To investigate during plant operation power conditioning performance, different power management/control techniques, battery State of Charge (SOC) control and battery degradation, PV array/module failure modes and repair techniques, to apply lessons learned from 2 lightning strike damages and to further improve plant reliability.
The Zambelli photovoltaic pumping station is producing precise and reliable basic data for the characterization and evaluation of system and plant component performance. The annually produced photovoltaic array energy increased from 58608 kWh in 1990 to 64581 kWh in 1991, while photovoltaic array energy utilization increased from 57.5% to 64.3%. A new solar sensor was installed to monitor solar irradiance. Improved on site automatic control system software to determine the performance advantage of maximum power point tracking was installed. The software also monitors the main plant components, allowing offline collection of data on efficiencies.
New hardware was installed to monitor battery state of charge and conditions; deep discharge conditions were never reached. Periodic investigations of photovoltaic array wiring identified damaged strings and repairs were carried out. Extensive damage was caused to the plant by lightning strikes and an outline of improved lightning protection has been prepared.
The direct current to direct current to direct current battery charger has performed at excellent efficiency. No decay in performance over 8 years was detected. Performance of the inverters could not be assessed, since measurements were subject to unknown error. Overall pumping efficiency averaged 72 to 73%. No degradation of photovoltaic module performance was detected; only a few modules had to be replaced.
Since start-up in 1984 the ZAMBELLI photovoltaic pumping station supplies drinking water to a village reservoir in the Lessinia mountain area near Verona (Italy) against a pumping head of 350 metres. This completely automatic remote monitored stand-alone system includes two variable frequency AC inverter 35 kW pumps connected directly to the PV array and a battery powered control/monitoring system.
Under Joule programme it is intended to improve further system reliability and to take advantage of this precisely monitored plant as an experimental test bench for PV systems, components, performance prediction, design and sizing techniques. The following activities are foreseen:
- The performance advantage of Max. Power Point Tracking in comparison to constant voltage control and to direct battery connection shall be measured over 1 year.
- Inverter and DC/DC battery charger performance shall be measured and characterized precisely.
- Battery State of Charge (SOC) control shall be validated through monitoring/testing of battery.
- Detailed battery monitoring shall allow to investigate actual battery behaviour (degradation) during lifetime, and to improve diagnostic and maintenance techniques.
- Malfunctions/failures/damages in PV modules, array cabling, diodes, wear and tear, water infiltrations shall be investigated to improve array design criteria.
- A repair/test programme shall identify suitable solutions for in-field PV module repairs, particularly concerning sealant failures caused by solar UV radiation.
- Improvements in lighting protections : lessons learned from 2 lightning strike damages suffered by the plant during its lifetime shall be brought to actual application.
Funding SchemeCSC - Cost-sharing contracts