Direct answer: A commercial rooftop solar plant in Bangladesh needs three coordinated layers of lightning protection, not a single device: an external lightning protection system (LPS) that intercepts the strike, a bonded earthing network that carries the current safely to ground, and surge protective devices (SPDs) on the DC and AC sides that clamp the voltage surges reaching the inverter. Omit any one layer and the other two cannot do their job — an SPD alone cannot carry a direct strike, and an air terminal alone cannot stop an induced surge from destroying inverter electronics.

Why Bangladesh roofs are high-risk

Bangladesh is one of the most lightning-exposed countries in South Asia. The Disaster Management and Relief Ministry reports an average of nearly 300 lightning deaths a year, with the highest fatalities in the north-eastern districts of Sunamganj, Netrakona and Sylhet, according to the Bangladesh Meteorological Department's Storm Warning Centre. Pre-monsoon (March to May) and monsoon (June to September) together account for about 94% of lightning fatalities from 2015 to 2022, and studies of the 2013-2017 period found an average of 1.73 deaths per day in the pre-monsoon season alone. The familiar Kalbaishakhi nor'wester storms of April and May are the peak danger window for a rooftop plant.

For a factory owner, the human risk is only part of the picture. A rooftop array is a large, conductive, elevated structure with long DC cable runs — an ideal collector for both direct strikes and induced surges. A direct strike can melt conductors, start a fire and shatter modules. An indirect strike, even one that hits a nearby building or overhead line, can induce thousands of volts on DC strings and AC feeders and destroy inverters, monitoring hardware and control boards in milliseconds. The cost is rarely just the inverter: it is the inverter, the lost generation during replacement, and often a voided warranty argument about whether the plant was protected to standard.

Layer 1: External lightning protection (IEC 62305)

The governing standard is IEC 62305, in four parts: general principles, risk management, physical damage protection, and electrical and electronic systems protection. A compliant design starts with a risk assessment under IEC 62305-2, which weighs the building's location, height, construction, the value of the equipment inside, and the consequences of a fire or outage. That assessment decides the Lightning Protection Level (LPL I to IV) — and therefore the air-terminal layout, down-conductor spacing and earth-electrode design. A proposal that specifies air terminals without a risk assessment has skipped the step that justifies everything else.

The external LPS itself has three parts. Air terminals (rods or a mesh) intercept the strike above the array. Down-conductors carry the current down the building, spaced according to the protection level. Earth electrodes disperse it into the ground. Two design rules matter most for solar roofs. First, the air terminals must protect the array without shading it — a rod that casts a shadow across a string in the morning creates a daily production loss, a problem our shading analysis guide explains in detail, since a shaded cell can limit a whole string. Second, the separation distance must be maintained between the LPS and the PV metalwork wherever possible: keeping the required gap prevents a partial lightning current from jumping into the array's frames and cables. Where the roof is fully covered with modules and the separation distance cannot be kept, the standard requires a direct conductive bond between the LPS and the PV metalwork instead — and that changes the SPD requirement, as explained below.

A common misconception is that installing panels increases the risk of a strike. It does not: the building's height and location decide strike probability, not the panels. But panels do increase the consequences of a strike, because they add a large conductive surface and long DC loops that couple induced voltage. Protection is therefore about consequences, not about attracting lightning.

Layer 2: Equipotential bonding and earthing

Earthing is the layer most often done badly on Bangladeshi rooftops, because it is invisible once the plant is running. Every conductive part — module frames, mounting rails, inverter chassis, cable trays, the LPS itself — must be bonded to a common earthing system so that no dangerous potential difference can appear between them during a strike. Without bonding, a strike current flowing through one path raises that path's voltage far above neighbouring metalwork, and the difference arcs across insulation, connectors and electronics.

Good practice for a commercial roof includes: a dedicated earth electrode system for the plant, tested for resistance and recorded (a single driven rod in dry, high-resistivity soil is rarely enough); bonding conductors sized to standard — typically 16 sq mm copper for equipotential bonding of PV metalwork where no direct lightning current is expected, and heavier lightning-current-carrying conductors where the separation distance is not kept; and a single common earth bar where DC, AC and LPS earths meet, so the whole installation rises and falls together. Separate, unbonded earth pits for solar and for the building are a defect, not a feature: they create the very potential difference bonding exists to prevent.

Earthing must also be tested, not assumed. Soil resistivity in Bangladesh varies sharply between wet monsoon and dry winter, and a resistance measured in July can be very different in February. The commissioning record should state the measured earth resistance, the test method and the date, alongside the other acceptance tests in our commissioning and handover checklist. If the handover file has no earth-test sheet, the earthing has not been verified, whatever the installer says.

Layer 3: Surge protection — Type 1 vs Type 2 SPDs

SPDs are the last line of defence, and the most commonly misspecified. They are classified by the surge they are built to handle. Type 1 SPDs are tested with a 10/350 microsecond lightning-impulse waveform and can carry partial lightning current — they belong where a direct or partial lightning current can reach the conductors, which is the case when an external LPS exists and the separation distance is not kept. Type 2 SPDs are tested with an 8/20 microsecond waveform and handle induced surges only; they are the right choice where there is no external LPS, or where the separation distance is kept so that only induced surges can reach the wiring.

