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Blocking Diode and Bypass Diodes in a Solar Panel Junction Box. Inside solar panel

Blocking Diode and Bypass Diodes in a Solar Panel Junction Box. Inside solar panel

    Bypass Diode and Blocking Diode Working used for Solar Panel Protection in Shaded Condition

    In different types of solar panels designs, both the bypass and blocking diodes are included by the manufactures for protection, reliable and smooth operation. We will discus both blocking and bypass diodes in solar panels with working and circuit diagrams in details below.

    Bypass Diode in a solar panel is used to protect partially shaded photovoltaic cells array inside solar panel from the normally operated photovoltaic string in the peak sunshine in the same PV panel. In multi panel PV strings, the faulty panel or string has been bypassed by the diode which provide alternative path to the flowing current from solar panels to the load.

    Blocking Diode in a solar panel is used to prevent the batteries from draining or discharging back through the PV cells inside the solar panel as they acts as load in night or in case of fully covered sky by clouds etc. In short, as diode only passes current in one direction, so the current from solar panels flows (forward biased) to the battery and blocks from the battery to the solar panel (reverse biased).

    What is a Diode?

    A diode is a unidirectional semiconductor device which only passes current in one direction (forward bias i.e. Anode connected to the positive terminal and cathode is connected to the negative terminal). It blocks the current flow in the opposite direction (reverse bias i.e. Anode to the.Ve terminal and Cathode to the Ve terminal).

    They are made off semiconductor materials such as Silicon and Germanium. They offer high resistance to the current in one direction (reverse bias) and act a short circuit path for current in the opposite direction (forward bias). Following is the generic symbol of a diode with anode and cathode terminal.

    Working of Blocking Bypass Diodes in PV Panels

    Solar panels system is the best alternative of wide range (mW to MW) of free electrical energy and can be used with On-Grid or Off-Grid power system. It can be installed wherever you want within the sunlight range to generate electrical power.

    Photovoltaic cell inside a solar panel is a simple semiconductor photodiode made from interconnected crystalline silicon cells which suck/absorb photon from the direct sunlight on its surface and convert it to the electrical energy. the photovoltaic cells are connected in series strings inside a solar panel and they generate electrical power in normal operation when sunlight hits these photovoltaic cells.

    But some factors affect the generating electrical power ability of solar cells such as abnormal environmental conditions i.e. rain, snowfall and humidity, full clouds covering the sky, solar degree radiation, temperature changes and positioning of panels array to the sun etc.

    blocking, diode, bypass, diodes

    One of the most factor which affect the output and efficiency is fully or partially shaded solar panels due to clouds, trees, leaves, building etc. In this case, some of the photovoltaic cells are not able to generate power as they are not exposed to the direct sunlight. In this scenario, the affected cells acts as a load and may be damaged due to hot-spot. That is the reason why we need a bypass diode in a solar panel.

    Lets see below how the shaded solar panels can be dangerous and how the bypass diode prevent the solar panels or damaging the the photovoltaic strings.

    PV Cells without Bypass Diodes

    A single photovoltaic cell generates about 0.58 DC volts at 25°C. In case of open circuit, typically the value of VOC is 0.5 – 0.6V while the power of a single photovoltaic cell is 1 to 1.5 W in case of open circuit. So a single photostatic cell of 1.5W with 0.5V will produce 3A current as I = P /V (1.5W / 0.5V = 3 Amperes).

    Suppose, there is no bypass diodes connected across the PV cells. As you can see, the photovoltaic cells are connected in series string (positive terminal is connected to the negative terminal of second one solar panels and so on).

    We know that current “I” in series is same at each point while the voltages are additive i.e. VT = V1 V2 V3 … Vn. So the total voltage VT = 0.5V 0.5V 0.5V = 1.5V.

    As a normal operation, all the photovoltaic cells are working perfectly i.e. all the three PV cells producing the rated power in currents and volts. The power is additive in both series and parallel connection. So we get the ideal maximum rated power in Amperes and volts. The flow of current is shown in blue dotted lines from PV cells to the output load.

    But what in case of shaded cell(s) ? And what if there is no bypass diode as well? Lets see what happens next.

    Shaded PV Cells without Bypass Diodes

    In case of fallen leaves or clouds, the shaded photovoltaic cells wont be able to produce electrical energy and acts as a resistive semiconductor load. In case of non-existence of bypass diodes, energy produced by PV cells string facing direct sunlight will start to flow to the shaded cells as they behaves as load as well. This excessive current will make the shaded load cells heated as they dissipate power which leads to hot-spot and may damage or burn the affected cell(s).

