Micro inverters, Optimisers and more

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Micro inverters & DC Optimisers - Updated January 2024

Micro inverter buyers.
In Australia we can simply call Micro inverters 'Enphase' because that's the dominant brand.
Enphase have 8 variants of their IQ7 micros and 3 variants of the IQ8 micros.
They cost about $200 each excluding installation.
You also need a $700 "Envoy Gateway" for reporting purposes.

The latest Enphase warranties are 15 years on the micros, 5 years on the Envoy.

Micros are a solution where there's partial transient shade on the solar panels.
They aren't the only solution though.
The diodes that come free inside every solar panel are often just as good.
Inverters that can rescan a string of panels regularly can also extract more power in shade.
Optimisers ($100) with string inverters do a similar job to micros with shade.

The biggest draw-back with Enphase micros is battery storage.
The problem is whether there's going to be enough solar power to charge a decent sized battery.
"Batteries are too expensive !!". True, but they won't be for much longer.
They are already at 'break-even' over 7-10 years, and 40% price falls are projected by 2025.

Let me explain, and remember, we are in Western Australia, and have some specific Western Power rules to follow.
80% of Perth homes have single phase power and a 5kW limit on solar inverter capacity.
If we take the Enphase IQ8 as an example, that is rated to 380W.
So divide 5kW by 380W and you get 13.
13 x IQ8 micros, coupled with, let's say 13 x 475W panels = 6.175kW of panel power.
That's it. You can't add more micros and panels when you want a battery.
If your home is already using the approx 30kWh per day average of solar power produced, then...
...what is left to charge a typical 10kWh to 13.5kWh 'AC Coupled' battery ?
...especially in Winter.

Hybrid 'string' inverters, the normal type, from Sungrow, Huawei/iStore, Goodwe, etc don't have this issue.
If you connect a battery to their 5kW models you can also add more panels to charge the battery.
Many allow 10-12kW of panels, all subsidised with STCs, to charge the battery.
5kW of panel power charging the battery plus 5kW of panel power converted to AC for loads or export.
That simply isn't possible with micros.

20% of Perth homes have three phase power. You can have 15kW of inverters, so 39 x IQ8 micros and panels.
No problem charging a battery with that much panel power.

Having said that, I frequently recommend Enphase to people looking to buy solar.
These people typically have a smallish house with limited roof space.
They need to install panels to all points of the compass just to get a decent sized installation.
Enphase are perfect for that.
You could do the same with a 'string' inverter with optimisers on every panel, but Enphase is usually best.

DC optimisers
Optimisers connect to the back of solar panels just like a micro inverter does.
Unlike micros, they also have a central 'string' inverter that converts DC power to AC.
If there's a battery needed, then the battery plugs straight into the hybrid inverter.
The battery is then charged by DC power directly from the DC power produced by the solar panels.

There are three optimiser brands currently in Australia.
SolarEdge that only work with SolarEdge string inverters.
Huawei, now branded iStore, that only work with Huawei/iStore string inverters.
Tigo that work with any string inverter except SolarEdge (but they do work with Huawei/iStore).

They cost between $80 and $100 each.

They handle shade the same as micros.
They allow panels to be installed on multiple roof orientations like micros.
They all have 25 year defect warranties.
They don't convert DC to AC up on the roof, they use a string inverter to do that.
Tigo and Huawei/iStore optimisers can be used 'selectively'.
You can use them only where you need them, extending panels onto different roofs, combating shade.

SolarEdge optimisers cannot be deployed 'selectively'; they have to be installed on every panel.

If the inverter is a 'hybrid' then a battery can be connected directly into the inverter.
It's called 'DC Coupling' whereas a battery connected to a house with micros will 'AC Couple' a battery.
The main difference between the two is the benefit of adding extra solar panels with a battery.
With a DC Coupled battery to a string inverter, that extra panel power will fast charge the battery.
You can't add extra panels with micros unless you also add extra micros, which often, isn't allowed.

Downside of optimisers.
Cost. You are buying a string inverter AND some optimisers.
That means that if you have optimisers on every panel you are paying as much, or more than an Enphase micro system.
If you are only 'sprinkling' a few optimisers here and there for shade, extending strings across different orientations
then the cost at $100 per optimiser isn't likely to blow the total cost out.

The other downside of optimisers can often be 'invisibility'.
By that I mean you can't always see whether they are working or not.
With Huawei/iStore, panel level reporting is free and available in their apps for all optimised panels.
So with that brand you CAN always see what they are doing.

With Tigo optimisers you need to also buy their 'Cloud Connect' box to see what they are doing.
That's a $700 or so cost that many people are not willing to spend.

With SolarEdge, where every panel must have a SolarEdge optimiser you would think reporting of each would be standard.
It's not. You either have to pay extra for this feature or buy the more expensive inverter models.

Going back to solving problems with shade.
Panels have diodes that shut down strings of solar cells if shaded.
This protects the rest of the panel and the string of panels it is connected to from being 'dragged down'.

Inverters have the ability to re-scan strings of panels looking for the maximum power point.
I cover all of this on my page about 'Shading'.

Other web pages worth reading...
For a great explanation of MPPTs, Global Maximum Power point tracking etc, then this one from Aurora Solar.
Closer to shore, this page from MC Electrical is a good, detailed read. I'm not saying I'm 100% on-board with all of it though.

A gentle reminder about the need to use common sense
"I have a big tree that shades my roof at certain times of the day/year"
At those times, your solar production might drop by 70%
Using micros, optimisers, it might only drop by 40%.
You've recovered, let's say 10kWh of power in the day with micros or optimisers.
Was it worth the additional investment in micros/optimisers?
Did you use that extra power in your house or did it get exported?
With feed in tariffs either at, or heading to zero soon, you certainly don't want to export that hard-earned solar power.

(08) 6102 2527

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This review was written by Andrew MacKeith, Solar4Ever service manager since 2011.
Solar4Ever is located in Morley (Perth), WA 6062