Cable routing and trenches
How DC, AC and medium-voltage runs are routed, what the conductor and trench totals mean, and how hand-drawn trenches change later runs.
Cable routing turns a placed layout into cable lengths you can cost: string cables from the tables to the inverters, feeders from the inverters onward, and medium-voltage runs between the control rooms. It also reports trench lengths, which are a different quantity from conductor lengths and are reported separately.
None of it happens unless you ask for it. Calculate Cables for PV Power Plant is off by default, and with it off no route is computed at all.
Turning cable calculation on
The option is in the inverter group of the input panel. Ticking it raises a notice: cable calculation can take a long time on a large or complex layout. The buttons are Enable Now and Not Now (Recommended), and the recommended one is the default.
Take the recommendation. The useful sequence is:
Generate without cables first
Leave Calculate Cables for PV Power Plant unticked and click Generate Layout. You get the tables, the capacity, the control rooms and the arresters quickly, which is what you need in order to judge whether the layout is right at all.
Fix the layout inputs
Row pitch, table configuration, the capacity block, obstructions — settle all of it while runs are fast. Cable routing on a layout you are about to change is work thrown away.
Tick the option and run once more
With the layout settled, enable cable calculation for the final run and read the lengths. Cable routing is the slow step on a large plant; on very large plants the application switches to a fast geometric estimate so that generation stays workable.
With cable calculation off you still get the inverter and monitoring-box counts — those come from the string arithmetic, not from routing — and every cable and trench column in the summary reads a dash. See Inverter settings for the option and the string limits that set those counts.
What is routed in each electrical mode
The electrical mode you chose at launch decides which legs exist. A conductor multiplier is applied to each leg, because a route drawn once on the plot is not the same as the cable you buy.
| Leg | Route | Counted | Why |
|---|---|---|---|
| String cables | Each table to its inverter | × 2 | A DC string needs a positive and a negative conductor over the same path |
| AC cables | Each inverter to the nearest ICR | × 1 | A three-phase AC feeder is counted once along its route |
ICR is the inverter control room — the building the AC feeders terminate in. Each inverter is routed to the nearest one, so the ICR positions influence the AC total as much as the inverter positions do.
Summary columns: StrDC(m) for the string cables and AC-ICR(m) for the AC feeders.
Both modes then have medium-voltage cables from the control rooms onward, which work the same way in either mode.
Where the inverters go
Inverters — or string monitoring boxes, in central mode — are not placed on a fixed grid. They are grouped from the positions of the tables themselves: the tables are gathered into spatial clusters, and one inverter serves each cluster, so a unit sits inside the group of tables it collects rather than at an arbitrary point.
Each one is then sited in the gap band between two rows — the pitch gap that already exists for shading — so the inverter does not cost you a table. A placed string inverter is drawn as a 2 m east–west × 1 m north–south marker.
How many there are is set by the string limits in the inverter group, not by the routing.
How a route is found
Three properties describe the routing, and the third one has a consequence worth being honest about.
Right angles only. Every route is made of horizontal and vertical segments. There are no diagonals, because a cable trench across a solar plant follows the row and column grid the plant is built on — that is how it is dug and that is how it is cabled.
Every candidate is checked against the usable area. A route is only accepted if it stays on ground that is actually available: it may run inside the perimeter road band, but it never leaves the plant fence, and it does not cross a water body, a line corridor, an obstruction or excluded terrain. See Obstructions.
A series of routing patterns is tried in turn. The application works through a fixed sequence of right-angled path shapes between the two endpoints and takes the first one that validates against the usable area. If none of them validates, it falls back to a last-resort route that is guaranteed to return something connected.
Because the fallback always succeeds, a route is always produced. On an awkward boundary — a narrow waist, a deep notch, a corridor cutting the plant in two — that last-resort route can be considerably longer than the run an engineer would draw, and it is still counted in the totals. Switch the cable displays on and look at the long runs before you cost them.
Segments that several inverters share through the same corridor are counted once. Routing many inverters toward the same control room naturally puts them on a common path for the last stretch, and that stretch is one trench, not one per inverter.
Medium-voltage cables
Medium-voltage — MV — cables run from each inverter control room to the main control room. They are not routed one by one. All the control room exit points and the main control room entry point are connected as a single shared-trunk network, so control rooms that are near each other feed into a common trunk instead of running parallel lines across the same ground to the same destination. That is both what gets built and what costs less.
Each branch of the network carries a termination allowance of 10 m, covering the terminations at its ends over and above the routed distance.
Nothing medium-voltage is routed until the main control room is placed — there is no destination before that, so the medium-voltage columns read a dash however the rest of the run went. Place it, and the lengths appear without regenerating. See Main control room, substations and street lights.
The summary reports the medium-voltage conductor length in MV(m).
Trenches and conductors are different totals
This is the distinction to carry into a cost estimate, and the summary reports both so you never have to guess which one a number is.
- A conductor total is the length of cable, including the multipliers above: a DC leg counted twice, an AC feeder counted once.
