Parameters with Eco-performance of Solar Powered Wireless Sensor Network Hung-Chi Chu (1)1, Fang-Lin Chao (2)1 and Wei-Tsung Siao(3)1 1 Chaoyang University of Technology, Taichung, Taiwan, R.O.C

Green wireless sensor network development platform 2

Wireless Sensor Node

Routing WSN energy-saving data gathered technology 4

TECHNOLOGY Solar powered Wireless Sensor Network Solar panel and LCA data Charging circuit Battery and environment

Solar panel and LCA data Amorphous silicon, the process step is simpler than mono-crystalline cell, therefore the panel requires less energy consumptions in production phase [7]. Mono-crystalline silicate cells have the highest energy conversion efficiency of 14 percent, but it requires the most energy to produce. emits 55 grams of global warming pollutant per kilowatt-hour

carbon emission's point of view solar powered systems are 90 to 300 times lower than those from coal powered plants [8]. This is caused by a two times higher solar cell conversion efficiency for m-Si modules compensates the two 2 times higher energy requirement during manufacture.

Charging circuit The solar energy to battery charge conversion efficiency reached 14.5% PV system efficiency of nearly 15%, and a battery charging efficiency of approximately 100%. Directly charging the battery from the PV system with no intervening electronics matching the PV maximum power point voltage to the battery charging voltage

Battery and environment Lithium-ion batteries is strongly temperature- dependent. operating at high temperatures can result in the destruction of the cell. higher temperatures. Unless heat is removed faster than it is generated, it possible causes thermal runaway [11]. The battery thermal management system must be designed keep the cell operating within its sweet spot avoid premature wear out of the cells. The cycle life quoted in specification assumes operating at room temperature.

GREEN DESIGN CONSIDERATIONS

GREEN DESIGN CONSIDERATIONS

The scenarios individual Circuit move to PCB factory PCB surface mount process Node Chassis assembly Distributed to sale point Network node placement Node connecting testing and trouble shooting Node take back during maintains

Green wireless sensor node 13

Green wireless sensor node

Spec. of wireless node (MCU) MCU clock 24.5MHz FLASH ROM 64K RAM 4K Radio freq frequency 2.4 GHz Max data rate 250kpbs Transmit distance 100m RF channel 16 (5MHz) Power Trans/Receive 29mA/27mA Sleep 4uA Working conditions Supply 2.7 - 3.6V Temperature -20 - 90°C Humidity 10 - 90%

Re-charging battery NOKIA Li-ion battery iNeno Ni-MH battery， 3.7 (V) capacity 1020mAh。 iNeno Ni-MH battery， 9 (V) Capacity 300mAh。

Charging performance (outdoors: 40000-80000 Lux) Initial 2.6V 6V 30 minute 3.6V 3.2V 3V 9V 60 minute 3.7V 3.4V 9.2V 90 minute 3.8V 9.4V 120 minute 150 minute

WSN and panel chosen

With three solar panels in series, it produces electricity for 5. 8V-6 With three solar panels in series, it produces electricity for 5.8V-6.4V and charging current 80mA-235mA. The battery voltage increase rapidly as the ambient light intensity increased. Normally the charging process reaches 95% of capacity within two hour period of time.

Measurement For long term evaluation of system performance, Onset HOBO U12 standalone data loggers were utilized. 12-bit resolution for detecting data, direct USB interface

Charging voltage measurement during 12 hours (light intensity, battery voltage, temperature)

Reliability issues Temperature Panel voltage 26℃ 7.50Ｖ 5.45Ｖ 28℃ 7.28Ｖ 5.35Ｖ 30℃ 7.17Ｖ 5.30Ｖ 32℃ 7.20Ｖ 5.22Ｖ 34℃ 7.23Ｖ 5.16Ｖ 36℃ 7.25Ｖ 5.09Ｖ 38℃ 7.22Ｖ 5.03Ｖ 40℃ 7.19Ｖ 4.97Ｖ solar panel power output voltage, between 26 and 40 degrees there was a drop in power output from a peak of 7.5V down to 7.19V maintaining a lower temperature, the system failure rate will decrease and output power can also be increased.

Solar Panel Configurations Once installed people can not easily change the reception angle Based on the situations of surrounding environment and the sunshine conditions, the actual installation maybe varied.

Measurement of penel temperature Configuration Temperature (a)-c 42.3 (b)-c 37.8 (a)-i 39.4 (b)-i 37.3 Highest temperature is configuration (a)-c, therefore it needs more open space to improve convection Reduce the heat transfer from structure.

Measured panel temperature while outdoor light intensity changed Ta 30 ° C)

Maintenance issue The PV panel has an expected life cycle of 20 years, but without routine maintenance the panel may fail after 10 years. The battery has an expected life cycle of 4 years, but this can be reduced to a range of 1 years. charge controller can last 5 years, depending on the level of misuse. The highest rate of equipment failure occurs with the battery is most often the result of battery misuse.

Conclusions By constantly monitoring the voltage level and smart routing protocol, the WSN with solar gives lower maintenance cost. The network can monitor the status of each node periodically to detect that if a WSN node fails or is defective. Through the integration of wireless sensor network technologies and solar charging system, the development of low power and long lasting networks can be achieved. Eco-design parameters can be compared from both cost and system maintenance in early development phase.