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frankvw asked

SmartSolar 100|MPPT with high power solar panels

I'm looking at installing a SmartSolar 100V|50A MPPT charge controller which I would like to connect to four Canadian Solar 605W Super High Power Mono PERC HiKU7 PV panels, each rated at 41.5Voc, 18.52A Isc, and 605W rated maximum power output. The plan is to put the four panels in 2-by-2 series/parallel, i.e. 2 panels in series, and 2 groups of these in parallel. If my school fees haven't been completely wasted, this should mean that the panel's output voltage and current should not (significantly) exceed 83V and 37.04A which is within the Smartsolar's limits. The total maximum rated power output, however, will exceed the 1400W maximum that the MPPT is rated for (at 24V, which is what I will be using).

I like the 605W panels because a.) the rated maximum power output is a theoretical maximum that in practice will rarely (if ever) be achieved, and b.) on cloudy days a bigger panel will still provide enough power to be useful. On bright sunny days this means of course that the PV panels will be under-utilized, but I'm cool with that.

So here's my question: is the Smartsolar protected against overcurrent and/or limited to pass no more than 1400W, or does it simply pass on whatever oomph comes out of the PV panels until it fries itself?

Knowing Victron I would assume the Smartsolar will not rely on the PV panels maxing out in order to prevent itself from burning out but has current limiting features. However, my supplier claims that I should order PV panels that have a lower power rating because the Smartsolar can't handle the larger ones.

Can I safely put oversized panels on the Smartsolar (staying within its voltage and current limits, of course) without starting a bonfire in my MPPT?

// FvW

MPPT SmartSolarSolar Panelpv limit
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2 Answers
nickdb avatar image
nickdb answered ·

This really is what the calculator is for, automatically linked to in the top right of this page.

the 100/50 is max 1200W at 24V.

Seems like a waste of those panels. Ultimately the MPPT will just throttle output power to it's max, but running it flat out will make it hot and possibly derate, imo, it is not a good fit for this scenario, and it is never wise to design for a device to run saturated for extended periods.

The limitations are on the PV side, Voc and Isc, if you are within those at cooler temps, then the charger is happy, you just will be throwing away available solar.


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frankvw answered ·

The calculator allows for oversizing the PV panels:

Oversizing a PV array means installing more peak power (Wp) than the
maximum charge power of the chosen MPPT charge controller. A common
reason to oversize is to cater for winter time when the sun is not as
powerful.

The MPPT solar sizing calculator will allow for a 130% PV array
oversizing when recommending a charge controller.

The design logic is that panels RARELY spend much time at their peak
rated output capacity, only maybe an hour in the middle of a sunny day. The rest of the time they are derated below their spec maximum, and
less than the maximum capacity of the charge controller.

Which is exactly what I have in mind. How much the panels will degrade over time remains to be seen, but oversizing would allow for that as well.

Your point on not running the MPPT at constant maximum rated power is well taken. I would probably limit the SmartSolar's maximum output current a bit in the settings, also because I don't want to hammer my battery. However, the SmartSolar will automatically limit its output current if it starts to run too hot. And as I said, I know I'm under-utilizing the PV panels in bright sunlight, but I'd rather do that and still have more power available on cloudy days than maximizing the output of the PV panels in bright sunlight and not have any power to speak of on cloudy days.

So while I agree with the inadvisability of running kit at maximum all the time (which I will prevent by limiting output current) and the fact that it's too bad that on sunny days I could get more out of my PV panels, will a bigger-than-necessary panel burn out the MPPT?

I could go with a bigger MPPT of course but the next model up is way more expensive.

// FvW

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nickdb avatar image nickdb ♦♦ commented ·
Yip. But 130% is common, this has been shown to be optimal, you are permitted to go above this, in your case it is over 200%, which is literally throwing solar away.

Personally I would spend less on the panels and spend more on the mppt, it is likely to work out better longer term.


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Duivert NL avatar image Duivert NL commented ·
You could also add another mppt and split the panels up…
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Michelle Konzack avatar image Michelle Konzack commented ·
Of course, a bigger MPPT is much more expensive, but with such panels and a 24V Battery, I would opt for the SmartSolar MPPT 250/85 or the 250/100 which charge with 100A even if your Battery is down at 24V. ;-)


Having a Vmpp of roughly 150V wth a 24V Battery give you from Autumn to Spring HUGE EXTRA POWER.


Degrading of Solarpanels?


I think, there are no solar panels out there anymore, which deliver the first 3-5 years LESSER then rated (my original 3s2p with 6x310Wp=1860Wp set on a SmartSolar MPPT 150/70-Tr VE.Can from August 2018 still deliver over 1900W/h and PeakPower up to 2015W) and usually solar panels reach there 80% capacity in 20-25 years but the lifetime can be 30 and more years.


Hence do not worry about degrading.

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