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Shedding New Light on Solar PV Electrical Testing Feature: Test & Measurement

Jim Wallace, product and technology manager at Seaward Solar answers your questions on solar PV electrical testing

Q. How does Solar PV electrical testing differ from conventional installation and what are the risks involved?

Solar PV systems are unusual in that the energy source cannot be switched off. If there is daylight falling on a PV panel it will produce electricity and it is possible for a relatively small array of only a few panels to deliver a lethal shock.

Another important point is that PV panels generate DC voltage, which is not always commonly used by electricians in their normal work. In addition‚ because of the current limiting properties of PV cells‚ they are incapable of producing sufficient fault currents to operate over-current protection devices such as fuses. Once established a fault may remain undetected, not only posing a hazard for an extended period but also wasting energy generated by the PV system.

Undetected faults may also develop into a fire hazard over time. Without fuse protection against such faults, elimination of a fire risk can only be achieved by both good system design‚ and careful installation with appropriate inspection and testing.

Special measures must therefore be taken during installation of PV systems to eliminate the risks of dangerous working and latest electrical problems.

The consideration of panel operation under both normal and fault conditions is essential in the design stage to ensure the required level of safety. It is then important to ensure that the long term safety of the system is not compromised by a poor installation or subsequent poor maintenance.

Much of this comes down to the quality of the installation and the system inspection and testing regime. Q. Should electrical contractors undergo any specialist training for testing of solar PV systems?

Grid connected PV system installation is quickly becoming a mainstream electrical contracting activity. Alongside MCS accreditation‚ the installation process itself is unlikely to be too difficult for a qualified electrician‚ although there are significant differences from the usual installation wiring technology that they are likely to be working with on a day to day basis.

Q. Are there any additional test requirements above and beyond those outlined in the IEE 17th Edition Wiring Regulations?

In general terms the installation of domestic grid connected PV systems also falls with the scope of Part P of the Building Regulations and it the responsibility of installer to ensure that systems are installed according to the existing BS7671 electrical installation standard – the 17th Edition IEE Wiring Regulations.

However‚ the inspection and testing of DC circuits associated with PV arrays requires special considerations. The IEE Guidance Note 7 Special Locations provides guidance on solar photovoltaic (PV) power systems.

The fundamental requirement for all Installers of PV systems in the UK is to satisfy the MCS requirement as detailed in the DTI‟s guide Photovoltaics in Buildings which is aligned to the IEC 62446 standard. IEC 62446: 2009 „Grid connected PV systems‟, sets out the minimum requirements for PV system documentation, commissioning tests, and inspection.

In short the standard sets out measures to ensure that:  The PV panels and electrical supply connections are wired up correctly  That the electrical insulation is good  The protective earth connection is as it should be

 There has been no damage to cables during installation

Under electrical tests, the standard sets out specific requirements for: Earth continuity of array frame to earth and connection to main earthing terminal Polarity of all DC cables PV string open circuit voltage test PV string short circuit current test PV array insulation test Operational test – PV string current Functional test Irradiance

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