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Low power efficiency regulation of battery hybrid inverters (EU and otherwise)

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Siwastaja:
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?

mzzj:
Growatt/Goodwe by any change?

Schneider, Victron and SMA seem to do ok on many models.

jbb:
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 cost

If 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

jbb:
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…

nctnico:

--- Quote from: Siwastaja on November 04, 2024, 06:51:42 pm ---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.

--- End quote ---
It 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).

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