Combining MicroInverters and String Inverters

[fastbike]

So long story short: we are commissioning the house with 27 panels on a 3 phase Solis 10kW inverter. The standalone garage is getting 14 panels which will have micro inverters due to some shading issues (rails installed today, Enphase gear ordered).

The garage and the house share a common meter for the connection from the street, but each is treated as a separate installation with its own distribution board with independent MEN connections.

We are using 3 phase Iammeter energy meters to measure the power drawn/exported to the grid, and a separate meter on the output of the house inverter.

The Enphase gear comes with some type of gateway device (I've not read enough about it yet to know exactly what it does). Will I need another Iammeter energy meter to measure what it is supplying and then use OpenHAB or similar to control daytime loads i.e. integrate the output of the two solar installations ?

Has anybody got a similar setup I can study ?

[Siwastaja]

You are planning using some kind of optimization device or DIY setup increasing your self-use? Then best would be to let it know total power flow (same which goes through the single meter from the street). Which you can do by adding measurement on common part of circuit, or by measuring the two branches and summing them somewhere. Read the documentation of whatever optimization product you are going to use if they support this kind of summing of branches.

Or, you can just optimize based on the house measurement and let the garage PV system live its own life. Maybe that is good enough.

It seems to me project like OpenHAB or HomeAssistant and similar are pretty good in integrating data of gazillion of devices together but they lack the big picture about doing automated control (energy or cost optimization). Expect some DIY.

[fastbike]

I've had two quotes back for the Enphase gear (can't find a local supplier for Hoymiles).

It's quite spendy: NZD$200 per inverter, plus another $30 for the cable per panel. And the Envoy is around $500. Another $140 for the disconnect relay. And then the mandatory box plus the breakers to put it all into.

Would a 5kW 2 MMPT 3 phase inverter be cheaper  - I think so. Would it handle the weird shading patterns that I can observe on that roof - don't think so.

So I'm about to pull the trigger. I hoping the Envoy has a local API that I can query for power production.

[Siwastaja]

Usually it turns out that if the place is shady enough for a microinverter solution to produce significantly more than a string inverter, then it still produces absolutely so little (due to all that shading) that investing in the more expensive system never pays for itself. I would primarily avoid installing PV in mediocre or poor places, because there is no lack of good places (if you look at the big picture).

But of course, there can be other type of motivation than just money. If you want to maximize the amount you are producing, then you are limited by the install locations you have, and maximizing production with microinverters could be emotionally the right thing to do.

String inverter does not care about the "weirdness" of the shading pattern. But if the minimum MPPT voltage is say equivalent of 6 panels (quite usual rating) and you have 10 panels out of which 5 are seriously shaded (so only 5 produce), then it falls below the minimum voltage and goes close to zero while microinverters would still produce 50%. But if this happens "all the time" then the question indeed is how much you are paying to be able to produce 50% of rated power. Like, you pay 30% premium to produce only 50% of an "optimal" system. Given long payback times of any PV install it makes no sense.

On the other hand, continuing with the same example, if you shade 3 panels out of 10 then string inverter and microinverter produce roughly the same: string inverter produces a tad below 70% of total rated; microinverter is able to get some power out of those shaded panels (but not much because, doh, they are shaded) so maybe it produces 75-80% of total rated during that condition, but loses that extra power, if not more, in generally 1-2%-point lower efficiency and usually higher idle power draw, which affect the system all the time.

TLDR:
* Partial shading of 20-30% of the roof for hour or two per day or so: just get a string inverter and verify you exceed minimum voltage most of the time
* Significantly more shading than that: don't install PV at all
* If you are desperate to get some power out of such crappy location, then microinverters or optimizers.

[nctnico]

I'd be careful with string inverters and shaded panels. From a quick scan I did recently, it turns out only the more expensive string inverters can deal with shaded panels. If there is no mention a string inverter can deal with shading in the manual / datasheet, then assume it won't deal with shading at all. Using optimisers which deal with individually shaded panels (for example due to a chimney, pipe, etc) could be a more economic solution.

[Siwastaja]

I'd be careful with string inverters and shaded panels. From a quick scan I did recently, it turns out only the more expensive string inverters can deal with shaded panels.

If true, it would be an alarming defect. My ages old Stecagrid seems to do fine, for example. Every cheap brand at least theoretically have proper wide MPP scan to avoid getting stuck in local minima, but of course there can be bugs and poor implementations. Still, it's 2024 now, not 2014, this is such fundamental basic feature that I would say "extraordinary claims require extraordinary evidence". So it would be interesting to see what sources you found for your "quick scan" and if the claims are credible.

