Interfacing components

(a) Combiner box

For connecting multiple strings, a combiner box is used. Most inverters have input terminals that allow to plug in 2 to 4 sets of conductors.

Fig.1: Combiner box [1]

(b) DC Disconnect

A DC disconnects houses a DC circuit breaker placed in the circuit to provide humans with a way to quickly power one section of the PV circuit. It is used to disconnect solar panels from the system for easy implementation of routine maintenance and extension works. Most inverters already include one.

Fig.2: DC disconnect [2]

(c) Over-current protection

This is provided by the use of fuses and/or circuit breakers on the DC side of your system because of shading that causes reverse current to flow across the circuit. Fuses should be placed as close as possible to battery connection as a safety measure. They are usually placed inside the combiner box or the DC disconnect. An important factor that should be considered is the correct rating of the fuse.

Fig.3: 1000V Solar PV DC fuse [3]

(d) AC disconnect / Isolator

It is connected between the production meter and the main distribution board (houses the breakers and RCDs) to interrupt supply of energy to AC load.

(e) Short circuit protection

A fuse or a circuit breaker is used at the positive output of the battery. In case of a short circuit, the device will open the circuit on the battery positive and take it out of the system.

(f) Ground fault protection

Ground-fault protection devices must detect a ground fault in the PV array and interrupt the flow of fault current. This feature is most of the times included in the inverter.

Fig.4: Ground fault protection device [4]

(g) Wires and connectors

All cables must have a current rating above that of the over-current device. Cable current ratings have to be adjusted using standard correction factors for installation method, temperature, grouping and frequency to BS 7671. Cables should be used with UV radiation resistible insulation. Exterior cables should be weather resistant and allow for temperature range from -45°C to up to 80°C or even more. The most common connector types used in PV are MC, Solarlok, and Huber+Sunher.

Fig.4: MC4 connector [5]


References:

[1] “Amazon.com: ECO-WORTHY 4 String PV Combiner Box with Lightning Arreste, 10A Rated Current Fuse and Circuit Breakers for On/Off Grid Solar Panel System: Industrial & Scientific.” [Online]. Available: https://www.amazon.com/ECO-WORTHY-Combiner-Box/dp/B07J42LCSH.

[2] “DC Disconnect Switch 32A 3P - Green Energy Solutions.” [Online]. Available: https://www.greenenergysolutions.business/product/dc-disconnect-switch-32a-3p/.

[3] “China 1000V Solar PV DC Fuse Holder for Over Current Protection - China Fuse, Fuse Link.” [Online]. Available: https://grl-electric.en.made-in-china.com/product/oOaneEkvhlcU/China-1000V-Solar-PV-DC-Fuse-Holder-for-Over-Current-Protection.html.

[4] “Ground-Fault Protection for PV Systems - IAEI Magazine.” [Online]. Available: https://iaeimagazine.org/features/ground-fault-protection-for-pv-systems/.

[5] “Amazon.com: WOLFWILL Solar Panel Adapter Cable to DC 5.5mm x 2.1mm - Universal Charge Adapter Connector for All Power Solar Panel and Portable Solar Generator Inverter: Home Improvement.” [Online]. Available: https://www.amazon.com/WOLFWILL-Connector-Solar-Panel-Adapter/dp/B07GFJM8LW.