    As voltage drops occurs at the shaded cells, the normal cells without shades try to adjust the voltage drop by increasing the open circuit voltage. This way, the affected shaded PV cells becomes revere biased and negative voltage appears in the opposite direction across its terminals. This negative voltage causes to flow the current in the opposite direction in the affected shaded PV cells which consume power at the rate of operating current and short circuit current ISC. This way, the shaded cell inside a solar panel will dissipates power instead of producing it as reverse voltage drops occurs in it due to flow of electronic currents. This whole process will decrease the overall efficiency or may lead to damage and explode the PV cells in a solar panel.

    The blue dotted lines shows the flow of currents i.e. some current are flowing from normal cellsand cellto the affected shaded cell# 2. In case of open circuit, all the currents may flow to the affected cells while in case of connected load to the PV panel, some current flows to the load with decreased rate.

    Now, these are the reason we need bypass diodes in a solar panel. Let’s see what happens when there is a bypass diode in PV panel as follow.

    PV Cells with Bypass Diodes

    Now, lets see how can we protect a solar panel or photovoltaic array and strings from partial of fully shaded PV cell effects. That is a Bypass diode. Bypass diodes can be used by connecting them in parallel with the PV cell of a series connected string array to eliminate the risk factor and protect the solar panels from overall damage and explosion in case of full or partial shades.

    Bypass diodes are connected externally across (in parallel) with the photovoltaic cells in reverse bias (Anode terminal connected to the Ve and Cathode to the.Ve side of solar cell) which provides an alternate path for current flow in case of shaded cells. The reverse bias bypass diodes wont allow the produced current in the normal cells into the shaded cells.

    The flow of generated currents are shown by the blue dotted lines. In case of clear sky, i.e. peak sunshine, the produced current will not flow through the bypass diodes as shown by red dotted lines as they are reverse biased and acts as an open circuit. So total power going to the battery charging or connected load without affecting the efficiency as expected.

    But what happens when there is clouds or building shades on partial cells? lets see follow.

    Shaded PV Cells with Bypass Diodes

    In case of clouds or snow etc, the cellis affected and wont be able to generate power thus becomes a semiconductor resistor acts as a load now. Now the shaded cells provides negative power (want to dissipates power instead of generating it), the bypass diodes across the cell activated (as it is in forward bias now) and divert the flow of current to the load as shown by the blue dotted lines bypassing the shaded cell in fig.

    In short, the bypass diodes connected across the shaded cells#2 provide an alternative path to flow currents from cell#1 to cell#3 and load then. This way, the bypass diode maintains the reliable and smooth operation of PV cells without damaging the PV cell or overall photovoltaic string array with reduced power rate as cell#2 is not able to generate the electrical power.

    There are two types of diodes are used as bypass diode in solar panels which are PN-Junction diode and Schottky diode (also known as Schottky barrier diode) with a wide range of current rating. The Schottky diode has lower forward voltage drop of 0.4V as compared to normal silicon PN-Junction diode which is 0.7V.

    It means when forward biased, the Schottky diode saves almost the voltage level of single photovoltaic cell (which is 0.5V) in each series string. In other words, it provide an efficient operation of photovoltaic cells due to lower power dissipation in blocking mode.

    Another advantage of bypass diode connected in parallel with solar cells is that when it is operated (i.e. forward biased), the forward voltage drop is 0.4V (and 0.7V in case of PN-Junction diode) which limits the reverse i.e. negative voltage produced by the shaded cell which leads to reduce the chances of making hot-spots. The rise in temperature may leads to burn or damage the PV cells, but in case of bypass diodes, it returns the shaded cell to the normal operation when Cloud has been removed. The above mentioned are the exact reasons why there are bypass diodes in solar panels.

    Why There is No Bypass Diode Across Each PV Cell?

    Connecting a bypass diode across each single PV cell will lead to expensive and complicated design. Thus, manufacturer install bypass diodes externally in solar panel junction box (back side of PV panel) to string arrays instead of single PV cells.

    Commonly, two bypass diodes are sufficient for a 50W solar panel having 36-40 individual PV cells and charging a 12V to 24V series or parallel connection of batteries system depends on the current and voltage rating which is 1- 60A and 45V in case of Schottky diode.

    Blocking Diodes in Solar Panels

    As mentioned above, the diodes pass the current only in one direction (forward bias) and block in the opposite direction (reverse bias).

