Finally going solar. I have a question about Enphase microinverters and Powerwall compatibility

[swedge]

Could someone explain to me of the advantage of using MicroInverters versus
a SCC (Solar Charger Controller) with MPPT (Maximum Power Point Tracking) solar system.

From what I can see, you need one MicroInverter for each solar panel, which is quite expensive.
Also the output of a MicroInverter is AC, so you need an AC/DC inverter to charge a battery.

I was thinking that MicroInverters were recommended when there was trees providing shade.
Also MicroInverters are simpler to use for Grid Ready systems without battery.

So in the case of a Solar system, without shade from trees, an using Powerwalls,
would you recommend using MicroInverters versus SCC MPPT ?

Microinverters offer several advantages: MPPT per panel is a big deal if there is any shading or panels with various orientations. Per panel monitoring. Low power per inverter means cooler, better reliability. Redundancy means failure of a single inverter is detected and the rest of the array continues to function while waiting for repair. Finally, a system can be easily expanded incrementally over time.

I think of it this way. String inverters are power electronics dealing in kW. Micro inverters are at power levels like a home hi-fi, so they run cooler which is a good thing. Over nearly 20 years with one string system and one Enphase system, I've had two string inverter failures and no micorinverter failures in spite of 10X as many micro inverters. Oh, and the microinvertes detected one weak solar panel which was replaced under warranty.

In my case, I have tall trees to the west, and each afternoon the shade sweeps across the array. With a string inverter with parallel wiring of multiple series strings, shading any single panel decreases production of the entire array.

In a prior home, we installed optimizers on the panels, but then a failure of the string inverter took the whole thing down while we waited for the repair.

In a non PowerWall installation, I recommend getting Enphase's consumption monitoring option. This give real time and logged home power use, so you can quantify your options for reducing your consumption.

 

[Watts_Up]

Microinverters offer several advantages: MPPT per panel is a big deal if there is any shading or panels with various orientations.

I agree for isolating solar production independantly for each PV, especially in case of shade or multiple oreientation,
but the output of microinverters is AC. So to charge a battery you need to convert back to DC.

Is there any efficiency and cost comparison available comparing MicroInverters versus Solar Charger Controllers when charging a battery?

 

[wwu123]

I agree for isolating solar production independantly for each PV, especially in case of shade or multiple oreientation,
but the output of microinverters is AC. So to charge a battery you need to convert back to DC.

Is there any efficiency and cost comparison available comparing MicroInverters versus Solar Charger Controllers when charging a battery?

I think many of the leading brand Energy Storage Systems are AC-coupled now, including Tesla Powerwall and Enphase's own batteries. So the ESS have their own inverters to convert AC to DC for the batteries. So from the panels, it's DC -> AC (string or micro-inverter) -> DC (ESS built-in inverter) -> DC battery (ESS cells).

I think the original 1st-gen Tesla Powerwalls were DC-coupled. Why it is more common to use AC-coupled now, I'm not sure why, as I'm sure there's inefficiencies in those redundant conversions.

 

[jjrandorin]

Why it is more common to use AC-coupled now, I'm not sure why, as I'm sure there's inefficiencies in those redundant conversions.

Im certainly not an expert, and wont even pretend to be, but my guess is that they are AC coupled because its compatible with more devices.

 

[sunwarriors]

I mentioned this before, but if you have a ton of clouds and it's an overall cloudy day, you're probably still not going to recharge batteries to 100% from solar alone whether it's DC or AC.

In most cases I can see, it's either 100% by noon or not even close. I think as ESS is more common, people will simply now start charging the batteries from the grid if there is any possible chance of an outage and most folks won't miss/think about the AC/DC lost.

Higher compatibility beats the conversion lost (IMO) people keep mentioning and the single point of "common" failure (plus another ugly box on your wall) is a higher annoyance I feel.

People almost always spout "cost savings" not to go micros, but for any home/residential project, it's more like a $2k difference (before any tax credits) which I think is not worth overthinking.

Assuming you don't have solar/storage yet, I think anyone who has gone with the purchase will never think about this efficiency mind exercise ever again (I certainly don't).

You're better off thinking of adding a generator, add more panels, add more batteries or finding ways to go off grid.

