Solar??? Eh?

[uksparks]

Hi,

ok, can someone explain because I'm confused and never know what to tell people.

so you have a normal supply into your house, and you have PV on your roof.

why or how is it that your consumer unit chooses to draw its power from the PV and not the grid?

how does the power back feed in to the grid? I know how it's all connected, just wondering why say the grid doesn't push in to the inverter and not the other way round?

am I missing the obvious?

 

[jackhammerJIM]

The inverter synchronises with the grid feed and pushes it back with a higher voltage

 

[uksparks]

Ah ok, I wondered if it had more power or something?

so what voltage is the inverter pushing out then?

so if the supply coming in is say 238v, what's the inverter doing?

 

[jackhammerJIM]

More power than the national grid , absolutely not .

The way it was explained to me is it works like water pressure .

voltage is the pressure .

Im sure somebody will be along to give a more technical explanation .

 

[Deleted member 26818]

Here's how I understand it:
Both supplies are used, but the greater current is drawn from the supply with the least resistance, i.e. your PV system.
Similar to how the shortest leg on a RFC will carry the greatest current.
If your PV system produces more current than you require, the excess is used by the grid, with the installations closest to you taking the greatest.
That current is metered and you receive payment, or a reduction in your bill.
If the demand on the grid was zero, then your system would not supply the grid, there would be nothing metered and you would not receive anything.

 

[Leesparkykent]

By monitoring the grid voltage so the voltage output from the inverter is slightly higher than that of the grid.

 

[uksparks]

I wondered if it chose the one with the least resistance, that makes sense!

 

[Deleted member 26818]

I don't believe it chooses anything.
The supply with the least resistance just provides more of the current, as per Ohm's law.

 

[jackhammerJIM]

I would love to know how it pushes it back through the national grid transformers ?

 

[Deleted member 26818]

It doesn't.
The nearest installations will again take the greatest current from the supply with the least resistance.
If you live in Kent, your PV system will not be supplying someone in Scotland.
It will be supplying your neighbours.

 

[jackhammerJIM]

It doesn't.
The nearest installations will again take the greatest current from the supply with the least resistance.
If you live in Kent, your PV system will not be supplying someone in Scotland.
It will be supplying your neighbour.

How do you explain installations with their own transformers getting paid for export ?

 

[davesparks]

How do you explain installations with their own transformers getting paid for export ?

Payments are calculated on a purely mathematical basis from the electricity recorded by the generation meter.
The chances of the PV generating more power than is actually required by a site which has its own Tx is pretty minimal. If it does actually export then it will just be stepped up through the transformer

 

[Deleted member 26818]

I assume that whatever power they supply is also metered.

 

[jackhammerJIM]

. If it does actually export then it will just be stepped up through the transformer

Thats what I'm getting at Dave . Didn't think a step down transformer would be able to step up a back fed voltage .

 

[Deleted member 26818]

Transformers are by their nature, bi-directional.

 

[davesparks]

Thats what I'm getting at Dave . Didn't think a step down transformer would be able to step up a back fed voltage .

Why not? A transformer is two coils of wire around a core, why would it care which way the flow of energy is?

 

[jackhammerJIM]

Why not? A transformer is two coils of wire around a core, why would it care which way the flow of energy is?

Yep been on google and have learnt something .

 

[Blademan_98]

A good question with some great answers! Nothing to add but it is good to see some helpful pointers for further research

 

[BruceB]

I thought I should mention Kirchoff's first law to the OP in case he wants further reading.

 

[davesparks]

I thought I should mention Kirchoff's first law to the OP in case he wants further reading.

I was racking my brain for ages last night trying to remember the blokes name to post that here!