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Efficient oversizing of an MPPT

I intend to clad the southern facade with PV panels. For this I bought 18 modules of the type DAH DHT-M60x10 fs 460 W. Of these, three modules are connected in series and three strings in parallel. According to the Victron MPPT calculator, the 250/70 is recommended for 3 rows and 3 parallel. Since I have 18 plates and therefore 2 x 3 rows 3 parallel, I need 2 x the 250/70. Each 250/70 is 103% oversized with this configuration. Based on the values of my three other systems and the values from PV Gis, I only calculate with 65% of the maximum module output. With this data, a 250/100 would be sufficient at 70% and oversized at 110%. I read that oversizing up to 130% would be possible. Does anyone have experience with facade PV and the yield? Can I use the 250/100 on my system? Does oversizing have any downsides in terms of warranty?

And most importantly, is it more efficient to use two 250/70 or one 250/100?

Addendum. Depending on the time of day, the facade is moderately to heavily shaded by the neighbor's house and a tree.

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JohnC answered ·

Hi @Vici

You could use the 250/100. There'll be no warranty issues, providing you don't exceed the string Voc or the parallel Isc. That seems under control.

There shouldn't be any efficiency difference. Usually shade devastates output, and nice if you can keep shaded panels in the same string.

I can't speak for your facade orientation or shade. Do you think you'd clip at 100A very often, then for how long? Only you can decide this. If it's only for a short while then the extra expense of 2x mppts would be hard to justify.

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vici avatar image vici commented ·

Many thanks for your fast response!


The facade has 25° azimuth.

Last Sunday I took a photo of the facade every 30 minutes. The shade (first a part from the neighbor's house and then his tree) is present 70% per day and moves from east to west and covers about 50% of the area.


PVGIs forecasts a yearly PV energy production of 5984 kWh. The best month is April with specified 673 kWh.

The Yearly in-plane irradiation is given as 949 kWh/m2.


I think that the 100A is rarely reached and not for a long time. I will test it with a 250/100 and monitor it continuously. If the peak is reached too often or for long time, I replace to two 250/70.


If I have to replace the mppt, I make three people happy.

My Victron dealer, Victron and the customer who buys my used 250/100. ;-)

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