Replacing a 4kW transformer based inverter for a PV system

Firstly, do you need the galvanic isolation?

In most cases the main implication of the change would be that the RCD provisions upstream would need to be reviewed but that might be far easier than finding a new inverter with transformer that also has an MPPT range compatible with the stringing arrangement.

It's also possible that the manufacturer holds replacement stock, though I'd not bank on it. More likely they could recommend a suitable replacement.

It's worth noting that omitting the transformer makes the inverter lighter and more efficient.... hence the general move towards them now that it's workable.

Hi Jam. An inverter with galvanic isolation was installed to prevent the possibility of a voltage appearing on the frame of the ground mounted array if the PME Neutral should be lost and if a fault DC to earth manifested itself on the array (seems unlikely but as I recall that was the COP at the time)

I am guessing that installers replace inverters with transformer-less inverters now, since they seem to be the only inverters available?

Hi LittlePlumb,

Have just revised the DTI Guide 2nd Ed which was the guidance at the time; the logic is ultimately the same as now save that galvanic isolation was preferred to keep things simple.They were heavy though!

Transformerless inverters are far easier to get hold of.nowadays, but since some module types do require galvanic isolation there are some products out there, though choices will be limited. If your manufacturer still exists I'd start by talking to them.

There is also a market for second hand inverters; Navitron is one as well as Fleabay.

Depending on your installation, making the necessary changes to accomodate TL inverters may not be insurmountable and I would recommend starting there... The best practice guidance re frame bonding has changed for galvanically isolated transformers too anyway.

Technically you could consider a separate isolation transformer but I suspect that'd be a pricy option and would affect efficiency.

Jam

PS - Do note that if you are replacing the inverter with a more modern unit it's likely you'll have to notify the DNO per G83/G98 as the grid parameters will have changed, plus it's a different SSEG

Thanks Jam. I will order the latest COP and take a look at the recommendations re transformerless inverters and array bonding. The array is ground mounted on a wooden frame, and the system earth is I believe PME, the installed RCD is I believe DP type AC, so there are a few things to consider before replacing the inverter. Not sure about bonding the array to a PME earth though, given that the PV modules are all Class II and the DC cabling is double insulated the array is probably not an extraneous conductive part, I'll need to measure it with respect to the MET.

Hi Jam. I have taken a look at the latest COP, which as you say requires that one installs Array Frame earthing. Not sure I like the sound of connecting the functional earth of the array to the MET on the TNC-S PME supply tho...Also RCD's are no longer necessarily required, and the PV array Earth insulation fault thresholds are only a min of 30 k ohms to earth. Seems like the original spec has been flipped on it's head. Functional earthing of an anodized Aluminium array is going to be fun if galvanic corrosion is to be avoided.