Elsam. Offshore Windmills. Power Supply for the Measuring Masts at Horns Rev and at Læsø South.

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1 REPORT Distribution: KKJ, PDN December 10, 2002 Phone: Fax: Our ref.: KKA/KKA Report no.: T Doc no..: D Page 1 of 7 Control: Elsam. Offshore Windmills. Power Supply for the Measuring Masts at Horns Rev and at Læsø South. The power supply for the measuring masts was designed in close cooperation with the supplier, oi-electric, who has great experience in stand alone power supplies. A combination of batteries and solar cells were chosen as power supply, as this system is very reliable and only requires a minimum of maintenance. In order to obtain greatest possible reliability, it was decided to divide the power supply into two independent systems one system for the meteorological measuring program and one system for the lights at the mast. Originally the two measuring masts, and thus the power supplies, were alike. These are the two systems described in sections 1 and 2. Since then, changes have been made to the towers. These changes, as well as the reason for them, will be clarified in the history. 1. Meteorological System This power supply system shall alone supply the meteorological measuring program, as well as temporary auxiliary functions in the measuring cubicle, such as lights and two sockets supplied through a 230 V inverter. The power supply for the meteorological system was executed with solar cells, whose charging voltage varies between 30 and 42 V. The design does not include a solar cell regulator, as the battery charging voltage is adjusted to the maximum charging voltage of the solar cells. A better battery charging is thus obtained during the winter months, as in days with strong sun, the solar cells will not be disconnected due to a quick voltage increase in the battery. Specification and design was as follows: is an Engineering company specialised Kraftværksvej 53 In energy and environment DK-7000 Fredericia

2 energy. environment. knowledge. Page 2 of 7 Specification: System voltage 24 V DC ± 10 % Power Consumption 16 W, continuously Peak Output 20 W Ah - Consumption per 24 hrs. 16 Ah Solar Cell Voltage Output peak Installation Batteries Battery Number of Cells / Capacity Nominal voltage Maximum Charging Voltage Charging Applied Charging System V DC 5 x 2 pcs placed in series, type SOL 50 D 500 W The solar cells are installed vertically on the south side of the tower. Vertical installation will reduce the maximum annual production by 30 %, but in turn the production during the winter months is increased by 10 %, which is preferable. Normally the charging during December and January is not large enough, but due to the size of the battery it is possible to keep the measuring program running. SUNICA Ni-Cd batteries, nominal 1,2 V per cell 25 pcs / 1070 Ah, 100 h 33,25 V = 100 % capacity 40 V Due to the reliability a balanced charging system has been chosen, without any type of regulator. The charging voltage may, in optimal weather conditions, theoretically reach 42 V with increased consumption of water to follow (depending on the battery temperature), but since periods of high sun irradiation, and thus very high charging voltage, do not exceed four hours, the battery lifetime is not reduced. Autonomy period 30 x 24 hrs. Battery Safety Factor 2,5 Voltage Supplies DC/DC converter AC/DC inverter 50 W, 24 V 1000VA, 230 V AC

3 energy. environment. knowledge. Page 3 of 7 2. Light System This system shall only supply the lights, which serve as warning lights for the meteorology tower. Equipment Chosen: Number of Lights 2 pcs VEGA VLB-27 Marine LED Beacon Voltage 12 V DC Power Setting 0,32 A Duty cycle 25 % Autonomy period 30 x 24 hrs. Battery Safety Factor 2,5 Solar Cell Voltage Output peak Installation Batteries Battery Charging System Used V DC 2 pcs connected in parallel, type SOL 50 D 100 W As solar cells for the meteorological system 2 pcs EXIDE S4 06/165 Ah in series The maximum battery charging voltage and the solar cell charging voltage are here not in balance as in the meteorological system. The charging must therefore be regulated. The regulator is built up by Zener diodes that begin to be conductive at a battery voltage of 12,5 V. The battery will be charged to a voltage of 13,7 V. When the battery is fully charged, all power will be conducted through the Zener diodes, in which it will be disposed as heat in a cooling plate. 3. Power Supply for 3D Wind Measurements Shortly after the establishment of the measuring mast at Horns Rev, it was decided that a 3D wind measuring program for estimating of turbulence conditions should be designed. Long term it should be a possible to move this system to the mast at Læsø. Due to lack of space at the mast, as well as lower requirements to safety of supply, a hybrid solution was chosen, consisting of one windmill and 4 solar cells. This solution, however, presents both advantages and disadvantages:

