Photovoltaic (PV) systems have unique characteristics, necessitating the use of surge protectors specially designed for them. They can have high DC system voltages of up to 1500 volts. Their maximum power point operation is just a few percent below the system’s short-circuit current.

To determine the appropriate surge protector module for PV systems and their devices, one needs to consider:

  • Lightning flash density
  • Operational temperature of the system
  • Voltage of the system
  • Rated short-circuit current
  • Level of waveforms to protect against (direct or indirect lightning strikes)
  • Nominal discharge current

PV array (1)

Surge protector requirements for devices protected by an external lightning protection system (LPS) depend on the chosen LPS category and whether the distance between the LPS and the PV device is isolated. IEC 62305-3 provides detailed requirements for LPS separation distances.

For effective protection, the voltage protection level (Up) of the surge protector should be 20% below the dielectric strength of system terminal equipment. Importantly, the short-circuit withstand current of the surge protector used should exceed the short-circuit current of the PV array strings to which it is connected. Surge protectors installed on the DC output side should have a DC MCOV equal to or greater than the panel’s maximum PV system voltage.

When lightning strikes at point A (refer to figure 1, which is not provided here), both PV solar panels and inverters may get damaged. If lightning strikes at point B, only the inverter may be damaged. Given that inverters are often the most expensive component of a PV system, it’s crucial to properly select and install surge protectors on both AC and DC lines.

Surge protectors on the DC side of PV systems must be specifically designed for DC applications. It is dangerous to use a surge protector meant for AC on the DC side and vice versa. Surge protectors must also be used on the AC side if they are being used on the DC side.

For AC, it’s equally vital to ensure the surge protector is designed specifically for the AC side. If multiple inverters are connected to a single grid, they can be linked to one surge protector. The installation of the surge protector should always be upstream of the device to be protected.

Proper installation of surge protectors is based on three values:

  1. Maximum continuous operating voltage: the voltage at which the surge protector will activate.
  2. Voltage protection level: the device’s overvoltage category must exceed the surge protector’s voltage protection level.
  3. Nominal discharge current: the waveform peak (for Type 2 surge protectors, it’s 8/20 µs) that the surge protector can withstand after repeated surges.

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Cables

In PV systems, cables often extend over long distances to reach grid connection points. However, using long cables is discouraged. This is because the impacts of lightning discharge, based on site and conductive interference, increase with cable length and conductor loop size. Induced voltage drops in connection cables can undermine the protection efficacy of surge protectors when transient overvoltages occur.

Surge voltages are a significant factor in cable failures. Each pulse on a cable results in a reduction in the cable insulation’s strength. If a surge is introduced into an isolated PV system (away from the grid), any equipment powered by solar energy (like medical devices or water supply) might get interrupted.

The position and number of surge protectors to be installed on the DC side depend on the cable length between the solar panels and the inverter. If it’s less than 10 meters, only one surge protector is needed, positioned near the inverter. For cables longer than 10 meters, one should be placed near the inverter, and a second one should be installed closer to the solar panel boxes.

Cable layout should avoid forming large conductor loops. Both AC and DC lines, as well as data lines, must be laid along the entire path with equi-potential bonding conductors to ensure that multiple conductors are laid or the inverter is connected to the grid without forming conductor loops.