Free CEG calculator

Roof solar panel layout calculator CEG

Choose the house location on Maps, enter dimensions and orientation: get an estimated panel layout and local PVGIS solar production. The drawing is a diagram, not a roof survey.

Your roof, step by step

Clear measurements. Two layouts. A summary to review together.

1. Choose the house location

The location is used by PVGIS to estimate solar production. Maps does not measure your roof automatically.

Address to find the house

Find the house on Google Maps ↗

In Maps choose Satellite and mark the roof location. Return here and paste the coordinates or the link to that selected point. Entering an address alone does not select a position.

How to copy the Maps location on a phone or computer

On a phone: press and hold on the roof to drop a pin, open its information and choose Share → Copy link. Alternatively copy its coordinates. On a computer: right-click the roof point and click the first row containing two numbers to copy them.

Paste the two numbers unchanged, for example 41.9028, 12.4964. Do not use directions links or just the map viewport centre. If a link contains no recognisable selected point, use the coordinates.

Paste coordinates or the Maps location link here

No location selected.

Google receives the address when you open Maps; the site contacts Google to resolve a short link. When you request production, the site sends coordinates, slope, orientation and system assumptions to PVGIS, without an address or name. Data details.

Enter numbers without thousands separators: write 3000. Results use English formatting, for example 3,000 W and 3.5 kW.

2. Describe one clear rectangular roof section

Use one roof plane, clear of chimneys, skylights and other obstacles. Calculate multiple sections separately without overlap. Prefilled values are examples.

How will the panels be mounted?Tilted rows also require row spacing and shadow analysis: this model does not size them.

How were dimensions measured?Map depth is horizontal; roof-plane depth follows the slope.

Width parallel to the ridge (m)The ridge is the highest line of the roof.

Depth from ridge towards eaves (m)Measure the clear section down the slope.

Roof slope (°)0° = horizontal. Use a measured or design value; the image cannot determine it.

Which direction does the roof face?Used to assess yield; it does not change how many modules fit the rectangle.

3. Modules and clearances

Module long side (m)Use dimensions from the selected module datasheet.

Module short side (m)Use external module dimensions, not cell dimensions.

Power of one module (Wp)Peak power is not continuous energy production.

Clearance at each edge (m)30 cm is an example, not a regulatory clearance. Enter 0 if already excluded from dimensions.

Gap between modules (m)2 cm is an example: verify against the mounting system.

4. Solar production at your selected location

What would you like to calculate?

PVGIS downloads the yield for the selected point using the slope and orientation entered above. You must know the orientation: we do not assume south for you.

Solar calculation assumptions

Crystalline silicon panels, fixed system, terrain horizon included. These assumptions do not check shading from trees, chimneys or nearby buildings.

System losses (%)

14% is a starting assumption for system losses. PVGIS models temperature and incidence-angle effects separately. This is not battery efficiency.

Airflow behind modules

Your starting estimate

Geometric estimate of two regular grids, not the absolute installable maximum. Shading, structural capacity, wind/snow, required clearances, fixings, wiring and electrical compatibility need an on-site assessment.

Second view: panels on your own roof photo

Optional, with no paid services. Upload your own overhead photo and mark the four corners of the same rectangular area used in the calculation. The same panels and clearances shown in the diagram will be drawn.

The photo must show one clear roof plane, with all edges visible. Do not use a street-level photograph: perspective can hide parts of the roof. This preview does not measure the house or detect obstacles.

How to prepare a roof photo or screenshot

Open the Google Maps link above and find the house.
Choose a top-down Satellite view without 3D tilt and zoom in to show the whole roof plane.
If you are allowed to use that image, save a screenshot using your phone or computer controls. Keep logos, copyright and attribution visible. Alternatively use your own overhead photo.
Return here, press “Choose a roof photo”, and select the saved image.
Mark the four corners of the measured area following the instructions below: the panels from the diagram will appear on the photo.

A screenshot is a picture of your screen. You can close Maps afterwards. The image does not replace the geographic point: for local production, import and confirm the coordinates too.

Choose a roof photo (JPG, PNG or WebP; maximum 15 MB)

The photo is processed only in your browser: it is not uploaded to the server or sent to Carmine. Use images you are allowed to use and keep any attribution. No photograph is downloaded automatically from Google.

Panels are an illustration with frames and cells, not a photograph of an installed system. Confirm the layout to download a PNG. The original photo and attribution remain visible.

Summary to send to Carmine

Discuss with Carmine

How the calculation works

The model subtracts edge clearances, compares portrait and landscape modules and selects the grid with more whole modules. Gaps are included. With plan-view dimensions, only the depth down the slope is converted by dividing by the cosine of the slope angle.

For each side: count = floor of (usable space + gap) ÷ (module side + gap). Power = module count × Wp ÷ 1,000. Annual energy = kWp × local yield in kWh/kWp. In PVGIS mode, yield comes from the European Commission service for the selected coordinates, slope, orientation and losses; monthly values are scaled to the calculated capacity. This is potential production, not self-consumption or guaranteed energy after battery losses.

Are satellite images enough?

They help locate the house and its orientation. They do not certify dimensions, slope, shadows or roof condition; imagery may also be outdated.

Can a flat roof be calculated the same way?

Only for modules parallel to the plane. Tilted rows and east-west mounting systems require their own spacing and shading assessment.

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