Inverter and cable settings

This group sets how the plant's DC output is collected and converted, how much of it one piece of collection equipment takes, and whether the application routes and measures the cables between the tables and the control rooms. Its title and its fields follow the electrical mode you chose at launch, because the two topologies collect the strings in different places. See Choosing a design mode for the choice itself.

One definition governs everything on this page. A string is one row of modules within an MMS-Table (MMS — module mounting structure). A fixed-tilt table configured with two rows therefore carries two strings; a half table carries half the strings of a full one. Everything you set here is counted in strings, so the table configuration and this group are two ends of the same decision — see Table configuration.

The group in each mode

In Central Inverter mode the string monitoring box — SMB — is the collection point. It does no conversion: it gathers the strings assigned to it and sends their combined DC output on to a central inverter, which sits inside an ICR (inverter control room) rather than out in the field. The field equipment and the conversion equipment are separate objects in that mode, and the group gives you a field for each.

Maximum strings per inverter

The first field caps how many strings one collection point is allowed to take. The application clusters the placed tables and puts down as many inverters or monitoring boxes as the cap requires, so a lower number means more equipment, each covering a smaller group of tables.

Set this from the inverter or monitoring box you intend to buy, counted the way the application counts: one string per row of modules in a table. The number of modules in that row does not enter into it — a row is a string whether it holds few modules or many. What the row holds decides the string's voltage and current, which is a separate question, settled by automatic string sizing.

The DC capacity that ends up attached to each unit is reported in the summary table, as Inv kWp in String Inverter mode and SMB kWp in Central Inverter mode, alongside the count itself. See Summary table columns.

Maximum SMBs per central inverter

Central Inverter mode only.

This field and the one above it multiply out to the capacity of a central inverter:

Central inverter capacity = SMB capacity × Max SMB per Central Inverter

So the two fields are the whole DC-side sizing chain in this mode. The strings per SMB fix what one monitoring box collects; the SMBs per central inverter fix how many of those collections one machine converts. Change either and the central inverter count changes with it, reported as C.Inv and CInv kWp in the summary.

One ICR building houses up to four central inverters. The control rooms themselves are sized and placed from the ICR Block capacity in the site parameters, not from this group — see Control rooms.

Calculate Cables for PV Power Plant

Off by default. With it off, the layout is generated, the equipment is placed and counted, and no cable is routed. With it on, the application traces every run and reports its length.

What gets traced depends on the mode, because the conversion happens in a different place:

Medium-voltage runs from the control rooms onward are a separate matter, routed in both modes. Conductor lengths and trench lengths are reported separately, because several cables share one trench. See Cable routing.

The notice that appears when you tick it

Ticking the box raises a notice before anything is enabled: cable calculation can take a long time on large or complex layouts, and the recommendation is to generate the layout first without it, review what you get, and enable it for the final run. The buttons are Enable Now and Not Now (Recommended) — and the recommended one, which does not enable cable calculation, is the default.

Screenshot pendinginputs/cable-calc-warning.png

Cable calculation notice

What it shows

The notice with its full text and both buttons, so the recommended choice is visible.

How to get there

Tick the cable calculation option. The notice appears immediately.

Why it is slow is worth knowing, because it tells you when it will not be. The AC runs are traced as horizontal and vertical segments only — no diagonals — and every candidate path is checked against the usable area before it is accepted, so a run may cross the perimeter road band but never leaves the plant fence. The work therefore grows with the number of tables and with how broken up the usable area is: a rectangular site with a clean fence routes far more cheaply than the same area cut by canals, water bodies and steep ground. On very large plants the application falls back to a fast geometric estimate of cable length so that generation stays quick.

What you still get with cables off

• The inverter and monitoring box counts are computed anyway. So are their capacities, the central inverter count, and everything downstream that depends on them — the AC capacity, the DC/AC ratio, the single-line diagram and the bill of materials.
• The cable columns of the summary show a dash. A — in StrDC(m), AC-ICR(m), DC-CInv(m), MV(m) or any trench column means the value was not computed, not that it is zero.
• The DC, AC and MV cable view switches have nothing to draw, and the cable layers are left out of the CAD export.

Everything else about the design is final. Only the cable numbers are missing, and one more run with the box ticked fills them in.

Loading a manufacturer inverter file

The group carries a row for a PVsyst inverter file — the .OND file the manufacturer publishes for the machine you intend to buy. Click Load .OND and pick the file.

Screenshot pendinginputs/ond-loaded.png

Inverter file loaded

What it shows

The inverter file row after a file has been loaded, showing the make and model, with the View button now enabled.

How to get there

Click Load .OND and pick an inverter file.

The file settles the AC side of the design:

• The maximum AC output drives the plant AC capacity. The application takes the file's maximum AC output as the rating of one machine and reports the plant's AC capacity from it — AC(MWac) and InvCap(MW) in the summary.
• The DC/AC ratio follows. With a DC capacity from the placed modules and an AC capacity from the file, the ratio is reported as DC/AC. It is the number a reviewer looks at first, and without an inverter file there is nothing to divide by.
• When the file declares no maximum output, the nominal power is used instead. Some files carry only a nominal rating; the design still sizes, from that figure.

Viewing what was read

View opens the file read-only, laid out the way PVsyst presents it, so you can confirm the machine before designing around it. The tabs are Main parameters, Efficiency curve, Additional parameters, Output parameters, Sizes and Technology and Commercial data.

Screenshot pendinginputs/ond-viewer.png

Inverter file viewer

What it shows

The viewer on its first tab with the whole tab strip visible.

How to get there

Load an inverter file, then click View next to it.

The Efficiency curve tab draws efficiency against load from the points in the file. Read it against the inverter loading your DC/AC ratio implies: a plant run at a high ratio spends most of its hours in the upper part of that curve, and the conversion loss you enter in the yield calculation should agree with what the curve shows there. That loss is a separate input — see Loss assumptions.

Screenshot pendinginputs/ond-efficiency-curve.png

Inverter efficiency curve

What it shows

The efficiency curve tab with the curve drawn and axes readable.

How to get there

In the inverter file viewer, open the efficiency curve tab.

The file is also what makes automatic string sizing possible

The number of modules you may wire in series is bounded by the inverter's tracking voltage window — the range of DC voltage over which the inverter can hold the maximum power point (MPPT — maximum power point tracking). That window is a property of the machine, and the application reads it from the inverter file. With no inverter file loaded there is no window, and therefore nothing to size a string against.

This is why the module file and the inverter file are usually loaded together at the start of a session, and why the question about calculating modules in series automatically leads back here. See Automatic string sizing.

Where to go next