Technical Requirements for Solar LED Lamps

09 Sep

As solar photovoltaic technology developed and advanced, solar cell, as a new type of energy, is firstly applied in illumination lamps in civilian areas, solar lighting products have double advantages of environmental protection and energy saving. Solar LED Lighting Products are a new generation of green and eco-friendly lighting products, its main components include solar photovoltaic cell (PV technology) and the semiconductor light source (LED). Because solar LED lighting systems are LED solar lamps which integrate both advantages of solar photovoltaic power generation and LED solid-state lighting, they achieve a perfect combination of new generation of energy and new light source. However, the design of solar LED lighting system concerns many factors such as light source, solar cell system, battery charge and discharge control and so on, failure of any link will cause product defects.

1. First let’s have a look at the composition of solar lamps:
The key factor that makes solar photovoltaic technology combine with LED lighting perfectly is both of them can driven by direct current, low voltage and they can match with each other. Therefore, the combination of the two do not need convert the direct current that solar cell produces into alternative current, which greatly improves the efficiency of the entire lighting system. Meanwhile, with the aid of grid technology or using battery to charge and discharge energy makes LED solar lamps have more obvious advantages.
1). Solar cell panels
2). Charge and discharge controller
3). Battery
4). Load
5). Lamp shell

2. Issues which should be paid attention to during the process of design and use: (take LED lawn lamp as an example)

1). The characteristic of LED is close to the voltage stablizing diode, when the working voltage increases or decreases by 0.1V, the operating current may increase or decrease by 20mA. For security, under normal conditions we use current limiting resistor in series, a great energy loss is obviously not suitable for solar lawn lamps, and LED brightness will change as working voltage changes. Using voltage booster circuit is a good way, you can also use a simple constant current circuit, in a word the current shall be limited automatically, otherwise it will damage the LED.

2). The peak current of normal LEDs is 50 ~ 100mA, reverse voltage is around 6V, be noticed that not to exceed this limit, especially when solar cells is reversely connected or the battery has no load, and the peak voltage of voltage booster circuit is too high, it is likely to exceed this limit and damage LEDs.

3). LED temperature characteristic is not good, when the temperature rises by 5 ℃, luminous flux will decrease by 3%, especially in summer we should be noticed.

4). Discreteness of working voltage is high, operating voltage of LEDs with the same model and same batch may be different, they should not be used in parallel. If they must be used in parallel, current equalization should be considered.

5). Super bright white LEDs have a color temperature of 6400k ~ 30000k. At present, the super bright white LEDs with low color temperature still does not enter the market, therefore LED solar lawn lights made with super bright white LEDs have very poor penetrating capability, so we should pay attention to the optical design.

6). Static electricity has a huge effect on super bright white LEDs, anti-static facilities are necessary when we install LED solar lamps, and workers should wear anti-static wrist. We may not recognize the the damage which caused by static electricity to super bright LEDs by our eyes, but life of LEDs will be shortened.

7). We should specially pay attention to photosensitive sensor among all the system components, solar lights need light control switch, and some designers will often use photosensitive resistor to automatically switch on or off lights, actually solar cell itself is an excellent photosensitive sensor, use it as photosensitive switch, its features are better than photosensitive resistor. There is no problem for the solar garden lights applications, but for solar energy lawn lamp which only uses a 1.2V Ni-Cd battery, solar cell component is composed of four pieces of solar cells in series, the voltage is low, the voltage is even lower under weak light, which causes that it is not dark and the voltage is lower than 0.7V, leading to the failure of light-control switch. In this case, adding one transistor and directly coupling and amplifying, the problem will be solved.

8). The load can be controlled according to voltage value of the battery, solar lights have high requirements on lighting time in consecutive rainy days, which increases the cost of the system. We can reduce the number of LEDs or solar lamps that connect with the battery, or reduce the daily lighting time of solar lamps when the voltage of battery decreases in cloudy and rainy days, which will reduce the cost of the system.

9). flashes and light changes, gradual light dimming is a good way to save energy, on the one hand, it can increase the lighting effects of solar lawn light, on the other hand, the battery can be controlled to output current uniformly by changing flashing duty cycle, and extend working hours of the system, or under the same conditions, the costs can be reduced.

10). three-color primary color energy-saving solar lamp’s switching speed. This issue is very important, it even determines the life of solar lawn lights, three-color primary color efficient energy-saving solar lamp has 10 to 20 times start-up current when it starts, if the system bears such a high current, the voltage will significantly drop, then solar lawn lights will not able to start or start repeatedly, finally will cause damage to the solar lawn lamps.

11). Currently solar energy cell can not be used for lighting on the main road. Main road lighting illumination has statutory illuminance requirements, the present solar cell’s conversion efficiency and price still can not meet these requirements. But in the near future as the improvement of all aspects of technical standards, solar cells will be used for the lighting on the main road.

12). As to the energy storage capacitor, solar cell has a lifetime of over 25 years, the life of ordinary batteries is about 2 to 3 years, so battery is the weakest link of solar power system. Energy storage capacitor can solve the problem to a certain extent. The service life of energy storage capacitor can reach more than 10 years, and the control circuit is simple, but the high price limits its applications, currently energy storage capatitors are only used in some traffic lights and decorative lamps. As the improvement of technical standards and the drop of product price, it will be the most promising and ideal energy storage components which can support solar cells.

In summary, the solar cell is a huge PN junction, it converts the solar energy into electricity. LED is another PN junction which can convert electricity into light, it’s conversion efficiency has been improving continuously, it is believed that the conversion efficiency can soon reach the level of CFL energy saving lamps while the lifetime of LEDs can reach over 10,0000 hours, which is the lighting which can be called true green lighting.



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