    This is what actually do the blocking diodes in a solar panel. During the normal operation of solar cells at clear sunshine, the solar cells generates electrical energy and let pass the flow of electron in one direction i.e. from solar panel to the battery or charge controller and other connected loads.

    During the night, clouds or no load in the shades, the connected battery will provide the current to the solar cells as they behave like a normal resistors. To overcome this issue, blocking diodes are used to block the current flow back to the solar panels which prevents the draining of battery as well as protect the solar cells from hot-spots due to dissipating power inside it which lead to damage the solar cell.

    In short, the blocking diodes only provide a single path for current from the solar panel to the battery and block the currents from the battery to the solar cells during night as solar cells are acting as a load instead of generating energy.

    Keep in mind that blocking diodes are installed in series with the solar panel. The following fig shows a combination of blocking diodes connected in series and bypass diodes connected in parallel with the solar panel.

    As shown in fig below, a leaf is fallen on cell# 3. This way, the generated current will flow from cell#1 and cellto the out put as it is in normal operation. The current will flow through bypass diode across cellwhich is affected and celland to the loads then through blocking diodes which is a reliable operation of solar power system as expected.

    I hope it cleared the concept that what are those bypass and blocking diodes in the junction box at the back side of solar a panel.


    Reviews and information on the best Solar panels, inverters and batteries from SMA, Fronius, SunPower, SolaX, Q Cells, Trina, Jinko, Selectronic, Tesla Powerwall, ABB. Plus hybrid inverters, battery sizing, Lithium-ion and lead-acid batteries, off-grid and on-grid power systems.

    March 20, 2020 Jason Svarc

    Solar panel technology is advancing rapidly with greater efficiency and lower resulting in a huge increase in demand. However, despite the massive advancements in technology, basic solar panel construction hasn’t changed much over the years. Most solar panels are still made up of a series of silicon crystalline cells sandwiched between a front glass plate and a rear polymer plastic back-sheet supported within an aluminium frame.

    Once installed, solar panels are subjected to severe conditions over the course of their 25 year life. Extreme variations in temperature, humidity, wind and UV radiation can put enormous stress on a solar panel. Fortunately, most panels are well-engineered to withstand extreme weather. However, some panels can still fail in several ways including water ingress, cell micro-fractures and potential induced degradation or PID. This is why it is vital solar panels are manufactured using only the highest quality components. In our other article, best solar panels, we highlight the leading manufacturers using the highest quality materials together with testing to the highest industry standards.

    How are Solar Cells Made?

    Solar panels use photovoltaic cells, or PV cells, which are made using silicon crystalline wafers similar to the wafers used to make computer processors. The silicon wafers can be either polycrystalline or monocrystalline and are produced using several different manufacturing methods. The most efficient type is monocrystalline (mono) which are manufactured using the well known Czochralski process. This process is more energy-intensive compared to polycrystalline (poly) and therefore more expensive to produce.

    Polycrystalline wafers, on the other hand, are slightly less efficient and are made using several purification processes followed by a simpler, lower cost, casting method. recently, cast monocrystalline or cast mono cells have been gaining popularity. The reason is due to the lower-cost casting process used to make cast mono cells which is similar to the process used for polycrystalline silicon cells. However, cast-mono wafers are not quite as efficient and pure mono wafers made using the Czochralski process.

    • Monocrystalline silicon cells. Highest efficiency and highest cost
    • Cast monocrystalline cells. High efficiency and lower cost
    • Polycrystalline silicon cells. Lower efficiency and lowest cost

    Manufacturing Solar cells

    Manufacturing common silicon-based solar cells require a number of different processes starting from a raw material called Quartzite, which is a form of quartz sandstone rock. First Quartzite, also referred to as silica sand, is converted into metallurgical grade silicon by combining Carbon and Quartzite in an arc furnace. This process occurs at very high temperatures and results in 99% pure silicon. The next step is to convert the metallurgical grade silicon into pure Polysilicon using either a chemical purification process called the Siemens process, or upgraded metallurgical-grade silicon (UMG-Si), using less costly metallurgical processes.

    Next, the polysilicon is doped with trace amounts of either boron or phosphorous to become either P-type or N-type silicon. At this stage, the polycrystalline silicon can be melted and cast into large rectangular blocks and thinly sliced using a diamond wire cutting method to produce the polycrystalline or multicrystalline wafers.

    To manufacture the more efficient monocrystalline wafer or cells, the doped silicon can be made into a pure solid crystal ingot using the Czochralski process. This process involves melting the polycrystalline silicon under high pressure and temperature to slowly grow a single large monocrystalline crystal known as an ingot.

