Prioritizing Solar/ Battery Over Mains Incommer

[RedBeard]

Electrical theory question here, please don't be to brutal if the answer is obvious...

Came across an install today with two supplies connected before the CU via henley blocks, one supply was mains and the other was the PV install.

My first question is this: how does the CU know to use the solar supply first and then the mains grid second?

Second question is: assuming it can't prioritise, when using both supplies simultaneously how does the current flow into the install? Is it 50/50 from each supply or is there a method to calculate the flow.

Not really important to me directly as PV installs are not my line of work, I am simply interested in how it works.

Thanks all in advance

 

[binky]

The solar inverter monitors grid voltage and outputs a slightly higher voltage, so that like water from a tank at a higher level, it flows first. If there is insufficient enrgy from the solar it tops up from the grid.

 

[RedBeard]

Fab that's a really good explanation and so simple to understand.

Thanks Binky!

 

[SPECIAL LOCATION]

Electrical theory question here, please don't be to brutal if the answer is obvious...

Came across an install today with two supplies connected before the CU via henley blocks, one supply was mains and the other was the PV install.

My first question is this: how does the CU know to use the solar supply first and then the mains grid second?

Second question is: assuming it can't prioritise, when using both supplies simultaneously how does the current flow into the install? Is it 50/50 from each supply or is there a method to calculate the flow.

Not really important to me directly as PV installs are not my line of work, I am simply interested in how it works.

Thanks all in advance

I am no expert..
but from my limited knowledge I would suggest that a key point you need to remember is the CU never does anything relative to Solar -vs- Grid..

i.e the function of the CU is to house appropriate protective devices for the various final circuits..
(plus typically a manual isolation switch).

It is the meter that is the critical position to deduce how much power is generated locally or consumed from the grid..

And remembering the basic physics stuff, where voltage is the pressure bit which causes current to flow..
and current flows through the least path of resistance..

So as long as solar is connected to the correct side of the meter...

and it is producing enough pressure to push current through the loads connected via the CU..
Then the local installation will be consuming as much power as the solar power can produce..
and if it needs more will draw the extra from the grid...

But.. as I said, I am open to correction?