Grid Connected System Still Importing Power from the Grid

Thanks for your answer

Hello Amineln,

Unusual to get a thanks [or often, a reply] from the original poster. It makes the day!

Raghun adds a very important point - the reactive power still has to come from the Grid, with an associated current. This is because the solar inverters are required to deliver AC at unity power factor.

Even if your load power factor is 0.95, the reactance side of the right angle triangle is √[1² - 0.95²] = 0.31. The lagging or leading part of the total current is over 30 %. That is not negligible when the Vars are measured.

You are most likely on a domestic type supply of 400/230V from a 3 phase transformer. Keeping your supply close to 230V, [+/- 6% ideally] depends mostly on the regulation of the transformer. Regulation is very good [0 to - 2% at rated current unity to 0.95 lead or lag] if power factor is close to unity but swings to +/- 4% for zero power factor.

So requiring solar inverters to work at unity power factor has minimum effect on voltage regulation & transfo supplying your reactive load is what it would do without any local generation.

The local requirements [UK] G98 applying to Inverters up to 16 amps/phase [400/230 volts 50 Hz] connecting to LV network is :-

<<9.5.1 The power factor capability of the Micro-generator shall conform to EN 50438. When operating at Registered Capacity the Micro-generator shall operate at a power factor within the range 0.95 lagging to 0.95 leading relative to the voltage waveform unless otherwise agreed with the DNO eg for power factor improvement.>>

DNO is the LV network operator. EN50438 is a European standard.

Consequently, the calculation of lead/lag current at 0.95 power factor compared to total generated current.

Load consumes reactive power, in addition to active power.

In your case, while the active power is coming from solar panels, grid is supplying the reactive power that is required by load as well as the inverter itself.

How much is a little power, and how are you measuring it?

What happens if you disconnect from the grid?

What is the make and model of your equipment?

I can't say why but I would say it's normal. My monitoring system shows power flow both to and from grid in the same hour (see screenshot). I don't thing you need to change anything.

https://photos.app.goo.gl/AZyCnHc8fwkd8Fps9

Ask the question "How does this thing know how to synchronise with the local power grid?"

Ask the question "How does this thing know how to disconnect from the grid so as to protect repair workers while the grid is down?"

Answers on a postcard, please.