    Steps to manufacture monocrystalline PV cells

    • Silica sand is purified in an arc furnace to create 99% pure silicon
    • The 99% silicon is further refined close to 100% pure silicon
    • The silicon is doped with boron or phosphorous (P-type or N-type)
    • The doped silicon is melted and extracted into a crystalline ingot
    • The round ingot is diamond wire-cut into thin square wafers
    • The thin base wafer is coated with an ultra-thin layer of either P-type or N-type silicon to form the PN-junction.
    • An anti-reflective layer and metallic fingers are added to the cell surface
    • Flat ribbon busbars (as shown) or thin wire (MBB) busbars are added

    How are Solar Panels Made?

    Solar panels are made using the six main components described in detail below and assembled in advanced manufacturing facilities with extreme accuracy. In this article we will FOCUS on panels made using crystalline silicon solar cells since these are by far the most common and best performing solar technology available today. There are other solar PV technologies available such as thin film and screen printed cells, but we will not be discussing these as they have limited use or are still in development.

    Six Main components of a solar panel

    Many well known solar panel manufacturers are ‘vertically integrated’ which means the one company supplies and manufactures all the main components including the silicon ingots and wafers used to make the solar PV cells. However many panel manufacturers assemble solar panels using externally sourced parts including cells, polymer back sheet and encapsulation EVA material. These manufacturers can be more selective about which components they chose but they do not always have control over the quality of the products so they should be sure they use the best suppliers available.

    Solar PV Cells

    Solar photovoltaic cells or PV cells convert sunlight directly into DC electrical energy. The performance of the solar panel is determined by the cell type and characteristics of the silicon used, with the two main types being monocrystalline and polycrystalline silicon. The base of the PV cell is a very thin wafer, typically 0.1mm thick, and is made from either a positive p-type silicon or negative n-type silicon. There are many different cell sizes and configurations available which offer different levels of efficiency and performance including half-cut or split cells, multi-busbar (MBB) cells, and more recently shingled cells using thin overlapping wafer strips. For more detailed information on the different cells and solar panels types, see the complete solar PV cell technology review.

    Most residential solar panels contain 60 mono or polycrystalline cells linked together via busbars in series to generate a voltage between 30-40 volts, depending on the type of cell used. Larger solar panels used for commercial systems and utility scale solar farms contain 72 or more cells and in turn operate at a higher voltage. The electrical contacts which interconnect the cells are known as busbars and allow the current to flow through all the cells in a circuit.


    The front glass sheet protects the PV cells from the weather and impact from hail or airborne debris. The glass is typically high strength tempered glass which is 3.0 to 4.0mm thick and is designed resist mechanical loads and extreme temperature changes. The IEC minimum standard impact test requires solar panels to withstand an impact of hail stones of 1 inch (25 mm) diameter traveling up to 60 mph (27 m/s). In the event of an accident or severe impact tempered glass is also much safer than standard glass as it shatters into tiny fragments rather than sharp jagged sections.

    To improve efficiency and performance high transmissive glass is used by most manufacturers which has a very low iron content and an anti-reflective coating on the rear side to reduce losses and improve light transmission.

    Aluminium Frame

    The aluminium frame plays a critical role by both protecting the edge of the laminate section housing the cells and providing a solid structure to mount the solar panel in position. The extruded aluminium sections are designed to be extremely lightweight, stiff and able to withstand extreme stress and loading from high wind and external forces.

    The aluminium frame can be silver or anodised black and depending on the panel manufacturer the corner sections can either be screwed, pressed or clamped together providing different levels of strength and stiffness.

    EVA Film

    EVA stands for ‘ethylene vinyl acetate’ which is a specially designed polymer highly transparent (plastic) layer used to encapsulate the cells and hold them in position during manufacture. The EVA material must be extremely durable and tolerant of extreme temperature and humidity, it plays an important part in the long term performance by preventing moisture and dirt ingress.

    The lamination either side of the PV cells provides some shock absorption and helps protect the cells and interconnecting wires from vibrations and sudden impact from hail stones and other objects. A high quality EVA film with a high degree of what is known as ‘cross-linking’ can be the difference between a long life or a panel failure due to water ingress. During manufacture the cells are first encapsulated with the EVA before being assembled within the glass and back sheet.


