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kevin-gr avatar image
kevin-gr asked

Mppt max Wattage input

Hi , ive tried and find my answer many places but cannot get it anywhere .

Im looking at getting an MPPT whose spec says as follow

Max. Photovoltaic System Input Power 550W/12V

1040W /24

It seems to be very easily archived to reach 550W with just a couple of panels and was wondering in order to benefit best from the mppt i would like to go into a 24 V so that i can input 1040W .

Would this count as 24 V if i was to put the panels in series and up the voltage? Or do the panels have to be 24V themselves ?

24V panels seem a lot more expensive and a lot harder to get which is why i would rather go the 12 V way but also would like to maximise the utilisation of the mppt .

Thanks

MPPT Controllers
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4 Answers
mrhappy avatar image
mrhappy answered ·

The 12V/24V spec is about the battery the MPPT is feeding. It can feed a 24V system with double the power because it is the current that limits it, so the panels you choose does not determine the power maximum of the MPPT, the voltage of the battery it feeds does.

What determines how high voltage the MPPT can receive from the solar panels is another spec number, usually called "maximum open circuit voltage" or someting like that.

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kevin-gr avatar image kevin-gr commented ·
Thanks for your time and answer john
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JohnC avatar image
JohnC answered ·

@kevin Gr

That isn't a Victron mppt, as Victron don't specify a max input wattage. Best to ask the maker.

It may well be a pwm dressed up as an mppt. Ink is cheap in China. If a Victron we'd need to know the model anyway. Victron can handle any panels, but their specs are also important to get the setup correct.

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kevin-gr avatar image kevin-gr commented ·
indeed the one i coped the spec from wasnt a Victrom .

Looking at the Victron 100/50 though it says Nominal Pv Power,12V 700W 24V 1400W

Which would bring the same question in my mind but adding John C and KevGermany together i understand now what this mean .

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kevgermany answered ·

I ran up against the same issue trying to size mine. Eventually realised I was looking at it the wrong way. Solar panels generate voltage, this is the key. Solar controller must be able to handle the panel voltage at all temps and lighting conditions, bearing in mind that voltage increases as temperature falls! When the panel manufacturer states wattage, it's basically the current it can deliver across its internal resistance. So work from the output/battery side. And remember that a 24V system is more like 27/28V. Which aids safety in the calcs below. So let's say your panels can deliver 480W max and 40V. This translates into 20A at 24V. (Actually less as voltage is higher) So you need a solar controller that can handle an input voltage of 40V and a current of 20A. There are benefits of connecting serially, but... Let's say you do. Input volts is now 80. So you pick a 100V controller. This takes care of the conversion to 24V. Same net current to the batteries. The gotcha is that in cold weather the panel voltage may go over 50 and if it does, your 100V controller is toast... Same for the parallel connections, but if you put in a 60V controller for safety, it's cheaper than a 120V one.

Advantage of connecting in series is that the panels are at a charging voltage for longer in the day. Victron controllers start charging when panel voltage is battery voltage +5 and stop at battery voltage +1.

Think carefully about a 24V battery system. Although it has advantages, it complicated life a lot.

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kevin-gr avatar image kevin-gr commented ·
thanks Kev , much appereciated answer
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kevgermany answered ·

If you look through the victron web site, there's a configurator for solar panels/controllers. One of the parameters is lowest temperature.


On the issues, I went with 24V in my camper.

What can run off 24V? Fridge maybe, usb sockets, led lights if you get the 24V ones, victron ccgx etc. For the rest it's 12V, via a DC:DC unit like the Orions. This includes trickle charging the starter battery. So, you have to size the 12V system, Orion, and have separate 24/12V wiring, fuse boxes etc.

One other possible issue is keeping the batteries balanced. Simplistically they stay at identical levels of charge. Reality is it can deviate, leading to shorter battery life. So a battery balancer between the 12V batteries is also needed.

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