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christern avatar image
christern asked

One or several MPPTs for panels with different orientation?

Hi all cleaver people. Have searched the forum but not sure I get the picture of the best way for me.

Today I have an MPPT of a different brand and it has been working OK since installed but now it has started to behave a bit unreliable so I aim at replacing it with a Victron Smart 75/15 (that would fit well when I am to install a BMV 712 later this year).

The situation is that I have two identical panels (44W each in parallel) on the roof of my boat and one (135W) above aft deck, also connected in parallel and with some downfacing angle to catch as much sun as possible when anchored with sunset on aft deck. The panels are almost never in direct sunlight all three at the same time, but it can happen. All specs of the panels are within ranges of the controller but not identical.

So, what is the best solution? One or two MPPTs?

Isn’t it so that two MPPTs would “challenge” each other (finding different Max Power Points) when operating at the same time but with direct sun on one and indirect on the other?

If that is not the case, what are the real benefits and is it really worth the extra cost? (Naturally the financial aspect is up to the individual but as always there are other priorities that needs to be considered.) Any input appreciated.

Thanks

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2 Answers
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marekp answered ·

@ChristerN It is better to have separate MPPT for each direction.

They will not compete with each other. Each MPPT will just charge battery with its own current.

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christern avatar image christern commented ·
Thanks @MarekP for reply.

I was thinking that since the MPPT process is to test one voltage and see what current is received by the battery and then test another voltage and compare the reception with the previous and so on until highest current is reached and when having two regulators doing so simultaneously would mess up the process for both. This assuming that both have a voltage that exceeds battery voltage by 5 V and thus starts tracking. This was one question but I trust your statement until something else is said.

The other question is what the real benefits are of having two regulators. One set of panels will always have the majority of sunlight and would be the major source for charging. Is there any way to explain why two MPPTs would be more efficient and to what extent?

(Sorry for these questions that may sound stupid but it is my way of understanding pros and cons.)

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marekp avatar image
marekp answered ·

@ChristerN

The max current searching is on the PV panels side. This is why it is called "MPPT" (Max Power Point Tracking).

On the charger side each MPPT puts out its own current to the battery if PV voltage is 5V over the battery voltage.

I have two MPPT units charging same battery.

The benefit of having two MPPTs is that with the different Sun exposure they can track max power point independently and feed the battery at individual max power point. Panels that are not exposed to Sun directly can also produce some power thus providing more efficient use of the available Sun.

"There are no stupid questions only stupid answers" :)

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