Low power efficiency regulation of battery hybrid inverters (EU and otherwise) - Page 1
Forum section: electronics / general

author: Siwastaja
author_rank: Super Contributor
timestamp: November 04, 2024, 06:51:42 pm
content: Anyone has any idea of current and future EU (other areas are of interest, too) regulations of battery inverters or hybrid inverters in partial load conditions?The question stems from the fact that we just added our fifth supported inverter brand to our control box. A very well known Chinese brand which weighs as much as an elephant despite measly 6kW power rating and is labeled over with some "European" branding. And this also happens to be the first battery hybrid inverter which doubles as an electric heater, all the time: at idle, at low power, at high power. Others only do it at high power. I mean, to supply a constant 130W for a house self-use, it discharges the battery at 260W. It can't be just measurement error; the heatsink, which is large, is always nearly too hot to touch, not only questioning component life but also the fact can this much energy waste be legal?Is it possible the EU regulators are so late to party, that they have not yet specified strict limits on zero or partial load efficiency for battery hybrid inverters? Compare to phone chargers. This inverter consumes as much as 300 phone chargers in standby, and these inverters are marketed with the idea that every home should have one.As usual manufacturer claims efficiency somewhere in 96-97% range but at average annual house load power I would bet it will be closer to 60-70%.Can this be legal?

author: mzzj
author_rank: Super Contributor
timestamp: November 07, 2024, 07:54:11 pm
content: Growatt/Goodwe by any change?Schneider, Victron and SMA seem to do ok on many models.

author: jbb
author_rank: Super Contributor
timestamp: November 07, 2024, 09:10:09 pm
content: Sad to say, but light load efficiency can be a bit of an afterthought for this sort of equipment.130 W drop is 2% of total power rating, which looks OK from a purely thermal design perspective. It’d be good if that was the loss at full load (ie efficiency of 98%). But it’s kinda shocking for light load operation.Stand by for rampant speculation…I suspect that they chose:- larger silicon area devices to reduce conduction losses at high load. This generally increases switching losses which are especially relevant at light load- ‘cost optimised’ inductors, i.e. lots of ripple current and not the best core material. This leads to higher core losses, which are again especially relevant at light load. To be fair, choosing the ‘best’ core materials can drive up the cost quite a bit so it’s reasonable to keep an eye on your wallet at this stage of the design- highest switching frequency they could get away with, in the name of reducing the inductor size and costIf designing an inverter from scratch, what can be done to improve the situation?- model inverter efficiency across a range of loads. This should include switching devices and filter inductors / capacitors- select power devices to balance switching loss, conduction loss and thermal resistance- design inductors with moderate ripple currents- consider wide band gap power semiconductors like Silicon Carbide (SiC) or Gallium Nitride (GaN)- consider multi-level topologies- reduce power consumption of the ‘auxiliary’ loads such as the control platform and cooling fans

author: jbb
author_rank: Super Contributor
timestamp: November 07, 2024, 09:11:48 pm
content: Forgot to say: this topic makes me wonder about the solar power stations which are a 48 V lithium-something battery and inverter in a box. They advertise a kWh rating, but I suspect that’s the raw rating of the battery pack and doesn’t consider inverter losses…

author: nctnico
author_rank: Super Contributor
timestamp: November 07, 2024, 09:26:48 pm
content: Quote from: Siwastaja on November 04, 2024, 06:51:42 pmIt would be good to actually name the brand & model, whether the problem was noticed on one unit or several units and whether there are configuration options which could affect behaviour. Also, what does the supplier / dealer say about it? A quick Google shows me that it looks like there are settings on some units to make the DC to AC part of inverter go into low power standby mode in case there is no load detected. It looks like the DC to AC part of the inverter is always on which causes the excessive power draw (which seems rather odd to me as well).

author: NiHaoMike
author_rank: Super Contributor
timestamp: November 08, 2024, 03:46:21 am
content: Sounds like they're always running the output stage and/or boost stage in CCM. Easier to design than transitioning to DCM but really drops the efficiency at light loads. A lot of synchronous DC/DC modules have the same problem, even from trusty name brands like TI.

author: jbb
author_rank: Super Contributor
timestamp: November 08, 2024, 06:20:29 am
content: Hmm. I hadn’t thought about operating an DC-AC inverter in DCM for ages. I agree that CCM operation will incur more losses.

author: Siwastaja
author_rank: Super Contributor
timestamp: November 10, 2024, 08:39:09 am
content: Quote from: nctnico on November 07, 2024, 09:26:48 pmYeah. It's Deye which I was initially uncertain to disclose because I have no basis to say they would be the only ones who do this poorly. Others we have tested seem to do better but notthat muchbetter, around 40W low-load consumption seems to be industry norm. Which is why I wanted to open this as more generic discussion because starting from 2025 EU is going to regulate stuff like energy meters and routers (usually 1/home) to nearly ridiculously low consumption requirements which are actually difficult to achieve while other products that are touted to go to every home as part of "green transition" then do 300 times worse.The technical support of the label company confirmed that 100W idle consumption would be completely normal so that pretty much rules out unit-to-unit problem.Configuration options I don't know, I have tried going through the menus and tried various tricks over modbus but could not find a lower power idle state and the support did not know about such either, just saying 100W is normal.QuoteThe problem is, there almost never is "no load" condition.There are actually two important aspects, availability of sleep mode you mention but also low quiescent consumption at near-zero power in active state. Latter is also very important, probably more important than the sleep state, because these battery inverters supply house loads often nearly 24/7 and those loads are occasionally like 100-300W. Well, from optimization viewpoint maybe we could enter a sleep state (if that was available) and buy that 100-300W from grid instead, but then what if consumption is 500W and electricity expensive, then we surely want to supply from battery and it makes a huge difference if the efficiency is 70% vs. 90% at that power level, so low-load loss matters.Sure, at 1/100 of rated power just enter sleep mode, but one of the primary purposes is to store solar and self-consume during the evening, night and morning hours, so during 10-20 hours or at C/10 - C/20.If I was dictator of EU I would write the requirements for certain peak efficiency at rated power but then also efficiency at say 1/20 of rated power and finally self-consumption at zero battery power, so that the inverter is allowed to enter some kind of sleep mode. Like, 97%, 90% and 5W respectively should be possible to engineer. But lacking regulation, manufacturers have no motivation to think about energy efficiency.100W continuous extra draw is is 900kWh a year or say 13MWh over the lifetime of the inverter. This extra electricity costs more than the inverter itself!

author: Siwastaja
author_rank: Super Contributor
timestamp: November 10, 2024, 09:12:17 am
content: Quote from: mzzj on November 07, 2024, 07:54:11 pmIs there something I need to know? We have Growatt support but remotely developed code so never been next to one physically to "feel the heat".

author: mzzj
author_rank: Super Contributor
timestamp: November 10, 2024, 09:48:15 am
content: Quote from: Siwastaja on November 10, 2024, 09:12:17 amIIRC some Growatt models are notoriously famous for high idle draw. Close to 2% of rated power. Deye probably does a bit better and best ones on the market seem to be about 0.5% of rated power.And some hybrid inverters put rather high idle load on both battery AND grid.

author: nctnico
author_rank: Super Contributor
timestamp: November 10, 2024, 10:57:00 pm
content: Quote from: Siwastaja on November 10, 2024, 08:39:09 amI agree this is crazy and it is good you brought it up. IIRC a refridgerator consumes around 300kWh per year and does something useful. Dave should do a video on this for sure.