If you have a garden, yard or landscaping at home, I guess you might have installed some solar outdoor landscape lighting guiding your path at night. These solar powered lights not only bring safety when you are back later in the night, but also add special atmosphere for your outdoor activities. But have you ever stopped to wonder how does the solar lighting work? Why it can shine for a whole night after put it in the sun for a day? This article will give you the answer.
The most important parts of a solar light are the solar panel or photovoltaic panel, battery and PCB with LED.
The solar panel is the part that converts the sunlight into electrical current; you can find it at the top of the solar light with black or dark blue color. During the day, sunlight is converted to electricity and stored in the battery; this process is called photovoltaic effect. The solar panel was embedded with the solar cells, that consists of multiple layers of crystalline silicone and chemicals that create layers of negatively-charged electrons and positively charged spaces. When the sunlight passes through the solar cell, it excites the negatively-charged electrons and push them into the positively-charged space. The positively-charged spaces then transfer the electron stream as a direct current of electricity through wires to a battery where the electricity is stored. In the day, as the sunlight continues to be converted to electricity and stored in the battery.
When evening approaches, the sunlight becomes weak and cannot hit the solar cells to generate the enough voltage to transfer the electrons, so the solar cells stop converting sunlight. when the voltage of the cells is lower than the battery voltage, it cannot charge the battery any more, and the battery start to supply the electricity to the light, which is usually made up of the LEDs. The power stored in the battery normally can make the LEDs can work 8-10 hours, in the last when it run out of power, it will become dim and off . Then in the next daytime with good sunlight, the new cycle begin.
The solar cells for solar lighting
The most used solar cells for solar lighting are mono-crystalline and poly-crystalline solar cell, and some are used of amorphous solar cell. Normally, the mono-crystalline are typically 10%-15% more efficient than the poly-crystalline cells with around 21% convert efficiency; the convert efficiency means the ability to transfer the sunlight to electricity. While the amorphous cell has only around 8% transfer efficiency.
Solar Panel for Solar Lighting
According to different production processes, solar panels currently used on solar lighting are mainly classified into three types, laminated solar panels, epoxy coated solar panels, and amorphous silicon solar panels. If you want to know the detailed production processes of them, visit our another post “the production processes of laminated solar panel and epoxy solar panel “. Here we only talked about the difference between laminated solar panel and epoxy solar panel.
Epoxy solar panel
Epoxy is a type of liquid resin known for its good adhesive properties and resistance to water ingression. That is why they are used for encapsulating solar cells. They also have high electrical insulation and good chemical resistance. However in the long time run; they will be aged prematurely under the sun. Turning yellowish and opaque, and become more brittle, that only a small amount of sunlight can go through the epoxy layer to reach the solar cells, which means that only a small amount sunlight is converted into electricity and stored in the battery, it will eventually reduce the run hours of the solar lighting at night .That is why we often find the solar landscape lights in our garden or yard can not keep working all night after one or half year. These solar outdoor landscape lights may cost you dozens of dollars, and it is a waste if it cannot rejuvenate.
The process of epoxy solar panel
When the solar cell is ready for encapsulation, it is placed on the backing board and the liquid epoxy resin is poured over the cells. These layers will be laminated together at a temperature of 50-60 Celsius degree, and will form a harden layers when it cools.
PET laminated solar panel
PET (also known as Polyethylene terephalate) is a type of plastic which is commonly used for bottled water, takeaway containers and household products due to their material stability, wear resistant and non-toxic nature. It’s high transparency and good scratch resistant also makes it suitable as a protective layer above the solar cell. Solar cells used can be monocrystalline or polycrystalline.
This allows good sunlight absorption while keeping the solar panel lightweight. It does not have the issue of turning yellowish and the lifespan is longer: 3 year+. But the cost of the PET laminated solar panel is higher than the epoxy solar panels that make it normally not used on the cheap promotional solar landscape light.
The PET laminated solar panel is made by placing layers of PET, EVA, solar cell and PCB together. They are then laminated by machine at a temperature of 135 degrees Celsius which will melt the encapsulating materials EVA , PET together to form a watertight bond.
Amorphous solar panel
The most common amorphous silicon solar panels we usually see are on the pocket calculator. The low power output of amorphous silicon solar cells limited their use to small applications only. For solar lighting, it was often used on the small and cheap promotional items, with low lumens output.
In addition to the solar panel, another important component for solar lighting is the rechargeable battery. For solar lighting, it must be used with rechargeable battery as the solar panel will charge and store the power in it. The normal used for solar lighting is NI-MH or Ni-Cd rechargeable battery with 1.2V voltage, and Lithium battery like LiFePO4 with 3.2V voltage. Due to the environment-friendly requirement, Ni-Mh battery is most used, but for some need higher lumens output like 15+ lumens, 3.2V LiFePO4 battery is the best option as it can store more power.
The LiFePO4 battery has different size with different capacity, like 14430, 14500,18500 and 18650, the first two No. like “14” means the battery diameter is 14mm , and the Number “43” means the length of the battery is 43mm. Due to the size 14500 is same as the AA battery , that there is a possibility of mixing 14500 3.2V battery with AA 1.2V battery, that will be in danger, so most used battery of LiFePO4 is the 14430 size , and the big one 18500 size .
LED Light Source
Another important parts for solar lighting is the LED, thanks to the technology improvement, the LEDs are getting more and more efficient. Which mean with the same power, LED can generate more lighting, higher lumens output.
LED color temperature or Correlated Color temperature (CCT) is measured on a Kelvin (K) scale, most of the package of the lights is marked with the color temperature, and you can find it on that. Color temperature 3500K and above are generally considered to be cooler temperatures that become bluer in tone as the value goes up. Color temperature 3000K and below are considered warmer, as value decrease, the light assumes a more amber tone.
For outdoor landscape lighting, stay away from cooler color temperatures, the bluish tones can make environments appear sickly or unnatural, imparting a sense of uneasiness and being on edge. While the color temperature 2700K-3000K offers a very soothing and nature tone that mimics the warm, comforting glow of campfire. As such, it is ideal for creating relaxing, comfortable outdoor environments. That is why most of the outdoor solar landscape lighting chooses the 2700K-3300K warm white color temperature.
For the outdoor solar landscape lighting, except the solar panel, battery and LED, the only difference is figures different, materials different or function different. Some are made of plastic; some are made of metal and glass.while some are used for path light, some are used for spot light. That depends on personal preference.
Anyway solar outdoor landscape lighting are more and more used in garden, yard or villa, although it has different pros and cons, but that is the best choice for areas where running electrical wires is not practical or possible, meanwhile it can bring a special tone in your garden. Let’s enjoy it and thanks it