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Technical Requirements for Solar LED Lamps

Update:05 Aug 2019
Summary:

With the development and progress of solar photovoltaic […]

With the development and progress of solar photovoltaic technology, as a new energy source, solar cells are first used in lighting fixtures for civil use. Solar lighting products have dual advantages of environmental protection and energy saving. Solar LED lighting products are a new generation of green environmental lighting products. Its main components include solar photovoltaic cells (PV technology) and semiconductor lighting sources (LED). Because the LED solar lamp integrates the advantages of solar photovoltaic power generation and LED solid-state lighting, and achieves the perfect combination of new generation of energy and new light source. However, in the design of solar illumination lamps, many factors are involved, such as light source, solar cell system, battery charge and discharge control. Any problem in any link will cause product defects.
First, let's understand the composition of solar lamps: the key to the perfect combination of solar photovoltaic power generation technology and LED lighting is that they are both DC, low voltage and can match each other. Therefore, the combination of the two does not need to convert the direct current generated by solar cells into alternating current, thus greatly improving the efficiency of the entire lighting system. At the same time, with the help of grid-connected technology or battery charging and discharging energy, its advantages are more obvious.

1. Solar panels
2. Charge and Discharge Controller
3. Batteries
4. Load
5. Lamp Shell

2. Problems needing attention in design and application: (Take LED lawn lamp as an example)
1. The characteristics of LED are close to voltage regulated diode. The working voltage varies 0, 1V and the working current may change about 20mA. In order to be safe, the series current limiting resistor is usually used, and the great energy loss is obviously not suitable for the solar lawn lamp, and the brightness of the LED varies with the working voltage. It is a good way to use boost circuit or simple constant current circuit. In a word, we must automatically limit the current, otherwise we will damage the LED.
2. The peak current of general LED ranges from 50 mA to 100 mA, and the reverse voltage is about 6V. Be careful not to exceed this limit. Especially when the peak voltage of boost circuit is too high and the solar cell is connected back or the battery is unloaded, it is likely to exceed this limit and damage the LED.
3. The temperature characteristic of LED is not good. The temperature rises by 5 C and the luminous flux decreases by 3%. Attention should be paid to the use of LED in summer.
4. The working voltage of the same type and batch of LED has some differences, so it is not suitable for parallel connection. It must be used in parallel and current sharing should be considered.
5. The color temperature of super bright white LED is 6400k~30000k. At present, ultra-high brightness white LED with low color temperature has not entered the market, so the penetration ability of solar lawn lamp made with ultra-high brightness white LED is relatively poor, so attention should be paid to optical design.
6. Static electricity has a great influence on ultra-bright white LED. When installing, anti-static facilities should be provided, and workers should wear anti-static wrists. Ultra-bright white LEDs injured by static electricity may not be visible to the eyes at that time, but their service life will be shorter.
7. Attention should be paid to the photosensitive detector in the system combination. Solar lamps need photocontrolled switches. Some designers often use photosensitive resistors to switch lights automatically. In fact, solar cells themselves are excellent photosensitive sensors. Using them as photosensitive switches has better characteristics than photosensitive resistors. The application of solar courtyard lamp is not a big problem, but for a solar lawn lamp which only uses one or two VNi-Cd cells, the solar cell components are composed of four solar cells in series. The voltage is low and the voltage is lower under weak light, so there is no black voltage lower than 0 or 7V, which causes the failure of the light-controlled switch. In this case, as long as a transistor is directly coupled and amplified, the problem can be solved.

8. Controlling the load size according to the battery voltage, the solar lamp often requires a high maintenance time in continuous rainy and cloudy days, which increases the cost of the system. We reduce the number of LEDs or energy-saving lamps connected when the battery voltage drops in continuous rainy days, or the daily light-emitting time of solar lamps, which reduces the cost of the system.
9. Scintillation and dimming is a good way to save energy. On the one hand, it can increase the illumination effect of solar lawn lamp, on the other hand, it can control the average output current of storage battery by changing the duty cycle of scintillation, prolong the working time of the system, or reduce the cost under the same conditions.
10. Switching speed of high-efficiency energy-saving lamps with tricolor primary colour. This problem is very important. It even determines the service life of the solar lawn lamp. When the three-color high-efficiency energy-saving lamp starts, the starting current is as high as 10-20 times. When the system withstands such a large current, the voltage will drop dramatically. The solar lawn lamp can not start or start repeatedly, resulting in the final. Damage.
11. At present, solar cells can not be used in the main road lighting. The illumination of highway trunk road has statutory illumination requirement, which can not be met in terms of conversion efficiency and price of solar cells at present. But in the near future, with the improvement of all aspects of technology, solar cells will be used in highway lighting.
12. With regard to energy storage capacitors, the service life of solar cells is more than 25 years, and that of ordinary batteries is 2-3 years. Therefore, storage batteries are the weakest link in the solar power system. Energy storage capacitance can solve this problem to some extent. Energy storage capacitor can be used for more than 10 years, and the control circuit is simple, but the high price limits its application. At present, it is only used in some traffic lights and decorative lights. With the improvement of technology level and the decrease of product price, it will be an ideal energy storage component for solar cells. In summary, solar cells are a huge PN junction that converts solar energy into electricity. LED is another PN junction that can convert electric energy into light. Its conversion efficiency is constantly improving. It is believed that it will soon reach the level of energy-saving lamp, but its service life can reach more than 100,000 hours. This is the true meaning of green lighting.

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