Direct answer: Protect a commercial rooftop solar plant in Bangladesh in four layers: external lightning protection per IEC 62305, Type 1+2 DC surge devices at the combiner box and inverter input per IEC 61643-31, AC-side Type 1+2+3 SPDs, and earthing below 10 ohms. With 3.3 million+ lightning strikes a year — 62% between April and June — skipping this is gambling a factory's entire solar asset on one Kalboishakhi storm.

Why Bangladesh is a worst-case site for lightning exposure

The numbers are stark. Regional Integrated Multi-Hazard Early Warning System (RIMES) data, reported by New Age, put Bangladesh's lightning death rate at 1.21 per 1,000 square kilometres — the highest in South Asia. More than 3.3 million lightning strikes hit the country every year, and 62% of them land between April and June, with May the single worst month. The disaster management department recorded 322 lightning deaths in 2024; 2020 saw 427. The worst-hit spot measured is Jamalganj upazila in Sunamganj, averaging 103 strikes per square kilometre per year. Lightning was declared a national disaster in 2016.

For solar, this matters because a factory roof is exactly the kind of tall, flat, metal-rich surface lightning prefers. Kalboishakhi nor'wester storms arrive with little warning through exactly the months when strikes peak, and industrial zones on open land have no taller neighbours to take the hit. Every rooftop plant in Bangladesh sits in a high-exposure zone — planning protection is not pessimism, it is arithmetic.

What lightning actually does to a PV plant

Damage comes in two forms. A direct strike hits the array or the building and injects tens of kiloamperes straight into the structure — impulses with peak currents around 31 kA have been measured on roof-mounted systems. Far more common are induced surges: a strike a few hundred metres away induces kilovolt spikes in the plant's long DC string wiring, which acts as a giant antenna. The longer and more looped the cable runs, the bigger the induced voltage.

The victims are predictable: the inverter's IGBT power stage and control boards, DC combiner-box electronics, monitoring data loggers, and optimizers. A fried string or central inverter is the single most expensive single-component failure a commercial plant faces — one strike can erase a year's worth of generation savings and leave a factory on expensive grid power for weeks while a replacement is sourced. Unlike dust losses, which steady maintenance recovers, surge damage is binary: the equipment is dead until replaced.

Layer 1: external lightning protection (IEC 62305)

The external lightning protection system (LPS) is the building's first line of defence: air-termination rods or a conductive mesh positioned above the array, with down conductors running to earth electrodes, designed per the IEC 62305 series. A risk assessment per IEC 62305-2 decides the required protection level.

Two details decide whether the LPS protects the solar plant or endangers it:

Separation distance "s". The PV array's metalwork must keep a calculated separation from the LPS conductors. If it does, a strike on the air terminal stays in the LPS and the array is shielded.
Bonding when "s" is impossible. On a crowded factory roof it often is. Then the PV frames and rails must be directly bonded to the LPS — but that bond imports part of the lightning current into the PV system, so Type 1 SPDs become mandatory on the DC side (see Layer 2).

Tell your EPC: "external LPS to IEC 62305 with a documented risk assessment, showing separation distances or the bonding scheme."

Layer 2: DC-side surge protection (IEC 61643-31)

This is the layer that saves inverters. SPDs for PV DC circuits are tested to IEC 61643-31 (EN 50539-11), and for a commercial rooftop you need two positions:

Type 1+2 combined SPD at each DC combiner box — the first defence at array level. It handles both the 10/350 microsecond waveform of a direct strike (impulse discharge current around 6.25 kA per pole on typical PV units) and the 8/20 microsecond induced surges (nominal discharge current 20 kA, maximum 40 kA).
Type 2 SPD at each inverter's DC input — the second defence, clamping whatever gets past the combiner box before it reaches the inverter's electronics.

Installation details decide whether SPDs work at all:

Distance: an additional SPD is required if the cable run between two SPDs exceeds 10 metres.
Lead length: keep the SPD's connecting conductors as short as physically possible — under 50 cm where you can, twisted together, minimum 6 mm². Every extra centimetre adds impedance and raises the voltage the protected equipment actually sees.
Voltage rating: the SPD's maximum continuous operating voltage (Ucpv) must sit above the string's highest open-circuit voltage — 1000 V and 1500 V classes for modern commercial strings.
Status indication: every SPD has a green/red status window with a thermal disconnector. Green means healthy; red means the cartridge has sacrificed itself and must be replaced immediately. Specify remote signalling contacts so the status reaches your monitoring system.