    The backsheet is the rearmost layer of standard solar panels which acts as a moisture barrier and final external skin to provide both mechanical protection and electrical insulation. The backsheet material is made of various polymers or plastics including PP, PET and PVF which offer different levels of protection, thermal stability and long-term UV resistance. The backsheet layer is typically white in colour but is also available as clear or black, depending on the manufacturer and module. For a detailed analysis of the various backsheet materials used, refer to the backsheet construction article from Taiyang News.

    The ‘Tedlar’ PVF material from Dupont is known as one the leading high performance back sheets for PV module manufacturing.

    Dual glass panels. Some panels such as bifacial and frameless panels, use a rear glass panel instead of a polymer backsheet. The rear side glass is more durable and longer lasting than most backsheet materials and so some manufacturers offer a 30-year performance warranty on dual glass panels.

    Junction Box and Connectors

    The junction box is a small weatherproof enclosure located on the rear side of the panel. It is needed to securely attach the cables required to interconnect the panels. The junction box is important as it is the central point where all the cells sets interconnect and must be protected from moisture and dirt.

    Bypass diodes

    The junction box also houses the bypass diodes which are needed to prevent back current which occurs when cells are shaded or dirty. Diodes only allow current to flow in one direction and a typical 60-cell panel is divided into 3 groups of 20 PV cells, each with a bypass diode for preventing reverse current. Unfortunately, bypass diodes can fail over time and may need to be replaced, so the cover of the junction box is usually able to be removed for servicing, although many modern solar panels now use more advanced long-lasting diodes and non-serviceable junction boxes. Learn more about how bypass diodes work here.

    Solar MC4 Connectors

    Almost all solar panels are connected together using special weather-resistant plugs and sockets called MC4 connectors. The term MC4 stands for multi-contact 4mm diameter connector. Due to the extreme weather conditions, the connectors must be very robust, secure, UV resistant and maintain a good connection with minimal resistance at both low and high voltages up to 1000V.

    The connectors are designed to be used with the standard 4mm or 6mm double insulated solar DC cable with tinned copper multi-strand core for minimum resistance and increased durability. To correctly assemble the connectors a special crimping tool is used to crimp the multi-strand cable to the inner terminal which is then inserted and snapped into the MC4 housing.

    NOTE: There are several different types of MC4 connectors that may look similar but do not always fit together securely. The same type and make of connector must always be used to reduce potential water ingress or plug failure which can result in arcing and even fire. The MC4 connectors shown above and next-generation MC4-EVO-2 connectors (not shown), are both manufactured by Staubli and the only dissimilar looking connectors which are allowed to be used together.

    Solar panel assembly and manufacturing

    Solar panels are assembled in advanced manufacturing facilities using automated robotic equipment and sensors to precisely position the components with extreme accuracy. The manufacturing plants must be extremely clean and controlled to prevent any contamination during assembly.

    Throughout the manufacturing process the panels and cells are checked and inspected using advanced optical/imaging sensors to ensure all the components are located correctly and the cells wafers, which are very delicate, are not damaged or cracked during the assembly process. Depending on the manufacturer the final panel assembly is thoroughly checked using a number of tests including electroluminescent (EL) or flash testing to identify any defects in the cells which could lead to failure once exposed to sunlight and high temperatures for many years.

    Below is a video from Tindo Solar, an Australian solar panel manufacturer.

    Video showing a modern solar panel assembly plant with automated assembly and testing processes and controls Video Credit Tindo Solar

    Solar Panel degradation and faults

    Solar panels are generally very reliable as they have no moving parts and require minimal maintenance. However, they can fail or underperform over the expected 25-year life due to a number of different reasons. It is normal for the cells will slowly lose power due to what is known as light-induced degradation or LID which results in an average 0.5% loss per year. This slow degradation is often not noticeable and most solar panels will still perform at 80% or higher of the original rated capacity after 20 years depending on the type of cell used. The amount of degradation is specified in the manufacturer’s performance warranty. Read more about solar panel warranties.

    Unfortunately, solar panels can also suffer from more serious issues such as micro-cracks and more severe degradation due to a number of reasons. Any high stresses due to impacts, poor installation practices or people walking on rooftop panels can cause small fractures in the cell. These issues are often very difficult to detect and if left for several years, can develop into hot spots and cause catastrophic failures such as arcing or fire. Fortunately, there are ways to reduce the likelihood of failure and most manufacturers are improving both the panel design and manufacturing to minimise short and long term issues. Learn more about solar panel problems such as micro-cracks and hots spots here.


