Solar roof tiles, the invisible PV solution

Solar roof tiles allow photovoltaics to be merged with conventional roof optics

The Dutch manufacturer ZEP B.V. has enabled photovoltaic systems to be combined directly with the roof for the very first time. This means clients who do not wish to abandon the conventional appearance of roofs now have an aesthetic alternative.

The solar roof tiles from ZEP can be used on any roof area that is also suitable for "normal" roof tiles; the load per square metre is the same.
The solar roof tiles are based on the traditional Nelskamp F10U pan tile. This makes the tiles ideal for any renovation or new construction project.

The structure is very simple: 2 solar cells, as can also be found in solar modules, are integrated in one tile and covered with glass. The rear contains a recess for the junction box and the connecting cables on top, these prefabricated with MC4 plugs.

Different versions are available, these completely identical in terms of technology and only differing in their colour and surface.

While the Silverline and Redline series have silver conductor tracks, these are covered black in the Blackline version. The optional “Refined” version of the black tiles has a somewhat more refined, shinier surface.

Electrical planning

As solar tiles basically involve a large number of mini solar modules and these are also installed in shaded regions, the use of module optimizers is indispensable for active shading management or for potential troubleshooting later. This means inverters made by SolarEdge have to be used along with the associated module optimizers as a prerequisite.

Each tiles has a nominal output of 9W. Approx. 30-40 items are connected in series on a SolarEdge optimizer P370. Therefore 30 tiles (60 cells) are typically treated as a normal solar module by the optimizer. The normal design guidelines for SolarEdge inverters remain unchanged.

Physical planning

An exact calculation based on the outer dimensions is difficult, as the files overlap. A simple and effective rule of thumb, indicated as such by the manufacturer, involves planning with 10 items per square metre roof area. The files have the same shape as the conventional roof tile Nelskamp F10U, so there’s no need to pay attention to anything special.


Your customer has a roof area of 20m x 10m

20m x 10m = 200m²
200m² x 10 items = 2000 tiles
2000 tiles / 40 = 50 x optimizer P370
2000 tiles x 9W = 18 kWp

Result: 1x SolarEdge SE17k with a total of 50 x P370 optimizers.

Assembly on the construction site

The assembly is somewhat more complicated, as each tile has to be connected electrically with the next one. As each roof has a different shape, pitch and obstructions over the course of the roof, proper planning in advance is absolutely essential and saves a great deal of time, money and nerves on the construction site. Suitable shading can be established with the help of the roof dimensions. We recommend working in rows, if possible, as the SolarEdge optimizers can easily be accessed for connection and joined at the end. A circuit diagram showing how the planning was realised at the customer can be seen below:

It is clearly discernible that SolarEdge optimizers 1 – 13 can be connected easily without major effort thanks to the favourable arrangement after successful assembly of the roof tiles.


Besides the roof-integrated solutions already available on the market, the solar roof tiles represent an almost invisible PV solution and are primarily of interest for roof renovations or new structures. Many hurdles in the assembly can be eliminated in advance with the right preparations.

Plus points at a glance:

  • Normal ceramic roof tile
  • Aesthetic integration: vertical and horizontal contours in the roof remain visible
  • No adverse shading effects
  • Easy to integrate around skylights/ dormers/ hip rafters/ valley gutters
  • The roof pitch can be in the range from 20-80 degrees
  • Permitted by many municipalities for buildings classified as “protected townscape”