LED solar street lights are powered by crystalline silicon solar cells, maintenance-free lithium batteries, ultra-bright LED lamps as light sources, and controlled by intelligent charge and discharge controllers, no need to lay cables, and subsequent installation is extremely simple; no AC power supply, no generation Electricity charges; adopt DC power supply and control. Solar lamps already occupy a large proportion of the lighting market.

 

There are relatively more varieties of LED components for LED solar street lights, mainly including solar panels, batteries, controllers, light sources, and other corresponding components.

 

 

 

 

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What Are Solar Panels?

 

 

The common panel in LED solar street lights in the market are polycrystalline silicon and monocrystalline silicon, and the difference between the two can be directly judged by their appearance. 70% of the solar panels on the market are made of polysilicon, which looks like blue ice flowers on the outside, while the appearance of monocrystalline silicon is solid.

 

Silicon (Si) is a tetrahedrally coordinated atom, usually tetrahedrally bonded to four adjacent silicon atoms. In Crystalline silicon (c-Si), the tetrahedral structure persists over a wide range, forming an ordered crystal lattice. Crystalline silicon is further divided into monocrystalline silicon (Monocrystalline) and polycrystalline silicon (Polycrystalline). Monocrystalline silicon is a single crystal of silicon with a substantially complete lattice structure. Polysilicon consists of small crystal grains, also known as grains. The difference between polycrystalline silicon and single-crystal silicon is mainly manifested in physical properties.

 

 

The conversion efficiency of monocrystalline silicon solar panels in LED solar streetlights is 20-24%, and the conversion efficiency of polycrystalline silicon solar panels is about 14-19%. The price of monocrystalline silicon is higher than that of polycrystalline silicon. Both have their own advantages and disadvantages, and the conversion rate of polycrystalline is a little lower, but because monocrystalline silicon cells can only be made into quasi-squares (the four sides are arc-shaped) when forming solar panels, some areas will not be filled, and Polysilicon is square, so there is no such problem.

 

Besides these two materials, Amorphous silicon (a-Si) is also used to make solar panels. It is a semiconductor that is a non-crystallizing product of the silicon manufacturing process. The atoms in it form a continuous random web, and besides not all atoms are four-way compatible. Due to the disorder of the material, some er atoms have dangling bonds, that is, electrons that do not bond with the surrounding silicon atoms, and these electrons can generate current under the action of an electric field.

 

The flexibility of solar panels made of amorphous silicon is much better than that of crystalline silicon solar panels, and the bending degree can reach 90-180 degrees. Now many people use this feature to cover large areas on LED street light poles and tree trunks. However, its conversion efficiency is only about 7-10%, and its price is higher than that of crystalline silicon solar panels, which is why it has not been widely used.

 

 

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So…How Should I Choose The LED Solar Street Light Battery?

 

A lithium iron phosphate battery (lithium battery) in LED solar street light is recommended. Another material on the market is lead-acid batteries. The difference between the two is that lead-acid batteries are not resistant to high temperatures and are prone to liquid leakage, while lithium batteries are resistant to high temperatures, but relatively not resistant to low temperatures. The conversion rate at low temperatures is lower than that of lead-acid batteries.

 

But in general, the conversion rate and safety of lithium batteries are higher than that of lead-acid batteries. Using lithium iron phosphate batteries, the charging and discharging speed will be faster, the safety factor is high, and it is more durable than long-life lead-acid batteries, and the service life will be almost 6 times longer than lead-acid batteries.

 

 

Lithium is an alkaline, flammable, soft, malleable, silvery, and light metal characterized by very rapid corrosion in contact with air. Lithium is found in the Earth’s crust at 65 parts per million and cannot be submerged in water. These lithium solar cells are batteries with fast charging, longer life, and higher energy density.

 

Also known as lithium-ion or “lithium-ion” batteries, they use lithium salt as an electrolyte, which manages to release electrons, and through a chemical reaction, they are able to store and release electrical energy. Lithium batteries are an excellent replacement for photovoltaic installations with high energy demands that require a lot of autonomy and less solar radiation throughout the day.