4 energy. environment. knowledge. Page 4 of 7 1) During the winter term, when production from the solar cells is low, the production from the wind turbine is high. The opposite applies for the summer term. 2) Physically, the production from a small wind turbine is relatively large compared to solar cells. 3) The wind turbine requires maintenance every six months. The maintenance is done when replacing cup anemometers and does therefore not involve any significant costs. Based on measurements from the measuring system, the following specifications were made for the power supply. Specifications: System Voltage 24 V DC Power Consumption 24 W, continuously Peak Output 65 W Ah Consumption per 24 hrs. 24 Ah Solar Cell Output peak Installation 2 x 2 pcs in series, type SOL 50 D 200 W As power supply for meteorological system Wind turbine Type Windside WS-0,30A (designed for wind speeds of = 60 m/s) Batteries Battery Number of Cells / Capacity Nominal Voltage Charging Charging System Used Autonomy period SUNICA Ni-Cd batteries, nominal 1,2 V per cell 20 stk. / 210 Ah, 100 h 26,6 V = 100 % capacity Like the light system this is also a non-balanced system and so it is necessary to limit the charging of the battery. The principal Shunt Charging has been chosen as regulator for the charging of the battery.this system ensures a very high degree of reliability. The Shunt consists of 40 diodes, connected in series. At an input voltage of 24 V the Shunt will begin to be conductive and at a battery voltage of 29,7 V all power is conducted to the Shunt. No more than 200 W shall be disposed of in the Shunt. 8 x 24 hrs.

5 energy. environment. knowledge. Page 5 of 7 Voltage Supplies DC/DC converter 50 W, 15 V 4. History August 2000: Extra solar Cells at the Horns Rev tower In connection with the surveing of the mast at Horns Rev, it was determined that the tower did not point north-south; it was turned 33º north-east. At that time it was expected that the solar cell production hereby would be reduced by 13 %. It has, however, been determined that the production is only reduced by 5 %. In order to maintain the same safety of supply, the number of solar cells was increased by 2 x 2 pcs connected in series. December 1999: Damage after the Hurricane at Horns Rev During the hurricane on December 3rd 1999 the tower was heavily damaged by waves breaking against the cubicle. The damages are shortly listed below. - DC/DC converter for meteorological system was knocked out of its connector, causing the measuring program to stop - The entire bottom row of solar cells on the mast were destroyed - Cords between the batteries for lights were shook off. The batteries were placed loose on the shelf - Terminal board for 3D measurements were knocked off the cubicle wall - External battery box, placed on the floor in level 6, was destroyed - Windmill was destroyed - Cross bracings on the tower were bent When designing the measuring mast, waves of more than six meters were not expected, due to the low water depth. Based on the experience from the tower, the turbine foundations were raised 3 meters. Subsequently everything on the tower was secured as good as possible. All connectors were secured and batteries were locked. It was not possible to raise the solar cells. The measurements were stopped from December 3 rd to December 14 th, on which date the tower was serviced for the first time after the hurricane. The solar cells were not repaired until January 25 th, During the operational period from December 14 th to January 25 th, only 4 solar cells were charging, but thanks to the size of the battery no problems arose. January 2000: Storm Damage at Horns Rev During the storm, once again one solar cell was destroyed. This was replaced in February February 2000: De-installation of Control Panel for 3D Wind Measurements Since the installation in October, the power supply for the 3D wind measurements had not been running satisfactorily. Therefore it was decided to bring the control panel