Layer 3: AC side and data lines

Lightning does not respect the inverter's DC terminals — surges enter from the grid side too:

Type 1 (or combined Type 1+2+3) SPD at the building's main low-voltage entry where an external LPS exists.
Type 2 SPD at the inverter's AC output / ACDB.
Cascaded SPDs must be energy-coordinated so the upstream device takes the brunt and the downstream device finishes the clamping.

And the forgotten victim: data lines. RS485 strings, Ethernet to the data logger, and the monitoring portal hardware are low-voltage electronics with thin insulation. In many Bangladeshi plants the first casualty of a storm is not the inverter but the monitoring system — which then silently blinds you to everything else that went wrong. Fit SPDs on the communication lines too.

Getting the inverter sizing right already protects your yield on paper; the surge layer is what keeps those correctly sized inverters alive through their first monsoon.

Layer 4: earthing and equipotential bonding

Every SPD is only as good as the earth it dumps surge energy into:

Target: earth resistance of 10 ohms or less; in high-lightning areas aim for 5 ohms or better.
Conductor: minimum 16 mm² copper for the earthing runs from combiner boxes and inverter stations.
Electrodes: multiple rods or a ring earth around the building; in dry, high-resistivity soil use bentonite backfill or chemical electrodes rather than accepting a bad reading.
Bonding: module frames, mounting rails, inverter chassis, DCDB and ACDB enclosures — all tied to one common earth bar. Floating metal is a voltage waiting to happen.
Testing: measure earth resistance with a proper earth tester (fall-of-potential method) every year before monsoon, and demand a test report at EPC handover. Soil dries, rods corrode, clamps loosen — an old "pass" is not a current "pass."

What to write in the EPC tender

Protection is cheapest when it is specified before the EPC prices the job. Put these lines in the technical schedule:

"External lightning protection system designed to IEC 62305, with risk assessment and documented separation distances or bonding scheme."
"Type 1+2 DC SPD at every combiner box and Type 2 DC SPD at every inverter DC input, tested to IEC 61643-31, with replaceable cartridges and remote status contacts."
"Type 1+2 SPD at main LV entry and Type 2 SPD at inverter AC output, energy-coordinated."
"Surge protection on all RS485/Ethernet monitoring lines."
"Complete earthing and equipotential bonding; earth resistance ≤ 10 ohms verified by fall-of-potential test report at handover."
"Single-line diagram marking every SPD position, type, and rating."

FAQs

Can lightning protection guarantee my plant will never be damaged?

No protection system offers a 100% guarantee — lightning carries too much energy. What IEC 62305-based design plus SPDs does is reduce the risk of damage to a level insurers and engineers accept. For the residual risk, keep the plant insured and the SPD cartridges fresh.

My factory building already has a lightning rod. Is the solar array protected?

Only if two conditions hold: the array sits inside the rod's protection zone, and the separation distance "s" between the LPS and the array metalwork is maintained (or the array is bonded to the LPS with Type 1 SPDs fitted). Most existing rods were sized for the building, not for a rooftop full of panels — have the EPC re-verify.

How often should surge protectors be inspected?

Visually every quarter — it takes seconds to check the green/red status windows, and it fits naturally into the quarterly maintenance round. After every major storm, inspect again. Replace any red-window cartridge immediately; a dead SPD protects nothing.

Do SPDs wear out even without a direct strike?

Yes. Type 2 devices absorb small surges from grid switching and nearby strikes throughout their life, and their metal-oxide varistors degrade with each event. The status window and thermal disconnector exist precisely because of this — treat a red window as an urgent maintenance call, not a suggestion.

Sources: New Age citing RIMES lightning data (3.3M+ strikes/yr, 1.21 deaths/1,000 km²); Daily Star and disaster management department figures (322 deaths in 2024, 427 in 2020); IEC 62305 series, IEC 61643-31, EN 50539-11, IEC TR 63227:2020; Citel and LSP.global PV surge-protection application guidance (31 kA measured impulses, SPD placement and ratings).

Lightning & Surge Protection for Commercial Rooftop Solar in Bangladesh: LPS, SPDs and Earthing Design