Integrating PV Modules with Building Materials

by the CADDET Japanese National Team

Introduction

To encourage the use of photovoltaic (PV) power generation in Japan, the power generation costs must be reduced to the same level as those of power purchased from electricity utilities. This can be done by significantly reducing the initial costs of the PV systems. In such systems, excluding the PV modules, the support frames and the installation work account for the majority of the costs. Integrating solar cell modules with the building materials for roofs and walls is therefore expected to be one of the most effective ways to reduce the costs of the systems.

The New Energy and Industrial Technology Development Organisation (NEDO) began a project in 1993, "the R&D of PV Modules Integrated with Construction Materials", which is investigating the integration of solar cell modules into a variety of buildings. The project is being subsidised by the Japanese government until 1996.

Building-integrated PV Moduless

Building-integrated PV modules must perform satisfactorily as power generation systems. However, it is also very important for these modules to be waterproof, easy to work with and aesthetically pleasing. The compatibility of the modules with building codes and standards such as fire-preventive and fire-resistive performance is also critical.
 This R&D project draws on previous studies on reducing the costs of PV modules themselves, removing the need for support frames and permitting the installation work of the modules to be executed as part of building work. The table below shows the R&D targets for three types of PV modules.

 

 The Photovoltaic Power Generation Technology Research Association was commissioned by NEDO to manage this project. Six R&D teams, each comprising a PV module manufacturer, a construction material manufacturer and a housing/construction company have been set up by the Association. Each Team is developing a specific type of building material-integrated PV module and studying:

  • interconnection of PV modules;
  • installation and fastening;
  • maintenance factors like ease of access for repair or replacement;
  • architectural design.

The teams hope to develop PV modules integrated with construction materials which meet building codes and standards and are low in costs and high in reliability. Six PV building materials are under development.

Table: Targets of the R&D Programme

 

Roof-integrated
modules

Wall-integrated
modules

 Flexible
 modules

Generation cost

JPY 25/kWh

JPY 20/kWh

JPY 45/kWh

PV module cost reduction

JPY 170/W

JPY 85/W

JPY 190/W

Durable life

20 years

20 years

10 years

Period of R&D

4 years

4 years

4 years

Market

Detached
 houses

-Commercial
 buildings
 -Apartment
 houses

Exterior covering materials for:
 -roofs and walls  of existing
  buildings
 -mobile units
 -leisure use

Integrating with Roofing Materials

These are PV modules which are mainly used for detached houses. Three forms are being investigated.

Exchangeable PV shingle
 This is a flat panel composed of PV modules that can be easily laid on and taken off a roof. The panel uses polycrystalline or other silicon solar cells. In 1995, a pilot house roofed with these modules was designed and constructed. The R&D team is looking at the structure and composition of a flat roof tile with PV modules which simplifies roofing work.

 

Pre-fabricated PV roof panel
 This is a roof-integrated PV module composed of a panel corresponding to a sheathing roof board and solar roof tiles. The R&D team is looking into the structure by which the PV module is united with a flat roof tile, and the composition with which roofing materials such as solar tiles, roofing paper and sheathing roof boards are bonded in a factory. This will simplify the on-site roofing work and permit mass production of the module. The module uses thin-film ceramic (CdS-CdTe) solar cells. In 1995, the specifications of the roof panel were defined and the safety of the panel for commercialisation evaluated. In 1996, demonstration tests will be conducted by a model house roofed with these PV roof panels.

 

Heat-insulated PV roof panel
 This is an insulating roof panel (not in the form of a roof tile) into which a large-area PV module is integrated together with surface protection glass, roofing paper, an insulation material and a sheathing roof board. The panel uses amorphous silicon (a-Si) solar cells and is designed to combat the initial degradation in the performance of this type of cell by increasing temperature through the panel's insulating structure. In 1995, the panel's performance was evaluated by using a demonstration test house built in 1994.

Integrating with Wall Materials

Two forms of wall-integrated PV modules: a glass curtain wall and a metal curtain wall are being considered for use in large buildings such as commercial buildings and apartment houses.
PV glass curtain wall
 This PV module can be used in the place of precast concrete or glass curtain walls. The module uses crystalline silicon solar cells and the variations in the colour of solar cells or back sheets enhance the flexibility in selecting wall colours for architectural design. In 1995, demonstration walls testing these PV modules were built, and their performance evaluated.
PV metal curtain wall
 The R&D team is looking at the way in which PV modules are combined with an aluminium curtain wall and how this lowers the total costs of the wall-integrated PV module. The module, using polycrystalline silicon PV cells, is designed to improve the efficiency of power generation by radiation cooling fins fitted to the back of the module. In 1995, demonstration walls testing these PV modules were built and their performance evaluated.

Flexible Integration

This is a flexible PV module using amorphous silicon solar cells. Topics for this R&D team include: the composition which would enable the flexible PV module to be used as roofing material; flexible plastic materials that are weatherproof and have excellent light transmittance; and the simple working method of laying surface protection glass on the flexible PV modules. Cutting the module to suit the shapes of roofs is also being investigated.

Conclusion

The purpose of this R&D project is to stimulate the widespread use of PV power generation by significantly reducing costs of PV systems. In 1994, the Japanese government also started a PV power generation promotion programme use which grants subsidies to homes installing PV systems. The next step is to put these building-integrated PV module technologies to practical use as quickly as possible.

For more information contact the CADDET Japanese National Team in Tokyo.

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