G59 relay panel

[Mac Jobio]

Hi Guys,
Apologies if this is a silly question or has been covered before but i can't find a thread related to this.

If you are installing a G59 certified inverter, is it necessary to also install a G59 relay panel?

or is this only necessary when using say 3 x SMA 3000TL which are G83 certified.


i would assume that G59 cert inverters have inbuilt relays.

or is there another explanation? solar newbie here - so go easy

 

[SibertSolar]

Hi and welcome to the forum. The main purpose of a separate G59/2 relay & suitable enclosure/control-gear is to provide protection of the SSEG and grid should either 3phase supply fall outside required parameters. The G59/2 engineering framework dictates the limits/parameters for under/over voltage, under/over frequency, vector-shift and ROCOF (rate of change of frequency) for >16A/phase parallel connection.

If, for example, the grid supply is switched off, or the SSEG feed falls outside the requisite parameters, then the grid operator does not want micro-generated power to continue to be fed into the grid. The actual relay itself (something like a ComAp Mainspro perhaps) monitors all these pre-set parameters and switches a main contactor that has the SSEG->Grid AC cabling wired through it. As a rule of thumb, most DNOs will accept the G59/2 type-test certification from the inverter manufacturer as sufficient proof of compliance for systems with greater than 16A/phase but <50kW DNC and, therefore, will not insist on an additional external G59/2 relay to be fitted.

Strictly speaking, a G59/2 type-tested inverter doesn't actually have a G59/2 relay fitted inside it - it just had a pre-set and "proven" set of parameters to work to the G59 grid-connection requirements.

 

[Mac Jobio]

Thanks Sibert Solar, that's a very clear answer.

In the case of using 3 x 3kW units with g83 certification I take it that a G59/2 relay panel would be required in order for the installation to comply?

Or in practice would it be more cost effective to just use a larger G59/2 certified inverter?

 

[SibertSolar]

Not necessarily. If you are fitting 3x 3kW single-phase inverters to provide a 3ph parallel grid connection of <16A/phase then you are not venturing into G59/2 territory, right? However, if you are looking to put >16A onto a single phase then you should speak to the DNO first as they may permit this with G83 certification....all depends on the nature of the install, the existing grid demand and the DNO tbh. Once you get that far, you can decide whether or not to go with a 1ph inverter(s) that also have G59/2 certification (they do exist) or some other solution.

Are you talking about a 3ph generation system, or all on a 1ph connection?

 

[Mac Jobio]

I was thinking of a single phase connection and what happens when you do use non G59/2 certified inverters to feed in what would be well over 16A on a single phase.

Your answer's pretty good so thanks again.

It seems the decision to install a G59/2 relay unit is really in the hands of the DNO, whether the inverters are G59/2 certified or not.