Lightning arresters

An LA — lightning arrester — is a mast that protects a circular area of ground around it against a direct strike. When you ask for them, the application places arresters across the plant on a grid sized so that every part of the layout falls inside at least one protected circle, then clears whatever module tables the arrester structure itself stands on.

Arresters are off by default. Nothing about the layout changes until you tick them on, and on a fixed-tilt plant turning them on reduces capacity — which is why the decision belongs to you rather than to a default.

Turning arresters on

Both settings live in the Site Parameters group of the input panel. They are read when you click Generate Layout; arresters are placed near the end of the run, after the module tables and the inverter control rooms are already down.

See Site parameters for the rest of that group.

What happens when arresters are off

No arresters are placed, no ground is reserved for them, and module tables fill the whole usable area — the plant boundary shrunk inward by the perimeter road width, with obstructions and terrain exclusions subtracted. The summary's LA column reads zero.

You can still add arresters individually by hand. In Sketch Mode the ➕ LA tool drops one wherever you click, and it clears the tables under its footprint exactly as an automatic one does. Leaving Sketch Mode recomputes the plant's module count, capacity and arrester count, so the summary follows your edits. See Sketch Mode.

The coverage model

This is the part worth understanding before you change anything, because every other consequence — how many arresters you get, how much capacity you lose, where the masts land — follows from it.

Two rules define it:

1. Each arrester protects a circle of the LA protection radius, measured from the arrester's own centre.
2. Arresters sit on a square grid whose spacing equals that radius. Not twice the radius, not the widest spacing the geometry would tolerate — the spacing is the radius, whatever radius you set.

Because the spacing equals the radius, neighbouring circles overlap heavily and every point of the grid interior is comfortably inside at least one circle.

Why the spacing equals the radius

The worst-served point inside a square grid cell is the centre of the cell — the point farthest from all four arresters around it. For a grid whose spacing equals the radius, that worst-case gap works out at the radius × √2 ⁄ 2, or about 0.707 of the radius. It is inside the protected circle with roughly 29 % of the radius still in hand, and that margin is the minimum overlap between neighbouring circles anywhere on the grid.

The margin is the whole point. A wider grid would still cover the cell centres on paper, but only just, and coverage would then depend on the grid landing neatly on the site, on the boundary not clipping positions away, and on the radius you typed being achieved in practice by the mast you actually build. Setting the spacing equal to the radius is the conservative choice: the circles overlap rather than meet, so the protection survives a ragged edge and a dropped position.

Which grid positions are kept

Only grid positions whose centre lies inside the usable area are kept. An arrester is therefore never placed on the perimeter road, in a water body, inside a transmission line or canal corridor, or on ground excluded by the slope limits. The consequence is visible on the plot: the arrester grid is regular across the middle of the plant and ragged wherever the boundary or an obstruction cuts into it.

Completing the coverage

Dropping positions at the edges would leave outlying tables unprotected, so a second pass fixes it. Every table is measured against every arrester already placed. Any table whose centre is farther than the protection radius from every arrester gets an extra arrester, placed at the nearest valid position to it.

Coverage is therefore completed rather than left with a hole. On a compact rectangular site the second pass adds nothing. On a long, thin or awkwardly notched site it adds the handful of arresters the regular grid could not reach, and those are the ones you will see sitting off the grid lines.

The footprint, and what it clears

The circle is the protection. The footprint is the physical structure, and it differs by mounting type — which matters, because on one of the two it costs you modules.

Screenshot pendinglayout/arresters-sat.png

Arresters on a tracker plant

What it shows

A zoomed tracker view showing the small square arrester markers positioned in the gaps between tracker columns, with no tracker units removed.

How to get there

A tracker mode with arresters enabled. Zoom in far enough that the markers are visible.

Callouts to add

Outline one marker and label the inter-row gap it sits in.

Raising or lowering the protection radius

The radius does two jobs at once — it sizes the protected circle and the grid spacing — so changing it changes the arrester count more than you might expect.

Two things to hold in mind:

• The grid spacing follows the radius in both directions, so the number of positions changes with the area of a grid cell, not with its side. A modest change to the radius moves the arrester count noticeably.
• The radius is a claim about the mast you will build. Raising it to thin out the grid only reduces cost if the installed arrester genuinely protects that far. The application takes the number you give it and does not check it against a protection standard.

Arrester height and pile

Two further arrester fields sit in the Structures & Shadow group, alongside the building footprints:

Neither field feeds anything. They are read from the panel and go no further: the height does not size the footprint, cast a shadow or clear a table; the pile diameter does not reach the pile count, the materials list or any export; and neither value is kept when the project is saved, so both come back at the figures above. Enter the mast you intend to build if it helps you keep track, and carry the real figures in your structural and civil documents.

The arrester is also not one of the structures whose shadow clears tables. The Clear tables inside shadows option in the same group names the ICR, the MCR and placed objects, and nothing else — so a taller mast never costs you a module. What clears tables is the arrester's own footprint, above. See Structures and shadow for the shadow window and what it does.

Reading arresters on the plot and in the outputs

• On the plot. The Lightning Arresters switch is OFF by default, even on a run that placed them — switch it on to see the masts and their protection circles. Arresters are drawn dark red.
• In the summary. The LA column reports the arrester count for each plant, and the TOTAL row aggregates it. Because arresters are placed after the tables, the module and capacity columns on the same row already account for the tables the arresters cleared.
• In the CAD drawing. The arrester symbols are written to their own LA layer, present only when arresters were actually placed. See CAD drawing export.
• In the Google Earth file. Arresters are exported with the rest of the plant.

Arresters and cleaning robots

An arrester footprint on a fixed-tilt plant interrupts the run of tables a cleaning robot drives along. The robot sizing tool lists every gap too wide for a standard inter-table bridge, separating gaps blocked by equipment — arresters, buildings, obstructions — from gaps in open ground, so you can decide which to bridge. See Robotic module cleaning.

Placing an arrester by hand

Use this to add protection the grid did not reach, or to place arresters on a plant generated with the option off.

A hand-placed arrester does not extend the automatic coverage check. The grid and the completion pass run during Generate Layout, so anything you place afterwards is yours to position.

Where to go next