Lightning risk assessment for renewable energy
Solar farms, wind turbines and substations sit in the open, run on sensitive electronics and cover a great deal of ground. That makes a sound IEC 62305 assessment both harder and more important than for a single building. This guide explains why renewables are so exposed, what each part of a site needs, and how the risk method scales across a portfolio.
Renewable energy sites are among the most lightning-exposed structures an engineer ever assesses.
A solar farm, wind site or substation sits in the open over a wide area, full of inverters, controllers and monitoring electronics that a surge can destroy in an instant. An IEC 62305 risk assessment, sometimes called a lightning risk evaluation, is how you decide what protection that site genuinely needs, structure by structure, and prove the decision to anyone who asks.
The standard itself does not change for a wind farm or a PV plant; the method is the same one a high-rise or a data centre uses. What changes is the shape of the problem. Renewables put together a large collection area, long internal cable runs and equipment that fails at low surge levels, so the assessment has to model a spread-out site and the lines that tie it together rather than a single box. This guide walks through why these sites are so exposed, how a lightning risk assessment for a solar farm is carried out, what wind and the balance of plant need, how the risk method scales across many structures, and which protection measures actually move the result. For the full solar method, read lightning risk assessment for solar farms.
The same site may be built to a different standard. A US project often follows NFPA 780-2026, which gives solar arrays and wind turbines chapters of their own, and an Australian one follows AS 1768:2021, which treats a solar farm as a distributed facility. The section on NFPA 780 and AS 1768 below sets out what each one asks for.
Why renewables raise the stakes
The same IEC 62305 method applies, but three things about renewable sites push the risk up and make the assessment harder than for an ordinary building.
A large, open footprint
More ground area means more strikes collected over a year, and an exposed rural or elevated site has little around it to take a hit instead. The collection area that drives how often a dangerous event occurs is large by definition.
Sensitive electronics everywhere
Inverters, trackers and controllers fail at low surge levels, far below what a strike can induce, so the protection of internal systems carries real weight in the risk result rather than being an afterthought.
Long internal lines
DC and AC cable runs cross the whole site and carry an induced surge a long way from where the strike actually landed, so the risk components tied to the connected lines matter much more than on a compact site.
Solar farms: a field-sized collection area
A PV plant is, from a lightning point of view, one enormous collection area dotted with vulnerable points. The array itself spreads conductive frames and modules across hectares of open ground, raising the chance that a strike lands on or near the site. The damage rarely stays where the strike lands. Long DC string runs feed combiner boxes, and the boxes feed inverters, and every one of those runs can carry an induced surge from a nearby strike into equipment that was never built to survive it.
The vulnerable points concentrate the risk. Inverters sit between the DC strings on one side and the AC collection network on the other, so a surge can reach them from either direction, which is why they usually need coordinated surge protective devices on both sides. Combiner boxes gather many strings into one point and are an obvious place for protection to sit. Tracker motors, weather stations and the monitoring electronics that report yield are all low-voltage devices strung along the same cable routes. The defence that ties it together is a well-bonded earthing and equipotential system across the whole field, so that when a surge does arrive, every part of the installation rises and falls together rather than developing the voltage differences that destroy equipment.
The assessment for a solar farm therefore leans heavily on the connected-line components and on the coordination of SPDs on the DC and AC sides. It is less about a single tall structure attracting a direct hit and more about a wide, wired field collecting and conducting surges, which is exactly the part of the IEC 62305 method that an ordinary building rarely stresses.
How a lightning risk assessment for a solar farm is done
A solar farm is not assessed as one building. It is a set of small structures joined by long cables, and the IEC 62305-2:2024 method is run on each structure with the cables modelled as its connected lines.
List the structures
Each inverter station, the control building, the substation and any other building on the site becomes its own structure, with its own dimensions, surroundings and zones.
Model the cables as lines
The DC strings, the AC collection cables, the data links and the grid connection are entered as connected lines, each with its length and whether it runs buried or overhead.
Set the lightning activity
The ground strike-point density NSG for the site location drives how many dangerous events each structure and each cable collects in a year.
Compute R and F per structure
Each structure gets its combined risk R, which matters where people work, and its frequency of damage F, which usually leads for inverters and SCADA. Each is judged against its tolerable value.
Choose the measures
Where a figure fails, add the measures that act on the components carrying the risk: coordinated SPDs on the DC and AC sides, buried or screened cables, field-wide bonding, or an LPS on a structure that needs one.
