How do these battery storage units, which come with an inverter, know not to export power to the grid?

With a normal grid tied inverter, any excess power is automatically exported, unless a diverter is fitted.  Does this mean that lots of diverters are fitted?

I understand that the batteries are charged by a diverter, but it is the discharge cycle I am wondering about.

Edited January 21, 20206 yr by SteamyTea

Some have a current transformer that clips on to the meter tails.  Certainly the unit I've been looking at has this.  It uses this, together with another current transformer clipped around the PV inverter output, to determine when to charge from excess PV generation, and to prevent the battery system exporting to the grid.

Not sure how a CC on the tails knows what direction the current it flowing. I could understand if it just had a set threshold (or several).

Be a bit of a bugger if you charge your batteries up from your PV to then give part of it away for free.

45 minutes ago, SteamyTea said:

Not sure how a CC on the tails knows what direction the current it flowing. I could understand if it just had a set threshold (or several).

Be a bit of a bugger if you charge your batteries up from your PV to then give part of it away for free.

 

 

From the phase relationship between voltage and current, the same way as most excess PV diverters work.  They are always connected to the mains supply, so can measure the voltage easily enough, and the output of the current transformer will show the relative direction of the current flow.

18 minutes ago, Jeremy Harris said:

phase relationship between voltage and current,

Makes sense.

Just never seen it mentioned when I have had a quick skim through the websites that advertise them.

I think too many people take too much on trust.

Take yesterday, a German was locked up for convincing people to wire themselves to the mains.

How can that happen, are people so dumb, really.