Low-cost Photovoltaic Power for a Swiss Bank

by O. Humm, Switzerland

Introduction

A standardised photovoltaics plant generating 100 kW peak output has been developed for the Union Bank of Switzerland. The plant, on the roof of the Bank's new headquarters, generates electricity at the lowest-ever price for photovoltaics in Switzerland.

Suglio Building

Solar-generated electricity, produced by the standardised photovoltaics plant on the roof of the Bank's "Suglio" building in Manno near Lugano, Switzerland, costs an amazing CHF 0.80/kWh, less than CHF 10,000/kW installed (where CHF is the Swiss franc). The generating costs were obtained from a detailed study taking building and operating costs into account. Even at this low price, photovoltaics cannot yet compete with normal power stations. However, the project emphasises that photovoltaic prices are now on the move; the price is now a factor of two lower than a few years ago.

From 1997, three installations will be operating at the Suglio building:

    the roof-mounted installation mentioned above with a peak output of 102 kW;

  • a 33 kW facade-mounted installation;
  • a 25 kW sun-shade system design.

Total costs are CHF 1.8 million, of which CHF 1 million is for the roof-mounted installation. Investment for the facade-mounted and sun-shade system designs is higher in comparison, because satisfactory integration into the building is more difficult. The energy cost calculation is based on the yield and costs of the optimised 100 kW standard roof-mounted plant.

The roof-mounted installation consists of 1,196 monocrystalline solar cell modules of type BP 585 L, with a peak output of 85 W per module. They were installed in 1996, and are mounted on 2,400 concrete stands of type SOFREL N95 which are made in Switzerland. The plant includes two inverters with a total output of 80 kW, and measuring and control devices.

Table: Breakdown of Net Investment for the Components of the Photovoltaic Installation

table

Strict Guarantees

The promoters and owners of the photovoltaic installation decided in favour of the BP 585 L cells, as these gave the lowest price for the complete plant. However, this depended on each individual system fulfilling minimum criteria.
Suitable criteria were developed specially for "Suglio" and require, firstly, that the contractor guarantees output both at start-up and after ten years' service. If the guaranteed output is not achieved, at the end of this period damages are payable amounting to twice the energy lost. Secondly, if an agreed number of randomly chosen modules do not fulfil the guarantee, the whole plant must be dismantled and returned to the contractor.
The nearby Solar Research Institute at Ispra, was chosen as advisory consultant to verify the results. This cautious procedure on the part of the owners in respect to performance is well founded since, until recently, performance data were always tagged " plus or minus 10", and measurements often showed peak output down 10 to 15% on values forecast. It is hoped that the procedure adopted by the Union Bank of Switzerland in quality-assuring its installation will influence cell manufacturers, as well as sending a positive message to investors.

Smart Cells

In the 1980s, a team at the University of New South Wales developed a modified version of the conventional monocrystalline solar cell. They laid the visible circuitry ie the external metallic conductors in laser-cut channels. Rotated at right angles to the surface, these conductors take up less of the sunshine. Measurements carried out at Cannobio Technical College show an efficiency of 16.2% for the cells and 13.2% for the modules. This type of cell was selected for the Suglio project.

Simple Frames

Since the photovoltaic cells come from abroad, Swiss specialists have no direct influence on their manufacture, but supporting structures and module interconnections are different. In recent years, considerable progress has been made, and in the Suglio project, the SOFREL supporting system and the multi-contact connecting system finally broke the CHF 10,000/kW barrier.
The photovoltaic modules, which are 120 cm high and 52 cm wide, are supported on two concrete frames. These are bedded in the gravel roof-covering at 60 cm intervals, and are unbolted to avoid piercing the weather-proofing. The weight of the frames - 70 tonnes in total - helps to ensure stability against side winds.
The modules are locked onto the frame with the help of a patented locking mechanism. This ingenious device enables module incidence to be set between 10 degrees Celsius and 30 degrees Celsius to horizontal. In Manno, the modules are inclined at 20 degrees to the horizontal, representing a compromise between collector yield and efficient use of roof space.
All modules in a row are connected in series, while the rows themselves are connected in parallel. Pre-assembly of the modules prior to delivery avoids any contact with live components.

Conclusion

Photovoltaic power prices have been greatly reduced through the Suglio project's well-designed building and operating schemes and quality-assured installation. This success is expected to stimulate investment and lead to a continued fall in the price of photovoltaic power.

For more information contact the CADDET Swiss National Team in Aarau

The CADDET Renewable Energy Newsletter is a quarterly magazine published by the CADDET Centre for Renewable Energy at ETSU, UK.

The articles published in the Newsletter reflect the opinions of the authors. They do not necessarily reflect the official view of CADDET.

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