The Imaginary PROBLEM with Enphase Solar Panel Micro Inverters

[EEVblog]

Enphase solar panel microinverters are great, but they have a BIG imaginary power problem!
How much power does your solar inveretr take in standby at night time?

IQ7+ datasheet:
https://enphase.com/sites/default/files/2021-04/IQ7-IQ7plus-DS-EN-US.pdf

Forum about upgrading the home solar power system AGAIN: https://www.eevblog.com/forum/renewable-energy/solar-upgrade-again/

[Psi]

It would be interesting, though probably not practical, to take one of them apart and see where the power is actually going.
I do wonder if maybe the high standby power is intentional to prevent too much thermal stress when continuously cycling between hot days and freezing nights.
I doubt there's a heating element inside, but they could be intentionally running the system in a way to produce heat at night.

But you'd think, if that was the case, they would add some 'smarts' to only enable the heating when night temps drop below some threshold. Night temps in Australia shouldn't be low enough to need it.
Then again, any reduction to the thermal cycling extremes should extend the lifespan.

It may just be a cost thing, they needed the heating effect for countries that drop to like -10C at night but adding extra electronics for a controllable heating system added too much BOM cost, so they didn't bother.

[Jeroen3]

I did notice this as well on the small din rail meter I have for it. About 610 mA for 8 inverters (including envoy), 0.03 pf, 5.4W, 138 var.

You're probably just looking at the output filter, inverter bridge capacitance and plc filter capacitance (it's ~100Khz).

Maybe enphase has a grid profile that switches the q-relay when the sun is down?

I believe traditional inverters have a contactor that disconnect the output when not producing, at much complaints from people having the thing in their attic clunking away in the morning waking them up.

I don't believe grid code currently has regulations for this issue.

_{(an enphase battery system will have the same problem I think because they use the same inverters inside)}

[SeanB]

Going to say most of that imaginary power is there because of the inverter output filtering, which is most likely composed of 2 LC sections per inverter, to filter out most of the PWM waveform from the inverter output. Same for the regular inverter, but there you will have a much larger LC filter section as well, simply because of the higher current output.

If you have a battery system then you will likely have a separate solar power input used to charge the batteries, so no apparent power at all, as all at DC.

The 1A total over 14 panels is low, roughly 70mA per panel, which means there is likely 2 0.47uF class X2 filter capacitors in each output stage acting as filter, with probably another 0.1uF class X2 capacitor after the cascaded LC sections as a final filter, then 2 22n class Y capacitors to the solar panel voltage rail, acting as RF noise returns.

[ejeffrey]

It would be interesting, though probably not practical, to take one of them apart and see where the power is actually going.
I do wonder if maybe the high standby power is intentional to prevent too much thermal stress when continuously cycling between hot days and freezing nights.
I doubt there's a heating element inside, but they could be intentionally running the system in a way to produce heat at night.

It's mostly reactive / apparent power so it isn't dissipated in the inverter as heat or anything else.

[bdunham7]

If you have a battery system then you will likely have a separate solar power input used to charge the batteries, so no apparent power at all, as all at DC.

Enphase has an 'AC Battery' system.  These systems, along with a lot of the newer Enphase systems with advanced features or sold in non-US markets, do have shutdown relays.  My older system has none of that.  I don't know exactly how and when these systems shut off or isolate the inverters in a standby-capable battery system. 

[EEVblog]

Got a response from Enphase:

The Microinverters are powered from the DC side, so if there is not enough power to start them up then there will not be any real power usage.

Any real and reactive power at night-time is likely from the envoy, which is require for measuring night-time consumption, this is around 25 VA and is stated on the datasheet. If any PV system has a consumption meter attached, which most do now then you will always have a power consumption from that meter to read consumption, solar analytics will be the same.
Powerline communication from the Q-relays and Envoy is present during the evening. Q-relays are required for mechanical protection and grid compliance as per AS/NZS 4777.2:2020.

The Q-relays are powered for the LED light and relay sensor again this is minimal power up to 18 VA per relay. The Q-relays must be powered for compliance reasons in Australia, they are not required in all regions.

All the power consumption numbers are available on the datasheet, so I would strongly disagree with your comment that we are “hiding it” as reactive power is not charged. Enphase uses reactive power to communicate via Powerline communications, when the system is not operating the PF will be close to zero as we want 100% reactive power (not paid for) compared to real power. The Power produced by the microinverters in the day (real power) will be of a PF close to 1 or affected by Volt-Var power factor correction as per AS/NZS 4777.2:2020.

The battery will also operate in real power and not reactive power, in most instances the PF will be 1 therefore it will only produce real power. The only instance it would have to come from the battery is if the system was totally off-grid and was unable to draw reactive power from another source.

