A decentralized wireless solution to monitor and diagnose PV solar module performance based on Symmetrized-Shifted Gompertz Functions

This paper proposes and assesses an integrated solution to monitor and diagnose photovoltaic (PV) solar modules based on a decentralized wireless sensor acquisition system. Both DC electrical variables and environmental data are collected at PV module level using low-cost and high-energy efficiency node sensors. Data is real-time processed locally and compared with expected PV module performances obtained by a PV module model based on symmetrized-shifted Gompertz functions (as previously developed and assessed by the authors). Sensor nodes send data to a centralized sink-computing module using a multi-hop wireless sensor network architecture. Such integration thus provides extensive analysis of PV installations, and avoids off-line tests or post-processing processes. In comparison with previous approaches, this solution is enhanced with a low-cost system and non-critical performance constraints, and it is suitable for extensive deployment in PV power plants. Moreover, it is easily implemented in existing PV installations, since no additional wiring is required. The system has been implemented and assessed in a Spanish PV power plant connected to the grid. Results and estimations of PV module performances are also included in the paper.The authors are very grateful to Esfera Solar Spain and Angel Turpin for technical support and important contributions to this paper. This work has been financially supported by Fundacion Seneca Regional Agency of Science and Technology, Spain (Ref. 15400/PI/10).Molina García, Á.; Campelo Rivadulla, JC.; Blanc Clavero, S.; Serrano Martín, JJ.; García Sánchez, T.; Bueso, MC. (2015). A decentralized wireless solution to monitor and diagnose PV solar module performance based on Symmetrized-Shifted Gompertz Functions. 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Variable link performance due to weather effects in a long-range, low-power LoRa sensor network

When aiming for the wider deployment of low-power sensor networks, the use of sub-GHz frequency bands shows a lot of promise in terms of robustness and minimal power consumption. Yet, when deploying such sensor networks over larger areas, the link quality can be impacted by a host of factors. Therefore, this contribution demonstrates the performance of several links in a real-world, research-oriented sensor network deployed in a (sub)urban environment. Several link characteristics are presented and analysed, exposing frequent signal deterioration and, more rarely, signal strength enhancement along certain long-distance wireless links. A connection is made between received power levels and seasonal weather changes and events. The irregular link performance presented in this paper is found to be genuinely disruptive when pushing sensor-networks to their limits in terms of range and power use. This work aims to give an indication of the severity of these effects in order to enable the design of truly reliable sensor networks

Resilient control in long-range sensor and actuator networks

This thesis will provide an insight on how weather factors such as temperature, humidity and air pressure affects radio links and use this body of knowledge to better understand how to mitigate unnecessary radio switching to take place and then use this knowledge to suggest ways of developing a Link Quality Estimator that utilize online weather data to be able to conduct smart link switching. In the context of this thesis, we focus on the case study of a water utility company as these entities are under increasing economic and environmental pressures to optimise their infrastructure, in order to save energy, mitigate extreme weather events, and prevent water pollution. One promising approach consists in using smart systems. However, a smart infrastructure requires reliable communication links which are difficult to provide. In particular, communication links that are distributed and geographically located in rural areas are highly affected by changing weather conditions, hence efficient control of these distributed hosts requires robust communications. Multiple communication transceivers are used to mitigate this issue and to enable nodes to switch to reliable links. Short-term link quality estimators are used to decide which link to use which often leads to the situation where a link switch is initiated which does not prove helpful in the long term. It is not beneficial to switch a link and associated routing for only a brief duration hence we conduct test bed experiments to better understand the relationships between the radio links and weather factors and use this body of data to devise a LQE that can use this data and then make a smart choice based on this data which reduces switching costs

Poster Abstract: Temperature Hints for Sensornet Routing

ABSTRACT Real-world experiments have shown that the transmission power and the received signal strength of low-power radio transceivers used in sensornets decrease when temperature increases. We analyze how this phenomenon affects the network layer, and find that temperature fluctuations may cause undesirable behavior by sensornet routing protocols such as CTP and RPL. Furthermore, we present an approach to make these protocols robust to temperature fluctuations by augmenting the ETX link metric with temperature hints