 

*On April 25, 2022, according to Drew Baglino, Tesla’s senior vice president of engineering, half of Tesla’s vehicles are now equipped with lithium iron phosphate (LFP) batteries when they leave the factory.

 

This echoes the statement made by Tesla CEO Musk at the financial report conference in July 2021. At that time, Musk said that Tesla will gradually turn to the solution of lithium iron phosphate batteries in the future. From the perspective of battery composition, two-thirds of Tesla cars in the future will use lithium iron phosphate, and one-third may use lithium iron phosphate. nickel battery.

 

Trend Force said that lithium iron phosphate batteries will account for more than 60% of the global power battery market by 2024 due to the cost-effective advantages of lithium iron phosphate batteries.

 

 

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How about Controllers?

 

 

There are many controllers on the market now, and new technologies will be more suitable for installing LED solar street lights. For example, MPPT control, using MPPT charging technology, can increase the efficiency of solar power generation systems by 50% compared with traditional ones, and realize efficient charging. It has been widely used in small and medium solar street lighting systems and small and medium off-grid solar power plants around the world. Because of its high quality and practicality, it has a very high share of the photovoltaic market.

 

The full name of the MPPT controller is the “Maximum Power Point Tracking” (Maximum Power Point Tracking) solar controller, which is an upgraded product of the traditional solar charge and discharge controller.

 

The MPPT controller can detect the voltage generated by the solar panel in real-time, and track the highest voltage and current value (VI), so that the system can charge the battery with the maximum power output. Applied in solar photovoltaic systems, coordinating the work of solar panels, batteries, and loads is the brain of the photovoltaic system.

 

Current-Voltage Characteristic Curve

 

 

There is a complex relationship between the maximum power a solar cell can output and the environment. The shape factor is defined as the ratio of the maximum power of the solar cell divided by the product of the open circuit voltage Voc and the short circuit current Isc. The shape factor is commonly used in calculations to estimate the maximum power P=FF*Voc*Isc that a photovoltaic cell can generate under certain conditions. In most applications, FF, Voc, and Isc can roughly simulate the electrical characteristics of photovoltaic cells under general conditions.

 

Under certain operating conditions, the battery will have an operating point where the product (electric power) of its current (I) and voltage (V) will be the maximum value. This value will correspond to a specific resistance, which will be equal to V/I according to Ohm’s law. The power can be calculated by P=V*I. Photovoltaic cells are approximately constant current sources within the range of their main application curves. However, in the range of the maximum power point of a photovoltaic cell, there is an exponential function-like relationship between its voltage and current. According to the basic circuit and calculus theory, if the slope dI/dV (differential component) of the I-V curve is equal to the value of the I/V ratio, and the signs are opposite, dP/dV=0, then the output power is the maximum value. This position is the maximum power point (MPP for short), which corresponds to the turning point of the curve.

 

If the load impedance R=V/I of the solar cell is equal to the reciprocal of the above value, the maximum power can be output from the solar battery at this time. Sometimes this value is also called the “characteristic impedance” of the solar cell. This value is a dynamic quantity, which is related to the degree of sunshine, temperature, and the life of the solar cell. If the resistance is less than or greater than this value, the power drawn will be less than the maximum power, so the solar cell will not operate under the most ideal and efficient conditions. MPPT uses several different control resistors or logic to find the maximum power point where the converter can extract the maximum power from the solar cell.

 

The Principle Of MPPT

 

 

To charge the battery, the output voltage of the solar panel must be higher than the current voltage of the battery. If the voltage of the solar panel is lower than the voltage of the battery, the output current will be close to 0. Therefore, for the sake of safety, when the solar panel is manufactured, the peak voltage (Vpp) of the solar panel is about 17V, which is set based on the standard when the ambient temperature is 25°C. When the weather is very hot, the peak voltage Vpp of the solar panel will drop to about 15V, but in cold weather, the peak voltage Vpp of the solar panel can reach 18V.

