The 98kW system had a total of 7 SMA inverters, all contained within one plant room. It was apparent that inverter ā€˜Gā€™ on the 98kW existing farm PV system had failed.

Initial indications were that a capacitor was likely to have exploded, causing the casing to crack as shown in the image above. The whole inverter was completely out of action and needed to be replaced immediately. NWT Energy agreed to investigate whether a warranty claim could be pursued so that this situation could be rectified.  The manufacturers sent one of their engineers to follow up and supplied a new replacement inverter since the product was still within the warranty period.

Inverter configuration errors

In addition to the faults, the designs for both existing systems were not ideal, as the number of panels per inverter input and the sizing of the inverters to the number of panels were not perfectly matched. The main issue was that the inverters were oversized, leading to a slight reduction in efficiency. Unfortunately, however, the cost of rectifying the problem would have dramatically outweighed the potential gains.

Inverter positioning issues

The SMA inverters on the 98kW system were installed closer together than the manufacturers recommendations in the large PV shed and in the smaller PV shed the inverters were sandwiched tightly between the front and rear of the room (although efforts had been made to maintain the airflow to the inverters integral fan by installing in-line duct vents in the front and rear of the smaller PV shed). These arrangements were by no means ideal, however the overall efficiency was not likely to have been substantially decreased, since both sheds were un-insulated and well shaded.

Re-wiring of all SMA inverters

Following the warranty claim, an SMA engineer attended the site and highlighted that the cable thickness was also insufficient. This recommendation saw NWT Energy replace a total of 40 metres of cable with 6mm 5-core flex cable.

Installation of a monitoring system to the existing 98kW array

In order to ensure that any future issues could be identified promptly and remotely, NWT Energy quoted to install data cabling and power supplies to allow for the introduction of a Solar Log 2000 unit for data transmission to the system. The existing SMA inverters of the 98kW system did not have data output terminals installed as part of their specification when they left the factory. An additional RS485 data card was required for each inverter. All inverters were then connected to the Solar Log 2000 GPRS for data transmission.

Monitoring extension to incorporate 22kW array

Following the success of this new monitoring system, NWT were also asked to return to the site to incorporate the remaining 22kW system into the monitoring arrangement. This required the installation of additional metering equipment in the utility cupboard, as well as a new radio data link between the existing and new arrays. Whilst on site NWT also undertook further monitoring setup work to enable the client to produce a display to monitor both the production of the system and also the amount of the total solar electricity being used on site.