Solar cells have a unit called "Wp". What does this mean?

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How to choose economical and practical solar lamps?

With the development and progress of solar photovoltaic technology, it is first applied to civil lighting lamps. In recent years, due to the dual advantages of environmental protection and energy saving, the application of solar garden lights, solar lawns and solar decorative lights has gradually formed a scale. How to choose a solar lamp product that is more suitable for local climate conditions and economical and practical among many dazzling commercial advertisements? This has always been the last question of users?

In the design of solar lighting, many factors are involved, such as light source, solar battery system, battery charge and discharge control, etc. Any problem in any link will cause product defects. Let's first understand the composition of solar lamps!

1, solar panels

2. Charge and discharge controller

Step 3: Battery

4. Load

5. Lamp shell

solar cell

The main function of solar cells is to convert light energy into electric energy, which is called photovoltaic effect. Among many solar cells, three kinds of solar cells are common and practical: monocrystalline silicon solar cells, polycrystalline silicon solar cells and amorphous silicon solar cells. In the eastern and western regions with abundant sunshine, polysilicon solar cells are better, because the production process of polysilicon solar cells is relatively simple and the price is lower than that of single crystal. In recent years, the conversion efficiency has been continuously improved. In the southern region with more rainy days and relatively insufficient sunshine, it is best to use monocrystalline silicon solar cells, because the electrical performance parameters of monocrystalline silicon solar cells are relatively stable. Of course, in the case of weak indoor sunlight, amorphous silicon solar cells are better, because amorphous silicon solar cells have lower requirements for solar illumination conditions.

First of all, for any solar lamp product, we must first understand solar cells. Solar cells have five electrical performance parameters:

1, Isc is short-circuit current.

This is the peak current.

3.Voc is the open circuit voltage.

4.Vm is the peak voltage.

5.Pm is the peak power.

Pm is the peak power = Im is the peak current ×Vm is the peak voltage.

Note: The above calculation is based on the external characteristics of solar cells.

For a single solar cell, it is a PN junction, which has all the characteristics of PN junction except that sunlight can generate electricity on it. Under standard lighting conditions, its rated output voltage is 0.48V V V. Solar cell modules used in solar lighting lamps are all connected by a plurality of solar cells.

Users can look at solar cells first to understand the price, performance and stability of solar lighting. I will introduce them according to the load and battery.

Charge and discharge controller

No matter the size of the solar lamp, a good charge and discharge control circuit is essential. In order to prolong the service life of the battery, it is necessary to limit its charging and discharging conditions to prevent overcharge and deep discharge of the battery. In addition, because the input energy of solar photovoltaic power generation system is extremely unstable, the control of battery charging in photovoltaic power generation system is more complicated than that of ordinary batteries. For the design of solar lamp, the success or failure often depends on the success or failure of charge and discharge control circuit.

Without a good charge and discharge control circuit, it is impossible to have a good solar lamp. The charge-discharge controller must have the following characteristics:

1, anti-reverse charging control

2. Anti-overcharge control

3. Overdischarge prevention and control

4. Temperature compensation

storage battery

Because the input energy of solar photovoltaic power generation system is extremely unstable, it is generally necessary to configure battery system to work, and solar lamps are no exception. Generally, there are lead-acid batteries, nickel-cadmium batteries and nickel-hydrogen batteries, and their capacity selection directly affects the reliability and price of the system. The selection of battery capacity should generally follow the following principles: firstly, under the premise of meeting the requirements of night lighting, try to store the energy of solar cell modules during the day and store the electric energy that meets the requirements of night lighting in continuous rainy days. The battery capacity is too small to meet the needs of night lighting, and the battery capacity is too large. On the one hand, the battery is always in a power-off state, which affects the battery life and causes waste.

The choice of storage battery also depends on the solar cell and load, which we will introduce in the following system design.

load

Solar lighting products take energy saving and environmental protection as advantages, and of course the load should also be energy-saving and long-lived. We usually use LED lamps, 12V DC energy-saving lamps and low-pressure sodium lamps.

At present, most lawn lamps use LED as light source, with long service life, exceeding 100000 hours and low working voltage, which is very suitable for solar lawn.

