Solved: The Voltage Mismatch Causing Sungrow Inverters to Drop Power

Like any complex modern technology, solar inverters often have flaws. In this post, I’ll explore one of the most curious problems I’ve seen in recent years. Thanks go to Sungrow for keeping my job interesting…

In my experience, Sungrow inverters are adaptable, powerful, and reasonably priced with great Australian support.

The hardware is solid¹ so I’m surprised they have a fairly widespread technical problem.

What’s Going On?

In some cases, Sungrow’s 4 MPPT single-phase inverters can’t handle the string configurations they’re rated for.

While they still work, I have seen firsthand a system yielding only 150 watts when it should be pumping out 5000 watts or more.

I’ve noticed this before with a vintage Xantrex inverter that would “start-up” and turn the green light on but never generate properly. In that instance, it had to be replaced with an SMA that had quite different input specifications.

It can happen to any manufacturer. This just happens to be Sungrow’s turn in the spotlight.

The lights were on, but nobody was home. Xantrex couldn’t cope with an array producing a maximum of 220VDC, and the peak power input of 180VDC was too low.

Of All The Gin Joints…

Let’s face it: If you were going to sell a new model line, you really wouldn’t want the General Manager of SolarQuotes to do beta testing in his own house. You could say it’s pretty embarrassing, but I prefer to look at it like this: What better way to prove your problem-solving prowess?

Trev, our GM, isn’t an electrician, but he’s technically savvy. He bought his new Sungrow SH10RS hybrid from a well-regarded business, and I’m comfortable saying the owner and electrician, Joe Deionno, is one of the sharper knives in the drawer. Joe’s experience ensured there wasn’t an installation or electrical design problem; everything was within the recommendations.

String D with 7 panels. At maximum power, there’s a 180-volt difference to string A

Sungrow Specifications are Impressive

Sungrow and many others have been kicking goals with 5kW hybrids offering a handy 27 amps (120%) surge capacity on the backup circuit. In an outage, this allows you to run your fridge and lights comfortably and even manage some luxuries like a small split system air conditioner.

The new 8 & 10kW (SH8.0RS and SH10RS) single-phase hybrids are a significant step forward. At nearly 60 amps surge capacity and up to 45 amps continuous, they’re designed to offer “whole-home” backup.

The inverter carries all the power to and from the grid² It makes the installation wiring straightforward, but that simplicity cuts both ways. If the inverter fails, you have no power, so Sungrow supply them with a bypass switch.

It’s something we highly recommend for any series hybrid inverter. If the hybrid inverter fails, with a flick of a switch you, your tenants or guests can restore mains power and avoid emergency callout fees for a temporary switchboard rewiring job.

String D is now 9 panels. At maximum power that’s only 150 volts different to string A

There’s Been Some Confusion

For Trev’s place, there were a few months of maddening symptoms. Inconsistent faults are the worst. The firmware was updated, the wiring was checked, the battery was inspected, the inverter was replaced, and the monitoring was interrogated again and again.

Voltages were measured, SAPN (the electricity network people) were harassed about their external export controls. Even though the system had a dumb 5kW limit, it was moved to the new flexible exports just to see if that changed something, and it didn’t.

The disappointment became palpable with each round of phone calls and installer appointments. A battery cell with an early-life failure under warranty confused matters. In retrospect, Trev says the support was great.

An Interesting Development

At the same time as Trev’s woes, Sungrow tech support made a post on Facebook to alert installers of a potential problem. Subsequently, there were some dirty deletes, wild rumours and innuendo, culminating in an official explainer from a most senior technical engineer:

Hi Installers, Please be noted that, for SH8/10RS, the different MPPTs need to be within 150V.

This was the problem with Trev’s system.  By moving two panels from one side of his house to the other, his string voltages were better balanced (within 150V), and the problem hasn’t resurfaced.

Sungrow gave a further, official explanation on Facebook:

UPDATED: Yesterday night, we organized an emergency technical meeting with Sungrow’s product team, now we can confirm that SH8.0RS and SH10RS have 4 real independent MPPTs, but, under some extreme conditions, the inverter could reduce solar production.

This Probably Looks A Bit Unseemly

Social media has become ubiquitous, forming the backbone of technical information and product awareness for many solar manufacturers in Australia. To be honest, I feel a bit awkward airing the dirty laundry, so I hope Sungrow isn’t mad at me. We’re demonstrating a culture that helps everyone by being well-engaged and super-responsive. Good manufacturers have  a brand and a community, too.

The take away is the message that Sungrow offers great support for their installers, which means end users should have the best overall experience.

Those who just look over the promotional flyer can still be misled if you miss the asterisks and fine print on the next page. ** Please refer to the user manual for the full load MPPT voltage range

 

The Solution; Designing For Rated Power

While the operating specs are very broad, technical support now states designs should stick to the “MPP voltage range for rated power”

190 – 480v are the magic numbers (a 290 volt window) because, to quote Allen Ding from Sungrow,

“160v on one string and 530v on another is too much difference”

Trev’s solar output would sometimes drop like a stone and stay low for hours.

Innovation Continues

Now installers are aware, it’s not a huge issue, but it has spurred further development in the industry.

Designers and salespeople rely on software to place panels and form electrical layouts. Most use maximum open circuit voltage as a ceiling. With a particular panel at your address, uprated for low temperature, the programs will flag a design that exceeds 600 or 1000VDC.

I’m happy to report that, as a direct result of “the Sungrow situation,” our friends at solar design software SolarPlus are working out an option for nominal design voltage instead of just a maximum ceiling figure. So, all installers using all brands will be able to stipulate whether they want peak efficiency or peak capacity when designing.

Once the string voltages were sorted out, Trev’s system has been cracking along

Quality Is Important, Support Is Supreme

At the end of the day, customer satisfaction can only be guaranteed by good service. You just don’t get it with crazy-cheap systems, especially those flogged by flimsy sales companies and spruiked by washed-up sports ball players on TV.

Not every solar power system is plain sailing. Trev has had a textbook case of new system difficulties but an even better example of stellar support.