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matthewmiles asked

Do solar panels only provide wattage required by load?

I have two 350 watt 24 volt panels in parallel connected to two 140 amp hour agm batteries through a Victron smart solar 100/30 MPPT. Just put the system together. Main load is a 12 volt 45 watt fridge. In ten days of good sunshine the MPPT unit has never displayed solar power above 269 watts. It’s usually showng Pmax around 160 watts. Batteries don’t drop lower than 12.8 volts at night and quickly get up to 13 volts or more and fridge running fine so all seems good. Will the panels only produce close to their maximum when the load is larger? Thanks

matthewmiles

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seb71 answered ·

Yes.

But you are also limited by that 30A maximum current which your 100/30 charger can output.

Since you are using a 12V battery, this means maximum power output is about 12Vx30A = 360W (slightly higher in practice - up to about 430W or so, because the battery voltage can go higher than 12V; I used the nominal voltage for simplicity).

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matthewmiles avatar image matthewmiles commented ·
Thanks. Maybe I should have chosen the 100/50 unit to get the most out of my panels.. But my load will never be very large - a few LEDs and the fridge is all I need.
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seb71 avatar image seb71 matthewmiles commented ·

Although at first look it might seem as a complete waste, you still benefit from your oversized PV array during cloudy weather, when the PV panels can produce only a fraction of their rated power.


Also, if you have no shadow issues and if the two panels are placed in the same plane (oriented the same), you could wire them in series instead.

Your 100/30 probably can take that configuration (string voltage should be under the maximum limit of 100V for your charger, even in the coldest weather).

The benefit is higher PV array voltage (the charging will start sooner), lower current (less loses on the PV array wires).

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matthewmiles avatar image matthewmiles seb71 commented ·

As you can probably see I’m a complete newbie. I was surprised how cheap the panels were (and they’re Australian made with good reviews) so bought two.
I had thought that the 30 amp figure on the Victron unit was referring to input from the panels

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nickdb avatar image nickdb ♦♦ seb71 commented ·
Oversized arrays to help during cloudy weather are such a myth and waste of money.

The reduction in power is so enormous, you'd need to erect 10X the panels to compensate.


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