Photovoltaic system dimensioning
Draw your solar layout and we suggest cable sizes in plain language.
Cable and breaker sizing, and the production charts (kWh), appear after you register (free).
Select a tool, a device, or a cable. We explain what it means without electrician jargon.
Selected cable
How are the batteries connected?
Device data
Capturing roof image…
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To start dimensioning
You need the exact Google Maps link of your home. Paste it above and click Lock with link to freeze the roof image, then place panels and calculate production.
Map unavailable. Configure the Google Maps API key.
Measurement
Roof face
Restriction
Vertical wall — shadow on the Left or Right of the map.
Horizontal wall — shadow Above or Below on the map.
Estimated production (kWh)
By hour — selected day
By month — year
Cables
Summary of every cable on the diagram — lengths and suggested sizes.
| Section | Cable type | From → To | Cable length | Suggested size | Current | Voltage loss |
|---|
No cables yet. Draw them on the diagram first.
Circuit breakers
Suggested size from the cable it protects (Ib ≤ In ≤ Iz). AC and DC.
| Photo | Suggested breaker | On cable | Poles | Curve | In | Ib (design) | Note |
|---|
No breakers on a cable yet. Snap a breaker onto a cable in the diagram.
Quantities and prices
Prices are per metre of a single core (from our table). The Quantity column shows cable run length (one span); the subtotal multiplies by the bundle cores. Panel 100 €, battery 2000 €, inverter 600 €. Each group has a subtotal.
Nothing to buy yet.
FAQ
Simple answers for this page — no electrician jargon.
How do I start?
1. Fill in your house power, panels and battery (we pre-fill what we already know).
2. Open the devices palette and click to place them on the canvas — or use the starter diagram.
3. Choose Connect cables. Click a blue connection dot, then another device’s dot — or a cable to snap a breaker on. You can also click the cable first, then a breaker.
4. Click the cable and type the length in metres in the box. We pick the thickness (mm²).
What is amperage (A)?
Amperage (A) is how much electricity is flowing in the cable — like water flowing in a pipe. It is not the same as Watts or kVA (those are “how powerful”). Single-phase: contracted power ÷ 230 V (one live). Three-phase shares the same power across three lives: each L carries about 1/3 — power ÷ (3 × 230 V). Example 10.35 kVA: mono ≈ 45 A; tri ≈ 15 A per phase. Then we add a safety margin (usually 20%).
What is mm²?
mm² is the thickness of the copper inside the cable. Thicker copper stays cooler and loses less voltage.
What is voltage drop?
Voltage drop is a little “pressure” lost along the cable, like a long garden hose. Longer cables or more current lose more. We try to keep the loss under 3%. If it is higher, we recommend a thicker cable (bigger mm²).
Why do panels in series not need a thicker cable?
Panels in series keep the same amps (about Imp). Eight 540 W panels at 10 A is still ~10 A in the cable — the voltage goes up, not the current. Watts do not add extra amps in series. In Portugal we still use 6 mm² solar cable as a minimum: stronger on the roof, and what installers normally stock.
What do the cable colours mean?
Red and black cables carry DC electricity from panels or the battery to the inverter.
Single-phase: brown, blue and green/yellow. Three-phase: brown (L1), black (L2), grey (L3), blue (N) and green/yellow (PE).
The bar at the bottom of the diagram only shows colours used on this drawing.
What is the difference between DC and AC?
DC (direct current) comes from the panels and the battery. AC (alternating current) is what the house uses between the meter, inverter and consumer unit.
What is Imp and the xN on the panel?
Imp is the panel current in normal operation, from the datasheet. xN is how many panels are in series. Series keeps about the same Imp — it does not add amps. Voc is the open-circuit voltage; in series, string voltage = Voc × xN.
What does In on the breaker mean?
In is the amp rating stamped on the breaker (for example 20 A). It should sit between the circuit current (Ib) and what the cable can carry (Iz). We suggest the smallest size that still fits.
Batteries in parallel or in series?
In parallel (usual at home at 48 V) voltage stays the same and currents add on the cable to the inverter. In series voltages add and current stays that of one battery. Choose this only on the cable between two batteries.
Why only one cable from the batteries to the inverter?
When batteries are already linked they form a bank. One feeder cable goes to the inverter. Extra feeders can unbalance the bank — we warn if that happens.
How do I change the cable length?
On the Diagram, choose Move, click the cable and type the metres in the box. The label on the cable shows the length but is not editable there.
Why is Save blue or green?
Blue: there are unsaved changes. Green: the last save on the server is up to date. The browser draft saves itself, but that does not turn the button green.
What are the other tabs for?
Sizing lists each cable and breaker with the suggested size. Quantities and prices groups matching metres and units and totals the € you type. FAQ is these questions.
Can I install from this page alone?
No. This is a learning aid. A licensed installer must confirm cable sizes, breakers and installation rules before you buy or install.
This is a learning aid, not a certified electrical design
A licensed installer should confirm cable sizes before you buy or install.