String Monitoring Solutions from Megamic

One of the most important assets in a Solar plant is, of course, the array of PV panels connected in the form of Strings. During the EPC phase, a lot of attention is paid to the strings like:
- Selection of PV panels with the right specifications and costs, 
- Optimizing their location and orientation accounting for site layout, topology and latitude

However, one area that gets less focus or priority is ‘Monitoring the Strings’. Project cost pressure often leads to implementation of a sub-standard string monitoring solution or worse, dropping the option completely! This is mainly due to poor understanding and appreciation of the important role played by Strings in determining the amount of power generated over the lifetime of the plant. 
A complete String Monitoring solution should consist of…
  1. String-level current and voltage Monitoring hardware Unit (SMU)
    More granularity: Often multiple strings are combined and then monitored, but it is always better to monitor as close to an individual string as possible.
  2. A SCADA solution…
    capable of interfacing to every SMU and highlighting any issues with the Strings and with the String Combiner boxes
  3. An Analytics back-end
    capable of extracting deeper information from the strings
    - Triggers to clean the panels
    - Alerts about issues with specific strings due to bad panels, shading etc
    - Impact of long-term degradation (Aging)

All the above…with reasonable accuracy, high reliability and all pieces of the solution (hardware, software) working seamlessly with each other.
Megamic has been working on all the aspects of String Monitoring described above. 
We have a wide portfolio of SMU cards for a variety of scenarios commonly found in plants. 
Scenario 1: No provision for String Monitoring and related wiring in the plant  
As mentioned earlier, often, String Monitoring is an after-thought. The need for it is felt or understood well after the EPC phase, when questions arise about shortfall in generated power versus original expectations.
Our product Direct SM unit with wireless is well-suited for such cases. It has multiple unique features…
  • Flow-through design: the cables carrying the individual string currents can simply be made to pass through the card. 
  • No communication wires: measured string current data is transmitted wirelessly to the nearest control room, where one of our wireless data concentrator card collects data from all the Direct SMU cards. This data can then be displayed by Megamic’s String Monitoring SCADAlite software
  • IP65 Enclosure: the Direct SM unit can be fit at a convenient location near the existing String Combiner box, even exposed to the elements
  • Panel-powered: the unit operates over a wide supply voltage range. It can be powered simply by tapping power from one of panels in the string itself or a dedicated panel.
Fig: Image of Direct SM Unit with wireless
Scenario 2: Replacing a faulty String Monitoring card in a SCB
As the blog on  SCADA restoration discussed, String Monitoring cards are one of the weakest links in a monitoring network in the solar plant. Before launching this portfolio, Megamic’s  in-house Design team studied and debugged the root-cause of the failures seen in commonly used SM solutions from competitors.
Megamic’s String Monitoring card designs feature 
  • Rugged, modular data communication ports: together with a suitable, external surge protection device, the RS485 communication  ports are capable of withstanding surges. In the rare instance of a failure, their modularity ensures they can be replaced with minimum downtime and cost.
  • ​Reliable built-in power supply: designed to operate over a wide voltage range
  • Non-terminating current measurement: In Direct Hall sensors SM the cables carrying the string currents do not terminate on the board, they just pass through the non-contact current sensors.
    In this way, high voltages are not seen directly on the card, improving reliability.
  • Quick, Easy replacement: Megamic can custom-design the SM unit to retro-fit in an existing combiner box, exactly matching the mounting locations of the original faulty monitoring card!.
Fig: Image of SMU cards with non-terminating Current Sensors
Scenario 3: Reliable, Accurate String Monitoring Cards for New Plants (EPC stage)
Megamic has launched new 8/16-channel String Monitoring cards with several interesting features…
  • High Accuracy: better than +/-100 mA accuracy up to 20 A currents
  • On-board String Combining up to 1500 V: Reliable design capable of operating up to 1500 V dc bus voltages
  • Isolated, ESD protected RS485 ports – two connectors provided for easy daisy chaining
  • Digital inputs to monitor the breaker and SPD status in the string combiner box
  • Field-proven!
Fig: Image of SMU cards with Combiner
String Monitoring Hardware Portfolio: Quick Glance
(1)Fibre-Optic (FO) based SM cards coming soon !!
(2)Can work with Megamic’s compact, external wireless modules mounted in same SCB
For your String Monitoring requirements, get in touch with us at Phone: +91-80-41162103