Courtyard lamps generally use 12V DC energy-saving lamps, and the voltage DC of DC energy-saving lamps has no inverter, which is convenient and safe.

Street lamps generally use 12V DC energy-saving lamps and low-pressure sodium lamps, with high light efficiency (up to 200LM/W). However, due to the high price of low-pressure sodium lamp, it is rarely used.

brachiopod

We have collected a lot of information about foreign solar lamps, and most of them choose energy saving between beauty and energy saving. The appearance requirements of lamps are not very high, but they are more practical. At present, many manufacturers have beautiful appearance and choose stainless steel shell. But what about the performance? This makes us think again!

system design

The key to a good solar lamp product lies in the system design. What is a reasonable system design? Then let's first understand several important factors that affect the system!

latitude

Annual total radiation on the surface of solar array

Maximum number of days without sunshine

Daily power consumption

Average daily peak sunshine hours

Let's think about it: What will happen if solar cells are not charged enough to discharge every day? If it rains for several years in a row, can the system still be on? These problems need the careful design of our designers. Next, I introduce a simple method to judge the performance of solar lighting system: the load power of the system must be known, 1: the power of solar cells must be more than 4 times higher than the load power before the system can work normally. 2. The battery capacity must be more than 3 times the daily power consumption of the load (in the western region), and it is better to be more than 5 times in the southern region.

A solar lamp

1 external characteristics of solar cells

From the application point of view, everyone is mainly concerned about the external characteristics of solar cells. First of all, for a single solar cell, it is a PN junction, which has all the characteristics of PN junction except that sunlight can generate electricity on it. Under standard lighting conditions, its rated output voltage is 0.48V V V. Solar cell modules used in solar lighting lamps are all connected by a plurality of solar cells. It has a negative temperature coefficient, and every time the temperature rises by one degree, the voltage drops by 2mV.

Solar cells generally have the following parameters: Isc is short-circuit current, Im is peak current, and Voc is open-circuit voltage. Vm is the peak voltage and Pm is the peak power.

In use, the solar cell will not be damaged by open circuit or short circuit. In fact, we use this feature to control the charging and discharging of the system battery.

Problems needing attention in the use of solar cells

2. 1 solar cell power supply selection

The output power Wp of the solar cell we are talking about is the output power of the solar cell under standard solar illumination conditions, that is, the standard defined by the European Council is 10 1, the radiation intensity is 1000W/m2, the air mass is AM 1.5, and the battery temperature is 25℃. This condition is similar to the sun around noon on a sunny day (it can only be close to this value in the lower reaches of the Yangtze River). This is not what some people think. As long as there is sunshine, there will be rated output power, and even solar cells can be used normally under fluorescent lamps at night. In other words, the output power of solar cells is random, and the output power of the same solar cell is different at different times and places.

The design of solar lamp is related to the use area of the lamp. The relationship between the rated output power of solar modules and the input power of lamps in East China is about 2~4: 1, and the specific ratio depends on the daily working hours of lamps and the lighting requirements of continuous rainy days. In addition, the output power of the solar cell is about 120W/m2.

2.2 Selection of battery capacity

Because the input energy of solar photovoltaic power generation system is extremely unstable, it is generally necessary to configure battery system to work, and solar lamps are no exception. Generally, there are lead-acid batteries, nickel-cadmium batteries and nickel-hydrogen batteries, and their capacity selection directly affects the reliability and price of the system. The selection of battery capacity should generally follow the following principles: firstly, under the premise of meeting the requirements of night lighting, try to store the energy of solar cell modules during the day and store the electric energy that meets the requirements of night lighting in continuous rainy days. The battery capacity is too small to meet the needs of night lighting, and the battery capacity is too large. On the one hand, the battery is always in a power-off state, which affects the battery life and causes waste.

2.3 the choice of solar cell packaging form

At present, there are two main packaging forms of solar cells: lamination and glue dripping. Lamination process can ensure the working life of solar cells over 25 years. Although the glue dripping was beautiful at that time, the working life of solar cells was only 1~2 years. Therefore, the low-power solar lawn below 1W can be encapsulated by dripping glue, and the laminated packaging is recommended for solar lamps with specified service life. In addition, there is a kind of silica gel used to encapsulate solar cells by dropping glue, which is said to have a working life of 10 years.