    Sunlight or solar energy is a free source of renewable energy which will never be depleted. Fossil fuels, on the other hand, are finite resources that emit greenhouse gases and other particulates during extraction, processing and combustion. In comparison, solar panels do not produce any emissions while in use, but they are made from several different materials which require different levels of resources and energy. The energy used to extract the raw materials and manufacture a product is known as the ‘embodied energy’. The amount of time it takes for a product to repay the embodied energy is measured in years. This is known as the total energy payback time (EPBT).

    A typical silicon crystalline solar panel will generate enough energy to repay the embodied energy within 2 years of installation. However, as panel efficiency has increased the payback time has reduced to less than 1.5 years in many areas with high average solar radiation.

    The chart below highlights the increase in emissions from the combustion of fossil fuels over the last 250 years. Image credit

    Modern efficient crystalline silicon solar panels generate enough energy to repay the embodied energy within 2 years. This is supported by multiple detailed studies and life-cycle analyses. However, many of the studies are now outdated as solar PV cell efficiency has increased from 15% to 20% (a 35% increase) over the last few years, and payback time is estimated to be as low as one year. Considering a typical solar panel will last 20-30 years, it will easily repay the embodied energy multiple times over and offset thousands of tonnes of emissions.

    Are Solar panels toxic?

    Despite the large amount of information circulating about solar panels being toxic, modern crystalline silicon solar panels contain virtually no toxic materials. The claims of toxic solar panels come from the mostly obsolete thin-film (Cadmium telluride. CdTe) solar panels which did contain trace amounts of cadmium and telluride. However, unless these (relatively rare) panels are broken up into fragments, the trace amount of cadmium is contained within the EVA layers and cannot leach out.

    Modern crystalline silicon solar panels contain only a trace amount of lead in the solder used for the cell interconnections. However, the use of solder is also being phased out with the new busbar compression joining techniques and conductive paste materials. It’s worth noting solder is used in hundreds of millions of electrical devices and appliances. There are far more toxic elements used in consumer electronic devices, mobile phones, computers, TVs, which is why electronic waste or E-waste is such a large global problem.

    Roughly 99% of the solar panels installed around the world today are of the silicon crystalline variety and do not contain cadmium or telluride. Solar panels are very benign and even when damaged they do not cause any contamination as the cells are encapsulated within very durable polymer layers and contain no readily soluble materials. However, like all appliances, solar panels need to be collected and recycled at the end of life which we discuss in the section below.


    Detailed life cycle analysis of solar PV panels and systems

    • Manufacturing Silicon Wafers
    • Electrical Engineering and Technology.

    Recycling Solar panels

    Since most solar panels installed over the last 20 years are still in use there is not a great volume of solar waste. However, over the next 10-20 years many systems will reach the end of life (EOF) and there is expected to be a very large increase in the volume of solar-related waste which will need to be recycled. Solar panel recycling is an emerging industry most of the materials are relatively easy to recycle such as the aluminium frames and mounting systems. Most solar panel manufacturers are pushing to be more sustainable and are now part of the not-for-profit PV Cycle organisation. “PV CYCLE offers members and waste holders better access to take-back and ensure recycling rates above the industry standards.”

    • In Australia, there are several companies that will recycle old or damaged solar panels including the Adelaide based ReclaimPV.
    • In Europe, the French waste management company Veolia has opened the first dedicated solar panel recycling facility in southern France which is able to recover and recycle 95% of the materials.
    • For further reading here is a great article from RENEW about solar panel recycling.

    Do Solar Panels Work Through Glass? – Houses, Campers or Cars

    Solar panels aren’t just available as large pieces of infrastructure to be placed in a field or on a roof for example. They now come in all shapes and sizes from ones that attach to your backpack to tiny ones for charging your phone. This increased portability and number of options finds us wanting to use solar panels in all sorts of places to get power. One of those places may be inside a building or vehicle and you may therefore ask, can you use solar panels through glass Windows? Well, the short answer is yes you can use solar panels through glass Windows but they will be nowhere near as effective as when placed outside. So it isn’t all bad news then, but why won’t they work optimally? Well to answer that we first need to look at how solar panels work.

    How do solar panels work?

    Solar panels are made up of lots of ‘photovoltaic cells’ which are housed between a material which is semi-conductive. The semi-conductive material is usually silicon (the material common inside all your electronics) or in older models could even be glass. An electrical field needs to be established in these photovoltaic cells. To do this the silicon is altered by adding some other elements, phosphorus to one end to give a negative charge and boron to the other to give a positive charge. This creates an electrical equivalent to a magnet with one end being positive and one being negative and this is an electrical field. So you now have electrons flowing around within these photovoltaic cells. So how does this generate power? Well, light is made up of millions of tiny particles known as photons. These photons from sunlight hit the photovoltaic cells and this knocks one of the electrons flowing around free. These electrons are then collected by metal conductive plates and can then be utilized to create electricity.