Highly reliable, low-latency communication in low-power wireless networks

Low-power wireless networks consist of spatially distributed, resource-constrained devices – also referred to as nodes – that are typically equipped with integrated or external sensors and actuators. Nodes communicate with each other using wireless transceivers, and thus, relay data – e. g., collected sensor values or commands for actuators – cooperatively through the network. This way, low-power wireless networks can support a plethora of different applications, including, e. g., monitoring the air quality in urban areas or controlling the heating, ventilation and cooling of large buildings. The use of wireless communication in such monitoring and actuating applications allows for a higher flexibility and ease of deployment – and thus, overall lower costs – compared to wired solutions. However, wireless communication is notoriously error-prone. Message losses happen often and unpredictably, making it challenging to support applications requiring both high reliability and low latency. Highly reliable, low-latency communication – along with high energy-efficiency – are, however, key requirements to support several important application scenarios and most notably the open-/closed-loop control functions found in e. g., industry and factory automation applications. Communication protocols that rely on synchronous transmissions have been shown to be able to overcome this limitation. These protocols depart from traditional single-link transmissions and do not attempt to avoid concurrent transmissions from different nodes to prevent collisions. On the contrary, they make nodes send the same message at the same time over several paths. Phenomena like constructive interference and capture then ensure that messages are received correctly with high probability. While many approaches relying on synchronous transmissions have been presented in the literature, two important aspects received only little consideration: (i) reliable operation in harsh environments and (ii) support for event-based data traffic. This thesis addresses these two open challenges and proposes novel communication protocols to overcome them

A Survey of Air-to-Ground Propagation Channel Modeling for Unmanned Aerial Vehicles

In recent years, there has been a dramatic increase in the use of unmanned aerial vehicles (UAVs), particularly for small UAVs, due to their affordable prices, ease of availability, and ease of operability. Existing and future applications of UAVs include remote surveillance and monitoring, relief operations, package delivery, and communication backhaul infrastructure. Additionally, UAVs are envisioned as an important component of 5G wireless technology and beyond. The unique application scenarios for UAVs necessitate accurate air-to-ground (AG) propagation channel models for designing and evaluating UAV communication links for control/non-payload as well as payload data transmissions. These AG propagation models have not been investigated in detail when compared to terrestrial propagation models. In this paper, a comprehensive survey is provided on available AG channel measurement campaigns, large and small scale fading channel models, their limitations, and future research directions for UAV communication scenarios

Controls of the sea ice extent in the Ross Sea and development of a wireless sensor network.

Polar sea ice is an important climatic variable. In the Arctic, the steady decrease in sea ice since the 1970's is a direct result of global warming. Due to the different land and ocean distribution in the Southern Hemisphere as well as circulatory effects from the ozone hole, Antarctica is isolated from these changes. These along with other factors have meant that Antarctic sea ice has experienced a slight increase over the same time period. Sea ice extent (SIE) is controlled by physical processes such as wind and ocean currents and temperature gradients, and these contribute to the seasonal and long term patterns in the formation and melting of sea ice. To date, climate models have had only limited success in modelling SIE and its geographic variation. The most commonly used measure to compare observations and models is the total sea ice area. However, observations suggest that the spatial variability of sea ice in response to climate drivers is complicated and differs markedly around the Antarctic. Various studies have suggested schemes for analysing SIE in terms of regional effects, although these schemes are generally somewhat arbitrary and may not be optimal for analysis of certain atmospheric circulation patterns. This research examines a new method for Antarctic sea ice analysis. Using sets of satellite based observations of the SIE over the entire Antarctic continent, the edge of the sea ice can be described in terms of an ellipse. This provides an integrated measure of sea ice that also describes geographical variations while being mathematically simple to describe in terms of the five parameters that completely define an ellipse (centroid coordinates; major and minor axes lengths; rotation angle of major axis). This study demonstrates that the elliptical diagnostic analysis of sea ice captures seasonal and long term behaviour in sea ice well, and this behaviour was analysed in terms of atmospheric circulation patterns such as the El Ni~no Southern Oscillation (ENSO) and the Southern Annular Mode (SAM). Analysis of the ENSO and SAM on the Antarctic SIE show evidence that both are potentially important in controlling sea ice. Patterns in the ellipse parameters display results consistent with previous studies of the effect of ENSO and SAM on sea ice, but the significance of these forcings on sea ice remains an open question. Part of this research involved development of a method to measure the atmospheric parameters that affect sea ice in situ in Antarctica, known as SNOW-WEB. The aim of the SNOW-WEB project is to design and implement a network of weather stations that can communicate wirelessly to each other, allowing near real-time measurement of weather variables over very high spatial and temporal resolutions, in the order of kilometres and minutes. Measuring the wind velocity, temperature and pressure over such high resolutions allow small scale atmospheric phenomena to be analysed in terms of their effects on sea ice. The first deployment of the SNOW-WEB system was in January 2011 spanning the area between Scott Base and Windless Bight on Ross Island in Antarctica. One of the most important components of SNOW-WEB was its power supply system. A system was designed that would allow the SNOW-WEB nodes to operate continuously for over a week by a combination of lead acid batteries and a solar trickle charger. In addition, a research grade weather station was deployed as a reference and calibration point for the sensors on board each SNOW-WEB node. Due to the difficulties involved with Antarctic field work, the expectations for the performance of the SNOW-WEB were conservative, but the SNOWWEB exceeded these comfortably