NWT Energy was tasked to perform an assessment of a 250 kilowatt-peak solar PV system installed in March 2016 by Conergy, who have now closed their UK operations. We had to ensure that the overall quality met the requirements of the original CDM contract and that the terms of the original O&M contract were honoured by Conergy.

Upon inspection it was clear that extensive repair work was required and our intervention would save the client tens of thousands of pounds in future costs. We provided a high-level report, addressing concerns already raised in a Risk Improvement report. We scheduled the work and with our highly-trained engineers, we brought the installation up to scratch. 


The modules were mounted on frames designed to be separated from the roof surface by EDPM rubber mats, in order to keep metal components raised from the actual roof fabric and to avoid damaging it.

In several areas these mats have either been placed incorrectly or have moved since installation, which has caused damage to areas of asphalt. The ballast method also presented issues and appeared haphazard.

‘Hard’ shading

Aside from the build-up of dirt on the module surfaces, several areas of the installation were subject to substantial ‘hard’ shading from fixed objects such as railings and vents.  Even one shaded module has the potential to reduce the output of an entire string of PV modules, substantially reducing the system output.


During the evaluation we documented the frankly bizarre inverter selection that had been installed, involving four separate manufacturers of varying quality. We can only assume that this was due to supply issues, since it did not make sense from a design, maintenance or warranty perspective.

Following the report, NWT were contracted to move the installation and site it more appropriately, at the same time as performing repairs to the roof fabric and undertaking a full electrical testing and inspection service. The system now performs better than it ever used to and as a result NWT have an ongoing operation and maintenance contract with the owner.