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Unwanted power Export

 
Solar Photovoltaic (PV)
Last Post by Transparent 4 weeks ago
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 DavidAlgarve
(@davidalgarve)
Reputable Member Member
Joined: 2 years ago
Posts: 244
Topic starter 26/04/2026 3:35 pm   [#2973]

I am seeing an increasing number of occasions when my Growatt inverter appears to be exporting power when logically it should be either contributing to consumption or charging the battery. 

Is this likely to be a real situation or is it something to do with the latency in the data logger?

Examples:

Screen Shot 2026 04 20 at 16.45.42
Screen Shot 2026 04 25 at 20.34.23
Screen Shot 2026 04 25 at 11.15.41

342sq m "Upside down" house in Algarve. Portugal
Mitsubishi PUHZ-120YUK 12kW ASHP
12 Solar Panels Growatt Inverter
2 x Growatt 7.5kW Batteries
Fronius EV Charger
Kia e- Niro 64kW


   
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Transparent
 Transparent
(@transparent)
Famed Member Moderator
Joined: 4 years ago
Posts: 3198
30/04/2026 12:26 pm  

We don't have time-stamps on those screenshots, nor do we know the parameters you've configured to set the times for charging from solar or grid.

Very low 'export to grid' readings can be due to a number of different reasons.

Sometimes inverter manufacturers deliberately keep the system at a low export current in order to operate correctly with pre-payment meters. That involves setting the inverter output voltage a volt or two above the grid potential, thereby preventing any demand being applied to the household incomer.

 

There will also be inaccuracies associated with measuring the current via a CT Clamp.

Typically a CT-clamp outputs the reading with max-current defined as a 50mA signal (AC).
That is rectified and fed across a 100Ω resistor at the input of an Analogue to Digital Converter, which might have 12-bit accuracy.

In theory, if the CT-clamp has a 100A max current rating, the inverter is presented with a reading within 20mA, which is about ±5watts for a 240v output.

In practice a CT clamp is unlikely to be better than 0.5% accurate, resulting in the inverter knowing the export current within 500mA, or ±120w (0.12kW).

To avoid any import from the grid, the inverter output voltage is set at least 0.5% above the 240v. That brings the measurement error to +240W (0.24kW), which isn't very different to what you're seeing.


Save energy... recycle electrons!


   
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