String Monitoring Evolution !

Strings
 
Did you know that a typical 1MWp Solar Power Plant can have upto 180 Strings spread across an area of 5 acres or more ?
 
To make the definition of a String clear, it is the series combination of 22 to 24 Solar PV panels. This ofcourse is assuming that the standard PV panel used is 230W rated with 30V approx. of MPP voltage. With a head count of about 4-5 onsite technicians, it is humanly a challenge for the onsite team to inspect and visually check each String cables/connections on a daily basis across acres of spreadout installations.
 
Imagine their plight for even bigger plants say a 5MWp or a 10MWp! For a 5MWp plant, the String count could be as high as 900 spread across more than 25 acres.

The Power generation from a String depends on various conditions, and the Generation could be low due to any of the following factors:
  • Damage to PV Module or Cabling
  • Loose contacts at MC4 connections over time
  • Hot Spots inside the PV module or in the SCB
  • Fuse Blown issues due to ageing / heating 
  • Bird Droppings, Shadows on Panels etc.

By the time, the onsite Technician is able to locate an issue with a string during his routine maintenance checks, it would have been late. Precious units of potential electricity wasted due to non-generation / low-generation. These kind of issues seen at string level cannot be caught at Control Room level monitoring. Because the currents entering the Control Room (Inverter Room) are already paralleled in sets of 16 strings or more. Few strings under-performing would go un-noticed. The granularity of monitoring achieved at per string level is lost when it comes to AJB (Array Junction Box) Level monitoring in the Inverter area.

Given the nose dive tariffs the solar unit prices are headed to, it is imperative to ensure all strings are performing to their best specification always. The financial losses occurred due to under-performing strings are not recorded presently in any metric, because these are not quantified.
 
The O&M site engineers themselves cannot be sure at any given time that 100% of the strings installed are performing as per expectation. The only solution to this problem, is to have String Level Monitoring installed in the Plant.
 
No doubt it comes at a cost, and need to be budgeted for. But the RoI is quick since any Low Performing/Under Performing Strings are immediately identified.