Renewable Heat Incentive.

[Bob Minchin]

I think it is regarded as transformerless in as much as it does not have iron core 50Hz transformers but instead the electrical isolation of provided by highly efficient HF ferrite transformers. I've not measured the frequency but like most modern SMPSU designs I would expect it to be at least 100kHz. I think all inverters must have some sort of transformer to provide isolation from the mains

An inverter per panel is approaching the ideal. I did seem one system where the main inverter communicates with a controller on each panel. Effectively it controls each panel to have the same impedance irrespective of the light level which might be different on each panel. In this way the maximum power can be extracted. I found this system after I had installed mine and sadly it is not retrofittable. I would have lost my original MCS certification and would have had to re apply and the tariff would have lower.

As you have a clear view of the sky at all times, then these clever schemes are not likely to benefit you.

Bob

[The Other Mike]

[Chris J Dixon]

No, this is not true. Where there is a wound transformer, there is indeed isolation. The more modern, and slightly more efficient, transformerless inverters do not have isolation.

This has significant implications on the earthing requirements.

Have a look at page 22 (14 of the .pdf), onwards in this document.

"Photovoltaics in Buildings Guide to the installation of PV systems 2nd Edition"

There is a decision chart which I am not going to reproduce, but the key details for average installs are

"...it is the electrical separation of the mains from the d.c. using an isolating transformer that is the key determining factor when assessing the requirement for array frame earthing."

"..freestanding ground mounted, or building roof mounted arrays (away from building metalwork) will normally not be within the equipotential zone."

"Where the incoming supply is PME (the majority of domestic supply arrangements), the PME earth cannot be taken outside the equipotential zone. This is to prevent the potential shock hazard should the supply neutral ever be lost."

"Install & bond to earth spike (Note: do not take PME out of equipotential Zone) (Note: Use 10 mm2 braid or equiv) "

When I was considering options for my installation, the marginally improved efficiency of transformerless inverters was not enough to pay for the additional earthing required.

Kit like this

[harry]

Ah well remain in ignorance half wit.

[BruceB]

There is now a draft 3rd edition around which changes the earthing requirements to what could be summarised as 'hardly ever'. Its issue is imminent, although I note it has been imminent for awhile.

The 2nd edition repeated the fallacy that there is a rule about not exporting an earth outside an equipotential zone. There is not. There may be good reasons not to in some cases, but mostly it can be considered extending the equipotential zone.

As an example, if the whole of a house is an equipotential zone, it is normally barking to say that something on the roof it outside the zone.

[harry]

I wonder how you go on with ground mounted PV panels? ie easily touched. My array frame is not earthed (roof mounted.) It is transformerless, so earthing the DC side is nor an issue. I believe where there is a transformer earthing the DC side is recommended.

[Chris J Dixon]

[attributions got chopped, but I wrote this]

We've been this way before Harry. You have got it round your neck.

Read it once more.

Chris

[geoff]

Not even a fossil fuel power plant at the other end of the plug?

[geoff]

In message , harry writes

You really are terminally stupid

Where does an aeroplane get it's lift from ?

What were you saying about elementary physics ?

Even if he was it would be half more than you

[geoff]

In message , harry writes

Ah - you're talking about a bungalow then

[Dave Liquorice]

From the pressure difference between the top and bottom surfaces of the aerofoils (wings) created by shoving those aerofoils through the air against the friction of that air.

[The Other Mike]

I think someone dangles a harry above the wing and the empty space sucks it upwards

[The Natural Philosopher]

Actually friction - viscosity - is a necessary component of aircraft being able to fly at all.

[geoff]

"Shoving the aerofoils through the air ..."

not making up for "frictional losses"

[Andy Champ]

Induced drag

Andy