- A trench total is the length of physical trenching — the de-duplicated path length for that cable type. Where several cables share one route, the trench is counted once.
So the conductor total is always the larger of the two, often by a lot. Neither number is wrong; they answer different questions. Conductor length prices the cable drum. Trench length prices the excavation, the sand bedding, the tiles and the backfill.
| Summary column | What it reports |
|---|---|
| StrDC(m) | String cable conductor length |
| AC-ICR(m) (String Inverter mode) | AC feeder conductor length, inverter to control room |
| DC-CInv(m) (Central Inverter mode) | DC trunk conductor length, monitoring box to control room |
| MV(m) | Medium-voltage conductor length |
| DC-Tr(m) | DC trench length, de-duplicated |
| AC-Tr(m) | AC trench length, de-duplicated |
| MV-Tr(m) | Medium-voltage trench length, de-duplicated |
The exported report goes further: its summary page carries the inverter and cable summary broken down per control room, which is the form you want when you are issuing the cabling to a contractor. See PDF report and Summary columns.
The inputs that move the cable totals
Cable lengths are an output, but they are an output of a small number of decisions. If a total looks wrong, these are the fields to look at rather than the routing:
| Input | What it changes | Effect on the cabling |
|---|---|---|
| ICR Block | The number of inverter control rooms | More, smaller rooms shorten the AC feeders — each inverter routes to the nearest room — and add branches to the medium-voltage network, each with its own termination allowance |
| Max strings per inverter (or per SMB) | The number of inverters or monitoring boxes | Fewer, larger units mean longer string runs to reach each one; more, smaller units mean shorter string runs and more collection points |
| Row pitch | The spacing of the rows | Routes run along and across the row grid, so a wider pitch tends to lengthen the north–south legs of the runs |
| The main control room position | The destination of the medium-voltage network | Sets the whole medium-voltage length. Place it where the export actually leaves the site |
Because all four are settled before routing runs, this is another reason to review the layout first and enable cable calculation last.
Drawing and deleting trenches by hand
Automatic routing does not know about the access track you intend to dig along, or the crossing you have already agreed with a landowner. Sketch Mode lets you route by hand.
| Tool | What it does |
|---|---|
| 🟢 DC Trench | Click points to draw a DC trench as a polyline |
| 🔴 AC Trench | Click points to draw an AC trench as a polyline |
| 🟩 MV Trench | Click points to draw a medium-voltage trench as a polyline |
| ✂ Del Trench | Click any cable trench — automatic or hand-drawn — to delete it |
- What it shows
- A zoomed view with one hand-drawn trench visible in its own colour, next to automatically routed cables for contrast.
- How to get there
- Generate with cable calculation on, then in Sketch Mode use a trench tool to draw a route.
- Callouts to add
- Label the hand-drawn trench and one automatic route.
What manual editing does to the next run
The moment you delete an automatic trench or draw one by hand, the layout's cabling becomes yours. From then on, Generate Layout keeps the current cables instead of re-routing them, so your edits survive the next run rather than being overwritten.
The consequence, plainly: once you have edited the trenches, a later change to an input will not re-route the cables. Change the row pitch or move a control room after hand-editing, and the tables move while the cabling stays where you put it.
There is no control that undoes this. Nothing clears manual trench edits and hands the cabling back to automatic routing — not deleting the trenches you drew, not generating again. The one route back to automatically routed cables is to lay the plant out afresh: a new layout, or File ▸ New Project.
The rule is not a defect; it is the only behaviour that makes hand-editing worthwhile. But it does make the order of work matter. Do the hand-editing last, after the inputs have stopped moving, and save the project first so the automatically routed design survives as a file of its own.
Seeing cables on the plot
All three cable displays are OFF by default, even after a run that routed them. Switch on the ones you want:
| Switch | Default | Draws |
|---|---|---|
| DC Cables | OFF | String cables, and the DC trunks in central mode — orange |
| AC Cables | OFF | AC feeders from the inverters to the control rooms — red |
| MV Cables (ICR→MCR) | OFF | Medium-voltage runs to the main control room — dark green |
- What it shows
- The whole block of switches with each label and its current state readable, at their default states.
- How to get there
- After a layout has been generated. Do not change any switch first.
Turning all three on at once over a whole plant is unreadable. Zoom into one block, or switch Plant Layout off to read the cabling on its own.
What reaches the drawing
The CAD export writes each cable type and each trench type to its own layer —
DC_CABLES, AC_CABLES, MV_CABLES, and DC_TRENCH, AC_TRENCH,
MV_TRENCH — and the cable layers are present only when cable calculation
was on for the run. Cables are exported to the Google Earth file as well. See
CAD drawing export.
Where to go next
Obstructions
Every kind of ground kept clear of modules — water, buildings, line corridors, terrain, shadows — and how to draw an exclusion by hand.
Multi-plot sites
One boundary file can hold several separate plant boundaries. Each becomes its own plant, with its own row in the summary and its own unit substation.