I checked the Envoy datasheet and it has no VA figure, and only says 5W. And they are wrong that the datasheet shows the power consumption, it does not, as I showed in the video and anyone can see.
They seem to be saying that the microinvreters are deliberately designed to operate near zero power factor so that you do not pay for the standby power. Yet they also seem to imply they take zero standby VA? I'm confused.

[ejeffrey]

In fact, in Dave's specific example, the "negative" (capacitive) reactive power from the microinverters is less than the positive (inductive) reactive power from the refrigerator/freezer.  So the micro-inverters in standby mode are actually doing power factor correction for the refrigerator and should *reduce* the total nighttime AC current draw from the grid or a future battery inverter.  Enphase could market this as a feature

Do you have a current sense on your main AC feed?  Can you compare that with the inverters disconnected?

[bdunham7]

That response from Enphase was not all that coherent technically and appears to be wrong about more than one thing--such as 'using' reactive power.    When I called them a decade ago I got someone who told me directly what the issue was and not to worry about it--which I still think is the mostly correct answer.   They do get the part right about the grid supplying the reactive power if it is present.  I also agree that it is a bit too much to claim that they are 'hiding' the standby VA simply because they don't mention it.  Believing it to be largely irrelevant is valid reason not to put it in the specs.

Edit:  In your video you refer to 'watts' and 'consumption' in relation to apparent and reactive power.  I think that's misleading--although there will be some consumption due to dissipation, you really need to put numbers to this.  My nighttime current was 3.3A for 30 panels IIRC and I think my actual power dissipated in the wiring as a result of that was something less than 2 watts total.

[EEVblog]

A follow-up response from Enphase. They have now confirmed 16.4VA per micro inverter @ 230V,  or 17.9VA at 240 as my system is. So spot on to the 18VA I measured.

I am stating the microinverters do not produce real power in W, as they are powered on the DC side. Reactive power is used for the powerline communication protocol, as you are not charged for reactive power, there is at no disadvantage for an on-grid battery with backup. The AC filter board will stay connected, but this is much like leaving your laptop or phone, or any load plugged in when it is fully charged. The amount of reactive power per PCU is estimated around 16.4 VA per microinverter. The reason for this is there are 3 x 330 nF capacitors = 900 nF total at 50 Hz this would be an Xc of 3215 ohms. So 230 V / 3215 = 71.5 mA (Reactive power) x 230 V (AC) = 16.4 VAR per microinverter.

There will be reactive power present in the Enphase system as it is always physically connected in a closed circuit, but this is not real power or a consideration to most people even with a battery, as any load plugged-in but not using real power (e.g. turned on) will have a reactive power present, unless you physically turned off the socket or removed it from the GPO. A Battery is usually set to self-consumption will not power the microinverters with reactive power. 

An off-grid system will be oversized significantly to be sufficient, so that the reactive power consumed at night would be negligible, it would also not use any energy (Wh) or charge from the battery. Remember reactive power is not energy transfer, so the reactive power will complete the circuit then end backup in the battery which will result in no loss of charge as no energy has been transferred. The battery in this case will keep discharging and charging each cycle with a net zero power for each cycle.

[EEVblog]

That response from Enphase was not all that coherent technically and appears to be wrong about more than one thing--such as 'using' reactive power.    When I called them a decade ago I got someone who told me directly what the issue was and not to worry about it--which I still think is the mostly correct answer.   They do get the part right about the grid supplying the reactive power if it is present.  I also agree that it is a bit too much to claim that they are 'hiding' the standby VA simply because they don't mention it.  Believing it to be largely irrelevant is valid reason not to put it in the specs.

Yes they are correct that most customers will not need to know this. But there are others will either will be charged for VA, or have some off-grid battery system where it could matter, or they care for some other reason like simply not being a bad grid "customer" with Amps of reactive current at night.

I think it should be in the datasheet.

[bdunham7]

I think it should be in the datasheet.

Well that is hard to disagree with.   

[EEVblog]

Edit:  In your video you refer to 'watts' and 'consumption' in relation to apparent and reactive power.  I think that's misleading--although there will be some consumption due to dissipation, you really need to put numbers to this.  My nighttime current was 3.3A for 30 panels IIRC and I think my actual power dissipated in the wiring as a result of that was something less than 2 watts total.

Yes, I'm redoing the video from scratch to better explain this.

[T3sl4co1l]

Just put a nice beefy 1.25H in parallel with it, she'll be right.

Tim

[bdunham7]

Yes, I'm redoing the video from scratch to better explain this.

Just before 38:00 in your new video you refer to "DC isolators", I think you mean the AC IQ switches?