How do PV charger/inverters 'control'?

WIAWSNB

In very basic terms!

I remember asking the installer at the time how the system 'knows' to prioritise supplying the house over the Grid, and he explained the inverter constantly monitors the exact grid voltage, and 'ups' the supply from the PV system a tiny amount to override it - the system therefore supplies the house (and Grid).

What about AC-coupled inverter/charger/controllers? It has to deal with it's own battery, the PV system, and Grid.

Does it require external sensors for this? Or all done by internal circuitry like on a normal inverter? I've read about current clamps being needed - is that just for monitoring, or also control?

Thanks for insight, but in simple terms, please 🥺

QrizB

The inverter puts power into your consumer unit. Your house uses it because in preference to the grid because it has to; as someone said when explaining this in a thread a few years ago, "current can't flow both ways simultaneously in a single wire".

When you bring a battery into the equation, software in the inverter decides (based on your settings) whether to prioritise charging the battery or supplying the house. The inverter will have a sensor (usually a current transformer, CT, that clips onto your wiring bnear your meter) that lets it measure whether current is flowing from the grid into the house, or vice-versa, and how much is flowing. This inverter can use this info to adjust the charging/discharging of your battery and achieve whatever goal you've asked.

You want to minimise export and be mostly self-powered by your own solar? It can do that.

You want it to charge your battery from the grid overnight? It can do that.

You want it to dump the battery into the grid from 1600-1900 when your export tariff is highest? It can do that.

QrizB

I've read about current clamps

That's another name for a CT, as many common models "clamp" around the cable they're sensing.

is that just for monitoring, or also control?

They are only sensors. They can't directly control the flow of current in a wire

WIAWSNB

https://forums.moneysavingexpert.com/discussion/comment/81976601#Comment_81976601

Thanks. I do understand they are only sensors - I have one for a solar immersion controller, heating up a storage heater with excess gen - it works really well (but will need turning off soon…)

So, the charger in the garage will need a signal from the Grid cable in the house. I take it there are WiFi versions available?

Ta.

WIAWSNB

Thanks.

I don't follow the 'it has to' part. With two supplies, at presumably equal voltages and in sync, why isn't the load sharing the two supplies equally? It doesn't have to do with voltage tweaks?

QrizB

So, the charger in the garage will need a signal from the Grid cable in the house.

For best results? Yes.

I take it there are WiFi versions available?

I think wireless ones exist but I've never seen one (to be fair I've not gone looking). Some systems can use Shelley smart sensors, and those are definitely wireless.

What options are available for any specific inverter may vary. That's somewhere that your installer can help - or if you're DIYing, maken100% sure before you buy anything.

Reed_Richards

I have been thinking about adding another battery. I would like to site this in the garage but it could go in the porch. Since my garage is detached and the power cable well-buried, I would need to use a wireless link to the current sensor. But my porch isn't far from the meter cupboard so it would be easy to run cables, including one for the current sensor. I would be interested to know if an inverter with a wireless connection to its current sensor is hard to come by or not.

WIAWSNB

https://forums.moneysavingexpert.com/discussion/comment/81976669#Comment_81976669

'Another' battery? You already have one? Where?

Reed_Richards

I have a PV system with a battery on the DC side of the inverter. It's a 6.5 kWh battery and it is sited in my loft; something that would not be allowed for a new installation. This is fine for six months of the year but I reckon I could save about £500 per year with more storage capacity. But if I am looking for payback in under 10 years that limits me to a £5k spend; not that easy to achieve.

QrizB

Reed could you easily add another Goodwe battery in your loft? It's not a "new installation", just a modification to an existing one.

(Also, the PAS that says not to put batteries in the loft is like the Pirate Code - "more what you'd call guideline than actual rules".)

https://youtu.be/WJVBvvS57j0

WIAWSNB

Which of these install locations makes more sense? Would they both 'work'?

I just realised the house CU is right against an outside wall, and there's room outside to locate a battery and AC-C charger. I'm guessing this might make more sense?

It'll work the same?

Thanks.

Original, Garage location;

'House' (just outside) location;