Australian solar install example

Saw the latest video that Dave from EEVBlog uploaded to Youtube, with his new 5KW addition to his existing solar set up.

Few interesting things I noted was the DC isolator switch they have on their roofs, and the new trend to micro inverters for each panel.

If the micro inverters stop the overall losses from shading on a few panels, why are they not more popular locally? Surely with a east west split or a non north facing roof, these would be ideal. Lower cabling requirements as well, as you can use normal AC wiring from the panels to the main controller. Software can also provide feedback on individual panel performance and if one panel is damaged, the rest can continue functioning.

Surely the benefits far outweigh their current cost? What am I missing?

My guess is its to do with the economics of feedback. On that side they are paid to feedback and extracting every extra watt to feedback therefore makes sense.
Here priorities are slightly different.

I initially looked at going the Micro Inverter route, but after calculating the costs it was not worth it.
It is not cheaper that the normal Inverters and it also does not have battery backup.

Possibly, but as he mentioned in the video, it looks like some Australian states are now planning on penalizing their users who feed back into the grid, in effect charging them for feedback.

So the “own usage, with battery backup” scenario should become popular there as well.

Ah, so you cannot add battery backup to the current range of micro inverters?

That is a big shortcoming, especially when load shedding.

My uneducated guess would be cost, availability and our ‘unique’ grid situation. I actually had a look at them last week and decided against them.

With a micro inverter you don’t need an inverter as the micro inverter does the inverting from DC to AC right then and there. But most South Africans (as far as I know) are getting inverter systems mainly for battery backup in case of loadshedding and adding PV to reduce reliance on Eskom. In those cases you do need an inverter to be able to make use of the energy stored in your batteries.

You also have a lot of inverters that comes with built-in MPPTs. With most South Africans trying to add PV along with batteries for loadshedding as cheaply as possible they tend to go for those inverters as it’s an all in one solution. As it already has an MPPT built-in the everyday Joe wouldn’t want to add micro inverters on top of the cost in order to prevent shading issues.

With split cell panels you are already not losing all your power with partial shading, so with the long string MPPT’s you’re at least still producing with partial shading of a panel.

Micro inverters for one aren’t generally available here in SA and I think there’s only really the one Hoymiles 600W micro inverter available at ~R3k each which is able to have 2x panels on them. That’s where I also decided to rather have 3x smaller MPPT’s with a small amount of panels in series on each one for my 3x directions.

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Yes, that’s in their regs. Must have a switch on the roof. Also one of the things that ironically caused a few roof fires. Some switches were said to comply, but didn’t, got recalled, etc etc. Dave himself has a video of a roof-mounted switch full of water.

I would not say that is a new trend. Micro inverters have been around for almost a decade now. I remember looking at them back in 2013, because I thought they’d make a good (if somewhat more expensive) way to add solar incrementally, one panel+inverter at a time. I believe the one I looked at back then was a Taiwanese brand called APsystems.

Sharp also made “AC” PV modules that had a built-in microinverter as early as 2011.

Also, Enphase is arguably the market leader when it comes to this, but they don’t even have a footprint in SA… at least not one to “write home about”.

If anything, the craze died down a bit.

In my opinion, the microinverter solution suffers from the same problems as the SolarEdge “optimizer” solution. You’re placing the inverter (or part of it in the SE case) in a very hostile environment, right below a very hot PV module. That means more expensive components, and a higher failure rate. Even with low failure rates (say 1 in 500), because you have multiple inverters in the installation, the odds of a single failure multiplies by the number of inverters.

Unless you have a big problem with shading, which requires panel-level optimisation, I would still opt for a string inverter (as they are called) downstairs rather than several small parts upstairs.

Edit: Also, as other posters have said, in SA we kinda want backup. And most microinverters do not support frequency-dependent power reduction. Or at least they didn’t the last time I looked. I think Hoymiles have one now that does…

Thanks Plonkster. Yes, saw the failure he had on the dc switch and he again mentioned it in the video. Just seems a stupid place to put the switch, but they no doubt had their reasons.

Do you see a future where we would have this level of monitoring on a dc string?

Maybe. It’s not a bad idea really. Trina already makes a “Smart” module that clamps the open circuit voltage on a panel level (which makes it much easier to use long strings without having to worry about cold mornings). If we’re already putting small amounts of electronics in PV modules, I suppose panel-level monitoring may be closer than we think!

PV modules already have bypass diodes (3 on a 72-cell module), so a few simple measurements could already give you panel-level “I am having shading issues” indications.

Of course this is thumb-suck… I have no idea if anyone is doing that :slight_smile: