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Antoine avatar image
Antoine asked

MPPT and excess solar power

Hi, When the MPPT charger has to limit charging due to the battery (e.g., full battery, absorption stage, float stage, etc), the solar current and power being reported by the app is the "throttled" value rather than what the solar can truly output at that moment. As a result, when looking at the trends or history, when seeing low charging power, it is not possible to know whether it is due to sufficient power that's being throttled vs insufficient charging power (e.g., overcast day, panels too small, etc). I don't know enough about how MPPT chargers work to know how this throttling is done. But it seems it should be possible for the charger to "know" how much energy is being unused when it is throttling the charge, and report it somehow? E.g., as a separate "excess power" band in the history, and as "true solar power/current" in the trends? This would also make it very helpful when sizing up whether a charging setup could potentially support a larger battery.

MPPT Controllersbattery chargingsolar
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2 Answers
hjohnson avatar image
hjohnson answered ·

You could theoretically guess at this, but there’s no way to be sure. It’s simply not taking the “excess” energy from the panel, and only taking what it needs. It’s basically allowing the panel to go momentarily open-circuit (at a very high freuquency).

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Antoine avatar image Antoine commented ·

My point is, since the charge controller defines when the circuit is open, it could record this information and use it to infer how much energy is left unused, couldn't it?

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secessus avatar image
secessus answered ·

when looking at the trends or history, when seeing low charging power, it is not possible to know whether it is due to sufficient power that's being throttled vs insufficient charging

2nd try, site didn't allow or save first post.

Watch panel voltage (Vpanel) and compare to the Vmp and Voc label ratings. Generally speaking,

  • Vpanel ~= Vmp when the system is struggling to meet demand
  • Vpanel >Vmp when the system is "throttling". This can climb to very near Voc when the controller has its foot completely off the gas





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Antoine avatar image Antoine commented ·
So it sounds like there should be a way the charger could calculate this and log it alongside the other data points, even if only approximately? What's the best way to ask Victron about this?
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