 

[swedge]

Is there any efficiency and cost comparison available comparing MicroInverters versus Solar Charger Controllers when charging a battery?

A grid tied solar system needs an inverter, so it outputs AC. Off grid systems are an all together different story, not what PowerWall or Tesla Solar systems are designed for. String inverters typically input hundreds of volts DC from several series connected panels, while batteries are typically 48 volts, so at least DC to DC conversion would be needed in any case.

If you are really curious, you can look up specs for various inverters and charge controllers.

I am not certain of this, but I suspect the losses in charge controllers come from the regulation of charge current and voltage, while rectifying and filtering AC to DC is pretty efficient.

One other point is that it is possible to charge PowerWall from the grid, a nice feature for those on time-of-use and net metering, with or without solar in the system. AC connected storage is pretty cool: backup, cost saving, and staying off grid during peak utility loads. Oh, and sometimes Virtual Power Plant events when our utility pays us an outrageous $2 per kWh when their only other option is rolling blackouts.

 

[Watts_Up]

• MicroInverters: IQ8M-72-2-US [240V] (17x)

In the case of a US eletrical AC panel with two or three 120V phases with Neutral,
how the 240 V output of the microinverters are connected to the grid?

- Do you separate the microinverters into separate branches for each grid's phase,
and each microinverter's branch getting converted from 240V to 120V?
- Does the microinverters get their frequency synchronized with the grid ?
- Does each microinverter's AC phase angle get triggered to match each grid phase angle?

 

[miimura]

On a North American grid, these micros can be used in 240V/120V split phase and 208Y120V 3-phase utility connections. In Split Phase, the micros have pure 240V output and the 120V is balanced by either the utility transformer or the micro-grid master (ie. Powerwall) when off-grid. I have never looked at how Enphase recommends wiring their micros on 3-phase. Presumably, their IQ combiner is offered in a configuration that handles distributing the strings of micros across the phases, with each micro seeing nominal 208VAC.

 

[BGbreeder]

On a North American grid, these micros can be used in 240V/120V split phase and 208Y120V 3-phase utility connections. In Split Phase, the micros have pure 240V output and the 120V is balanced by either the utility transformer or the micro-grid master (ie. Powerwall) when off-grid. I have never looked at how Enphase recommends wiring their micros on 3-phase. Presumably, their IQ combiner is offered in a configuration that handles distributing the strings of micros across the phases, with each micro seeing nominal 208VAC.

@Watts_Up It is as simple as selecting the appropriate grid profile in the configuration. The procedure is here, if you are curious.

https://support.enphase.com/s/article/How-to-change-or-select-the-right-grid-profile-for-my-Enphase-system

Pretty much any device generating power (inverters, microinverters, or powerwalls, etc.) needs to have a grid profile configured, either to match the local grid characteristics, or when off grid, to match the home appliances. I find the range of possible configurations an amusing reminder how small choices made over a hundred years ago locked regions into particular power configurations. (Did you know Japan has a 100V home voltage in both 60 and 50Hz? Until the advent of high power MOSFETs, the Japanese grid operator had to use truly enormous motor/generators in the grid interconnects to move power from one grid to the other to even out generation and load demands. Electricity sector in Japan - Wikipedia )

All the best,

BG

 

[jjrandorin]

If a generator has a breaker in the main panel, then it's not being connected via the BPTM in the first place.

But if there were a scenario where the generator and solar both had breakers in the main panel, would it be possible to had them on opposing sides of a manual transfer switch, feeding into a shared breaker in the main panel? I'm not sure what use case would need something like this though, and then seems like you'd still need another standard generator interlock kit to prevent the main breaker from being on with the generator on. (None of this having any relevance to the BPTM scenario....)

Note to moderator: I tried desperately to move the BPTM discussion over back to my thread that started it, but folks still prefer to discuss it here, ha ha

You did, yeah (thanks for trying). I am not going to be a stickler here in this thread about it though, since its mostly "regular members discussing / helping another regular member" so Its fine imo.

