The solar road stud is a traffic facility which uses the solar battery as its source of energy, and it does not need to use the accumulator, and it can give out light automatically. The working condition of the solar road stud can be controlled according to the intensity of the brightness of the environment, which is different with the ordinary reflective road stud. The solar street light has the features of easy installation, wireless, maintenance-free and environment protection, and it can be applied on the roads, bridges, areas where fog appears frequently, seaside, riverbanks or accident black spots.
A. The choose of the light source of the solar road stud
Huge progress was achieved on the technology of LED, and the cost performance of it was also increased greatly. The LED has long service time, which can be over 100,000h, and has low working voltage, which is suitable to be used on the solar road stud. In addition, the low voltage DC supply makes the LED has low cost, and the brightness can be adjusted, and the frequently turning on or off will not have negative influence on the features of the LED. Considered from the aspects of reliability, cost performance, color temperature and luminous efficiency, it is wise to choose the LED as the light source. The LED that we choose are the superbright LED, whose rated voltage is 3.3V and working current is 6mA. For the solar road studs are installed on the edge of the roads, only one side to give out light is OK, and 2 LEDs are enough.
B. The choose of the solar battery
The solar battery is a semiconductor which can transform the solar energy into electrical energy through the photovoltaic effect of the semiconductor of PN junction, and it is the core part of the solar road stud. The performance of the solar battery decides the conversion efficiency and the stability of the output voltage, which also decides the performance of the solar road stud directly. The solar battery that we used is the monocrystalline silicon solar battery which performs well. For the total solar radiation and the average peak sun hours are different in different areas, the design and application of the solar road stud is decided according to the geographic position. The relationship between the rated output power and the input power of the road stud is 2-4:1, and the detailed proportion can be decided according to the working time of the solar road stud everyday and the lamination demands in continuous rainy days. The calculation of the power of the solar battery is as below:
Power of the LED: 3.3 V×0.006×2＝0.0396 W, proving the work hour everyday is 14h, and suppose the power of the solar battery is Wt, and efficiency of it is 40%, the effective working time is 5h,
Then: Wt×5 h×40%＝0.0396×14 h
Then: Wt≈0.3 W
C. The choose of the solar battery
For the input energy of the solar battery is unstable, and it can give out light when the surrounding light is weak, the electric storage system should be equipped to make it work effectively. Now the accumulators applied are lead-acid accumulator, Ni-Cd accumulator and the Ni-H accumulator, however, there are weak points if the accumulator is provided as the electric storage system: first, the chargeable accumulator has limit on charge time, which is less than 1000 times, and overcharge will have negative influence on its service time; then, the chemical structure makes it cannot be charged with heavy current; third, the accumulator should have the control circuit to provide over charge and over discharge protection and temperature compensation, which may make the circuit complicated; fourth, the chargeable accumulator use the chemical reaction to charge and discharge the accumulator, and the wastes inside the accumulator may pollute the environment.
So we choose the ultra-capacitor, which is small with large capacity as the energy storage device. Compared with the accumulator, the ultra-capacitor is reliable and it has long service time, which performs well in low temperature condition.
D. Light control switch circuit
The solar road stud should use the light control switch to control the LED. When the like of the surrounding is weak, the LED will turn on to give out light; when the light of the surrounding is bright, the LED will turn off. Some light control switch circuit uses the photoresistor to control the LED, and we use the solar battery as the photosensitive switch, for the solar battery performs better than the photoresistor.
The design of the solar road stud uses the ultra-capacitor and the integrated voltage regulator chip, which makes the whole circuit simple and reliable, and it belongs to the green product. Now the design is applied in our products.
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