A German utility and one of the world's leading PV module manufacturers have combined forced to prove that large-scale PV can work in the urban environment

The Munich Trade Fair Centre incorporates 7 812 of Siemens Solar's newly developed frameless SM130-L (130 Wp) modules across the roofs of six of its twelve halls. This gives a total array power of 1 016 kWp - by far the biggest large-scale urban PV plant in the world today. Bayernwerk AG, Bavaria's largest power utility, was overall manager of the 14 million DEM (8,4 million USD) project. Siemens Solar as general contractor commenced installation of the plant in August 1997 and officially commissioned the turnkey system in November that year.

The system is innovative in many ways: the large area modules are designed to be manipulated by one person for easy installation; electrical and mechanical connections were designed for on-site simplicity to minimise installation time and cost; and shock-proof connections ensured the safety of field staff during cabling. Perhaps he most significant innovation is that the entire array, consisting of 12 equal sub-arrays, feeds into a central bus system and a single central inverter unit (CIU). Megawatt plants to date have consisted of sub-systems of around 300 kWp feeding into separate inverters connected in parallel on the AC side. But the extremely high resistance of the new modules allows the full array to feed into once central inverter. The CIU actually consists of 3 x 330 kVA standard series inverters, but these operate in master/slave/slave configuration, such that the slave unites are only called into operation when the total array power requires this. Because inverters are less efficient when operating at low power inputs, this CIU arrangement with additional slave switching on demand gives a much better efficiency at lower insolation levels than AC side parallel inverter connection. The plant is expected to generate around 1 GWh of electricity annually for direct use within the centre. This will satisfy around 4% of the annual on-site power demand and offset 1 000 tonnes of CO2 emissions each year.

Information

• Siemens Solar GmbH Germany
  Fax: +49 89 36 59173

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