Aside from the sun itself, solar cells and solar panels are the critical piece and centerpiece of many products listed on PhotonBuzz.com. When you're browsing on our store, you'll notice that nearly all of our products have some type of solar panel integrated into the device. Some products are actually standalone portable panel chargers that provide solar energy to another device only. Other products marry the panel with the integrated battery and other functions.
The chemical makeup and/or the construction characteristics of these panels and products are often listed in our "More Details" tab on product page. Many of the manufacturers and brands we carry highlight the solar panel design and chemistry because it may be a high performance panel with a high efficiency rating (See our article on the meaning of solar panel efficiency). This information is important to understand when selecting a product and considering options.
Our mission here in Part 2 of the Solar Electric Component series is to take some of the mystery out of solar cells and solar panels. Hopefully, by the time you read through this, you will have a better understanding of the basic types of solar panels, which will be helpful when you read our product descriptions. Frankly, there are numerous variables and information that you could consider when contemplating the purchase of a portable solar panel or solar electronic product, but being comfortable with the solar cell and solar panel is a pretty important first step.
In general, based on information from the US Department of Energy, most solar cells are made from either (a) crystalline silicon or (b) thin-film semiconductor material. Silicon solar cells are found to be more efficient at converting sunlight to electricity, but generally have higher manufacturing costs. Thin-film materials typically have lower efficiencies, but can be simpler and less costly to manufacture. A specialized category of solar cells - called multi-junction or tandem cells - are used in applications requiring very low weight and very high efficiencies, such as satellites and military applications.
Let’s start this summary by reviewing the different types of solar panels that generate electricity for your product and/or store energy in your portable solar recharger or solar gear.
Depending on the source of information, it's pretty clear that Crystalline Silicon (c-Si) or some close variation of silicon represent the largest proportion (87 to 90 percent or more) of the photovoltaic solar cells in the world. This includes residential and all forms of solar cells on electronic equipment too. A silicon in solar panel can come in many shapes and sizes and also varying levels of purity. Purity is pretty significant because the more perfectly aligned the silicon molecules are, the better the solar cell will perform at converting solar energy (sunlight) into electricity (the photoelectric effect). Based on information from the US Department of Energy, crystalline silicon PV cells have laboratory energy conversion efficiencies as high as 25% for single-crystal cells and 20.4% for multicrystalline cells. However, industrially produced solar modules currently achieve efficiencies ranging from 18%–24%.
The efficiency of solar panels goes hand in hand with purity, but the processes used to enhance the purity of silicon are expensive. Please keep in mind when you are shopping on PhotonBuzz.com that crystalline silicon forms the basis of mono- and polycrystalline silicon solar cells, which are commonly found in solar energy electronic gear.
Monocrystalline Silicon Solar Cells
Solar cells made of monocrystalline silicon (mono-Si), also called single-crystalline silicon (single-crystal-Si), are quite easily recognizable by an external even coloring and uniform look, indicating high-purity silicon, as you can see on the picture below:
Monocrystalline solar cells are made out of silicon ingots, which are cylindrical in shape. To optimize performance and lower costs of a single monocrystalline solar cell, four sides are cut out of the cylindrical ingots to make silicon wafers, which is what gives monocrystalline solar panels their characteristic look.
A good way to separate mono- and polycrystalline solar panels is that polycrystalline solar cells look perfectly rectangular with no rounded edges.
Monocrystalline solar panels have the highest efficiency rates since they are made out of the highest-grade silicon. The efficiency rates of monocrystalline solar panels are typically 15-20%. According to the US Department of Energy, a company by the name of SunPower produces the highest efficiency solar panels on the U.S. market today. Their E20 series provide panel conversion efficiencies of up to 20.1% and in April 2013, SunPower released the X-series at a record-breaking efficiency of 21.5%.
Since these solar panels yield the highest power outputs, they also require the least amount of space compared to any other types. Monocrystalline solar panels produce up to four times the amount of electricity as thin-film solar panels. Monocrystalline solar panels live the longest. Most solar panel manufacturers put a 25-year warranty on their monocrystalline solar panels and these panels tend to perform better than similarly rated polycrystalline solar panels at low-light conditions.
Disadvantages of the monocrystalline solar panel is expense. Monocrystalline solar panels also tend to be more efficient in warm weather. Panel performance suffers as temperature goes up, but less so than polycrystalline solar panels.
Polycrystalline Silicon solar cells are made of many tiny crystalline grains of semiconductor materials. The materials used in these cells have properties that are different from those of silicon. Polycrystalline silicon solar cells have been around for a while. The first solar panels based on polycrystalline silicon, which also is known as polysilicon (p-Si) and multi-crystalline silicon (mc-Si), were introduced to the market back in 1981. These solar cells are different than monocrystalline in that raw silicon is melted and poured into a square mold, which is cooled and cut into perfectly square wafers
The main advantage of the polycrystalline based solar panel cost. The process used to make polycrystalline silicon is simpler and cost less. The amount of waste silicon is less compared to monocrystalline panels.
