Would you like to learn more knowledge for solar lawn light?

If you want to know how to buy an appropriate solar lawn light, it is necessary for you to learn more about it.

Solar lawn light is to exploit the energy of solar cells to work, solar cells converts solar power into electric power when it is radiated by solar in daytime, the electric power would be stored into battery, the battery would provide power for LED lamp when it is in night. Its main advantages are safety, energy-saving, convenient and environmental friendly, etc.

The main component of solar controller is an integrated circuit which includes charging circuit, drive circuit, photosensitive control circuit and PWM (pulse width modulation) circuit, etc.

The lighting source and power system design method of solar lawn light have got rapidly developing in recent years because of its special features. The power of solar law light is small, which is mainly used for decoration, it can be moved easily. In addition, solar lawn light don’t need pave cables and it has high waterproof in outdoor, which presents the irreplaceable advantage. Especially in European and North American market, they have a large demand for this light. In 2002, just in GuangDong and ShenZhen, the solar cells consumption for manufacturing solar lawn light to export has reached 2MW, amount to one third of solar cells yields in China at that year. This year, the developing is extremely progressing, which is out of our expectation.

How to choose lighting source for LED lawn light ?
Presently, most of solar lawn light is to exploit LED as lighting source, the lifespan of LED is long, it can reach over 100,000 hours, low working voltage, it is very suitable to apply for solar lawn light, in addition, its characteristic has got great improvement in the past 5 years, and its cost performance has got greatly improvement as well. Moreover, LED is powered by low voltage, its lighting control cost is low, to make it be easy to adjust strong or weak lighting or turn on or off frequently, and it don’t have any damage to the performance of LED. Its lighting color also can be controlled, to change the distribution of light to have dynamic variable scene, so it is very applicable for solar lawn light.

The improvement of boost circuit efficiency
Usually, most of small power solar lawn light have boost circuit, presently, manufacturers adopt oscillation circuit and electrical inductance to boost. Electrical inductance is to adopt standard color code inductor which is to adopt open magnetic circuit, magnetic flow loss is high, so the circuit efficiency is low. If to adopt closed magnetic circuit manufactures inductance to boost voltage, such as magnet ring, the efficiency of boost circuit would get large improvement. We ever exploited δ10 magnet ring to manufacture electric inductance, under the same condition to make contrast experiment, the efficiency of inductor which is made by closed magnetic circuit has been improved 20%~40% than the inductor which is made by standard color code inductor.

1) The working voltage would become 0.1V when the LED characteristic is closing to voltage stabilization diode, the working current may change around 20mA. For safety, it should utilize series connection and current-limiting resistance under ordinary circumstances. Boost voltage is a good idea, simple constant current circuit also can be adopted, anyway, it should auto to limit current, otherwise it might damage LED.

2) Usually, the Peak current of LED is 50~100mA, it might exceed this limitation to damage LED if the peak voltage of boost circuit is too high.

3) The temperature performance of LED is not good, its luminous flux would decrease 3% if temperature increases 5%, please notice it when use in Summer.

4) The discreteness of working voltage is big, each working voltage of LED has some difference even if they are the same items or batch, which is not good to use parallel connection. If you must use parallel connection, you should consider current-sharing.

5) The color temperature of super brightness LED is 6400L-3000K, presently, low color temperature super brightness LED still don’t enter into market.

6) Static electricity has a big effect to super brightness LED, please prevent electrostatic apparatus when making installation, workers should wear electrostatic prevention wristband, the LED which is damaged by electrostatic can’t be found by eyes at that time, but its lifespan would be shorter.

The charging and discharging control and temperature compensation for battery

As this electric power from solar panel is not stable, the charging and discharging control for battery in solar pv system is more complicated than to control in ordinary battery. The success of charging and discharging control circuit design for solar lawn light would decide the product success, a correct control circuit should include below function: Over-charge protection, over-discharge protection, Reverse-charge protection, and temperature compensation function for battery. In terms of solar lawn light, there don’t have to prevent battery over-discharging if to exploit Ni-Cd battery, if the power of solar panel is not high being relative with battery, over-charging protection function also can be overlooked. That is the reason why most of solar lawn light is to adopt Ni-Cd battery. If it is to adopt other batteries, above function should be considered.

1) Reverse-Charge Protection function.
Usually it is to series connect a diode in the circuit of solar cells, the diode can prevent reverse-charging, this should be Schottky diode whose voltage drop is lower than ordinary diode.

2) Over-Charge Protection Function.
A discharge transistor can be series connected or parallel connected in the input circuit, by voltage to discern the power on/off of circuit control transistor, superfluous electric power from solar cells can be discharged via transistor, to guarantee not more high voltage to charge battery.

3) Besides Ni-Cd battery, other batteries should prevent over-discharging, because battery over-discharge would cause the permanent damage. In addition, solar cells is small rate to discharge to battery, so discharge cutoff voltage don’t be so low.

4) Temperature Compensation.
The voltage control point of battery is variable with circumstances temperature, therefore, solar lawn light should have a reference voltage which is controlled by temperature. It is -3~-7mV℃ for single Lead-acid battery, we use -4mV℃ as usual.

Some solution for Solar Lawn light
1) Light Sensor.
Solar lawn light need have light-operated control, usually designer would exploit photosensitive resistance to realize automatically turning on or off. In fact, solar cells itself is a superb light sensor, to adopt it as photosensitive power switch, its character is better than photosensitive resistance. Regards to the solar lawn light which is just to adopt 1pcs 1.2V Ni-Cd battery, solar panel is made up of 4pcs solar cells with series connection, voltage is low, its voltage is more low under low light circumstance, so that it is lower 0.7V even it is still not arriving night, to cause light-operated switch power no work, just need add one transistor to interconnect and expand under this situation, then this problem can be solved.

2) The Loads can be controlled according to the voltage of battery.
Usually, solar lawn light has a high requirement to sustain for continuous rainy days, which has increased system cost. We can reduce the working LED quantity under the continuous rainy days to cause the voltage of battery decreasing, or reduce the working time of solar lawn light, which can reduce system cost.

3) The Encapsulation for Solar Cells.
Presently the encapsulation type for solar cells has two methods, that is lamination and Epoxy Plate. Lamination craft can guarantee the lifespan of solar panel over 25 years, although epoxy plate is beautiful, most of their lifespan is just 2~3 years. Therefore, the small solar lawn light whose power is under 1W can be encapsulated by epoxy plate when don’t have high requirement for lifespan. For those solar lawn light which has high requirement for lifespan, it is suggested to adopt lamination encapsulation type.

4) Twinkle and Lighting Variation.
Gradual strong and weak lighting are good method for energy-saving, on the one hand it can increase its illumination effectiveness, on the other hand it can control battery to even discharge current by twinkle duty rate, to prolong system working time, or we can reduce the power of solar cells under the same condition, then cost would be reduced largely.