Solar PV Electrical Testing Q&As
Jim Wallace of Seaward Solar answers some typical questions being asked about solar PV electrical testing
- How do I test a PV installation to comply with MCS and IEC 62446?
- Why is it important to test PV installations?
- Is there a standard for testing PV systems that I should be following?
- Is periodic inspection and testing of PV installations necessary? If so, why?
- What are the key warning signs that a system may not be performing as it should?
- What equipment is required for testing a solar PV installation?
- What are the key considerations that should be addressed prior to selecting a piece of test equipment?
- Why measure solar irradiance?
- How is solar irradiance measured?
How do I test a PV installation to comply with MCS and IEC 62446?
Please watch the short video below to see how you can test a solar PV installation with the Seaward Solar PV150 test kit
Why is it important to test PV installations?
The infographic below illustrates 10 reasons why you should carry out regular tests on PV installations
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The essential need for all installers of PV systems in the UK is to satisfy MCS requirements (for systems up to 50kW), as detailed in the DTI’s guide Photovoltaics in Buildings. This is fundamentally aligned to the BS EN 62446:2009 standard for grid connected PV systems.
In short, this document sets out the minimum requirements for PV system documentation, commissioning tests, and inspection to ensure the safety and quality of system installation. The standard includes specific measures to ensure that:
- The PV panels and electrical supply connections have been 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
The standard describes various electrical tests to ensure that the solar installation fully complies with MCS requirements.
While many of the more reputable and discerning solar PV installers recognise the importance of testing to the standard, it is of serious concern that some installers are failing to perform the required tests, or at best only partly fulfilling this obligation.
Clearly where testing is not being carried out in accordance with BS EN 62446, the system will be in breach of MCS requirements and should not be eligible for feed in tariffs or be connected to the grid. This has potentially serious implications for the quality and safety of the solar PV installations in question.
For example, it was recently reported that a house fire in Kent was caused by a fault in a rooftop solar PV installation. This mirrors the situation in the USA, France and Australia where property fires and surveys of solar PV installations have raised specific concerns over incorrectly installed PV systems and their role as both a fire hazard and as a cause of increased risk of electrocution.
All involved in the solar PV industry need to take responsibility for the correct and proper installation of solar PV systems and the recent MCS/Gemserv consultation on the competency of solar PV installers seeks to address such concerns. The MCS is due to publish new guidance in the next few weeks which will further clarify the testing requirements for PV installations.
However, the solution lies in ensuring compliance with all relevant standards, including the solar PV testing and documentation requirements of BS EN62446. Only when this happens can the certification body be given the evidence that the work has been performed correctly and the customer given the assurance that absolute best practice has been followed in the installation of their PV system.
Is periodic inspection and testing of PV installations necessary? If so, why?
The verification of system performance and energy output from the panels is particularly important and a major reason why periodic verification and testing of the system can also be very important – as well as being essential to comply with warranty and PV system guarantees.
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.
What are the key warning signs that a system may not be performing as it should?
In many cases simple electrical faults or wiring failures can cause a serious inefficiency in the ability of the panel to produce power. This is particularly important for installers working on ‘roof rental’ schemes were installation has been provided free of charge in return for receipt of the feed-in tariff payments.
Although metering will always give an indication of system performance, effective electrical testing is also vital not only to prove the safe installation of a new system but also to verify ongoing functional performance.
What equipment is required for testing a solar PV installation?
The absolute minimum testing that needs to be undertaken involves continuity measurements, open circuit voltage, short circuit current, insulation and irradiance.
Other tests involving the use of I-V curve tracers, power analysers and thermal imaging cameras are not mandatory but may be regarded as useful to carry out certain diagnostic testing or to assess different performance parameters of the solar PV system.
It is therefore largely up to the installer to decide whether he wishes to purchase individual items of equipment or select one or possibly two instruments which provide a combination of tests to enable measurements to be taken in a fast, safe and efficient fashion.
What are the key considerations that should be addressed prior to selecting a piece of test equipment?
There are many instruments available on the market that are sold under the title of Solar Testing so it is vital to ensure that the instruments selected are capable of performing all of the tests required by the IEC 62446 standard.
The nature of PV testing is such that it can expose the installer to high voltages, so the selection of an instrument which is capable of automatically and safely performing tests greatly improves efficiency and safeguards the installer.
The availability of new multi-purpose solar PV test instrumentation also means that the functions of a number of individual test instruments can be combined in a single tool – with consequent savings in cost and improved practical considerations.
Why measure solar irradiance?
The electrical output will vary significantly with changes in the level of in-plane irradiance.
Solar PV panel manufacturers quote the electrical output at standard test conditions (STC) with an irradiance level of 1000W/m2. Therefore, when commissioning a PV system, it is necessary to measure the level of irradiance at the same time as testing its electrical output, to know whether it is working to its potential under the existing irradiance levels. If the electrical output is different from the manufacturers’ quoted
values, it must be determined whether this is due to a fault in the PV installation, or simply because irradiance was different from STC.
Simultaneous measurement and recording of irradiance, open circuit voltage (Voc) and short circuit current (Isc) is required for the PV Array Test Report for IEC 62446.
How is solar irradiance measured?
Solar irradiance meters that assess PV modules must have a spectral response close to that of a PV module in order to measure ‘true irradiance’ as a PV system would.
There are two irradiance measurement methods defined and accepted by international standards covering the performance measurement of PV systems:
High precision, high cost instruments using thermal sensors in a glass dome.
2. PV Reference Cell
Effectively a small scale version of a PV module, having the same response to solar energy.
Temperature compensation ensures accuracy is not affected by heat. Devices such as light meters, lux meters or devices using photo diode sensors do not have the same spectral response as a PV module, they do not compensate for temperature and are likely to introduce significant measurement errors if used for solar PV applications. They are not suitable for use on PV systems.