6 energy. environment. knowledge. Page 6 of 7 ashore. During the January storm the wind turbine was blown off the mast, probably because of heavy vibrations caused by asymmetry. During the December hurricane the mill had lost a wing and it was not possible to lock or de-install the turbine at the service visit in December. The analysis of the control panel showed that the turbine originally had been delta connected, which means that charging does not commence at wind speed of 12 m/s or more. By star connection charging commences at 5 m/s and only at wind speeds of = 15 m/s the delta connection will provide a higher production than a star connection. In order to avoid i.a. this type of error, a 14-day full-scale test was completed before the first installation. The limited charge from the turbine during the testing period was not detected, because the production from the solar cells was sufficient to keep the measuring system running. When re-establishing the power supply for the 3D wind measurements in August 2000, the turbine was star connected and a new mill control (WGU-22) was installed. The wind turbine was strengthened i.a. by extra bracings, and the battery box was moved to the top of the cubicle. There was not enough space to move the batteries into the cubicle. Since August 2000 the power supply for 3D wind measurements has worked without problems. February 2000: DHI Connected to Power Supply for Measuring System at Horns Rev The power supply for DHI s measuring system for measuring current and water levels was originally based on batteries placed on the seabed. These batteries had to be replaced approx. every six months, which made the operation of this system very vulnerable. It was therefore decided to connect the system to the power supply for the meteorological system. The average consumption for DHI s measuring system was given as 2,7 W. In order to secure against excessive discharge, due to the additional load, an undervoltage relay was installed between the battery and DHI s measuring system. The under-voltage relay will disconnect the measuring system when the battery voltage drops below 30 V. When the battery reaches a voltage of 34 V the measuring system will be reconnected. In this way it is ensured that the battery has reached a certain capacity before the load once again is increased. Furthermore, a DC/DC converter was installed between the battery and the measuring system in order to ensure galvanic separation between the mast and the current and waterlevel meter. Subsequently no problems have arisen in DHI s measuring system due to the power supply. The measuring system has never been disconnected by the under-voltage relay. August 2000: DHI Connected to Power Supply for Measuring System at Læsø South

7 energy. environment. knowledge. Page 7 of 7 Based on several problems with regards to the batteries for DHI s measuring system, and good operational experience from Horns Rev, it was decided to connect DHI s measuring system to the power supply for the meteorological system. The average consumption for the measuring system was given by DHI as 9,2 W, which corresponded an approx. 50% load increase. In order to maintain the safety of supply, 2 x 2 solar cells and an under voltage relay of the same type as the one at Horns Rev, were installed. It was not possible to install more than four solar cells, as it was necessary to leave space for moving the 3D measuring system to Læsø South. Subsequently no problems have arisen in DHI s measuring system due to the power supply. The measuring system has never been disconnected by the under-voltage relay. February 2002: Storm Damage at Horns Rev During the storm four solar cells in the bottom row and one solar cell in the second row were destroyed. The solar cells were replaced in the beginning of March Thanks to the large battery capacity, no problems arose with regards to maintaining the power supply during this period in spite of the fact that only four solar cells were charging. 5. Experience In all the experiences with the power supplies have been good, especially the power supply for the meteorological system. The power supply for the meteorological system at Horns Rev has been operational since May 14 th, The period December 3 rd 14 th 1999 is the only longer period in which the meteorological system has been stopped. Otherwise the measurements have only been stopped during normal maintenance. The measurements stopped in December 1999 because the DC/DC converter for the measuring system was knocked out of its connectors. All connectors have since then been secured. The security of supply at the Horns Rev mast has, to date, been 99 %. The Læsø tower has been operational since April 24 th, 1999 and there have been no power supply failures. This gives a security of supply of 100 %. After the reestablishment of the power supply for the 3D wind measurements on August 31 st, 2000 no operational failures have occurred. Also here, this means a security of supply of 100%.