PV projects

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Roof retrofit of 5 houses in
Leiden (NL)

The Zonnewende project consists of ten houses, five of which have been equipped with PV systems during recent renovations. Originally, all ten houses had solar thermal systems installed on the roofs. Constructed in 1977, the houses were the first in The Netherlands utilising active solar systems for both hot water and heating.
Through the years, most of the systems have been deactivated due to malfunctioning. In addition, poor detailing of the roof-integration of the collectors led to severe leakage problems, leading to the necessity of renovation.
In 1992 a feasibility study was carried out for the renovation of the houses with roof integrated PV systems. This study resulted in a proposal to equip 9 of the 10 solar-energy family houses with PV modules. Due to financial reasons, only five of the houses were included in the project.
The goal of this project was to gain experience with architectural and constructional integration of PV in existing buildings, taking into account the individual requirements of the occupants. Through this first renovation project, information can be collected on the influence of the design of an existing building on the design of a PV system.

Houses with roof-integrated PV system. The 6th house has a dummy system.

The following stages can be distinguished.

  1. Preparation of the renovation scheme and the design of the PV roof and integration system. The occupants of the houses are consulted on specific wishes for the renovation, such as additional balconies, dormers, skylights, etc. These wishes must be included in the design.
  2. Negotiations with the municipality, utility and occupants. This leads to the formal approval of the design by the municipality. An agreement on net-metering is made with the utility. The occupant agrees with the design and the financial scheme. NOVEM approves the project.
  3. Realisation of the PV systems. The PV systems are installed turn-key by the supplier, R&S Renewable Energy Systems. On-site inspection of the work is carried out by the architect and by BDA Buro Dakadvies a recognised authority on the subject of roofs and its physical building qualities.
  4. Monitoring of the PV systems. After the realisation of the systems, all of them are monitored globally for a period of two years. The utility EWR has installed two additional meters. This results in a meter for the return supply of energy to the public grid, a meter which measures the amount of energy taken from the grid and a meter which registers how much energy is produced by the PV system.

In addition, three systems are monitored analytically by Ecofys, in accordance with the guidelines of the Joint Research Centre. This detailed monitoring will provide information about, for example, the inverter and the effects of shading on the performance ratio.

Constructional Aspects.

In 1993 the original roofs were in poor condition. There was no moisture or damp barrier in the construction and leakage problems often occurred, either caused by roof problems, malfunctioning of the solar collectors or condensation inside the construction.
In the new construction, the PV modules are mounted in profiles originating from greenhouse technology. At the rear of the PV modules a cavity is required, both for ventilation as well as for the connector boxes on the rear side of the modules.
The necessary air cavity can be obtained by varying the height of the profile as well as by varying the height of the trusses. In practice it is more convenient to maximise the height of the profile.
A vapour-tight layer of 0.3 mm foil between the multiplex and the trusses is required to prevent the diffusion of vapour into the roof construction. This foil also seals the roof while allowing removal of the inside cladding. Between the trusses, 120-mm mineral-wool insulation packages are placed. All of this is covered by a strong vapour-permeable foil, which serves as a wind-, snow-, and water-tight layer.
Small latches are mounted on the trusses and horizontal battens are placed on these latches.
The free space between the battens is necessary to guarantee the drainage. The profile system which carries the unframed modules, is mounted on the battens. A plastic gasket which is slid over the mullion, fixes the modules in place.
The cabling of the PV system is guided into the houses through the original pipes of the solar thermal system.

The roof retrofit during construction and after finishing the projects.

Architectural integration and roof zoning.

The houses originally had two 60° tilted collector areas on the south side of the roof and a tilted roof on the north side. The collector areas are separated by a roof terrace.
Some occupants had specific wishes concerning the renovation, for instance, a dormer in the lower roof, or the replacement of the terrace by an additional bedroom. In order to meet these wishes, and to allow future construction of dormers or replacement of terraces, the following roof zoning was applied.

  • Three zones for the solar panels (the 'PV-zones'): two in the lower roof and one in the upper roof. These zones are not affected by dormers or extensions of the building.
  • A zone in the central part of the lower roof which may be needed to install a dormer. In the upper roof, a zone is defined which may be needed to build an additional bedroom. These two zones will not be used for PV systems.
Model and roof with the zoning system.
Based on the size of the entire roof, it is possible to mount 70 modules on each house. Because of the shading of the panels by the dormer, the panels next to it are omitted. By utilising only the PV zones, the number of PV modules is reduced to 48. The 2.3-kWp PV installations thus created, consist of 48 mono-crystalline R&S IRM modules with a 1.8-kW Sunmaster inverter which is under designed with respect to the peak power to an extent of 78%. The system is grid-connected. Their is a no price difference between buying and selling electricity.
  • PV nominal power/house 2,300 Wp
  • PV nominal power/total 11,500 Wp
  • PV-system operating hours 4,400 hours/year
  • The PV-system is manufactured and assembled by Shell Solar (Helmond, The Netherlands). Monitoring by Ecofys Utrecht. The project is financed by the NOVEM, EWR (utility) and the owners of the homes.

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