Which Controller

[CatNewBee]

Originally Posted by SailsWithFists

...
Steve O. - wiring in series, and using the MPPT controller allows for shadows/low light charging because the spooled excess voltage is then used to push up the charging voltage as necessary for given conditions....

I learned something new already today.

That is partially true and also wrong.

true is, shading has very little impact on voltage. The Solar cells are a current source not a voltage source when it comes to light, that said, the voltage only slightly changes with increasing radiation, it is almost constant, but the current raises almost linearly to the saturation point.

So voltage is always high. The MPPT transferes not voltage to current unfortunately. it transfers higher voltage * lower current to lower voltage * higher current. So power remains equal (- some due to efficiency issues)

Unfortunately in a serial connection the current is equal along the chain, only voltage varies and sums up. That said, a shaded panel limits the power for the whole string and therefore you loose power when connected in series and not gain power because of the higher voltage. The bypass diodes mitigate somehow this losses, but they remain significant.

In opposite in a parallel setup, voltage is equal everywhere, but the current sums up - and because the panels produce current from light and voltage remains almost constant - a parallel set up is ways more efficient than a serial setup. Each panel contributes the current it can provide at the given voltage, the weaker less, the stronger non-shaded more, and all sums up in contrast to series, wher the weakest current is the maximal current all other panels can deliver.

With one exception - if the voltage of the battery is too high or too close to the cell voltage, there is not enough tension to drive the current. But then again - a serial set up with high voltage and almost zero current cannot provide Amps either because of the almost zero current in the equation P=V*A.

[DotDun]

Originally Posted by CatNewBee

That is partially true and also wrong.

true is, shading has very little impact on voltage. The Solar cells are a current source not a voltage source when it comes to light, that said, the voltage only slightly changes with increasing radiation, it is almost constant, but the current raises almost linearly to the saturation point.

So voltage is always high. The MPPT transferes not voltage to current unfortunately. it transfers higher voltage * lower current to lower voltage * higher current. So power remains equal (- some due to efficiency issues)

Unfortunately in a serial connection the current is equal along the chain, only voltage varies and sums up. That said, a shaded panel limits the power for the whole string and therefore you loose power when connected in series and not gain power because of the higher voltage. The bypass diodes mitigate somehow this losses, but they remain significant.

In opposite in a parallel setup, voltage is equal everywhere, but the current sums up - and because the panels produce current from light and voltage remains almost constant - a parallel set up is ways more efficient than a serial setup. Each panel contributes the current it can provide at the given voltage, the weaker less, the stronger non-shaded more, and all sums up in contrast to series, wher the weakest current is the maximal current all other panels can deliver.

With one exception - if the voltage of the battery is too high or too close to the cell voltage, there is not enough tension to drive the current. But then again - a serial set up with high voltage and almost zero current cannot provide Amps either because of the almost zero current in the equation P=V*A.

The cells within a panel are connected in series. If the panel has bypass diodes internal to itself and one trips, the loss of power is the same whether the panels are in a series or parallel configuration.

[SailsWithFists]

Originally Posted by CatNewBee

With one exception - if the voltage of the battery is too high or too close to the cell voltage, there is not enough tension to drive the current.

I was referring to this^^

Now my question is: If the MPPT regulator fails, does it fail open or closed? One way is safe, the other is quite destructive, especially if you are away from your boat when it happens.

[newhaul]

Originally Posted by SailsWithFists

I was referring to this^^

Now my question is: If the MPPT regulator fails, does it fail open or closed? One way is safe, the other is quite destructive, especially if you are away from your boat when it happens.

Can go either way hence the recommended fuse at the battery on the positive side.

[DotDun]

Originally Posted by newhaul

Can go either way hence the recommended fuse at the battery on the positive side.

Huh? The recommended fuse size is normally higher than the max output of the panel(s). What will it do?

[SailsWithFists]

Originally Posted by newhaul

Can go either way hence the recommended fuse at the battery on the positive side.

A fuse is blown by over amperage, not voltage. If the controller fails closed, then a solar panel bank wired in series is sending damaging amounts of voltage into the system. A fuse helps not in the least bit.

[Sailmonkey]

Originally Posted by CatNewBee

Wow, some serious miss-conceptions, but the right answer.

"WOW"???

Care to elaborate on the misconceptions? I’d like to know how I’m wrong? And right at the same time. the second set of text you quoted was not mine.

Keep in mind I was typing a quick reply on my phone, so did not elaborate on my numbers.

[CatNewBee]

Originally Posted by Sailmonkey

"WOW"???

Care to elaborate on the misconceptions? I’d like to know how I’m wrong? And right at the same time. the second set of text you quoted was not mine.

Keep in mind I was typing a quick reply on my phone, so did not elaborate on my numbers.

Voc is relevant, not Vmp for maximal voltage consideration.

