Twelve years on: still going strong home >  pv power >  issue 6 >
Last updated: 18 March 2001

Since 1984, the Italian Electricity Board, ENEL, has been monitoring the performance of an 80 kWp PV plant located on the Island of Vulcano. Twelve years on, the plant is still operating perfectly and it has yielded some valuable performance data.

The Vulcano PV plant on the island of Vulcano, Italy

The PV array consists of 44 kWp of polycrystalline and 36 kWp of monocrystalline modules mounted on galvanized steel supports at 35 degrees inclination and oriented due south. The plant is configured to operate in either stand-alone or grid-connected mode. In stand-alone configuration, the plant supplies AC power via a suitable inverter and two 1400 Ah batteries to a low voltage loal grid, feeding about 50 isolated houses. The grid-connected format utilizes a different inverter and feeds power at 20 kV into the mains. At the time of construction the plant cost 40 million ITL/kWp installed (about 46 000 USD/kWp today), but this was due in part to the high level of monitoring facilities that the system incorporated, partly to the experimental plant dual-mode operating arrangement and partly to high module costs, which were equivalent to 18 USD/Wp - four times more expensive than would be typical now. Today, it is estimated that to replicate the entire plant would cost in the order of 14-18 USD/Wp.

Very few problems have been encountered during the life of the plant. A few modules have had to be replaced due to the cover glass cracking, and there has been some discolouration of cell contacts, but performance measurements confirm that there has been negligible degradation of the array over twelve years operation.

The inverters have also proved generally reliable, apart from a few early troubles (due to sizing errors for instance). The biennial maintenance regime has been sufficient to limit the faults in the stand-alone inverter to two in 10 years. The grid-connected inverter required no maintenance until the tenth year when some capacitors needed to be replaced.

As for the storage system, the original battery was replaced and storage capacity was increased in September 1991.

Recently a dedicated Data Acquisition System was installed to monitor characteristics such as battery State-of-Charge, component performance evaluation and to provide a continuous health status diagnostic facility.

Since commissioning almost twelve years ago, the plant has produced close to 800 MWh of electricity, split fairly equally between stand-alone and grid-tied mode. The overall Performance Ratio - that is the ratio of PV energy actually used to the PV energy theoretically available - during this period was 0,61, with a high of 0,81 being encountered during October 1994 when the plant was feeding to the grid.

On the whole, the plant has produced very positive performance results, which will assist utilities to evaluate the effectiveness of the technology both for interconnection with the grid as a 'fuel saver', and as a visible means of providing power to remote 'island' locations.

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