Open source data logger modules
An open source data logger is being developed to enable accurate measurement of the electrical and the environmental parameters of a small wind turbine installation, while similar data logging concepts can be used for many monitoring aspects in off-grid micro-energy systems. The open source data logger is based on the Raspberry Pi 3 platform and the design focuses on ease of use, robustness and modularity.
Taking advantage of the significant processing capabilities of the Raspberry Pi platform, the data logger features both data acquisition and processing in one device, thus further decreasing the overall cost of the logging unit, currently being a considerable fraction of the overall installation cost. It implements a three phase multifunction energy meter to acquire the AC current and voltage as well as the active and reactive power produced by the wind turbine. In addition, the DC voltage and current are measured with a high accuracy analog-to-digital converter, along with environmental parameters such as wind speed, wind direction, humidity, temperature and barometric pressure.
Preliminary experiments at the NTUA lab facilities indicate high accuracy, less than 1% uncertainty for AC current, at the operating frequencies of the majority of the open source hardware small wind turbines tested at the NTUA.
An Arduino shield has also been developed, featuring the same AC data acquisition modules, for an even lower cost data logger that is focused on robustness and reliability, as a result of the microcontroller architecture (AVR) present on the Arduino platform.
Post-processing and storage capabilities are under research at the moment, along with further improvements, regarding the visualization of the real time measurements, using open source software frameworks, already developed and field tested, such as the one developed in the context of the OpenEnergyMonitor project, namely Emomcms (https://emoncms.org/). Finally, remote monitoring capabilities are being studied, taking into account the particularities present in the majority of small wind turbine installations sites and off-grid micro-energy systems in general (e.g usually no Internet or cellular coverage).