2.4 Selection of installation inclination angle of solar cell and decorative cover

Many solar lamp factories put solar cells horizontally for the sake of beauty. In this case, the output power of the solar cell will be reduced by 15%~20%. If a decorative cover is added to the solar cell, the output power of the solar cell will be reduced by about 5%, and the solar cell is expensive. We have collected a lot of information about foreign solar lamps, and most of them choose energy saving between beauty and energy saving. The ideal tilt angle of solar cells in the lower reaches of the Yangtze River is about 40 degrees, and the direction is due south.

2.5 heat island effect

Generally, a single solar cell cannot be used, but actually a solar cell module is used. The solar cell module is composed of a plurality of solar cells to achieve the desired voltage value. When the solar cell module is used, if a single solar cell is shielded, such as leaves and bird droppings, the shielded solar cell will heat up and be damaged under strong sunlight, so that the whole solar cell module will be damaged. This is called the heat island effect. In order to prevent the heat island effect, solar cells are generally placed obliquely, so that leaves and so on can not be attached, and at the same time, anti-bird needles are installed on solar cell modules.

3 Control of battery charging and discharging in solar lamp

No matter the size of the solar lamp, a good charge and discharge control circuit is essential. In order to prolong the service life of the battery, it is necessary to limit its charging and discharging conditions to prevent overcharge and deep discharge of the battery. In addition, because the input energy of solar photovoltaic power generation system is extremely unstable, the control of battery charging in photovoltaic power generation system is more complicated than that of ordinary batteries. For the design of solar lamp, the success or failure often depends on the success or failure of charge and discharge control circuit. Without a good charge and discharge control circuit, it is impossible to have a good solar lamp.

3. 1 Anti-reverse charging control

Generally speaking, the function of preventing reverse charging is to connect a diode in series in the solar cell circuit to prevent reverse charging. This diode should be a Schottky diode, and the voltage of Schottky diode is lower than that of ordinary diode. In addition, the field effect transistor can also be used to control the function of preventing reverse charging. Its tube voltage drop is lower than that of Schottky diode, but its control circuit is more complicated than before.

3.2 Anti-overcharge Control

In order to prevent over-charging, a discharge transistor can be connected in series or in parallel in the input circuit, and the voltage discrimination circuit controls the switch of the transistor to release excess solar cell energy through the transistor to ensure that there is no excessive voltage to charge the battery. The key is to prevent the choice of overcharge voltage, and the single lead-acid battery is 2.2 V.

3.3 Anti-Overdischarge Control

Except nickel-cadmium battery, other batteries should generally have the function of preventing battery from overdischarge, because overdischarge will cause permanent damage to the battery. It should be noted that the solar cell system generally discharges at a smaller rate than the storage battery, so the discharge cut-off voltage cannot be too low.

3.4 Temperature compensation

Temperature compensation, the control point of battery voltage changes with the ambient temperature, so the solar lamp system should have a temperature-controlled reference voltage. For a single lead-acid battery, it is -3~-7mV/℃, and we generally choose -4mV/℃.