Report per structure
Issue one report for each structure and keep the site view that shows how many structures pass. Lenders, insurers and EPC contracts usually ask to see both.
| Part of the solar farm | How the assessment treats it | What usually decides its result |
|---|---|---|
| Inverter station or power conversion skid | A structure of its own, with DC lines coming in and AC lines going out | Surges over the connected lines, judged through the frequency of damage F |
| Control building and SCADA | A structure with people inside and critical electronics | The combined risk R for the people, and F for the control and monitoring systems |
| Substation | A structure, usually the one with the line that leaves the site for the grid | The grid line and the collection cables arriving from the field |
| DC and AC cable runs | Connected lines of the structures they feed, each with its own length and installation | Length, and whether the cable is overhead, buried, or buried inside a meshed earthing grid |
| Array field and combiner boxes | Reached through the lines that serve them, and protected by bonding across the field | Field-wide equipotential bonding and SPDs at the combiner boxes and inverter inputs |
This is a summary. The full method, with the collection area of a long cable, the installation factors for buried cables and the tolerable frequency for inverters, is in lightning risk assessment for solar farms. On a US or Australian project, see NFPA 780 solar arrays and solar PV under AS 1768.
Wind turbines: tall, isolated and struck often
A wind turbine is close to the worst case for lightning exposure: a tall, isolated structure standing alone in open or elevated terrain, which is precisely the geometry that attracts strikes. Tall turbines are struck repeatedly over their working life, and the strike usually arrives at the most awkward possible place, the tip of a rotating composite blade. From there the current has to be led down the blade, through the nacelle and the tower, and into the ground without passing through anything it can destroy.
That path runs through the most expensive and most delicate parts of the machine. Blades carry receptors and an internal down-conductor to capture the strike and carry it inboard. The nacelle houses the generator, converter and control electronics. The current then crosses the main bearing and the pitch and yaw systems, rotating interfaces where leading the current across safely is a real engineering problem, before reaching the tower and the foundation earth. Each of these is a point where a poorly designed path turns a survivable strike into a destroyed component and weeks of lost generation.
This is where a second standard comes in. IEC 61400-24 is the dedicated standard for lightning protection of wind turbines, and it addresses exactly the parts that the general standard does not: blade protection, the down-conductor route through a rotating structure, the bearings, and the pitch and yaw systems. It works alongside the risk thinking of IEC 62305 rather than replacing it. The general standard frames how much protection a structure needs and how to judge the risk; the wind standard sets out how to protect a turbine specifically. A sound turbine assessment uses both together.
The blade question gets the same answer under the other two standards. NFPA 780-2026 Section 9.1.2 leaves the blades and the generating equipment outside Chapter 9, and AS 1768:2021 Clause K.2.3 says blade protection comes from the blade manufacturer. Both then protect the rest of the turbine, as the section below explains.
Substations and the rest of the site
A renewable plant is far more than its panels or its turbines. The substation that steps the generation up to grid voltage is itself a high-value, surge-sensitive structure, and it is usually the single point through which the whole plant connects to the wider network. Switchgear, transformers and the protection relays around them all sit in the path of any surge that travels in on the collection cables or the incoming grid line.
Behind the high-voltage equipment sits the control side: the control room, the SCADA and protection systems that monitor and operate the plant, and the communications links that report back to the operator. These are low-voltage, high-value electronics doing a job the plant cannot run without, and they are reached by exactly the long internal cable runs that carry induced surges across the site. The assessment has to treat the substation and the control building as their own structures with their own risk, not fold them into a single figure for the plant, because their loss profile, an outage of the whole site, is quite different from the loss of one inverter or one turbine.
Renewables spread the risk across many structures and the lines that tie them together.
The measures that move the result
For renewables, a handful of protection measures do most of the work. The assessment decides which are needed and where, so the spend lands on the structures that carry the risk rather than blanketing the site.
Coordinated SPDs, DC and AC
Surge protective devices sized for the chosen lightning protection level, fitted on both the DC and the AC side and coordinated so each stage hands the surge down to the next. This is usually the single most effective measure on a PV plant, because the surge path runs through the inverters from both directions.
A well-bonded earthing system
An equipotential earthing and bonding network across the whole field gives every surge a low-impedance path to ground and stops dangerous voltage differences building up between structures. Without it the SPDs have nothing solid to refer to.