Polycrystalline solar panels tend to have slightly lower heat tolerance than monocrystalline solar panels. This technically means that they perform slightly worse than monocrystalline solar panels in high temperatures. Heat can affect the performance of solar panels and shorten their lifespans, but this is only a minor issue.
Compared to the mono-crystalline based solar panel, the efficiency of polycrystalline-based solar panels is typically 13-16%. Because of lower silicon purity, polycrystalline solar panels are not quite as efficient as monocrystalline solar panels. You generally need a larger area of solar panel coverage to output the same amount of electrical power as you would with a solar panel made of monocrystalline silicon. However, this does not mean every monocrystalline solar panel performs better.
A third solar cell type is called Thin-Film or (TFSC). By depositing one or several thin layers of photovoltaic material onto a substrate, manufacturers are able to create a thin "film" product, also known as Thin-Film photovoltaic cells (TFPV). The different types of thin-film solar cells can be categorized by which photovoltaic material is deposited onto the substrate. These types are: Amorphous silicon (a-Si), Cadmium telluride (CdTe), Copper indium gallium selenide (CIS/CIGS), and Organic photovoltaic cells (OPC).
In today's world of consumer electronics and integrating solar cell technology into microelectronics, fabrics and flexible materials, Thin-film cells have many advantages over their thick-film counterparts. For example, they use much less material. The cell's active area is usually only 1 to 10 micrometers thick, whereas thick films typically are 100 to 300 micrometers thick. Also, thin-film cells can usually be manufactured in a large-area process, which can be an automated, continuous production process. Finally, they can be deposited on flexible substrate materials. The term "thin film" comes from the method used to deposit the film, not from the thinness of the film itself. Thin-film cells are deposited in very thin, consecutive layers of atoms, molecules, or ions.
Thin-film Solar Panels
Depending on the technology, thin-film module prototypes have reached efficiencies between 7–13% and production modules operate at about 9%. Future module efficiencies are expected to climb close to the about 10–16%. The market for thin-film PV as grown considerably (about 60%) in the early to mid-2000's. In 2011, close to 5% of U.S. photovoltaic module shipments to the residential sector were based on thin-film.
The main advantage of Thin-Film panels is that mass-production is simple. This makes them and potentially cheaper to manufacture than crystalline-based solar cells. The clean and homogenous appearance of these panels makes them look more appealing. Of course, they are capable of being made flexible and open to a wide variety of applications...many of which you can see on PhotonBuzz.com. High temperatures and shading appear to have less impact on solar panel performance.
The primary disadvantage to Thin-Film is the space required to capture solar energy. Being less efficient per area, means these systems may not be the best option for residential or commercial application. For camping, the top of a golf cart, or integrated into a tent or backpack, Thin-Film may be a better solution. In situations where space is not an issue, Thin-Film may make sense. Another disadvantage is that Thin-Film panels tend to degrade faster than mono- and polycrystalline solar panels, which is why they typically come with a shorter warranty.
Finally, solar panels based on amorphous silicon, cadmium telluride and copper indium gallium selenide are currently the only thin-film technologies that are commercially available on the market:
Because the output of electrical power is low, solar cells based on amorphous silicon have traditionally only been used for small-scale applications such as in pocket calculators. However, recent innovations have made them more attractive for some large-scale applications too.
Cadmium telluride is the only thin-film solar panel technology that has surpassed the cost-efficiency of crystalline silicon solar panels in a significant portion of the market (multi-kilowatt systems). The efficiency of solar panels based on cadmium telluride usually operates in the range 9-11%.
Compared to the other thin-film technologies above, CIGS solar cells have showed the most potential in terms of efficiency. These solar cells contain less amounts of the toxic material cadmium that is found in CdTe solar cells. Commercial production of flexible CIGS solar panels was started in Germany in 2011. The efficiency rates for CIGS solar panels typically operate in the range 10-12 %. Many thin-film solar cell types are still early in the research and testing stages. Some of them have enormous potential, and we will likely see more of them in the future.
We hope this short summary of solar panels and solar cell technology was helpful. Our goals was to take some of the mystery out of solar cells and solar panels. You've now been introduced to the three major categories of panels found in the residential home, commercial and solar electronic industries. When you read our product descriptions and see information about the solar cells/panels and the type and efficiency ratings, it will make some more sense and be more relevant toward your decision making.
Use the PhotonBuzz.com search tool to locate monocrystalline or polycrystalline solar panels. Not all manufactures provide full technical details on their product line information cards. PhotonBuzz.com will always post this type of information on the product page, but if you do have questions do not hesitate to let our customer service team know and will try and chase down an answer for you.