    How do glass Windows affect this process?

    You might think that being behind glass might actually be better for solar panels. We’ve all been in a greenhouse or building with lots of Windows on a sunny day and the temperature can get much much higher than outside. This is mainly due to a lack of airflow inside making it feel much hotter than if you were standing outside with a breeze.

    But regardless of this fact, to get solar panels to work we aren’t interested in temperature and the amount they heat up, we are interested in the number of photon particles which reach the photovoltaic cells (as explained above).

    Reflection/ Refraction

    So now you know solar panels are reliant on these photons reaching the photovoltaic cells to work it will be no surprise to learn that the more photons that reach the panels, the more effective they will be.

    Putting something such as a sheet of glass in the way will affect this. Even though glass lets some photons through it also reflects some as well. Those photons that do pass through the glass slow down and therefore change direction (are refracted).

    This reflection and refraction is shown simply in the image below, the incident ray is the light coming from the sun and then once that hits the glass (the light blue section) some light is reflected back at an angle and some that passes through is refracted and changes direction slightly. :

    This will always occur no matter how clean or transparent the glass but by different amounts. So for tinted glass more reflection will occur.

    blocking, diode, bypass, diodes

    Those photons that are reflected away never reach the solar panel and therefore this decreases the number of photons and thus the likelihood of an electron being knocked out of the electrical field in the photovoltaic cells.


    If your Windows are in a house or another fixed building the orientation will cause further issues.

    Outdoor solar panels are usually fixed to a south facing surface in the northern hemisphere. This is so they are exposed to sunlight for the most amount of time. Studies showed this actually makes quite a big difference to efficiency, with east and west facing panels averaging around 20% and north facing around 40% less efficient than south facing panels. In the southern hemisphere the opposite is true and panels should face north to get the most sunlight and thus generate the most energy.

    In a house you are unlikely to have Windows that face directly south and even they are unlikely to be in the roof (or facing directly up) and so will only receive sunlight through them either earlier in the day or later in the day when the sun is not at its strongest. The sun is at its strongest (highest irradiance) when at its highest point, i.e directly overhead.

    A car or caravan will give you slightly more flexibility as you can turn it to face the correct direction, even moving it to maximise the amount of sunlight entering throughout the day. But if you are driving then this is going to keep changing and Windows tend to be small in size not letting much light through.


    Being inside means you are more likely to encounter shading for many reasons. This might be a window frame or a branch of a tree outside the window. Every time your solar panel ends up in the shade this is time when it will not be able to generate electricity.

    Outside, a south facing panel will still receive some sunlight even when the sun is shining to the east or west. But inside, unless you are in a greenhouse or room with Windows all around you are likely to find the panel is in the shade for a large proportion of the day.

    Higher temperatures can make the panels less effective

    You may or may not have heard that solar panels actually work better in lower temperatures. This is partly true and very high temperatures can actually cause solar panels to work less effectively. This is because the silicon in the photovoltaic cells is an excellent conductor of heat. Studies have shown that efficiency decreases by 0.5% per degree increase over 25 o C.

    So as you can imagine inside a car or house (without the air-conditioning) it can get extremely hot due to the insulation of the external materials. It is not unusual for temperatures inside a parked car to get very high indeed and therefore this will cause even more inefficiencies on top of all the other factors already mentioned in this article.

    How to optimize panels for use behind glass?

    If you still insist on trying to use your solar panel behind glass then there are a few things you should do to optimize your chances of getting useful amounts of electricity:

    • Use a south facing window if you have the option to get as much direct sunlight onto the panel as possible.
    • If the panel is a small portable one that can be easily moved around then you can move it to different Windows depending on where the sun is at that time of day. This will give you the maximum amount of sun throughout the day.
    • Place the panels as close to the glass as possible to minimise loss from refraction and also to prevent shading from window frames or other objects in the room.
    • If you can open a window and allow the sunlight through then that is, of course, the best option but you are unlikely to be asking the question if that was an option.


    So there you have it, solar panels will work when placed behind glass but don’t expect any great results.

    That said it really depends on what you need. Obviously, if you are attempting to power your entire house, then putting panels behind glass isn’t really feasible. However, if you just want to charge a mobile phone or some small appliances in a caravan then you should be able to do that.

