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AS/NZS 1768-2007
Why Solar Systems Are Particularly Vulnerable to Lightning
A rooftop solar array is, in electrical terms, a large collection of metal conductors elevated above the surrounding terrain, connected to sensitive electronics by long DC cable runs. This makes it one of the most lightning-vulnerable additions you can make to a residential or commercial building.
Lightning damage to solar systems occurs in two ways:
Direct strikes — rare but devastating; destroys panels, inverter, and often the distribution board
Indirect transients (surges) — the most common cause of solar system damage. A nearby strike induces a voltage transient into DC string cables and AC grid connections, burning out inverter IGBTs and input capacitors
AS/NZS 1768-2007 — Lightning Protection
This standard provides the risk-based framework for deciding whether a dedicated lightning protection system (LPS) is warranted and how to design it if so.
The Risk Assessment Process
AS/NZS 1768 uses a quantified risk assessment (Method A or Method B) to calculate lightning risk. For solar, the key parameters are:
Parameter | Description | Solar Impact |
|---|---|---|
Ground flash density (Ng) | Strikes per km² per year — from BoM lightning maps | Northern Australia has 10× the strike rate of Tasmania |
Collection area (Ae) | Effective capture area of the structure | A solar array significantly increases the effective collection area |
Structure risk factor | Based on construction materials and use | Metal-framed arrays on masonry buildings: moderate risk |
Consequence factor | Risk to people, equipment, and continuity | High for commercial systems; moderate for residential |
Surge Protection Devices (SPDs) — The Mandatory Solution
Even when a full external LPS (air termination rods, down conductors, earth electrodes) is not required, surge protection devices are mandatory for grid-connected solar under AS/NZS 1768 and AS/NZS 5033.
Location | SPD Type | Standard Reference |
|---|---|---|
DC combiner / array junction box | Type 1 or Type 2, 1000V DC rated | AS/NZS 5033 Cl. 4.3.6 |
Inverter DC input | Type 2, integrated or external | Most modern inverters include this |
Inverter AC output / switchboard | Type 2 (or Type 1 for LPS buildings) | AS/NZS 3000-2018 Cl. 4.9 |
Metering enclosure | Type 2 on export connection | Network distributor requirements |
Earthing and Equipotential Bonding
AS/NZS 1768 and AS/NZS 3000 both require that all metal parts of the solar installation be bonded to the main earthing system. For solar specifically:
Panel frames must be earthed via the mounting rail system
The mounting rail must be bonded to the structure earth at a minimum of one point (two points for arrays >20 m long)
The inverter chassis must be earthed independently of the DC circuit earth
For TN-S and TN-C-S systems, the solar AC output earth must not create earth loops that allow fault current to flow through panel frames
External Lightning Protection — When Is It Required?
Scenario | Recommendation |
|---|---|
Residential, Region A/B, no LPS on building | SPDs only — no external LPS required in most cases |
Commercial, Region C/D (cyclonic, high flash density) | Full risk assessment required — LPS likely needed |
Building already has an LPS | Solar array must be incorporated into existing LPS design — isolation or bonding required |
Ground-mounted array in open paddock | High risk — earthing grid and SPDs mandatory, external LPS assess |
Array installed on telecommunications tower or elevated structure | Full external LPS mandatory |
Practical Tip: Most inverter warranties are voided by lightning damage if there is no evidence of SPDs fitted at the time of damage. Always install SPDs at both the DC and AC sides, and photograph them during commissioning. Keep the commissioning record.
Engr. Jason Morales — Founder, SolarEnergyPH