 

[wwu123]

(Did you know Japan has a 100V home voltage in both 60 and 50Hz? Until the advent of high power MOSFETs, the Japanese grid operator had to use truly enormous motor/generators in the grid interconnects to move power from one grid to the other to even out generation and load demands. Electricity sector in Japan - Wikipedia )

That's OK, the U.S. can't move electricity between California and Texas, even though the voltages and frequencies match, amongst many regional limitations here. And my visiting in-laws from Japan laughed at us when even the slightest breath of wind seems to knock out power due to falling branches ... actually no, they didn't laugh, they were truly shocked and frightened when we lost power, as they'd never experienced a power outage before.

 

[jjrandorin]

That's OK, the U.S. can't move electricity between California and Texas, even though the voltages and frequencies match, amongst many regional limitations here. And my visiting in-laws from Japan laughed at us when even the slightest breath of wind seems to knock out power due to falling branches ... actually no, they didn't laugh, they were truly shocked and frightened when we lost power, as they'd never experienced a power outage before.

As seismically active as japan is, I am surprised they never experienced a power outage in any of the earthquakes they probably have lived through. I know I have lost power through several earthquakes here in southern ca during my lifetime.

 

[BGbreeder]

As seismically active as japan is, I am surprised they never experienced a power outage in any of the earthquakes they probably have lived through. I know I have lost power through several earthquakes here in southern ca during my lifetime.

I think that your inlaws have been quite lucky. I can attest to a number of power outages in Tokyo, caused by earthquakes and typhoons. The Tohoku earthquake that disabled the Fukushima power plant caused the authorities to shutdown all (54?) Japanese nuclear plants. That lead to widespread shortages of power and outages, due in part to the limited ability to transfer power from the 50Hz grid to the 60Hz grid, which is how I learned about the interconnect problems. I will say that I think that, in general, the Japanese do a far better job of planning for earthquake proof designs, e.g. flexible large bore water piping, sewage, gas lines, electricity a little less so, and enormously careful building design for earthquake survival, and minimal damage. IIRC, there is some rule on glass in big buildings to the effect of glass must be retained in the window, even in 7+ quakes. There is also a cultural view on responsibility toward others, and one's own responsibility for one's own fortunes. (Insurance against things like fire and earthquakes is much less common, only around a third of the homes have it.) Statista has the Japan grid as being about a percentage point better than the US, 99.7% vs 98.6, but as we all know that is a national statistic. Quality of electricity supply - country ranking 2019 | Statista

Generally, I think humans have short memories, and getting people to make sacrifices after recent earthquakes is comparatively easy. Getting them to do so 4-500 years after the last big one (e.g. Seattle at Richter 9-ish, or Boston at Richter 7+) is much harder. Nobody remembers the damage. Certainly, I don't see much earthquake proofing going on in, say Missouri. (New Madrid anyone?)

@wwu123 the reason that power can't be generally moved from California to Texas is that it is against the law in Texas. Texas forbids interstate electricity transfer to avoid federal regulation of the Texas grid and electricity policies, which may have something to do with why there are so many news stories on Texas energy dysfunction...

All the best,

BG

 

[wwu123]

I think that your inlaws have been quite lucky. I can attest to a number of power outages in Tokyo, caused by earthquakes and typhoons. The Tohoku earthquake that disabled the Fukushima power plant caused the authorities to shutdown all (54?) Japanese nuclear plants. That lead to widespread shortages of power and outages, due in part to the limited ability to transfer power from the 50Hz grid to the 60Hz grid, which is how I learned about the interconnect problems. I will say that I think that, in general, the Japanese do a far better job of planning for earthquake proof designs, e.g. flexible large bore water piping, sewage, gas lines, electricity a little less so, and enormously careful building design for earthquake survival, and minimal damage. IIRC, there is some rule on glass in big buildings to the effect of glass must be retained in the window, even in 7+ quakes. There is also a cultural view on responsibility toward others, and one's own responsibility for one's own fortunes. (Insurance against things like fire and earthquakes is much less common, only around a third of the homes have it.) Statista has the Japan grid as being about a percentage point better than the US, 99.7% vs 98.6, but as we all know that is a national statistic. Quality of electricity supply - country ranking 2019 | Statista

Generally, I think humans have short memories, and getting people to make sacrifices after recent earthquakes is comparatively easy. Getting them to do so 4-500 years after the last big one (e.g. Seattle at Richter 9-ish, or Boston at Richter 7+) is much harder. Nobody remembers the damage. Certainly, I don't see much earthquake proofing going on in, say Missouri. (New Madrid anyone?)

