Testing times: solar safety and performance

Rob Barker is the director of Power Quality Expert Ltd and has over 25 years’ experience in electrical test and measurement.

Testing times: solar safety and performance

Specialising in power, energy and harmonics, Rob established Power Quality Expert as a specialist provider of Power Quality and Harmonic Surveys, BS:EN50160 Compliance Reports, UNIPEDE assessments, Energy Load Profiling and Power Quality Training.

Studying Information Technology at Salford University ignited an early interest that has grown into a passion for electrical test and measurement. From his early days in sales of electronic test equipment, Rob’s deep technical understanding saw him involved in new product launches and the development of new electrical test equipment as well as educating distributors and end users on the benefits and applications of electrical test equipment, primarily in the power quality and high voltage sectors.

Realising that a lot of equipment sales were going to those who didn’t understand the outputs, Rob took a decision, in 2007, to set up his own company – Power Quality Expert – to provide power quality and energy survey solutions direct to clients and electrical contractors as well as through a network of selected electrical test equipment distributors.

His passion for the subject also sees Rob provide power quality training, seminars, webinars and tech-talks to help educate and inform on power quality topics and issues as well as submitting and advising on technical papers on power quality and energy.

With accelerating growth in the solar sector and PV set to play an increasing role in energy delivery, Rob looks at the importance of testing installations for both safety and performance.

The very rapid and dynamic development of photovoltaic installations that has been taking place in the world in recent years is impressive. It is largely driven by a desire to move away from traditional, non-renewable energy sources. Greater social awareness and a desire by government to encourage people and businesses to take responsibility for the climate around us has forced a shift in the energy sector towards green energy.

Alongside the moral imperative, we have also seen the technology constantly evolving, which is resulting in lower costs for consumers to adopt solar PV solutions. This, combined with the constant increase in energy prices, makes an economic shift more and more favourable for the photovoltaic sector and is a key factor moving customers towards further investment in solar PV systems.

Safety and efficiency

With an increasing push for energy saving, and resultant sector growth, it is important to remember that testing the safety of the photovoltaic installation and the servicing of these installations is a growing business.  Because of this, it is very important that the installation complies with all safety requirements after installation and that its operation complies with the applicable regulations.

We can only be sure of this by carrying out the appropriate test and inspections and periodic checks. The requirements for these are described in Section 712 of the 18th Edition Amendment 2 of The Wiring Regulations (BS 7671) along with the standard EN 62446 (Photovoltaic (PV) systems – Requirements for testing, documentation and maintenance).

These are the standards that set the minimum requirements for installations and safety. The standard also defines the method and scope of safety control of photovoltaic installations. 

Measurements allow you to determine not only the safety, but also the efficiency of a photovoltaic installation. The EN 62446 standard divides the tests into category 1 and 2 tests and additional tests.

The right tool for the job

A meter such as the Sonel PVM-1020 allows you to carry out all measurements for the obligatory category 1, which include:

  • Measurement of open circuit voltage (for a single panel or a string of PV panels) up to 1000 V DC
  • Measurement of short-circuit current (for a single panel or a string of PV panels) up to 20 A DC
  • Measurement of the operating current of PV panels with the use of external clamps
  • Polarisation test
  • Measurement of insulation resistance of PV panels with a test voltage of 250, 500 or 1000 V, simultaneous measurement of two values (plus to earth and minus to earth)
  • Measurement of resistance of protective connections and equipotential bonding with ±200 mA current

Additionally, it is possible to perform measurements not included in category 1, which are found in everyday measurement practices. These are:

  • RMS voltage of AC network up to 600 V and frequency
  • Insulation resistance of AC circuits with the test voltage of 250, 500 or 1000 V
  • AC current
  • AC/DC power
  • Low current resistance with audible and visual signalling
  • Diode test with 200 mA current with automatic polarity detection
  • Blocking diode test with 1000 V DC voltage

By measuring the parameters of the PV installation, such as the short-circuit current Isc or the open-circuit voltage Uoc, you can quickly verify the correct connections of the modules in the string, their polarity and operation.

Measurements can be made for the entire chain of panels or for a single module. The continuity of protective connections and the grounding resistance on the DC side are measured in the same way as in AC installations.

In the case of insulation resistance tests, the difference is that the measurements are carried out under voltage, therefore special care should always be taken.

The values of operating currents and power on the DC and AC sides must be checked during the operation of both installations.

Based on these measurements, we can verify the efficiency of the inverter and compare it with the efficiency declared by the manufacturer.

Standard test conditions

The manufacturer of the inverter will usually specify the parameters of individual elements of the PV system which are measured in STC (Standard Test Conditions: 25° C, 1000 W/m², AM 1,5). For comparison purposes, solar installation testers, such as the Sonel PVM-1020, can automatically convert the results to STC conditions.

This is done by the use of an irradiance and temperature meter such as the Sonel IRM-1.Both meters cooperate with each other and normally work over long distance through radio link. The automatically transmitted data is then converted to measurement values of short circuit current and open circuit voltage referenced to the standard STC conditions.

In any rapidly growing sector, there is always a temptation to increase profitability by reducing quality with a resultant decrease in the safety of the installation as well as an increase in the risk of operating and servicing the facility.

Acceptance testing and periodic checks are the only way to ensure both the safety and efficiency of an installation and significantly reduce the risk of poor performance or far worse, electric shock or fire.