Panels, Performance & Electrical
The last three steps turn a roof into a system: what goes on it, what it makes, and how it connects.
System design — placing the panels
The panel picks up the module chosen on the quick proposal and reports what will fit: the number of positions available and the maximum size those positions make.
Three ways to place, and they answer three different questions.
| Button | Use it when |
|---|---|
| Fill the roof | You want the biggest system the roof will take. |
| Best N panels | You have a panel count in mind — from the bid, or from the customer's budget. |
| Offset X% of Y kWh | You are sizing to the bill. Takes the usage and the offset from the quick proposal. |
Positions are ranked by modelled output, so a target keeps the best-producing positions rather than the first ones drawn. Asking for 24 panels gives you the best 24, not the first 24.
If no usage target has been set, the offset button says so rather than pretending; set the usage on the quick proposal and it becomes live.
The roof is locked from this step onward. Editing it here would silently invalidate a layout that has already been checked — go back to 2D design to change a pitch or move a wall, then come forward again.
Performance — what it will actually make
Run simulation produces the annual result, and the panel is built so every figure can be checked rather than taken on trust.
Annual
- Production — the yearly kWh.
- Specific yield — kWh per kW installed. The number that lets one design be compared against another.
- Solar access — how much of the available sun this roof actually gets.
- TSRF — total solar resource fraction: orientation and shade together.
By month shows where the year's energy sits, which is how a winter shading problem becomes visible instead of averaging away.
Where the energy goes breaks the losses down, including given up to shade — the figure the trees you measured are responsible for.
Compliance warns where a layout breaks a rule it has been checked against.
Loss assumptions lists every assumption the simulation used. A proposal has to be able to print what it assumed; a number without its assumption cannot be checked by the person signing it.
Weather shows the clear-sky to typical-year ratio — the discount between a perfect year and a real one.
Electrical — how it connects
Topology
Three choices, and the rest of the step follows from the one you pick.
| Topology | What it means |
|---|---|
| Microinverters | One per module, AC from the roof down. |
| Optimized string | Optimizers on the modules, a string inverter below. |
| String only | No module electronics. |
With microinverters, every panel keeps its own maximum power point — so a shaded one costs its own output and not its neighbours' — rapid shutdown is satisfied by the units themselves, and there is no string voltage to size against a cold morning.
Sizing
Modules, system kWp, string inverters, AC branch circuits, the strings themselves, the DC/AC ratio and the AC output. Change the topology and these change with it.
Interconnection
Before anything is placed, the service panel is checked. Enter the busbar rating and the main breaker, and the panel computes the 120% allowance, what is already used, the backfeed needed and the headroom left.
There is no point placing a disconnect for a system the panel will not accept, which is why this sits between sizing and equipment.
Wiring
Auto-wire the arrays builds one array per roof face, ordering the modules serpentine — left to right along one row, right to left along the next, the way a string is actually run. Ordering every row the same way adds a full row of wire per row.
It reports circuits, arrays, the conductor chosen and the longest run, and lists any issue against the array it belongs to.
Equipment
Pick what you are placing from the rail's Equipment tool, then click to put it down. The tool stays armed — a service comes with a set of these and they get placed in one pass, while you are looking at the same photograph.
Two of them are load-bearing for the rest of the tool:
- A main panel is what the interconnection check needs in order to have a busbar to check.
- A sub-panel, where there is one, is what a ground array's run actually terminates at — so the conductor is sized to the barn rather than past it to the house.
Mount height is a real leg of the conductor, not a detail. A run from a ground array to a panel 1.4 m up a wall climbs that 1.4 m at the far end, and on a short run it is a measurable share of the wire. The preset gives a sensible starting figure; replace it when you have measured the wall.
Conduit runs
The Conduit run tool joins two pieces: click one, then the other.
A run goes between pieces, not between points, and that is what makes it a takeoff rather than a drawing — its ends follow the equipment when you move it, and the length re-measures itself.
Choose the routing before you draw the run. It is the most consequential thing about one and the easiest to forget once the line is on screen: a trench is a day with a machine, a crew and a permit; a surface run is a morning with a ladder. Asking afterwards makes "surface" the answer for every run somebody drew quickly, which is the one direction that under-quotes.
A trench cannot go under the house. The service panel is on the building, so the straight line from a ground array to it very often runs straight through — and that is not a route, it is a foundation. A trench route goes around, keeping clear of the footing by a metre unless you say otherwise, and it takes the shorter of the two ways round. That detour lengthens the run, which re-prices the trench, the conductor and the voltage drop — all of which were short before.
It is a minimum, not a site plan: the driveway, the septic field, the neighbour's fence and the tree roots are all reasons a real route is longer still.
A trench is also the only run whose path stays where it was dug when the building is moved — its endpoints re-derive from the equipment they join, but the ground between them has to be looked at again.
Wall-mounted gear travels with the building when it is moved; ground gear does not, because it is a feature of the site.
Until every piece a topology expects is on the map, the panel says which are missing and why the numbers are blank: conduit lengths and voltage drop are computed between placed equipment.
Handing off to the quote
The last step's forward button hands the design to the quote. That is the point of the whole tool — a design nobody can price is a drawing.