I'm not saying you are necessarily 100% wrong, just that if you are right then the situation is pretty bad and worse than I think it is.

BTW, I think that if a string inverter gets seriously stuck in local minima even when minimum MPPT voltage is clearly satisfied that is enough reason for demanding a repair or replacement with an inverter which works in the expected way. People should not accept crap like that.

[nctnico]

Growatt is a pretty popular brand and it won't deal with shading at all. The supplier confirmed that. As I added above: If there is no mention a string inverter can deal with shading in the manual / datasheet, then assume it won't deal with shading at all. This could be a patent related issue BTW where the inventor wants crazy money to implement searching for a better optimum.

[Siwastaja]

Maybe you are right that Chinese are still behind in this. Western inverters have had this since forever and I have assumed Chinese would have implemented it too being such fundamental feature and these inverters otherwise being quite mature already.

Goodwe (another cheap Chinese brand) is at least discussing about it: https://community.goodwe.com/solution/How%20does%20Shadow%20Scan%20Work?
But even they say it's OFF by default and needs to be enabled (so in practice remains disabled because no one reads the manual).

Solinteg, a Chinese brand which I have never heard about talks about it, too. Maybe it's their strong point.

Googling says that Solis S6 series should have a decent scan and people are happy with the results.

My system (Stecagrid) has been working as expected. I had partial shading (4 out of 10) with string going below minimum MPPT voltage which obviously killed the performance. After adding four new panels in series, in unshaded area, the problem basically went away: 10 of 14 panels are producing fully and the four shaded panels bypassing. Been monitoring it since installing the new panels with no surprises, the global scan clearly works and does not get stuck in another local maximum at higher string voltage.

[tszaboo]

I wouldn't do that. I would either get Solaredge inverters with optimizers on every panel. Or use your selected inverters and place Tigo optimizers on the shaded panels. I have solaredge at home. It's good. Not affiliated. Enphase is just really bad value.

[nctnico]

Putting an optimiser on every panel gets expensive quickly. The price difference between cheap and more expensive inverters can be hundreds of euros. It takes careful analysis to determine whether having a more expensive inverter is actually worth the money. In the end you want to have a solar panel installation to pay for itself.

[tszaboo]

Putting an optimiser on every panel gets expensive quickly. The price difference between cheap and more expensive inverters can be hundreds of euros. It takes careful analysis to determine whether having a more expensive inverter is actually worth the money. In the end you want to have a solar panel installation to pay for itself.

The Tigo inverters are like 40 EUR, so 14 of them is like 560 EUR, which is probably 5% of the total system cost for such a big  installation. Solaredge inverters are also a lot cheaper than comparable Fronius, SMA or ABB inverters, and a lot cheaper than anything from Enphase. Of course Chinese inverters are going to be cheaper, but I don't think it will be worth it down the line.
Plus, this is not just about the ROI, there are other considerations.

[Siwastaja]

Solaredge inverters are also a lot cheaper than comparable Fronius, SMA or ABB inverters,

Of course anything is a lot cheaper compared to three most expensive "Western" brands. It seems to me everybody really installs Chinese inverters because they give good price - quality ratio, though. You should be comparing to those.

If the online claims about Solis handling MPPT "shadow scan" much better than others, that places Solis into pretty good position because it's not expensive. My biggest complaint about Solis is that external MODBUS RS485 port shares the same interface with the datalogger so you can only have either one, not both. For some companies this is a showstopper for our control box, for others they are fine accessing data through our service only instead of Chinese cloud.

[nctnico]

Putting an optimiser on every panel gets expensive quickly. The price difference between cheap and more expensive inverters can be hundreds of euros. It takes careful analysis to determine whether having a more expensive inverter is actually worth the money. In the end you want to have a solar panel installation to pay for itself.

The Tigo inverters are like 40 EUR, so 14 of them is like 560 EUR, which is probably 5% of the total system cost for such a big  installation.

Assuming you mean 14 optimisers on all 14 panels then paying 11k euro for such an install (around 5500Wp) is way too much anyway. There is no ROI to be had -ever-. I paid 3800 euro for my 4500Wp install. That over 2 times cheaper and I'm looking at an ROI between 4 to 5 years already. And I consider myself 'lucky' I had a good year in 2023 due to the high electricity prices.

[Siwastaja]

I paid 3800 euro for my 4500Wp install.

