MEASUREMENT SYSTEM

• The minimum period for monitoring an individual micro-location is one year. This is sufficient to determine the daily and seasonal variability of the wind resources. If the time period is shorter, we can make use of the reference stations’ data (nearby airports, meteorological data). In this case, the wind resources of the rest of the year, which were not measured, are evaluated using the measured data and the abovementioned reference stations’ data.
• The data saved in the internal memory are divided into smaller packets when they are being transferred through the GPRS network, and are sent to the server in this form. Each packet is equipped with a checksum (CRC16), which enables verification of accuracy on the reception side. If the checksum does not match, a repeated transfer of the same packet is requested. When a packet with a certain number of measurements is successfully transferred to the server, it is marked as successfully sent and is deleted from the internal memory. Only then is the next packet sent. This ensures the consistency of all the sent data.
• The data are sent using a TCP/IP protocol. For this, a private APN channel (a protected 3DES/IPSEC channel) is used. This ensures that the data transfer is safe, and no additional protection needs to be implemented in encrypting the sent data.
• On the server, a service is installed that operates in the TCP/IP server mode and “listens” to a specified port. This means that it receives connections in parallel from several measurement stations. Simultaneous connections of measurement stations are thus enabled, regardless of their set data-transfer time intervals.
• Every measurement includes the time of the measurement, and the data on the wind speed and direction, and air temperature and relative humidity. This set of data corresponds to one measurement at an exact time. The data are encoded and transferred in the RAW format. This has the advantage of all corrections and temperature compensations being done on the side of the server. It also means that the corrections can be changed later or re-implemented throughout the measurement history.
• The data are saved in an SQL database. Measurements from all measurement stations are entered into the database. For accuracy, it is important that the ID of the station is also stored with every measurement. This ID is later referenced in processing, analyzing and presenting the data.
• The settings of the measurement station enable setting the data-sampling time, the average-value storing time and the time of the data transfer through GPRS network to the data server. The default settings are as follows: measurement lasts 10 seconds. In this time, an averaging of one-second measured values is performed. After this, the packet is stored in the internal memory as a whole. The unit is then in hibernation mode for 50 seconds. After this, the process is repeated. Every six hours the modem is turned on, a GPRS connection is enabled, and the data is sent to the data server. After the data are successfully sent, the modem is turned off. This achieves optimal operation on the internal battery and charging of the latter on sufficiently sunny days.
• An automatic remote firmware update mechanism is implemented to automatically retrieve firmware upgrades from the remote server through the GPRS network.
• A web application is implemented on the server, enabling registered users to access the measurement stations’ data. The data of any time interval can be viewed graphically, in tables, or they can be exported to a local file for processing in other specialized applications.