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3. Early performance: measurements for Geneva :
For such a high voltage plant, the module specifications have to undertake an insulation voltage of 1'300VDC. Modules are disposed in 7 sheds of 200 modules each, with a very low tilt (5°). Due to the low tilt, the modules are frameless to avoid water, dirt and mosses accumulations. Only one shed has been equipped with framed modules in order to compare the results over a long term.
Connexions of each shed are collected in a coupling box, including safety diodes, para-lightning protections, swiches, and current measurements for each string. Power is driven to the main power cupboard through about 200 m cables. There is no MPT nor other power conditioning system: the array is directly coupled to the trolleybus DC-line, through an ultra-fast swich (URL) and a HF filter.
A monitoring system records all relevant parameters, including the 60 individual string currents, with a very short time step. Data can then be collected in hourly or sub-hourly values for system operating analysis.
3.1 System operation and monitoring :
The Heliotram power plant operation started in July 1999. The operating conditions were satisfactory during the 6 first months up to now. No serious defect was encountered.
The main following tests were conducted during the starting-up :
- Current leakage during an insulation voltage test at 5 kV (the PV modules of Class II are required to be certified for an operating voltage up to 1300V, and the module "fast" connectors has been certified for operation up to 1500 VDC).
- Test the high speed circuit breakers and power DC contactors for high voltage and a large scale of intensities (0.5A to 250 A bidirectional, under 1000VDC).
Monitoring is performed by a PC computer; data are collected all over the array through decentralised data acquisition modules, interconnected by a RS485 bus. The monitoring system records the following data :
- Array voltage
- Grid voltage at injection
- Plus and minus branch global currents
- Individual currents of the 60 module strings
- Fuse and lightning protections states in the connexion boxes, and other general system protections,
- Disconnector states
- Box temperatures, module and ambient temperature, etc.
In order to ensure an early detection of any system misfunctioning, a very fast acquisition rate was chosen, resulting in a great amount of data. For this report, we have 3 periods of detailed data.
3.2 System Performance Data :
Putting together the meteo data from the GAP, and the TPG detailed and hourly data, we obtained 60 days of clean data which have been carefully analysed.
These data are summarised on the table 2 and fig 2. They are presented using the reduced "universal" normalised variables proposed by JRC/Ispra (ref ), which allow to show properties of the system performances itself, independently of the geographical situation, the plane orientation or the system size.
3.3 Input-output diagram
The system's instantaneous behaviour can also be visualised as the Input/Output diagram(fig.3), which displays the System Output energy as a function of the Incident Irradiation in the collector plane.
The linear adjustment indicates the average Power Output, which will be 112 kW for an irradiation of 1 kW/m2.
Dividing by the Module rough area (including frames) indicates the global system efficiency , that is 9.4%.
We can see on the diagram that the dependence is not quite linear: the system production decrease for higher powers, essentially due to temperature effect. This behaviour will be analysed in the next section.