Which is about right. Or maybe a bit more can be accepted, but definitely not 2x or 3x.

PV needs to be bought at correct timing, especially turn-key. There is this cycle of mass psychosis, rise of prices, demise of market, bankruptcy wave of install companies, dropping of prices to sane levels due to healthy competition, and then the cycle repeats. Here a "normal size" system cost for full turn-key install varies between 6000 - 15000 EUR depending on the timing / psychosis level. What is "normal size" increases as time goes by. And always some people are getting too large systems (e.g. 8-10 kWp). Well in some rare cases that size is a good idea but that needs design of the whole, not just slapping a 10kWp inverter and 25 panels on the roof.

With too large systems, self-use% becomes a problem. In some countries there are indirect or direct subsidies where you get paid for export at all times but I don't think it leads to right decisions. It makes no sense trying to absolutely maximize production. PV is best distributed and mostly self-used. This also prevents any last-mile voltage rise problems you can see happening in countries which subsidize export price and people get 10kWp systems.

[tszaboo]

Putting an optimiser on every panel gets expensive quickly. The price difference between cheap and more expensive inverters can be hundreds of euros. It takes careful analysis to determine whether having a more expensive inverter is actually worth the money. In the end you want to have a solar panel installation to pay for itself.

The Tigo inverters are like 40 EUR, so 14 of them is like 560 EUR, which is probably 5% of the total system cost for such a big  installation.

Assuming you mean 14 optimisers on all 14 panels then paying 11k euro for such an install (around 5500Wp) is way too much anyway. There is no ROI to be had -ever-. I paid 3800 euro for my 4500Wp install. That over 2 times cheaper and I'm looking at an ROI between 4 to 5 years already. And I consider myself 'lucky' I had a good year in 2023 due to the high electricity prices.

OP wants a system with 27+14 panels, and ~15KW peak capacity. I think including installation 10K is a reasonable price.
My 4KW system was also ~4K, including installation costs, including the optimizers, and has about paid for itself already.

[fastbike]

OP wants a system with 27+14 panels, and ~15KW peak capacity. I think including installation 10K is a reasonable price.
My 4KW system was also ~4K, including installation costs, including the optimizers, and has about paid for itself already.

We've done the original system with 27 panels and a 4 MPPT input Solis inverter. There is no shading on this part of the system (2 story house, roof facing almost due north) but we ran out of room to use the remaining panels from the pallet.
From analysis and observations of the second roof on the site (garage) we figured we could get up to 18 panels installed but 14 was much easier as the additional 4 required some funky rails due to roof purlin spacing etc. So 14 it is !

I have had 3 local quotes for the Enphase gear (equipment only) and the price differences are +50%  between the official dealer (cheapest) and the others. My installer is happy for me to do the physical install, as long as I take a photo of each panel/inverter. He will do the inspection and installation/connection of the switch gear.

The cost delta between the Enphase and a good quality 5kW 3 phase inverter is not that high when taken as a a percentage of total system cost. So Enphase it is at this stage.

One other question - last night I did the basic Enphase online training and got my certificate. Most of the questions / info was reasonably straight forward.

One thing I picked up was with the 3 phase IQ cables they have three variants with different spacing between the plugs: 1.3, 2.0 and 2.3 metres. The first is for portrait and the other two are for landscape. However they say for portrait panels 1100mm and wider you should pick the 2.0m cable. My panels are 1134 - with an 18mm clamp between - so on 1152mm spacing.
Should I order the 2.0m (more expensive cable) ?

[nctnico]

I'd be careful rating expenses as a small percentage of total system cost. It is easy to fool yourself that way. Better calculate ROI. Especially when those 14 panels are not in an ideal location.

It is like saying a 5k bathroom sink is peanuts compared to buying a 300k home but it still is a 5k bathroom sink (with a 30 years mortgage payment + interest)!

[fastbike]

I'd be careful rating expenses as a small percentage of total system cost. It is easy to fool yourself that way. Better calculate ROI. Especially when those 14 panels are not in an ideal location.

It is like saying a 5k bathroom sink is peanuts compared to buying a 300k home but it still is a 5k bathroom sink (with a 30 years mortgage payment + interest)!

The main system has a cash payback of 5 years. The additional one will be around six years. With interest rates currently low (I can finance for 3 years at 1%) I'm happy to use a cash payback rather than a discounted cashflow approach.

[Siwastaja]

The additional one will be around six years.

How did you calculate it? For a partially shaded microinverter system paybacks are usually in range of 20-100 years, that is why I'm suspecting you have miscalculated.