Shielding and zoning
Routing cables thoughtfully, screening the most sensitive runs and grouping equipment into protection zones reduces the surge that ever reaches the controllers and the SCADA, before any device has to clamp it.
Protection that fits the risk
The assessment is what decides which measures a given structure actually needs. That avoids both the danger of under-protecting an inverter station and the waste of over-specifying protection on a structure that the numbers show is already safe.
How the risk method applies to a whole site
The IEC 62305 risk method does not change for a renewable plant; it is applied more times. Each structure on the site, an inverter station, a control building, the substation, the array, a turbine, is modelled in turn with its own surroundings, its own connected lines and its own loss profile, and the method computes the risks for each. The results then roll up so the plant can be judged as a whole as well as structure by structure. A portfolio of several sites under one owner is the same idea one level higher: many projects, each a collection of structures, assessed on a consistent basis.
What stands out on a spread-out site is the weight of the connected-line components. On a compact building the risk is dominated by direct and nearby strikes; on a renewable plant the long power and data runs between structures mean the components for surges arriving over the lines often carry as much of the risk as the direct strike does. Getting those line lengths, routes and the SPDs that protect them right is the part of the assessment that decides the answer. For the full walk-through of how the components are computed, see how an IEC 62305 assessment works or read the dedicated guide to the IEC 62305-2 risk method.
Under NFPA 780 and AS 1768
Both standards cover solar and wind, but they split the work differently. NFPA 780-2026 writes requirements for arrays and turbines into the body of the standard. AS 1768:2021 keeps both in informative appendices and sends a solar farm through its distributed facility method.
| Question | NFPA 780-2026 | AS 1768:2021 |
|---|---|---|
| Where solar arrays are covered | Chapter 12, which applies on top of Chapter 4 to arrays on roofs and on the ground (12.1, 12.2.1) | Appendix N, informative and one paragraph long, which points to AS/NZS 5033 for detail |
| Air terminals on an array | On the rack or beside the array, never fixed to a panel frame; none needed inside a zone of protection (12.2.2, 12.3.1, 12.3.3) | Placed under Section 3 like any structure (1.1.2); no array-specific placement rule |
| PV surge protection | Required on PV dc circuits, 20 kA (8/20 µs) on each mode, and at the inverter ac output (12.4.2.1, 12.4.2.1.1, 12.4.3) | Section 4 and Table 4.1 cover a.c. power SPDs; no rating is given for SPDs on d.c. array wiring |
| Grounding a field array | A ground ring around each ground-mounted array with a metal structure, rings within 25 ft (7.6 m) joined (12.5.1.1, 12.5.1.1.2) | No array-specific earthing rule; the earth termination follows Section 3, and the array's own earthing is a matter for AS/NZS 5033 |
| Assessing a whole solar farm | Annex L, informative, run on the structures; energy facilities are listed as critical facilities (L.5.3.1) | Distributed facility method: site area times Ng, then the spreadsheet on each standalone structure (2.5.4.2) |
| Where wind turbines are covered | Chapter 9, requirements; blades and generating equipment excluded (9.1.2) | Appendix K, informative; blades left to the blade manufacturer (K.2.3) |
| Turbine earthing | A common grounding system tied to the site system where there is one, with a ground ring bonded to the foundation steel (9.4, 9.4.2) | An earth termination system for every turbine, its resistance measured before it joins the others (K.3) |
Solar and wind under NFPA 780
NFPA 780-2026 protects structures, not generating plant. Section 1.1.2 keeps the equipment of generating, transmission and distribution systems out of scope, and names Chapter 9 (wind) and Chapter 12 (solar) as the exceptions. That is why a renewable site gets more specific rules from NFPA 780 than an ordinary industrial plant does.
For solar, Chapter 12 offers two ways to protect an exposed array: strike termination devices on the rack, or air terminals, masts or overhead ground wires beside it that put the panels inside a zone of protection (12.2.2). Surge protection is not optional. Section 12.4.2.1 calls for it on PV systems and their dc circuits, with extra PV SPDs beside the inverter when it sits over 100 ft (30 m) from the nearest combiner or recombiner box (12.4.2.1.3), and Section 12.4.3 adds an SPD at the inverter's ac output. A ground-mounted array with a metal structure gets a ground ring around its perimeter (12.5.1.1). The clause-by-clause guide is NFPA 780 solar arrays: Chapter 12 explained.
