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Solar PV DC earthing.

Jake Morgan

Hi all, I'm in the process of designing a solar install where the DC strings are going to have to be buried in the fabric of the building. I am planning to use PV ultra SWA cable or earthed steel conduit and make sure there are plans to record where it is, as per IET COP for Solar PV 5.10.3. 

It has got me thinking about what actually happens in a scenario where someone drills through it. With 230V AC systems the earthed containment would contact the Line and cause a short circuit that would hopefully trip an MCB/RCD. DC strings do not have a reference to earth nor is there any device to trip so what happens? Or is one of the poles earthed in the inverter?

Can anyone point me towards further reading on this?

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    Hi Jake. 

    I agree with your assessment regarding the requirements for embedded cables in accordance with the COP. However, it is still advisable to avoid embedding DC cables whenever possible and to also minimise their length if possible. The guidance also says functional earthing of one of the current-carrying conductors is generally not recommended but may be necessary to comply with the module manufacturer’s requirements to mitigate the effects of Potential Induced Degradation (PID). MCS-approved inverters are typically equipped with integrated Arc Fault Circuit Interrupters (AFCI) for DC arc-fault protection and short circuit protection. These inverters continuously monitor floating systems for earth insulation resistance using insulation monitoring devices suitable for IT systems. Additionally, they provide surge protection, grid monitoring, anti-islanding protection, and temperature protection, thereby safeguarding the DC side of the system.

    I have just completed a Solar /PV & EESS course this week and It is also worth noting that some insurance companies now mandate the inclusion of fire shutdown systems. This often necessitates the use of module-level power electronics, such as microinverters, which have the capability to shut down independently in the event of a fire.

    - Andrew

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  • 0

    Hi Jake. 

    I agree with your assessment regarding the requirements for embedded cables in accordance with the COP. However, it is still advisable to avoid embedding DC cables whenever possible and to also minimise their length if possible. The guidance also says functional earthing of one of the current-carrying conductors is generally not recommended but may be necessary to comply with the module manufacturer’s requirements to mitigate the effects of Potential Induced Degradation (PID). MCS-approved inverters are typically equipped with integrated Arc Fault Circuit Interrupters (AFCI) for DC arc-fault protection and short circuit protection. These inverters continuously monitor floating systems for earth insulation resistance using insulation monitoring devices suitable for IT systems. Additionally, they provide surge protection, grid monitoring, anti-islanding protection, and temperature protection, thereby safeguarding the DC side of the system.

    I have just completed a Solar /PV & EESS course this week and It is also worth noting that some insurance companies now mandate the inclusion of fire shutdown systems. This often necessitates the use of module-level power electronics, such as microinverters, which have the capability to shut down independently in the event of a fire.

    - Andrew

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