OverSizing a Solar inverter

Oversizing an inverter means connecting more panel power than the inverter's rating.
e.g. 6.6kW of panels on a 5kW inverter
or 13.2kW of panels on a 10kW inverter
If you stay within 133.33% oversizing then you get paid STCs, the still generous Government subsidy on panels

The rationale for this allowed oversizing is that solar conditions are not always ideal.
Early morning, late afternoon, or entire seasons like Winter, if you only had 5kW of panels on a 5kW inverter your inverter wouldn't be able to pull down enough power from the panels to hit its 5kW limit.

With the latest generation of hybrid inverters from Huawei, Fronius, SolarEdge, Goodwe, Sungrow and others can add even more panel power if you connect a battery.
Huawei and SolarEdge allow 200% oversizing (so 10kW of panels on a 5kW inverter), as do Growatt and Sungrow with their single phase hybrid inverters and most of the rest are happy with 150%.
STCs (Subsidy) are paid on the extra panels as long as the manufacturer's datasheet/brochure says it is ok.

We have had quite a lot of experience recently putting in Huawei batteries on 5kW Huawei single and three phase inverters and installing 9.6kW to 10kW of panels and have always been paid the STCs.

1000VDC string limits instead of 600VDC

A change (late November 2021) to the standards allow us to install strings of solar panels up to 1000VDC
So, if we say that a solar panels voltage is 45V, then under the previous 600V rule we could install 13 panels on a string, and now we can install 22.
So if a manufacturer's datasheet says that as long as the input voltage and current stays under their limits, then in theory we could oversize systems now much further than before.

However... it is still down to the electrical distributor, which in Perth is Western Power, to decide whether they will allow 1000V solar panel strings on their network or not.
At the moment I am told by others (inverter manufacturer reps) that Western Power and others are NOT allowing it, unless a battery is also connected.
Additionally, STCs (Government panel subsidy) of approx $190 a panel, are only paid if the oversizing is restricted to 133.33%, again, unless a battery is connected.

The new WA DPM rules

Western Australia is now going down the same path as South Australia, allowing Synergy/Western Power to turn off solar inverters altogether, or ramp down their output.
They call it 'Distributed Photovoltaic Management' and you can read about it here.

It also goes by 'Emergency Solar Management' just in case people didn't understand what 'Photovoltaic' meant.

There are two paths to these new rules:
(A) For inverters 5kW or less installed after March 14th 2022.
(B) For inverters over 5kW installed after March 14th 2022.

(A)
Your inverter must be connected via WIFI/Ethernet to the inverter manufacturers reporting portal.
(e.g...Huawei Fusionsolar, Fronius solarweb, Sungrow iSolarcloud etc).
This allows Synergy to shut down your inverter (and everyone else's simultaneously) during a 'low load' event.
A low load event is where solar production is excellent but it's not hot or cold enough for people to be using their aircon.
Too much exported solar, raising grid voltages to unmanageable levels...so they stop the flow by turning off your inverter for a while.
Anyone installed prior to March 14th 2022 is unaffected (for now).

(B)
If your inverter(s) capacity exceeds 5kW then you have to export limit your surplus solar to 1.5kW per hour.
This involves buying and installing the inverter smart/consumption meter because that's the device that controls export limiting.

There has never been a feed-in-tariff paid to people in WA who have more than 5kW of inverters but until March 14th, their inverter could draw down as much power from their solar panels as it could, to meet household loads, store in a battery, and then export the rest into the grid.
That usually meant that solar production was about 6kWh per day per kW of inverter. (10kW inverter = 60kWh per day production.)

Now that inverters aren't allowed to draw down anything more than what household loads are + 1.5kW, people with large solar installations are going to see MUCH lower solar production.
I would expect that most will see 3kWh per day per kW of inverter (10kW inverter = 30kWh).

What about batteries?
If everyone had their own battery then it wouldn't do much to reduce solar exports.
The modern hybrid inverters from manufacturers like Huawei, Sungrow, SolarEdge, Fronius, Goodwe, Q.Cells... are able to pull down 5kW from the panels to send to loads in the house and export out to the grid, AND draw down extra power, often another 5kW to charge the battery.
It doesn't solve the problem at all.

What about Virtual Power Plants? (VPPs)
Imagine thousands and thousands of Perth homes with solar storage batteries.
Now imagine its a stinking hot afternoon or evening, and everyone turns on their airconditioning.
This puts a huge strain on the grid, possibly causing it to fail.
Instead, the grid draws on those batteries providing the extra bit of power it needs to stop the grid collapsing.

Part of the DPM plan does include the possibility of VPPs but on my reading of it, only for larger 15kW three phase systems only.

 

 


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Written by Andrew MacKeith, Solar4Ever Service Manager since 2011.
Most recent update December 2021