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mark1961 avatar image
mark1961 asked

Is MPPT 250/100 suitable for 8kw 48v pv array?

Hi everyone - first post so hope it’s not too stupid! I’ve just had a home solar system fitted 8 kw, 48 v feeding a 250/100 MPPT into 2 x Li-ion 4.8 kva batteries ( plus 5 kva inverter). The maximum power output I get ( midday, mid summer, high sun, clear sky, clean panels) seems to be c 5.5 - 5.7 kw when I would expect more like 7.5 kw - is this right?

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seb71 answered ·

250/100 can output maximum 100A.

With a 48V (nominal) battery/system that means maximum of about 57.6Vx100A = 5760W. So exactly what you get.


When the sky is not clear, having more than 5760W in PV panels will help.

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mark1961 avatar image mark1961 commented ·
Thanks. Does that mean that to take full advantage of what the array should output, which is 8kw that I have to add another MPPT or swap what I have for one with increased capacity -( if there is one? )
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seb71 avatar image seb71 mark1961 commented ·

Besides the RS 450/200 (which has 4 trackers), 100A is maximum charge current from Victron MPPTs.

If you want to produce more than 5760W, you would need a second MPPT and move some PV panels to that.

If buying a second MPPT makes sense depends on how many clear days you have during a year and if you can use all that power.

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mark1961 avatar image mark1961 seb71 commented ·
Thank you. I think I am right in understanding then, that even though I bought an 8 kw pv system that the MPPT that was installed (250/100) can’t cope with the full output of the array, and instead ( under optimum conditions) throttles it back to what it can cope with - 5.7kw rather than 8 kw.
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seb71 avatar image seb71 mark1961 commented ·
Correct. But that only happens when the Sun is in the perfect position (relative to your PV array), the sky is clear and the PV panels are cold.


In all the other times, the 8kW PV array will not be able to actually produce 8kW (even if it would not have been limited by the MPPT). So you not always "lose" 2.3kW of potential power. There will be periods during cloudy days when your 8kW PV array will produce only 4kW for instance. Or only 2kW. On those occasions, the 250/100 will not be a limiting factor. The available solar radiation will be the limiting factor.


Having said that, your PV is "oversized" by quite a large factor, especially if you have mostly clear days at that location and if your PV is facing exactly South and it is angled for the summer Sun elevation. Maybe an oversize to about 7kW would have been enough (if oversizing is/was desirable).

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