5 years for the main system sounds plausible.

How is the pricing model for exporting excess to grid where you live? This is pretty fundamental question for large PV systems. Usually it's significantly worse than import price (for good reasons) therefore marginal cost for a larger systems gets worse and worse.

[nctnico]

FYI: I based my decission to get/install solar panels on having a worst case ROI of 5 years and a lifespan of 10 years. Initially I projected and ROI of less than 3 years but electricity prices dropped faster than expected and now there is a feed-in tariff as well which set the ROI back to nearly 5 years. It is impossible to foresee what is going to happen where it comes to energy / electricity distribution & pricing beyond 10 years. This is also why I choose to get the cheapest inverter. It will probably last 10 years. When it breaks there are likely better inverters or it may even be possible new regulations or home storage systems make it necessary / worthwhile to replace the inverter long before the panels are end-of-life. And it is also possible it makes no sense to replace the inverter at all.

[Siwastaja]

FYI: I based my decission to get/install solar panels on having a worst case ROI of 5 years and a lifespan of 10 years. It is impossible to foresee what is going to happen where it comes to energy / electricity distribution beyond 10 years. This is also why I choose to get the cheapest inverter. It will probably last 10 years. When it breaks there are likely better inverters or it may even be possible new regulations or home storage systems make it necessary / worthwhile to replace the inverter long before the panels are end-of-life.

This is good thinking, and usually cheapest per kW panels should be used. It is specifically stupid to invest more money into "premium" panels with salesmen pitching about "longer lifetime" (without giving any concrete extra warranty compared to cheaper ones) or "local manufacturing" (when they really all come from China anyway) or "much better efficiency and these produce even under snow" type bullshit.

[tszaboo]

OP wants a system with 27+14 panels, and ~15KW peak capacity. I think including installation 10K is a reasonable price.
My 4KW system was also ~4K, including installation costs, including the optimizers, and has about paid for itself already.

We've done the original system with 27 panels and a 4 MPPT input Solis inverter. There is no shading on this part of the system (2 story house, roof facing almost due north) but we ran out of room to use the remaining panels from the pallet.

My bad, I seem to have misunderstood. In any case good luck with your system.
I just dislike Enphase passionately, because IMHO it's a worse system for more money with more drawbacks, clipping, extra boxes for the data and disconnection, and subscription. But it's a free market.

[Geoff-AU]

I spend more money than necessary in other areas of life and derive pleasure from the extra expense so if people want to pay too much for DC optimisers or microinverters and feel good about it then so be it.

I bought good quality string inverters with global MPPT scan and they just chug out power day after day, reliably and efficiently.

[Siwastaja]

I spend more money than necessary in other areas of life and derive pleasure from the extra expense so if people want to pay too much for DC optimisers or microinverters and feel good about it then so be it.

Of course but people should have access to the information and know what they are doing. Pay premium for premium features that actually do what is promised. We (as a player on the smart energy business) have seen aggressive microinverter sales companies who sell FUD (false claims about others) and false promises of their own systems.

I would like to see microinverter systems evolve and gain real traction on the market through real advantages but currently it seems they are falling behind in the competition, i.e. quality is going down (e.g., they have no resources to update their product lines for new higher-power panels -> hence they clip power, totally unacceptable!), while competion is going forward (string inverters having more and more MPPT inputs, smaller start/minimum voltages, battery option for very little extra cost, better efficiency...

I hate to see it when the underdogs don't get their shit together but instead start to play dirty. FUD and lying in marketing are reasons alone I will not recommend microinverters to anyone. If a fresh new player who does something new on the field pops up I'm super happy to change my mind.

[tszaboo]

I spend more money than necessary in other areas of life and derive pleasure from the extra expense so if people want to pay too much for DC optimisers or microinverters and feel good about it then so be it.

I bought good quality string inverters with global MPPT scan and they just chug out power day after day, reliably and efficiently.

I understand why people would spend more money on something rather than absolutely necessary. In the end, the system I bought is more expensive than some chinese inverter and panels making some power. Which made the ROI like what, half a year longer? But then,
Meanwhile I have data per panel, higher efficiency, open modbus protocol on the inverter to read out data even if the cloud thingy gets shut down, and global 10% DC overprovisioning in the system instead of like 30% per panel, like you do with an Enphase. I just don't get why people spend more on a worse system. Probably marketing, and installers getting a kickback for offering it.
Like their battery offering, which was a bunch of microinverters slapped on a battery pack. Does one really need to explain why that's a bad idea?