The Imaginary PROBLEM with Enphase Solar Panel Micro Inverters - Page 1
Forum section: electronics / general

author: EEVblog
author_rank: Unknown
timestamp: July 18, 2022, 06:53:41 am
content: 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.pdfForum about upgrading the home solar power system AGAIN:https://www.eevblog.com/forum/renewable-energy/solar-upgrade-again/

author: Psi
author_rank: Super Contributor
timestamp: July 18, 2022, 07:55:26 am
content: 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.

author: Jeroen3
author_rank: Super Contributor
timestamp: July 18, 2022, 08:20:58 am
content: 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)

author: SeanB
author_rank: Super Contributor
timestamp: July 18, 2022, 08:34:54 am
content: 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.

author: ejeffrey
author_rank: Super Contributor
timestamp: July 18, 2022, 05:09:16 pm
content: Quote from: Psi on July 18, 2022, 07:55:26 amIt's mostly reactive / apparent power so it isn't dissipated in the inverter as heat or anything else.

author: bdunham7
author_rank: Super Contributor
timestamp: July 18, 2022, 05:22:00 pm
content: Quote from: SeanB on July 18, 2022, 08:34:54 amEnphase 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.

author: EEVblog
author_rank: Unknown
timestamp: July 19, 2022, 03:08:23 am
content: Got a response from Enphase:QuoteI 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.

author: ejeffrey
author_rank: Super Contributor
timestamp: July 19, 2022, 03:34:32 am
content: 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 featureDo you have a current sense on your main AC feed? Can you compare that with the inverters disconnected?

author: bdunham7
author_rank: Super Contributor
timestamp: July 19, 2022, 03:37:43 am
content: 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.

author: EEVblog
author_rank: Unknown
timestamp: July 19, 2022, 08:39:59 am
content: 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.Quote

author: EEVblog
author_rank: Unknown
timestamp: July 19, 2022, 08:45:06 am
content: Quote from: bdunham7 on July 19, 2022, 03:37:43 amYes 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.

author: bdunham7
author_rank: Super Contributor
timestamp: July 19, 2022, 04:08:23 pm
content: Quote from: EEVblog on July 19, 2022, 08:45:06 amWell that is hard to disagree with.

author: EEVblog
author_rank: Unknown
timestamp: July 19, 2022, 11:38:34 pm
content: Quote from: bdunham7 on July 19, 2022, 03:37:43 amYes, I'm redoing the video from scratch to better explain this.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: July 20, 2022, 04:50:10 am
content: Just put a nice beefy 1.25H in parallel with it, she'll be right.Tim

author: bdunham7
author_rank: Super Contributor
timestamp: July 22, 2022, 04:03:42 am
content: Quote from: EEVblog on July 19, 2022, 11:38:34 pmJust before 38:00 in your new video you refer to "DC isolators", I think you mean the AC IQ switches?