater efficiency and the advanced charging algorithms, which allow an MPPT controller to continually apply maximum amps at "just enough" vols, rather than a conventional 3-stage charge.

Outback is also claiming to use a "5 stage" charging process, which is frankly crude compared to a continuous charging profile that another vendor uses.

Overall? Let's say your solar panel puts out 17.5V at 30A during peak sunlight, that's 525 watts. With a REGULATOR, you will get 14.4V at 30A, or 432W, some 82% of the real available power. You've lost 18%.

But with an MPPT charge controller, that 525 watts will be converted to 14.4V at 36A, fully 20% more power than the regulator was giving you. So the controller loses are still gaining 16% and the battery may charge 10% more efficiently at the same time. Even if you figure a 16% gain--that's a lot. (MPPT controllers are putting out pulsed DC, not the pure DC from a direct panel, so while the controller absorbs some power, the batteries still charge faster because they are not gassing internally the same way that pure DC would make them.)

And since a good controller will optimize the voltage/amperage even further than that (i.e. if your battery only needs 13.6V to charge it, it could be fed 38A instead of 36A)...there are some really significant gains to be had.

Against that, the MPPT controllers are outright expensive, and there's no easy way to combine an MPPT controller and a conventional engine-driven alternator/regulator running at the same time. (Each will drive the other nutso.)

Now, if you want to talk about moveable panels and automatic solar trackers that move them to track the sun--that's not for sailboats. Sailboats rock and roll in three dimensions, there's no tracker on the planet that can swing solar panels around that way and still spend less energy than it gains.

Last edited by hellosailor; 03-07-2008 at 03:09 PM.
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