The 100V are the voltage limit for the FET transistors inside, they may be fried when no power is drawn and Sum (Voc) exceeds the allowed 100V at the input. I dont know if Victron has an over voltage protection on the input side.

also the amps calculation is wrong.

2.9x4=11.6 amps (less than 15 amps)

You must divide the maximum input power by the battery voltage to judge if 15A are OK or not. The Imp is irrelevant here, it is the OUTPUT current after the transformation..

The right way would be (4x50Wp) / 12V = 16.6A maximum expected current. But if you consider losses along the line, also due to design, angle, heat, efficiency 10% over the 15A nominal current are still acceptable. The Controller has a over-current protection too.

There are more relevant parameters in the data sheet like maximum input current (is usually ways lower than the output current), but with this panels and a serial set up not relevant.

Sorry for the second text, I know it wasn't you, but there was no quote button on the editor, so copy & paste.

The second post was wrong about wattage, it is not a 48V 50W, it is - if at all - a 48V 200W setup in series or 24V 200W in 2s2p or 12V 200W in parallel. The wattage does not change, it's the Voltage and the Amps.

[Steve O]

WOW I thought I was just asking a simple question.

[Sailmonkey]

Originally Posted by CatNewBee

Voc is relevant, not Vmp for maximal voltage consideration.

The 100V are the voltage limit for the FET transistors inside, they may be fried when no power is drawn and Sum (Voc) exceeds the allowed 100V at the input. I dont know if Victron has an over voltage protection on the input side.

also the amps calculation is wrong.

2.9x4=11.6 amps (less than 15 amps)

You must divide the maximum input power by the battery voltage to judge if 15A are OK or not. The Imp is irrelevant here, it is the OUTPUT current after the transformation..

The right way would be (4x50Wp) / 12V = 16.6A maximum expected current.

Ok, Thank you. Everything I already knew.....but was generalizing too much while typing on a phone.

You are correct, max current should be 16.6 amps.....although likely to never occur.

[GTom]

Originally Posted by CatNewBee

The right way would be (4x50Wp) / 12V = 16.6A maximum expected current. But if you consider losses along the line, also due to design, angle, heat, efficiency 10% over the 15A nominal current are still acceptable. The Controller has a over-current protection too.

He'll need that bucket of dry ice, perfect alignment, 100% Sunshine on the equator AND a charging profile that produces 12V for some battery chemistry unknown to me to see that 16.6A. Then the over-current protection will step in and the worse thing that happens is he loses 5% of the peak production.

Even with all conditions perfect, you charge with 14V+ voltages which fits the 15A envelope.

My panels are on their way now, I'll pair 450W (4x100+50Wp) worth of panels with a 100/30, maybe I'll separate the 50W unit and put it on a small cheap controller.

Originally Posted by CatNewBee

As I said, right answer, wrong calculation

^^ Correct

[CatNewBee]

As I said, right answer, wrong calculation

[sparrowhawk1]

Something that hasn't been mentioned is that the main advantage of series is that you can use smaller wires or have better performance for same size as wired parallel. Now I understand that if I have four panels in parallel and one gets shaded I'll have one quarter less power. But am I to understand if I have two sets of them in series and then hooked up in parallel for 24 volt output and one gets shaded I will only have half output? And for this scenario I'm simplifying it to say that the Shaded panel will be putting out 0 amperage. I understand in real life the Shaded panel still puts out some amperage.

[GTom]

Originally Posted by sparrowhawk1

Something that hasn't been mentioned is that the main advantage of series is that you can use smaller wires or have better performance for same size as wired parallel. Now I understand that if I have four panels in parallel and one gets shaded I'll have one quarter less power. But am I to understand if I have two sets of them in series and then hooked up in parallel for 24 volt output and one gets shaded I will only have half output? And for this scenario I'm simplifying it to say that the Shaded panel will be putting out 0 amperage. I understand in real life the Shaded panel still puts out some amperage.

Add that MPPT controllers have an efficiency curve, which has a maximum somewhere above 30V. Nothing dramatic, but seriously low voltages below 15V tax the charging efficiency.

A question related to the topic: I am thinking on a separate low-cost controller for my 50W panel (Vmpp=18V), which should serve the batteries during winter. Any suggestions? I guess float charging a 200Ah bank won't need a huge infrastructure, I just need a reliable PWM unit...

[Steve O]

I had previously emailed Victron in NL. Today I got a reply email and within seconds of the email arriving a phone call from the Canadian Representative - Sébastien. He has suggested a 2 + 2 Series/parallel setup. (ie two sets of 2 panels wired in serial and the sets joined in parallel). This would maximize my low light threshold and maximize my output. He also suggested a 100/15 Controller but to allow me to add additional panels in the future (which I will probably do) he said a 100/30 might be a better choice. He also suggested a Smart Controller so i could monitor the output via Bluetooth.