4 the choice of solar lamps and lanterns light source

At present, most lawn lamps use LED as light source, with long service life, exceeding 100000 hours and low working voltage, which is very suitable for solar lawn. In particular, LED technology has achieved a key breakthrough, and its characteristics have been greatly improved in the past five years. At the same time, the cost performance has also been greatly improved. In addition, the LED is powered by low-voltage DC, so the light source control cost is low, and the light and shade can be adjusted frequently without adversely affecting the performance of the LED. It can control color, change light distribution and create dynamic illusion, so it is especially suitable for solar lawn. There are many inherent characteristics, which will cause bad consequences if you don't pay attention when using them. At present, the luminous efficiency of LEDs sold in the market can only reach 15Lm/W, which can only reach 1/3 of tricolor high-efficiency energy-saving lamps, and the luminous efficiency of tricolor high-efficiency energy-saving lamps can reach 50Lm/w ~ 60lm/w. From the price point of view, the current production cost of tricolor high-efficiency energy-saving lamps (including electronic ballasts) per lm is 0.022 yuan, 2002. At present, the production cost per Lm is high, and the price varies greatly. In terms of service life, the service life of tricolor high-efficiency energy-saving lamps (including electronic ballasts) can reach 6000 hours, and the led can reach 100000 hours or more. On the surface, the service life of led is dozens of times that of tricolor energy-saving lamps (including electronic ballasts), but this is not the case. At present, most ultra-bright white LEDs are used in solar lawn, and the time (life) when the luminous flux of ultra-bright white LEDs reaches 50% of the initial intensity at 20mA is less than 10000 hours, which has been proved by Fudan University Electric Light Source Research Institute. That is to say, at present, LED is not the best solar lawn light source in many cases, unless it is a low-grade solar lawn with a service life of only 1~2 years, or a solar lawn with a service life of less than1w. For solar lawns above 1W, it is best to use three-color high-efficiency energy-saving lamps. At present, there are 30~40 ultra-bright white LEDs in the solar lawn, and the input power is above 2W. In this case, if you use tricolor high-efficiency energy-saving lamps, the price is only110 of LED, and the luminous flux is four times of the original. Now, 2~ 10W low-voltage DC tricolor high-efficiency energy-saving lamp has been successfully developed, and its service life can reach 6000 hours. According to the above analysis, we think that the low-power solar lawn below 1W should use LED as the light source, which has the function of adjusting light and shade and switching frequently. However, special attention should be paid to the maintenance rate of luminous flux when using ultra-bright white LED, otherwise it will easily lead to accidents. For high-power solar lawn, it is more reasonable to use tricolor high-efficiency energy-saving lamps at present. What needs to be emphasized here is that the above conclusions are only the current analysis. With the improvement of LED technology, the price will drop, and the above conclusion needs to be changed.

Considering the reliability, cost performance, color temperature and light efficiency of solar garden lights, we think that the most ideal light source at present should be tricolor high-efficiency energy-saving lamps.

Five points for attention in using LED

1) As the working voltage of LED changes by 0. 1V, the working current may change by about 20mA. For safety reasons, series current limiting resistors are usually used. The huge energy loss is obviously not suitable for solar lawn, and the LED brightness changes with the working voltage. It is a good idea to use a boost circuit or a simple constant current circuit. In short, the current must be automatically limited, otherwise the LED will be damaged.

2) Generally, the peak current of LED is 50~ 100mA, and the reverse voltage is about 6V. Be careful not to exceed this limit, especially when the solar cell is connected reversely or the battery is dead, and the peak voltage of the booster circuit is too high, it is likely to exceed this limit and damage the LED.

3) 3) The temperature characteristics of LED are not good. When the temperature rises by 5℃, the luminous flux decreases by 3%. Pay attention in summer.

4) The working voltage is discrete, and the working voltages of the LEDs of the same model and batch are different to some extent, so it is not suitable for series use. It must be used in parallel, and current sharing should be considered.

5) The color temperature of ultra-bright white LED is 6400k~30000k. At present, the ultra-bright white LED with low color temperature has not entered the market, so the solar lawn made of ultra-bright white LED has poor light transmission ability, so attention should be paid to the optical design.

6) Static electricity has a great influence on ultra-bright white LED. There should be anti-static facilities during installation, and workers should wear anti-static wrists. The ultra-bright white LED damaged by static electricity may not be visible to the naked eye at that time, but its service life will be shortened.

Several problems in 6 system combination

1) photosensitive sensor, solar lamps need light-controlled switches, and some designers often use photoresistors to automatically switch the lamps on and off. In fact, the solar cell itself is an excellent photosensitive sensor with better characteristics than the photoresistor. It is not a big problem for solar garden lights, but for solar lawns, only one 1.2VNi-Cd battery is used, and the solar cell module is composed of four solar cells in series. The voltage is low, even lower in weak light, so that the voltage is lower than 0.7V before dark, which leads to the failure of the light-controlled switch. In this case, the problem can be solved by adding a transistor for direct coupling amplification.

2) The load is controlled according to the battery voltage, which requires the solar lamp to last for a long time in continuous rainy days, which increases the system cost. We reduce the number of LEDs or connected solar lamps, or reduce the daily light-emitting time of solar lamps when the battery voltage drops in continuous rainy days, thus reducing the system cost.