@wwu123 the reason that power can't be generally moved from California to Texas is that it is against the law in Texas. Texas forbids interstate electricity transfer to avoid federal regulation of the Texas grid and electricity policies, which may have something to do with why there are so many news stories on Texas energy dysfunction...

All the best,

BG

You may well be right they were lucky, the in-laws have not visited within the past dozen years since Fukushima and other global/national fuel and energy crises have hit Japan. Certainly there have been power outages within parts of Tokyo, prob not all of Tokyo, both before and after these major events. The relatives may have also discounted outages they'd experienced after a strong earthquake or typhoon, knowing the cause, whereas here they may have been shocked the power just dies on a beautiful calm summer evening for no apparent reason.... also does "quality" of electricity supply have more to do with stability of voltage and frequency, than number of outages? 98.6% quality doesn't seem to mean much if we're all here so interested in buying Powerwalls and generators....

I am aware that we regional grids in the U.S. That some parts of one country politically WON'T agree to connect power to each other even in the face of death and blackouts seems a bit more ironic to other nations, than that they electrically CAN'T, doesn't it?

 

[BGbreeder]

You may well be right they were lucky, the in-laws have not visited within the past dozen years since Fukushima and other global/national fuel and energy crises have hit Japan. Certainly there have been power outages within parts of Tokyo, prob not all of Tokyo, both before and after these major events. The relatives may have also discounted outages they'd experienced after a strong earthquake or typhoon, knowing the cause, whereas here they may have been shocked the power just dies on a beautiful calm summer evening for no apparent reason.... also does "quality" of electricity supply have more to do with stability of voltage and frequency, than number of outages? 98.6% quality doesn't seem to mean much if we're all here so interested in buying Powerwalls and generators....

I am aware that we regional grids in the U.S. That some parts of one country politically WON'T agree to connect power to each other even in the face of death and blackouts seems a bit more ironic to other nations, than that they electrically CAN'T, doesn't it?

Yes, power dying on a clear, still, cool day seems more than avoidable.

I'm totally with you about the illogic (nearly wrote insanity there) of not being willing to connect to other grids in the face of death and widespread damage, but I have some sympathy for a principled stance, even if it isn't my principle. However, I hate to see things mismanaged, and there is no way to describe ERCOT as well managed. I haven't been able to pin down the cause of the Japanese grid issue for sure, but I think it is an artifact of trying to please both the Europeans and Americans, by buying equipment from both...

Frequency on a grid is incredibly stable, as any drift causes massive flows of energy, so quality is mostly about power being present and within specification. Tornados, typhoons, earthquakes, fires, heat, poor maintenance, old wires / equipment, bad drivers all contribute to degrading the grid quality. There is also the rarely mentioned importance of grid interconnects for stability that can shift power to where it is needed, when it is needed. There are some big high voltage interconnects going in in Northern Europe that will enable renewable energy to readily flow over long distances across many countries. Those will have, I think, a significant impact in grid stability, but also pricing, and more predictable pricing enables more logical energy investments. Closer to home, the Pacific Intertie (interconnect) helps move Pacific Northwest power to Southern California during summer heat, and vice versa to provide power for winter heat to the northwest.

Pacific DC Intertie - Wikipedia

en.wikipedia.org

Fun side note: using DC not only move more power for the same size wire, but in the case of the Pacific Intertie above, you use half as many wires by grounding the north and south ends in the Pacific ocean, and using seawater for the return path.

Side note on frequency: If your local generator has a higher voltage, it supplies energy to the grid, and if it has a lower voltage it draws energy from the grid. That's true for AC or DC. However, the subtlety on AC power is that if the frequency is not synchronized between two grids, A &B, you have massive power flows as grid A has a momentarily higher voltage relative to B due to the phase mismatch, and vice versa. It is a great way to overheat and destroy anything between A and B. Having DC interconnects make it easy to connect 50Hz to 60Hz, or even separate 60Hz grids to each other.

