Are micro-inverters/ AC battery tie the way to go currently?

[Ampster]

I think you’re right and I get caught up in it myself. Our grid power is extremely reliable. It’s kind of like preparing for an EMP thing.

I feel the same way about spending a lot of time on perfecting AC coupling when the grid is down. I have hedged against grid outages on sunny days by having 3kW in DC coupled solar.

 

[Dmac1958]

Read through this and someone was looking for measurements on micro inverters, I follow

Projects With Everyday Dave on you tube and he is running an 8KW system for his house and is always running test with inverters, bi focal panels and snow issues with his array. Not saying he has all the answers but he seems to really try to be upfront and honest. Just my 2 cents more information for better decisions hopefully.

 

[solartist]

The technical complexity of EVSE is quite low. GFCI, PWM PHY for the current, basic handshake. All the necessary components were easily available and can be done in erector set style by electronics generalists. ... Also there isn’t the same regulatory oversight as for paralleling to the grid.

OpenEVSE is an important accomplishment. It's one thing to hack together a DIY EVSE prototype that works off-grid in a deficiently-regulated jurisdiction. It's quite another to get international regulatory approval for your EVSE and scale it up to commercial production and international sales.

By contrast you actually need to design custom power electronics for microinverters.

Are the DC to AC power electronics in a microinverter really so much more challenging than the AC power electronics in an EVSE? Might depend on national regulatory requirements.

Anyhow, the point here is more about creating a FOSS solution that is legal in as many jurisdictions as possible, rather than necessarily creating a fully open hardware solution.

Sounds like what you need to do is collaborate with people in your country to revise the regulations in an incremental fashion.

You're joking, I presume? I mean, lovely idea and great if it happens, but... it would almost certainly cost less time and money to design and build a FOSS microinverter.

 

[Ampster]

Are the DC to AC power electronics in a microinverter really so much more challenging than the AC power electronics in an EVSE?

As mentioned an EVSE is basically a relay. No power electronics at all. There is a pilot signal that determines what current the onboard charger will pull. The power electronics are in the charger, which is in the vehicle. To answer your question the power electronics in a microinerter are more complex than in an EVSE.

 

[Atetra]

AC coupling to battery-based inverter is not without risk. Without grid present to dump to, frequency shifting of hybrid inverter to control GT inverter's PV power output is rather slow reacting taking about 2 seconds or more. Without grid to dump to, turning off a large house AC load can create a sudden over-production of PV power that must be swallowed by battery-based hybrid inverter pushing excess power to battery until PV GT inverter's reduce their output power by frequency shifting of battery-based hybrid inverter.

1. Am I right in assuming that this is not a concern in a zero export setup as the micro inverters would only be producing power required by the load attached to it.

 

[Hedges]

"Load dump"
If microinverters are delivering 3kW and A/C is consuming 3kW then suddenly shuts off, the 3kW briefly exports, is detected by CT, microinverters are commanded it curtail output.

Grid is a bottomless battery, so can absorb the power while inverter ramps down.

If battery backed up and grid is down, regardless of whether zero-export or not, then battery has to deal with it.

 

[Atetra]

"Load dump"
If microinverters are delivering 3kW and A/C is consuming 3kW then suddenly shuts off, the 3kW briefly exports, is detected by CT, microinverters are commanded it curtail output.

Grid is a bottomless battery, so can absorb the power while inverter ramps down.

If battery backed up and grid is down, regardless of whether zero-export or not, then battery has to deal with it.

so if I understand this

1. if Hoymiles micro inverters are coupled to a hybrid inverter with battery backup.

2. The Hoymiles with frequency shifting is set up for zero export to the grid. So even though it can produce say 5kw, there is only a 3 kw load from the home and so by my understanding, it is only producing 3kw because the production was curtailed before the grid went down.

3. the hybrid inverter provides a grid (island) when the main grid is down, so if I understand what you are saying, since the CT is on the main grid line, in the absence of the grid the microinverter can’t see the CT will throttle up to the full power of the panels and that energy needs somewhere to go?