For wind, Chapter 9 protects the tower, nacelle and hub. Nacelle air terminations are placed with the blades turned to give the smallest zone of protection (9.2.1). The tower needs at least two down conductors, or a tubular or structural metal tower that meets Section 4.18 (9.2.6). For the control systems in the nacelle, hub and tower, Section 9.3.1 asks you to consider bonding, shielding and surge protection, and the SPDs follow Section 4.19 (9.3.2).
Annex L, the NFPA 780 risk assessment, is informative and has no solar or wind inputs of its own. Two clauses still matter on a renewable project. L.5.3.1 lists energy facilities, power plants among them, as critical facilities. L.5.3.2 then advises that a critical facility should either be protected to the standard or go through the detailed assessment of L.6. Whether a given solar or wind farm counts as a power plant is a call for the owner and the authority having jurisdiction. L.1.1.1 also puts statutory, regulatory and insurance requirements ahead of any risk result.
Solar and wind under AS 1768
AS 1768:2021 says little about PV directly. Appendix N is informative and brief: an array is exposed and spread over a wide area, so direct and nearby strikes can do more damage, and lightning and surge protection should be designed together. For the array itself it refers you to AS/NZS 5033. The clauses that apply to every structure sit in the main body: the risk method in Section 2, the protection system in Section 3, equipment and surge protection in Section 4, and testing and maintenance in Section 5. Clause 5.4.3 also names installing PV panels as an example of an alteration after which the protection should be reassessed.
The clause that shapes a solar farm assessment is 2.5.4.2. It defines a distributed facility as standalone structures joined by conductive services inside a site boundary, names ground mounted PV arrays as an example, and says the spreadsheet does not apply to such a site as a whole. Instead it recommends a staged method. First, estimate the yearly flashes to the site from its area and the ground flash density Ng. Then choose measures by the hierarchy of controls in Clause 2.3, and protect the equipment and the cables between structures under Section 4. Last, run the spreadsheet on each standalone structure, such as an inverter station, a control room or a substation building. Services leaving the site, such as the grid connection, may need further calculation.
Wind turbines sit in Appendix K, also informative. It protects the turbine under Section 3, with the blades treated as stationary in their worst position when the protected zones are drawn (K.2.3). For control circuits it advises SPDs as close as practicable to the equipment and notes that fibre optic signal cables, used properly, are very effective (K.2.7). Each turbine gets its own earth termination system, typically a ring electrode bonded to the foundation reinforcement, and its resistance is measured before it is connected to any other turbine (K.3). For the full PV picture in Australia, read lightning protection for solar PV in Australia.
The compliance and commercial drivers
For a renewable project the assessment is rarely optional. Several forces, regulatory and commercial, push it onto the critical path.
Approval and insurance
An IEC 62305 assessment is commonly required for building or grid-connection approval and demanded by insurers before they will cover a plant. It is the recognised evidence that the lightning decision was made on the numbers, not assumed.
Lender and EPC requirements
Financiers and EPC contracts routinely write the assessment in as a condition of funding or handover, so a missing or weak study can hold up a milestone payment or a project completion.
Downtime cost
A struck inverter or turbine is not just a repair bill; it is days or weeks of lost generation and revenue. The cost of an outage is usually what makes the protection pay for itself many times over.
Warranty
Equipment warranties on inverters and turbines often assume that the surge protection meets the relevant standard. A claim after a strike can turn on whether the protection was specified and documented properly.
A whole portfolio, zone by zone
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Questions answered
Which renewable energy sites does an IEC 62305 assessment cover?
How is a lightning risk assessment for a solar farm carried out?
Why do the cables matter so much on a solar farm?
Are wind turbines covered by IEC 62305 or IEC 61400-24?
What surge protection do PV inverters need?
Why are renewable energy sites more exposed to lightning?
How does IEC 62305 apply to a site with many structures?
What protection measures matter most for renewables?
Is lightning protection a compliance requirement for renewable projects?
What do NFPA 780 and AS 1768 say about solar farms and wind turbines?
Does Lumex™ handle a portfolio of renewable sites?
The tolerable risk in IEC 62305-2 is not a fixed constant.
Clause 7.3 NOTE 1 gives RT = 1 × 10⁻⁵ per year as a
representative value of tolerable risk and adds that another value may be set once
the case has been investigated in detail. The standard's introduction then lets national or local regulations fix
RT, the tolerable frequency of damage FT
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