PV Operation and Maintenance

January 2016

Despite having no moving parts, a PV system needs to be inspected at regular intervals to ensure smooth operation. Generally this involves annual detailed visual inspection, cleaning and electrical testing. Monitoring systems are necessary to ensure that the PV array is operating optimally and that relevant parties are alerted in the event of any potential issues so that they can be investigated. Monitoring systems are central to the analysis of the system’s generation, and therefore financial performance, over time. Cleaning of the modules is also recommended in order to ensure maximum yield from the installation.

PV Operation and Maintenance



All NWT’s installations are supplied with monitoring technology as standard.  This allows you to keep track of how much electricity has been generated by your system throughout the year, and also to analyse the data in order to establish when the generation has occurred.  This in turn gives the opportunity to begin to match energy use with solar generation, for instance by operating energy-intensive equipment in the middle of the day.

Depending on the project, the monitoring system may also be configured to measure consumption at the site, therefore allowing a calculation of the proportion of the solar electricity that has been used on site.

After the first 12 months, there is often an annual fee for the web portal associated with these services, which allow you to monitor the system remotely as well as via a tablet or smart phone.  NWT’s installations using SolarEdge optimiser and inverter technology have the added benefit of free monitoring for the lifetime of the system.

SolarEdge product_monitoring



An annual site inspection is included within NWT’s Operation & Maintenance package.  Any remedial repair works required to the PV installation, outside of product warranties, will incur additional costs for parts and labour.

The following inspections will take place at each site visit:

General site inspection

  • Check for vegetation growth or other new shade items.
  • Check for ground erosion near the footings of a ground mount system.
  • Confirm proper system signage is in place.
  • Check for corrosion on the outside of enclosures and the mounting system.
  • Check for cleanliness throughout the site.  There should be no debris in the inverter area or elsewhere.
  • Check for displaced wires and cabling.
  • Check for signs of animal infestation under the array.

Detailed visual inspection

A visual inspection will include the following actions:

  • Inspect the inverter to make sure it does not show signs of cracking or excessive wear. The inverter should be bolted to the wall at all mounting points per the manufacturer installation requirements. Depending on the size, location and accessibility of the system, the inverters and combiner boxes should require tools to prevent unauthorised access to the equipment.
  • Inspect roof drainage is adequate, roof drains are not clogged, and confirm that there are no signs of water pooling in the vicinity of the array.
  • Inspect PV modules for defects that can appear in the form of burn marks, discolouration, de-lamination, or broken glass.
  • Check modules for excessive soiling from dirt build-up or animal droppings.
  • Inspect mounting system for defects including rust, corrosion, sagging, and missing or broken clips or bolts.
  • In roof-mounted systems, check the integrity of the penetrations.
  • Inspect all system isolation points, and look for signs of corrosion or damage.
  • Check to make sure the cabinet penetrations are properly sealed and there is no evidence of water ingress.
  • Perform a visual inspection of the interior and exterior of the inverter. Look for signs of water, rodent, or dust intrusion into the inverter.

 Manufacturer-specific inverter inspection

Each inverter manufacturer will have specific requirements for inspection, testing, Services, and documentation to meet its warranty obligations.  Typical requirements or inverter inspections include:

  • Record and validate all voltages and production values from the display.
  • Record last logged system error.
  • Clean the inside of the cabinet.
  • Check seals.
  • Confirm warning labels are in place.
  • Look for discolouration from excessive heat build-up.
  • Check integrity of surge arrestors.
  • Check mechanical connection of the inverter to the wall or ground.
  • Check internal disconnect operation.
  • Verify that current software is installed.
  • Contact installer and/or manufacturer about any issues found.
  • Document findings for all work performed.
  • Continuity of the equipment earthing at the inverter, combiner boxes, and isolators.
  • Continuity of all system fuses at the combiner boxes, isolators, and inside the inverter(s).
  • Open-circuit voltage (Voc) of all strings with the inverter off.
  • Maximum power current (Impp) of all strings.

Additional testing

(Used when problems are identified or required by contract terms)

May include:

  • Thermal images of combiner boxes (opened and closed), isolators, inverters (external and internal at a specified operating point), and modules;
  • Short circuit (Isc) testing of strings;
  • Insulation resistance test of conductors at specified voltage


Module cleaning

Electricity is generated by PV panels when light hits the semi-conductor surface beneath the protective glass.  Ensuring that the maximum amount of light reaches this surface will ensure that they perform optimally.

Depending on the inverter configuration, the modules may also be connected in “strings”.  This arrangement means that if even one of the modules is obstructed, the output of the whole string may suffer.  This means that it is essential to ensure that the modules are free from dirt, leaves, bird droppings, etc.

How often the modules will need to be cleaned is very site specific.  For example, if there is a lot of airborne dust from crops in the vicinity then the modules will need to be cleaned more frequently.


NWT use German “QLEEN” high performance professional cleaning systems.  ROTAQLEEN, a rotating brush that cleans quickly and smoothly, is specifically designed for use on solar PV installations.

With two 12 volt engines integrated into the brush head instead of using water flow to rotate the cleaning surface, ROTAQLEEN achieves substantially better cleaning results than standard brushes on the market.


Cleaning PV modules is a relatively inexpensive process, which can improve the output of a system fairly substantially, depending on the situation.  NWT use specialist lifting equipment in order to access all areas of the PV array in order to clean them effectively.

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