دانلود رایگان مقاله انگلیسی اندازه گیری تابش انرژی خورشیدی با یک انرژی کم مصرف انرژی خورشیدی - الزویر 2018

ABSTRACT

Solar energy radiation measurements are essential in precision agriculture and forest monitoring and can be readily performed by attaching commercial pyranometers to autonomous sensor nodes. However this solution significantly increases power consumption up to tens of milliwatts and can cost hundreds of euros. Since many autonomous sensor nodes are supplied from photovoltaic (PV) panels which currents depend on solar irradiance, we propose to double PV panels as solar energy sensors. In this paper, the inherent operation of the low-power solar energy harvester of a sensor node is also used to measure the open circuit voltage and the current at the maximum power point (IMPP), which allows us to determine solar irradiance and compensate for its temperature drift. The power consumption and cost added to the original solar energy harvester are minimal. Experimental results show that the relation between the measured IMPP and solar irradiance is linear for radiation above 50 W/ m2 , and the relative uncertainty limit achieved for the slope is ± 2.4% due the light spectra variation. The relative uncertainty limit of daily solar insolation is below ± 3.6% and is hardly affected by the so called cosine error, i.e. the error caused by reflection and absorption of light in PV panel surface.

4. Conclusions

Solar radiation energy in low-cost and low-power autonomous sensor nodes can be estimated from the PV solar energy harvester in the node. Since parts of the solar energy harvester and the MCU of the sensor node are also used to implement the sensor, only an extra-lowpower MOSFET and a resistor are needed. By taking advantage of the inherent operation of FOCV PFM MPPT, Voc sampling and the duration of the charge and discharge states are used to estimate solar irradiance with temperature drift compensation. A prototype, implemented to assess its performance both as energy harvester and solar radiation sensor, has achieved a power efficiency comparable to commercial lowpower solar energy harvesters IC, such as BQ25504 and ADP5090, and daily solar insolation deviation is below ± 3.6%. This error is similar to that of commercial photodiode-based pyranometers which exhibit similar spectral response uncertainty but, in contrast to the proposed sensor, include optical diffusers to avoid light reflection and absorption. This error, however, has limited effect on the assessment of infection risk of fungus diseases and to estimate evapotranspiration estimation.