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Final report of the first prototype of the solar roof tile



This report is owned by the Foundation For A Better World (FFABW) and is under the free Open Source License


Eindrapport van het eerste prototype van de zonnelei3 html 4df1a34453a29f8e



1.  Why a solar roof tile

2.  Results

2.1.  Pros

2.2.  Cons

3.  Conclusion

4.  Proposal


1. Why a solar roof tile

The solar panels only cover part of the roof.
They bring extra weight and do nothing to insulate the roof.
The solar roof tile is the first prototype designed and made to investigate what and how the above problems can be tackled and improved.

Description of the roof tile
The first type of the solar roof tile is made of double-layered glass that is glued into a plastic frame.

Eindrapport van het eerste prototype van de zonnelei3 html 6666e8c04f7d072c
Solar roof tile design drawing prototype 1

Eindrapport van het eerste prototype van de zonnelei3 html a5eec8fa248bdcad


Connection between the solar roof tiles

Solar roof tile top


Eindrapport van het eerste prototype van de zonnelei3 html 97dddb46e9454b9f


Eindrapport van het eerste prototype van de zonnelei3 html 258177205e9ced92

This is the situation that can arise at a temperature of 70 C. This must be taken into account when laying.

Half of the space between the solar roof tiles can be used to lay out on the total width of the roof. The remainder is for shrinkage and expansion due to temperature differences.

Eindrapport van het eerste prototype van de zonnelei3 html 52878ef1f5d240c9

Eindrapport van het eerste prototype van de zonnelei3 html 7e3a286874222dd7

In order not to have an insulation leak at the connection of the solar roof tiles, the bottom part is provided with insulation foam.

Eindrapport van het eerste prototype van de zonnelei3 html c5cdaeb3d37f24ae

The top of the solar roof tile is provided with expansion space and space for a module to connect the solar roof tile to electricity.
There are also screw holes to secure the pan against blowing away.

The plastic edge is made of ABS. Each side of the prototype is made from several pieces. In real production, the sides are each pressed as a part.
The effective covering of the roof by the roof tile is 40 cm in width and 33 cm in height and weighs 4.1 kg. The space between the double glazing is 2 cm. The insulation value “R” depends on the version and can be between 0.33 and 1.
The part that is provided with solar cells is 31.5 cm by 31.5 cm.
Per roof tile, an effective result of 2 W at 0.5 V with full sun exposure is to be expected with the currently selected solar cells. The efficiency depends on the type of solar cells used. Newer or older types can have a higher or lower return.
It is also known that the efficiency of current solar cells is declining.
The ratio between the dimensions indicates that 75% of the roof is equipped with solar cells.
Solar roof tiles that have no yield due to shade, must still be deducted from the roof yield.
Because the edges are provided with a rubber sealing strip, large overlap is not necessary and they can be used on a roof pitch of more than 10 degrees.
A flexible segment is included in the rim to absorb the stress of the pressure difference that arises at high and low temperatures.
The pressure difference is the main cause of double glass leakage. Because the insulation is part of the function of the pan, the guarantee of proper functioning must be guaranteed.
The estimated costs for 1 pan are around € 35.00. It is possible to make a calculation for the depreciation and payback period, but it depends entirely on the existing insulation situation of a building.


2. Results

The design is made to realize the feasibility of a pan replacement with insulation and solar energy generation. It was not the intention to test solar cells. To develop solar cells under the open source license, a much larger budget is needed than that which the FFABW has available.

2.1. Pros

The model could be made in large quantities.
The use of the rubber creates a good wind and watertight connection.
Every roof can now be fitted with solar panels and insulation in one.

2.2. Cons

Because the pan consists of different materials, the production process has been expanded with a higher chance of production errors.
Recycling will cause problems because sealants have been used for adhesion and vapor tightening.
If the insulation needs to be increased, this can be done by increasing the space between the double glazing. However, the tile cannot be used on roofs with a small angle of inclination.
The effective area is only 75% of the entire roof area.
The risk of leakage of the double glazing remains, which makes it possible to retract the roof insulation.
The edges that have to absorb the shrinkage and expansion give a slight reduction in insulation, precisely during the period when the heat loss is greatest.
The solar roof tile can be attached to the roof, but that makes it more difficult to replace a few copies.


3. Conclusion

The effective efficiency of the roof can be higher if a different type is chosen.
The aim is to make solar roof tiles that can last for at least 30 years, provided that the energy efficiency is still sufficient.
The double glass production process has improved significantly in recent decades. Yet there is a chance of insulation loss. If the suppliers knew that the double glazing will last for 30 years, they would also dare to give a similar guarantee, but that is still only 10 years.


4. Proposal

The design of a second prototype that does not work with double glazing and entails more constant insulation. It is also desirable that the materials can be separated better.
Replacing some solar roof tiles should be abandoned because the increasing wind increases the chance of being blown away. This also gives the possibility to use it as facade cladding.


©FFABW december 2019