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TERSCHELLING REPAIR AND OPTIMIZATION PROJECT

Cel


The control strategy for grid connected operation has been improved and now functions satifactorily. The overall performance during grid operation was not as good as predicted, mainly due to the malfunction of the maximum power point trackers and decreased battery capacity. The connection of the photovoltaic generater to the battery should be changed to increase system performance and reliability.

The function of the photovoltaic generator poses no problems, but problems do arise with the wind generator, the AC power management and the coverage. The feasibility of autonomous operation has been proved, and can be realised in 2 hours. Coverage of the current load demand is calculated to amount to approximately 62% annually with this system. Extension of the coverage can only be achieved by considerable extension of the photovoltaic/wind system, or, more economically by using a back up diesel generator.

In this system, reactive power can be satisfacterily compensated using fixed compensation capacitors and a 6O kVA synchronous generator. Simplification of the system has been achieved by connecting the wind turbine to the accumulators by a diode bridge.

The number of start up/shut down actions of the wind turbine has been reduced by making it possible to disconnect the capacitors on the asynchronous generator.

The inverter is used to supply power to the 3-phase AC grid from the photovoltaic generator and the battery.

The efficiency of the inverter in the lower load range is less than that reported in 1983. The measured overall efficiency is 87 +
- 2%, the calculated value is 88.5%.

The chosen nominal power of 50 kW is not optimum for grid connected operation. Computer simulation shows that an inverter with 30 kW nominal power would have the highest energy yeild in the Terschelling system, when operating without a battery. For operation with a battery, the optimum power of the inverter is 20 kW.

In a grid connected system, the size of the inverter in a photovoltaic system should be based on the whole system, calculated using a computer design code. In an autonous system, the inverter size must be based on the maximum load.

The battery consists of a 360 cells Varta Bloc 2305 (250 Ah). It is of the posted rod plate type with 1.6% antimony and microporous polyester separaters reinforced with fibre. The battery is divided in 2 parallel banks of 180 cells of 2V nominal.

During normal operation, differences sometimes arise in the performance of the 2 battery groups. At lower charge currents and at discharge, the currents within the 2 battery banks are in good agreement.

The apparent internal resistance can be calculated to be about 0.6 ohms during charge and 0.45 ohms during discharge. This means that the capacity which can be taken from the battery before the final voltage is reached has become small, especially at higher currents.

During periods of charge/discharge, a hysteresis in the voltage occurs of about +
- 0.05 V per cell. After disconnecting the battery, it takes 2hours for the battery to reach equilibrium. Half of this voltage change takes approximately 30 minutes. After restart of charge/discharge, half of this voltage change takes about 5 minutes.

At a current of 12 A, the capacity decreased by about 35%. Increased internal resistance of the battery means that it will not be possible to obtain more than 30 kW of power for the AC grid.

Corrosion of the positive grid and sulphonation of the negative plates cause ageing of the battery. The former is probably caused by overcharging by the reconditioning rectifier and by extended periods of gassing, and the latter is caused by prolonged discharge without effective recharge. The corrosion can severly weaken the weld between the positive plate lugs and group bar. Fracturing could ignite an explosion.

The Lagerwey LW 15/75 wind turbine with 30 metre hub height was selected for the project after a feasibility study concluded that it would have the best economical performance, in comparison with other turbines in the 50 to 80 kWh energy range.

Energy output calculations were performed using the Ecofys program, WINDPRO. The power curve of the wind turbine has been determined and was in accordance with expectations. The energy production was lower than expected due to regular down situations caused by turbine imbalance, which has now been improved by the manufacturer.

At a windspeed of 5 m/s, the noise level of the turbine is 92.2 dB. The turbine does not use air brakes for the protection of the turbine, which means a reduction in noise levels.

The function of a maximum power point tracker (MPPT) is to ensure that the photovoltaic generator operates at the maximum of its current voltage characteristic. The efficiency of the MPPT DC/DC converters have been assessed.

The efficiency curve of some MPPTs in the photovoltaic generator has been measured, and found to be lower than the expected curve. Due to conversion losses, the use of MPPTs can be estimated to lead to a yearly energy production loss of 350 kWh, compared to a direct coupling of the photovoltaic arrays to batteries via a diode.

