Domestic EESS, island mode and island mode isolator

Do you plan on having EPS output power supply a dedicated consumer unit, independently connecting your essential circuits, separate from the main household consumer unit ?

The inverter’s EPS output, active during both normal operation and island mode, inverter creates a neutral-earth bond in power cuts. The EPS connects to a 100 mA time-delayed RCD, feeding a dedicated consumer unit with RCBOs for essential circuits, independent of the main household consumer unit. The other option is using a Gateway for complete installation backup.

Yes this is correct :)

Thank you and this confirms my understanding - if the EPS output is only supplying dedicated CU/circuits then we can rely on the inverter to disconnect and isolate from the grid in island mode.

Downdraft said:

then we can rely on the inverter to disconnect and isolate from the grid in island mode.

I would caution, that I have been made aware that some inverters do not disconnect from the grid using devices that BS 7671 would recognize as providing 'isolation'. See Regulation 826.1.1.1, last para, which states 'A switching device suitable for isolation according to Chapter 53 shall disconnect all live conductors from the public distribution network.'

It's also worth remembering the provision in Regulation 21 of ESQCR [Regulation 22 of ESQCR(NI)] which conains the requirement that 

21.  Where a person operates a source of energy as a switched alternative to a distributor’s network, he shall ensure that that source of energy cannot operate in parallel with that network and where the source of energy is part of a low voltage consumer’s installation, that installation shall comply with British Standard Requirements. 

(British Standard Requirements means BS 7671 in the ESQCR.)

Hi Graham. Is this the best way to ensure compliance to check the inverter model on the ENA Type Test Register (via the Energy Networks Association website) for G98/G99 certification. Also perhaps, contact the manufacturer, ask Does their  inverter provide Chapter 53-compliant isolation per 7671 Reg 826.1.1.1 & ESQCR Regulation 21.  Do you have any additional advice or steps we should consider?

I agree that it is very likely that relays are being used inside of the hybrid inverters that do not comply with chapter 53. I will ask the manufacturer and I will share the information.

What may be tripping me up is that without battery storage my understanding is that these internal relays meet the requirements of G98/99 for anti islanding. So if we are using the EPS for dedicated circuits only why can we not rely on this relay?

AMK said:

 Is this the best way to ensure compliance to check the inverter model on the ENA Type Test Register (via the Energy Networks Association website) for G98/G99 certification.

G98 certification doesn't cover island mode operation.

G99 might have been gained on "connected mode" operation only? Even if it does cover both, it might not necessarily cover the requirements of BS 7671 in this regard.

AMK said:

perhaps, contact the manufacturer, ask Does their  inverter provide Chapter 53-compliant isolation per 7671 Reg 826.1.1.1 & ESQCR Regulation 21.  

That might be the way to go. But ... I would add that there are ways you can, for example, build Product A into Product B, and "defeat" some of the provisions of the safety standard for Product A. If the safety standard for Product B doesn't have a way of verifying the provisions of Product A have not been defeated, that could be an issue.

Downdraft said:

What may be tripping me up is that without battery storage my understanding is that these internal relays meet the requirements of G98/99 for anti islanding. So if we are using the EPS for dedicated circuits only why can we not rely on this relay?

Anti-islanding is the ability of the inverter to stop squirting power into the grid, when it stops converting.

If it starts converting again, for island mode, is there any way power can "leak" (AC or DC) from one side of the converter to the other when you re-earth the "IPS" side ? This depends on a number of factors, and the particular topology ... but in some cases, there may well be a problem.

There are also some considerations for multipole vs single-pole switching devices that might need to be considered.

AMK said:

 Is this the best way to ensure compliance to check the inverter model on the ENA Type Test Register (via the Energy Networks Association website) for G98/G99 certification.

G98 certification doesn't cover island mode operation.

G99 might have been gained on "connected mode" operation only? Even if it does cover both, it might not necessarily cover the requirements of BS 7671 in this regard.

AMK said:

perhaps, contact the manufacturer, ask Does their  inverter provide Chapter 53-compliant isolation per 7671 Reg 826.1.1.1 & ESQCR Regulation 21.  

That might be the way to go. But ... I would add that there are ways you can, for example, build Product A into Product B, and "defeat" some of the provisions of the safety standard for Product A. If the safety standard for Product B doesn't have a way of verifying the provisions of Product A have not been defeated, that could be an issue.

Downdraft said:

What may be tripping me up is that without battery storage my understanding is that these internal relays meet the requirements of G98/99 for anti islanding. So if we are using the EPS for dedicated circuits only why can we not rely on this relay?

Anti-islanding is the ability of the inverter to stop squirting power into the grid, when it stops converting.

If it starts converting again, for island mode, is there any way power can "leak" (AC or DC) from one side of the converter to the other when you re-earth the "IPS" side ? This depends on a number of factors, and the particular topology ... but in some cases, there may well be a problem.

There are also some considerations for multipole vs single-pole switching devices that might need to be considered.