3) Blinking and dimming are good ways to save energy. On the one hand, it can increase the irradiation effect of solar lawn; On the other hand, the average output current of the battery can be controlled by changing the flicker duty ratio, which can prolong the working time of the system or reduce the cost under the same conditions.

4) Switching speed of tricolor high-efficiency energy-saving lamps. This problem is very important and even determines the service life of solar lawn. When the tricolor energy-saving lamp is started, the starting current is as high as 10~20 times. Under such a large current, the system voltage may drop sharply, and the solar lawn cannot be started or repeatedly started until it is damaged.

5) At present, solar cells cannot be used for main road lighting. There are legal requirements for the lighting of highway main roads, but the conversion efficiency and price of solar cells can not meet this requirement at present. However, in the near future, with the improvement of various technical levels, solar cells will definitely be applied to the lighting of main roads in expressway.

6) As for the energy storage capacitor, the service life of solar cells is more than 25 years, and that of ordinary storage batteries is 2-3 years, so the storage battery is the weakest link in the solar power generation system. Energy storage capacitor can solve this problem to some extent. The service life of energy storage capacitor can reach more than 10 years, and the control circuit is simple, but its price is expensive, which limits its application. Currently, it is only used in some traffic lights and decorative lights. With the improvement of technical level and the decline of product price, it will be the most promising ideal energy storage element for solar cells. Of course, colloidal batteries are also used at present, and the general quality can guarantee the service life of 5~7 years, which greatly improves the first maintenance cycle of solar garden lamps and street lamps.

7 On the application of solar cell technology in lighting lamps and lanterns

7. 1 Used for lawn lamp high-efficiency booster circuit.

Low-power solar lawns generally have booster circuits, and at present, all manufacturers use oscillating circuits and inductors to boost the voltage. The standard color-coded inductor is used as the inductor, and the standard color-coded inductor adopts an open magnetic circuit, so the magnetic flux loss is large, so the circuit efficiency is low. If a closed magnetic circuit is used to manufacture an induction booster such as a magnetic ring, the efficiency of the booster circuit will be greatly improved. The sensor is made of f 10 magnetic ring. Under the same conditions, comparative experiments show that the efficiency of making closed magnetic circuit inductor is 20%~40% higher than that of making standard color standard inductor. However, due to cost considerations, most manufacturers still use standard color standard inductors.

7.2 RJ0 1 solar lamp control circuit

RJ0 1 controller adopts patch design and has the following functions:

1) battery over-discharge protection;

2) Automatic recovery of discharge function after charging;

3) Battery overcharge protection;

4) Anti-reverse charging (the battery charges the solar battery);

5) Temperature compensation function;

6) Automatic light-on function (the load is turned on at night and turned off during the day);

7.3 Time-sharing/voltage-dividing intelligent solar lamp control device

As a new energy-saving lamp, solar lamp has many advantages compared with traditional lamps, but its high price is the bottleneck of popularization and application. Therefore, how to reduce the cost of solar lamps is an important topic. Time-sharing and voltage-dividing control of solar lamp technology is a good method to solve this problem.

The core of time-sharing and voltage-sharing control technology of solar lamps is to control the input power of solar lamps according to the different requirements of illumination at different time periods at night, and to control the input power of solar lamps according to the energy absorbed by solar cells during the day, so as to design solar lamps that can meet people's most basic requirements under the worst meteorological conditions at the minimum cost.

Prospect-Green Lighting from PN Junction to PN Junction

Solar cells are developing at an amazing speed beyond people's expectations. According to scientists' conservative estimation, in the next 10 year, the average conversion efficiency of solar cells will reach more than 20%, and the price will drop by half. That is to say, today, after 10 years, half of the power we use for lighting may come from solar energy, realizing real green lighting from PN junction to PN junction. As we all know, solar cell is a huge PN junction, which converts solar energy into electric energy. LED is another kind of PN junction that can convert electric energy into light. Its conversion efficiency is increasing day by day, and it will reach the level of energy-saving lamps in the future, and its service life can reach more than 654.38+ 10,000 hours. This is the real green lighting.

See the link below /new/news 1.asp for the comparison table of the use cost of solar photovoltaic lighting lamps and public electric lighting lamps. id=48

References:

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