 

[SolarSamAK]

Hey guys,
As for Mirco Inverters versus String Inverters there is little difference between them in regards to production and life span. I quote PV magazine Nov 29 2021. In this study out of France, failure was more common on the micro inverter side but a system using micro inverters has many more inverters than a traditional string inverter. Of note, the durability of the string inverters was betters as they were 5 years older on average than the micro inverters in the study.

I copied this from above:

SOLAREDGE OPTIMISER FAILURES​

Here are MC Electrical’s updated SolarEdge failures as of December 2020. It has been 6 years since our first install.

• 130 SolarEdge systems installed since Nov 2015
• 138 inverters installed
• 3293 optimisers installed
• 75 approved optimiser warranties
• 36 approved inverter warranties
• 1 rejected inverter warranty (SE claimed lightning with no evidence).

So percentages work out as a whopping…

• 2.2% optimiser failure rate
• 27% inverter failure rate

I find this a bit misleading. Rather than % rate of failure why not mention a single inverter failure per system be it string or micro? I mean if a single system has say 25 micro inverters verses one single string inverter, then numbers are misleading. I bet every micro inverter system has at least one failure after 5 years while most Sting Inverters had none. Up front costs will weight heavy on the micro inverters. String inverters likely have a shorter life span, though that was not the case in the study. That being said, systems are advancing so after 10 years you may be replacing you inverters regardless, well if that is if they are string inverters. Given the new movement to mirco inverters I ask MC Electrical the average age of the Solar Edge system? Also do you install many MMPTs like a Sol Ark?

Of note, I am in northern cold weather climate. My friends who have Enphase have a much higher than average failure rate. Yes, Enphase inverters are rated to -40C but they experience about 50 to 100% failure of at least one mirco inverter yearly with an average system having about 20 micro inverters. They say heat kills a inverter but I feel extreme cold weather does as well. A nod to Enphase, they send replacements no questions asked. Labor costs to install and replace in Alaska far exceed the cost of the micro inverters. Installers love using them though. Most string inverters have a 10 year warranty verses mirco inverters, that vary from 10 to 25 years depending on location of installation.

Sam

 

[Brett V]

I have a SolarEdge grid tie system that’s about 6 years old. Three optimizers have failed so far. With 29 panels, that’s just a smidge over a 10% failure rate. The equipment and labor are still under warranty so I’m not changing anything yet. But when I have to start paying someone to climb on the roof, I’ll pay someone once to remove all the optimizers and replace the SE inverter with either a more conventional string inverter or split the panels in to 4 lower voltage strings and go totally off grid.

 

[SolarSamAK]

I have a SolarEdge grid tie system that’s about 6 years old. Three optimizers have failed so far. With 29 panels, that’s just a smidge over a 10% failure rate. The equipment and labor are still under warranty so I’m not changing anything yet. But when I have to start paying someone to climb on the roof, I’ll pay someone once to remove all the optimizers and replace the SE inverter with either a more conventional string inverter or split the panels in to 4 lower voltage strings and go totally off grid.

Per my previous message:

Enphase inverters are rated to -40C but they experience about 50 to 100% failure of at least one micro inverter yearly with an average system having about 20 micro inverters.

So your results are similar at 1 failure every 2 years of an optimizer, though your system is bigger at 29 panels. Over 6 years at one failure per 2 year that is 50% failure of one at least one unit per 2 year period (3 have failed). Similar to Enphase micro inverters in Alaska.

May I ask what climate you live in?

 

[Brett V]

Per my previous message:

Enphase inverters are rated to -40C but they experience about 50 to 100% failure of at least one micro inverter yearly with an average system having about 20 micro inverters.

So your results are similar at 1 failure every 2 years of an optimizer, though your system is bigger at 29 panels. Over 6 years at one failure per 2 year that is 50% failure of one at least one unit per 2 year period (3 have failed). Similar to Enphase micro inverters in Alaska.

May I ask what climate you live in?

I'm in south central Pennsylvania, near Gettysburg. Hot in the summer, cold in the winter, and during the spring and fall, it's not uncommon to use heat and air conditioning in the same day!