A Photovoltaic(PV) module which is generally termed as a solar panel is an assembly of photovoltaic cells electrically connected to each other and mounted on a laminated frame. The solar cells are primarily made up of silicon material which absorbs the photons emitted by the sun. There are three major types of PV modules. Mono-crystalline Poly-crystalline Thin-film Each solar PV module type has its own unique features. These PV modules also vary based on how they are manufactured, their appearance, performance, costs, etc.
Solar photovoltaics are made with a number of parts, the most important of which are the solar cells which are connected and sandwiched between glass and metal. Major components of a PV module are: Module Frame Glass Encapsulant Back Sheet Backsheet is a film of that protects the solar cells from severe environmental conditions. A solar back sheet is the last layer at the bottom of the solar PV module and is typically made of a polymer or a combination of polymers. Junction Box
Both mono-crystalline and poly-crystalline solar PV modules have cells made of silicon wafers. To build a mono-crystalline or poly-crystalline module, wafers are assembled into rows and columns covered with a glass sheet, and framed together. Poly-crystalline cells are square-shaped whereas mono-crystalline cells are square with missing corners. While both of these types of solar PV modules have cells made from silicon, mono-crystalline and poly-crystalline modules vary in the composition of the silicon itself. Mono-crystalline solar cells are cut from a single, pure crystal of silicon. Alternatively, poly-crystalline solar cells are composed of fragments of silicon crystals that are melted together in a mold before being cut into wafers. Mono-crystalline modules have better efficiency and power capacity.
Solar panels react differently to the operating temperature. The efficiency of a solar panel decreases as it increases above the ambient temperature. Each solar panel has a temperature coefficient (which is defined in datasheet of panels). The temperature coefficient represents the rate at which the panel will underperform at each increase in degree Celsius (°C). Most panels have a temperature coefficient of between -0.2% /°C to -0.5%/°C, when tested under standard laboratory conditions, where ambient temperature is set to 25°C. For example if the temperature coefficient of a particular type of panel is -0.5%, then for every 10C rise, the panel’s output power will reduce by 0.5%. [Source: Youtube] [Publisher: altE Store’s Educational Video Channel]
Hot spots are areas of high temperature that affect only one zone of the solar panel and resulting in a localized decrease in efficiency, and therefore, lower output power and accelerated material degradation in the area affected by the high temperature. Hot spots are not visible to human eyes and are detected and verified using infrared measurement technique. Above image shows of a solar panel showing a hot spot developed due to bird droppings Causes and its effects The reasons for the appearance of hot spots are multiple and can be classified into functional or operational. Defect severity and remediation actions also vary widely as a result. Functional reasons Cell mismatch: It occurs when cells of different current are connected in series. Cell damage: It occurs during manufacture, due to the fact that the silicon cell will be subjected to a stressful process during rolling, handling and transportation. Operational reasons Seasonal shadows: When cells are completely or partially shaded for a long period of time, it results in increased temperature in the shaded cell and further creates hot spots. The loss in power output due to a hot spot in solar panels is not directly correlated with the area of the panel that is shadowed. Even a small shade can have a significant impact on the output power of the module. Soiling or dirt accumulation: Solar panels become dirty from dust, suspended sand, dirt and other contaminating impurities if not cleaned periodically during their service life. The dust accumulated on the […]
What would happen if the solar panels deployed in the system have different electrical characteristics?
When solar panels with different electrical characteristics, interconnected with each other are deployed in the system, it creates serious power losses & adversely affects the overall energy generation. These losses are referred as “Mismatch losses”. The current (Isc) in the string in which the panels are connected in series with each other, is limited to the lowest output current from any of the panel. Thus mismatch causes the lower output power from the string & the system efficiency and performance becomes lower.
The performance of the solar panel is affected by its tilt angle and orientation with respect to the horizontal plane. Orienting the solar panel in a direction and tilt to maximize its exposure to direct sunlight can ensure a better generation. The solar panel collects solar radiation most efficiently when the sun’s rays are perpendicular to the panel’s surface. Solar panels should always face south if the plant is in the northern hemisphere, or north if the plant is in the southern hemisphere & the tilt of the solar panels should be proportionate to the latitude of the plant site to optimize their power generation throughout the year. The installer of the plant analyses the optimum tilt & orientation before installing the solar plant. [Source: Youtube] [Publisher: altE Store’s Educational Video Channel]
Weather conditions are unlike in each location. As solar plants are installed around the world, solar panel manufacturers test their products to ensure that they are dust & storm resistant, salt mist & ammonia corrosion resistant, capable to withstand hail storms & heavy snow loads & extreme temperature variations. The junction box attached with the modules are made waterproof.
When one (or more) solar photovoltaic cells becomes faulty or provides no power due to shading, the current then flows through the solar bypass diode and prevents hot spots and losses in yield. When part of a photovoltaic panel is shaded, the shaded cells will not be able to produce as much current as of the unshaded cells. Since all cells are connected in series, the same amount of current must flow through every cell. The unshaded cells will force the shaded cells to pass more current. This causes the solar panel to heat up, have a severe power loss. As a result, those shaded solar cells become consumers of electricity instead of producers. The function of bypass diode is, when a cell or a panel becomes shaded its bypass diode becomes “forward biased” and begins to conduct current through itself. The effected portion of the solar panel is bypassed, thus drastically reducing the amount of local heating & current loss at the shaded area. [Source: Youtube] [Publisher: altE Store’s Educational Video Channel]
The solar panel efficiency or conversion efficiency is the percentage of the solar energy striking on the panel that is converted into usable electricity. Not all of the sunlight that reaches a photovoltaic cell is converted into electricity. When light strikes the surface of a solar cell, some photons are reflected, while others pass right through, some of the absorbed photons have their energy turned into heat & the remainder have the right amount of energy to separate electrons from their atomic bonds to produce charge carriers and electric current. Most solar panels provide an energy efficiency rating between 11 to 18 percent, which is the percentage of solar energy that is being converted into usable electricity. A solar panel specification sheet usually contains a panel efficiency value at Standard Test Conditions(cell temperature of 25°C and an irradiance of 1000 W/m2). The higher the efficiency rating, the less number of panels you’ll need to make up a system that meets your energy requirements. However, choosing a more efficient solar panel may not always be the most cost-effective decision available.