The practical rules for a rooftop plant are:

DC side, at the inverter input (and at the array for long runs): a DC SPD rated for the string voltage (Ucpv above the array's open-circuit voltage with margin), Type 1 where the LPS bond carries lightning current, otherwise Type 2. An inverter's built-in overvoltage protection is not a substitute unless the manufacturer explicitly specifies it as a DC-side SPD of the required type — many inverters protect only the AC side, and a varistor alone is not a complete SPD to EN 61643-31.
AC side, at the inverter output and the main distribution board: a Type 1 or Type 1+2 SPD where the building has an external LPS and the separation distance is not kept, otherwise Type 2, coordinated with the DC SPD so the two do not fight each other.
Data and monitoring lines: often forgotten, and often the first casualty — communication cables between inverters, meters and the monitoring gateway need their own data-line SPDs, or a single strike can take out the whole monitoring chain while the power electronics survive.
Cable routing matters as much as the device: keep DC positive and negative conductors close together and close to the earth conductor, avoid large loops between strings, and keep SPD connecting leads as short as possible. A long, looping SPD lead adds inductance that lets the surge voltage rise before the SPD can clamp it.

After any nearby strike, SPDs must be inspected: most carry a mechanical status window, and many offer a remote signalling contact for the monitoring system. A spent SPD that is never replaced leaves the plant unprotected for the next storm — the most common failure mode of an otherwise good design.

What a lightning event costs vs what protection costs

Protection is a small fraction of a commercial plant's cost — typically a few percent for the LPS, earthing and SPDs combined — while a single inverter replacement can cost many times that, before counting lost generation, fire damage and insurance disputes. It also protects the investment case itself: the payback arithmetic in our commercial rooftop solar ROI guide assumes the plant generates for 25 years, and a plant that loses an inverter every monsoon season does not. Insurers, too, increasingly ask for the LPS design and SPD schedule before covering a rooftop plant; a plant with no documented protection is a harder risk to insure at any price.

There is also a sequencing point. Lightning protection cannot be retrofitted cleanly after the array is built: air-terminal positions, separation distances and earth-electrode routes all interact with the module layout. Specifying it in the original tender — with the risk assessment, the LPL, the SPD types and the earth-test acceptance limit written into the contract — costs almost nothing extra at design stage and is expensive and compromised later.

What to demand in a tender or proposal

An IEC 62305-2 risk assessment stating the Lightning Protection Level, not just a line item for "lightning arrester".
An air-terminal layout drawing showing the protected volume over the array and confirming no new shading on strings.
A separation-distance calculation, and where it cannot be kept, the bonding and Type 1 SPD consequences stated explicitly.
An earthing design with electrode type, conductor sizes, a single common earth bar, and a measured resistance acceptance limit with a test sheet at handover.
A complete SPD schedule: DC and AC, Type 1 or Type 2 with justification, Ucpv and voltage protection level, plus data-line SPDs for monitoring.
Post-strike inspection in the O&M scope: SPD status checks after every major storm, with replacement of spent modules before the next one.

If a vendor offers a single rooftop rod and calls the plant protected, they have supplied one component of one layer. A protected plant has all three layers, designed together, tested at handover, and inspected after every storm.

FAQs

Do solar panels attract lightning?

No. Strike probability is set by the building's height, location and surroundings, not by the panels. Panels do, however, increase the consequences of a strike, because they add conductive area and long DC cable loops that pick up induced surges. That is why a building that never needed lightning protection before can need it once a large array is added.

Is the inverter's built-in surge protection enough?

Usually not on its own. Many inverters protect only the AC side, and even a DC-side built-in device is typically Type 2, which cannot carry partial lightning current. Where an external LPS exists and the separation distance is not kept, Type 1 SPDs are required on the DC conductors. Always ask the manufacturer to confirm, in writing, the SPD type and which side it protects.

What is separation distance, and why does it change the SPD type?

Separation distance is the minimum gap between the lightning protection system and nearby metalwork that prevents a lightning current from jumping across. If the gap is kept, only induced surges can reach the PV wiring, so Type 2 SPDs suffice. If it cannot be kept — common on roofs fully covered with modules — the LPS must be bonded to the PV metalwork, and partial lightning current can then flow in the DC conductors, so Type 1 SPDs are required.

How often should earthing and SPDs be checked?

Earth resistance should be measured at handover and at least annually, ideally in the dry season when resistance is highest, and SPD status windows should be checked after every major storm and at each scheduled maintenance visit. A spent SPD looks identical to a healthy one from the outside except for its status indicator — checking it is a five-minute job that prevents an unprotected monsoon.

Can lightning protection be added to an existing rooftop plant?

Yes, but it is harder and more expensive than designing it in. Air terminals must be placed without shading strings, earth routes must be found, and SPD types depend on whether separation distance can be achieved with the array already in place. If the array layout leaves no room for compliant air terminals, a bonded design with Type 1 SPDs is usually the practical answer — but it must be designed, not improvised.

Sources: IEC 62305 parts 1-4 (risk assessment, LPS design, separation distance, SPD coordination); BS 7671 regulation 712.443 on DC-side SPD requirements; Bangladesh Meteorological Department Storm Warning Centre / Disaster Management and Relief Ministry figures (about 300 lightning deaths per year, north-eastern districts highest, pre-monsoon and monsoon about 94% of 2015-2022 fatalities); Heliyon GIS-based spatial analysis of Bangladesh lightning fatalities 2015-2022; Holle et al. pre-monsoon lightning climatology for Bangladesh (2013-2017, 37.2 million strokes).

Commercial Rooftop Solar Lightning Protection and Earthing in Bangladesh: LPS, SPD and Separation Distance