The maximum power point (MPP) tracking concept does not function properly. The production of an array with an MPPT becomes relatively lower at higher levels of solar irradiation. It is estimated that the malfunctioning MPP tracking concept can cause an energy loss of more than 30% compared with an array directly coupled to batteries.

The photovotaic (PV) generator consists of 2748 polycrystalline silicon modules (AEG PQ/10/20/01) and has a nominal rated power of 50 kW. The principal problems associated with it are glass cracks, cable cracks, earth leaks, and cable ducts. Every year 5 to 8 new glass cracks occur, of which 2 to 5 arise from incorrect fastening, and around 3 arise from vandalism. On average, around 6 cable cracks occur per year which can occur at any place on the cable. The number of cracks occurring in the cable ducts has decreased, while the number of cracks where the cables leave the modules has increased. About 2 modules with earth leaks are detected per year, which mostly have to be replaced since repair is rarely possible. New cable ducts have been fitted with rubber kit and cable ties, which are resistant to weather and seawater, and adhere well to both polyvinyl chloride (PVC) and galvanised iron. Aluminium tape on the top side of the ducts prevents accelerated ageing of the material by ultraviolet radiation. The new ducts reduce moisture penetration and are more accessible for cable repair.

The 14 arrays of the PV generater measured have shown no significant deterioration after 5 years in operation. The performance of the PV generator has improved because of repair of defects. It needs yearly repair for optimum operation.
THE TERSCHELLING PV/WIND PLANT WAS ERECTED IN 1983 WITHIN THE EUROPEAN PV PILOT PLANT PROGRAM. THE SYSTEM IS USED TO SUPPLY ELECTRICITY TO A MARINE TRAINING SCHOOL AND FOR RESEARCH ON THE SYSTEM LEVEL. ECOFYS IS CARRYING OUT THE TERSCHELLING REPAIR AND OPTIMIZATION PROJECT. WITHIN THIS PROJECT SYSTEM COMPONENTS HAVE BEEN IMPROVED IN 1987 AND 1988. THE SYSTEM PERFORMANCE HAS IMPROVED CONSIDERABLY SINCE THEN.

FROM THE SECOND HALF OF 1988 TO 1990 THE CONTROL OF TE SYSTEM IS BEING OPTIMIZED, STARTING IN THE FIRST 6 MONTHS FROM NOW WITH THE CONTROL OF THE BATTERY SUB-SYSTEM. THEN THE CONTROL OF THE POWER CONDITIONERS AND THE ELECTRICITY DEMAND WILL BE OPTIMIZED DURING GRIDCONNECTION. IN THE LAST PERIOD THE CONTROL OF THE SYSTEM WILL BE OPTIMIZED DURING AUTONOMOUS OPERATION. IN THIS PERIOD SPECIAL ATTENTION WILL BE GIVEN TO THE REACTIVE POWER COMPENSATION AND THE COMBINATION OF THE TWO RENEWABLE SOURCES.
A WORKSHOP ABOUT THE LESSONS LEARNED WITH THIS SYSTEM IS PLANNED IN 1990.

THE PV/WIND PLANT HAS SCORED IN ITS FIVE YEARS OF EXISTENSE VARYING SUCCESS. THOUGH THE PRODUCED ENERGY WAS LESS THAN EXPECTED IT CAN BE CONCLUDED THAT THIS IN PRINCIPLE WAS NOT DUE TO THE RENEWABLE ENERGY SOURCES: THE PV MODULES OR THE WIND TURBINE. SMALL PROBLEMS LIKE CABLE CRACKS HAVE CAUSED ENERGY PRODUCTION LOSSES. MANY OF THESE PROBLEMS HAVE ALREADY BEEN RECOGNISED AND IMPROVED IN NEWER PRODUCTS.

Temat(-y)

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Zaproszenie do składania wniosków

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System finansowania

CSC - Cost-sharing contracts

Koordynator

ECOFYS B.V.
Wkład UE
Brak danych
Adres
Kanaalweg 16 G
UTRECHT
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