All the best,

BG

 

[charlesj]

That's OK, the U.S. can't move electricity between California and Texas, ...

Isn't Texas a closed system, hence their great difficulty during that ice storm not that long ago?

 

[holeydonut]

Isn't Texas a closed system, hence their great difficulty during that ice storm not that long ago?

Yeah, this chart shows the major grids across the USA (ignoring Alaska/Hawaii). If you look very closely at Auburn, CA. You'll see @h2ofun's house which is it's own power grid.

 

[charlesj]

Yeah, this chart shows the major grids across the USA (ignoring Alaska/Hawaii). If you look very closely at Auburn, CA. You'll see @h2ofun's house which is it's own power grid.

View attachment 933862

I tried to zoom in, but it got too pixelated, so I trust your private grid depiction a pixel wide, or less.

 

[jrmnet]

Personally, I would not pair the IQ8M with that large of a panel. The microinverter is only able to output 325w of power continuously and the panel has a PTC of about 370w. I have used this exact panel on my neighbors roof and used an IQ8A instead for this exact reason. This will output 349w and so is a better match for this size module. Its probably not a significant issue though, just a bit more losses, depending on your azimuth. If you have a non-ideal orientation you may never notice the lack.

I agree with what others said regarding V2X, don't count on it as it is too bleeding edge to really be deployed practically.

Most installations here need module-level rapid shutdown, so this requires mid-circuit interrupters (MCI) placed between the panels anyway if you have a string inverter. With microinverters, you do not need any box on your wall outside, and you do not need any special rapid shutdown hardware to accomplish module-level rapid shut down.

In reference to the recommendation to NOT use an IQ8M another vendor has suggested an IQ8+.

IQM has these specs:

• Peak output power: 330 VA
• Input power: 260 - 460 W
• Maximum continuous output power: 325 VA

IQ8+ has these specs:

• Peak output power: 300 VA
• Input power: 235 - 440 W
• Maximum continuous output power: 290 VA

I was concerned that the Maximum continuous power is lower on the IQ8+, but they say that shouldn't be an issue for where I am located. They say that the benefit of the lower input power is helpful on the IQ8+ when the sun is lower in the sky.

Any thoughts on that recommendation?

 

[jrmnet]

Personally, I would not pair the IQ8M with that large of a panel. The microinverter is only able to output 325w of power continuously and the panel has a PTC of about 370w. I have used this exact panel on my neighbors roof and used an IQ8A instead for this exact reason. This will output 349w and so is a better match for this size module. Its probably not a significant issue though, just a bit more losses, depending on your azimuth. If you have a non-ideal orientation you may never notice the lack.

I agree with what others said regarding V2X, don't count on it as it is too bleeding edge to really be deployed practically.

Most installations here need module-level rapid shutdown, so this requires mid-circuit interrupters (MCI) placed between the panels anyway if you have a string inverter. With microinverters, you do not need any box on your wall outside, and you do not need any special rapid shutdown hardware to accomplish module-level rapid shut down.

Vines,

Below are the specs of the 2 I was recommended, plus the one you mentioned. I called Enphase and they think the 8A is overkill for my panels, not wrong, just overkill. They say in the Bay Area and the panel specs of what was proposed to me, most installers use the 8M or the 8+. Enphase says that if they had to pick one they would recommend the 8M. One installer explained to me to pay attention also to the input power. The number on the low end indicates if it will still be getting power when the sun is lower in the sky. The 8A has a low end of 295 which is much higher than the others. Any thoughts on that? Also, the installer that recommended the 8+ says that between the 8M and 8+ the difference in energy I'd get over a year is about 2kW according to whatever solar calculator it is that they use.

IQ8M specs:

• Peak output power: 330 VA
• Input power: 260 - 460 W
• Maximum continuous output power: 325 VA

IQ8+ has these specs:

• Peak output power: 300 VA
• Input power: 235 - 440 W
• Maximum continuous output power: 290 VA

IQ8A specs:

• Peak output power: 366 VA
• Input power: 295 - 500 W
• Maximum continuous output power: 349 VA
• Operating range: 16 – 58 V