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info7060 avatar image
info7060 asked

Does MPPT know it current maximal output without load?

Hi,

I'm still waiting for my solar system to be installed but already writing home automation system scripts, so the answer to this will help me a lot.

Let's say that load is 300W only. But there is enough sunshine that MPPT can draw 1000W from the panels. Does MPPT know it, or is it possible to know only after load increase to more than 1000W?

In other words, do I need to increase the load until I know I draw more than sun can provide or is there a better way?

I guess MPPT has no way of knowing it but I want to be sure.

Thanks a lot!

MPPT Controllers
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4 Answers
joepah avatar image
joepah answered ·

MPPT controllers always optimizing input voltage and current to maximize output.

It senses battery voltage, and will either bulk charge, boost or float.

' Voltage sensing
An optional Smart Battery Sense or battery monitor measures the battery terminal voltage and sends this via Bluetooth using the VE.Smart [28] network to the solar charger. If the battery voltage is less than the solar charge voltage, the solar charger will increase its charge voltage to compensate for voltage losses '

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info7060 avatar image info7060 commented ·

Thanks for the answer. But if the battery is full for example and there is no other load, MPPT wont output all it can get from the solar panels because there is no place to send it, right? So it does not know what is the potential. Or am I missing something?

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nickdb avatar image nickdb ♦♦ info7060 commented ·

It won't know what the potential is until it tries to scan under load.

You could get yourself a light sensor which will tell you what is available and use that as the reference.

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info7060 avatar image info7060 nickdb ♦♦ commented ·
That is what I thought I would need to do, or just try start something and check if battery or grid is used. The idea is to consume as much of the production as possible without using grid and without excessively using battery. I have a set of electric heaters that I can programmatically control. So I can change the load pretty neatly, but to do that I would need to know what is possible to draw.
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nickdb avatar image nickdb ♦♦ info7060 commented ·
I track a rolling average of PV generation via node red, it's not perfect but seems to work as long as there are regular loads. If everything goes idle it starts to tail off. It's a work in progress.
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info7060 avatar image info7060 nickdb ♦♦ commented ·
Thanks for the idea.
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bigbadbob76 avatar image
bigbadbob76 answered ·

I have looked into this as well, my problem was when using the PV voltage to measure available power I switched in additional loads which then dropped the voltage.

Better way was to have a separate small PV panel driving into a fixed load resistor and a current sensor. this gave me an estimate of solar irradiation at any given moment.

I have yet to use that information to switch in additional loads, maybe this summer.

Alternatively, if you have the cash, Victron sell an irradiation meter that can be interfaced to the GX device and report on VRM.

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usernamepasswordbs avatar image
usernamepasswordbs answered ·

So I suppose the load would keep dropping out once the voltage reduced. I never thought that far ahead! The panel voltage seems useful just because the MPPT has the relay ready and waiting and it has a minimum "on" time.


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usernamepasswordbs avatar image
usernamepasswordbs answered ·

I am thinking that if I change settings to allow grid infeed (currently switched off) then the MPPT will never need to throttle back so the infeed current could be used to switch on loads.

Edit: I mean that the control system would be constantly measuring in-feed to grid and constantly switching loads in or out to keep in-feed at -50w just like the Multiplus does now.

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