 

Now, let’s go back and compare the difference between MPPT solar controllers and traditional solar controllers. The traditional solar charge and discharge controller is a bit like a manual gearbox. When the engine speed increases, if the gear position of the gearbox does not increase accordingly, it will inevitably affect the speed of the vehicle. But for the MPPT solar controller, the charging parameters are set before leaving the factory, that is to say, the MPPT controller will track the maximum power point in the solar panel in real-time to maximize the efficiency of the solar panel.

 

The higher the voltage, the more power can be output through maximum power tracking, thereby improving the charging efficiency. Theoretically speaking, the solar power generation system using an MPPT controller will increase the efficiency by 50% compared with the traditional one, but according to our actual test, due to the influence of the surrounding environment and various energy losses, the final efficiency can also be increased by 20%-30%.

 

In this sense, the MPPT solar charge and discharge controller in LED solar street light is bound to eventually replace the traditional solar controller.

 

 

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OH! I Know Light Sources(LED Chip)!

 

 

Wait, I’m afraid your understanding of the chip of LED solar street lights is wrong. This thing is called a lamp bead(Picture 1&2). The chip is an integral part of the lamp bead. The neatly arranged small squares under the lamp beads are the LED chips.

 

 

The LED chip is equivalent to the heart of the LED high-power lamp bead. An LED chip is a kind of solid-state semiconductor chip, and one end of the chip is attached to the support, one end is a negative pole, and the other end is connected with the positive pole of the power supply, and the whole chip is encapsulated by epoxy resin. A complete packaging process can ensure the normal use of LED high-power lamp beads. International brands of LED lamp beads include CREE, Osram LED, Philips PHILIPS, Nichia, Seoul SEOUL, Samsung, etc.

 

Pin Insertion Row (DIP)

 

Ordinary people: Straw hat lamp beads with two pins. This is the simplest and cheapest form of lamp beads.

Features: Good safety performance, stable performance, low voltage when emitting light, low loss, high efficiency, and long service life. But the general power is low, and the scope of application is generally inside the lights, indicator lights, and displays.

This energy is usually between 0.02 W and 0.1 W.

 

Small And Medium Power Surface Mount Ability (SMD)

 

This spherical light source is made by soldering the LEDs to the surface of the board, not through it.

 

Due to the small size, there are many models of this lamp bead, the most commonly used ones are 2835 (PCT), 4014, 3528, 3014, 5050, 3030, etc. The two digits of each model number indicate the width “x. x mm”, and the last two digits indicate the length “x.x mm”. For example, 2835 means 2.8mm wide and 3.5mm long.

 

The scope of application is wide, and it can be applied to various lamps such as linear lamps, light strips, downlights, and surface lights.

The power of this type of spherical package is generally designed around 0.1 W, 0.2 W, and 0.5 W, but due to chip technology and heat dissipation brackets (PCT, red copper), etc., the power can be increased to 1 W, 1.5 W or even 2 W later.

SMDs such as 5050, and 7070 have appeared, and the power can reach more than 3 W.

 

High Power Surface Mountability

 

The third type is also a patch type, which is similar in essence to the small patch type, except that the high power and volume of the patch type are slightly larger; in terms of detailed structure, there is an extra lens, which can better capture The rays come together.

 

Integrated Package (COB)

 

 

The chip encapsulates multiple lamp bead chips on the same board and connects them with gold wires through a certain number of series and parallels. Usually, the number of parallels is 10-string or 12-string design, because they are all designed under the extremely low safety SELV 42 V.

 

 

But the same lamp bead, with a good driver, can withstand 5 to 7or8 years, and the impact of the driver on the life is far greater than that of the LED chip. In addition, there is heat dissipation, the same LED chip, and the same driver, one uses professional heat dissipation treatment, and the other uses the cheapest plastic shell as a light bulb. The front one can withstand 15,000 hours, and the latter one will not light up for hundreds of hours due to high temperatures. up. The impact of heat dissipation on LED lights is greater than that of LED chips.

 

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