    Rob is the head writer at Innovate Eco sharing knowledge and passion cultivated over 10 years working in the Environmental Sector. He is on a mission to build a community of people that are passionate about solving environmental problems.

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    Most of us know that we need to act now on environmental issues. From climate change to biodiversity loss, it is clear these are some of the biggest challenges of our time. But in an ever polarised.

    As I’m sure many of you did, I sat down to on Sunday evening to watch David Attenborough’s latest ‘last ever’ series Wild Isles (David it’s time to accept you will live till at least 150.

    About Me

    Hi I’m Rob. I’ve spent over 10 years working in the environmental sector, with the belief that innovation gives us the best chance of solving the biggest issues currently impacting the planet.

    Solar Panel Diagrams – How Does Solar Power Work?

    If you are anything like me, then you find that a picture speaks a thousand words. I’ve learned all about how solar panels convert the sun’s light into electrical energy, but things only really fell into place when I saw it all laid out clearly in diagrams.

    It’s great to have visual representations to help us to understand how scientific processes work. So I’m going to use some solar panel diagrams to show you how solar cells work and then describe all of the elements that go up to make a complete home solar system.

    A basic solar cell

    The diagram above shows the key elements in a solar cell. Solar cells collect energy from sunlight and convert it into electricity using a chemical reaction called the photovoltaic (PV) process.

    Sunlight reaches our solar panel in the form of photons, small energetic particles/waves. These photons carry energy in the form of light, heat, and radiation, but it’s the light energy that a solar cell uses.

    There is an anti-reflective coating on the front of a solar panel that protects the cell inside while allowing through as much light as possible. Glass is an excellent material for antireflective coatings, so solar panels are coated in strengthed laminated glass.

    The inside of a solar cell contains a semiconductor material. Silicon is the semiconductor we use in home solar panels. A semiconductor is a material that is sometimes a good conductor of electricity and sometimes not. This changing conductivity is what we use to generate electricity.

    When photons come into contact with the semiconducting silicon, they produce a flow of charge-bearing particles called electrons. The PV cell has a front contact with a cable attached and the back contact also connected by cable. In the diagram, you can see how the contrast in electrical charge between these two contacts creates a flow of electricity to power a light bulb.

    How a photovoltaic cell works

    The diagram above gives us a more detailed look at what happens inside a solar cell. The solar cell contains two separate discs of silicon sandwiched closely together. These silicon discs are doped or specially treated to give them an electrical charge.

    The N-Type silicon on the top level of the disc has an excess of electrons (negative charge), and the P-Type silicon underneath has a deficiency of electrons (positive charge). The N-Type silicon on the top level of the disc has a positive charge, and that P-Type silicon underneath has a negative charge.

    When no light is shining on a PV cell, the differently charged positive and negative discs of silicon create a barrier between each other, and electricity can’t flow between them.

    But when photons from the sun hit the silicon discs, something special happens. When photons from the sun hit the silicon discs, they impart energy to the electrons in the P-Type silicon, enabling them to move into the N-Type layer. This movement of electrons creates an electrical current. This photoelectric effect is what produces electricity in a solar cell.

    That’s how the process works. But if our home solar systems were made up only of solar cells, they wouldn’t be of much use since we wouldn’t be able to store or use the electricity we generate. Clearly, we need several more elements to make up a complete home solar system.

    The component parts of a solar PV system

    The diagram above is a good representation of the individual components that make up a home solar PV system. Let’s look at what all of these elements do and then see how everything connects together.

    Solar Cell to Solar Array

    solar modules are sealed units that contain either sixty or seventy-two solar cells. These are carefully mounted and sealed to protect them from the elements and allow them to produce electricity for around twenty-five years. Several solar modules are connected to create a solar panel, and then several solar panels are connected to form a complete solar array.

    Note that solar modules are more often called solar panels. Even though a solar panel is a collection of several solar cells, you will find that the term solar panel, or solar module, is often used interchangeably to describe a unit of several solar cells.

    Tracking System (not essential)

    one of the key goals when positioning a solar array is to ensure that it receives the maximum possible exposure to direct sunlight.

    With most home solar systems, this simply involves angling the solar panels correctly and pointing them to the South in the northern hemisphere and the North in the southern hemisphere.

    Solar tracking systems are a way to improve on this. They use various manual or automated systems to change the angle of the panels in a solar array so that they track the movement of the sun across the sky. Tracking systems increase the amount of time that solar panels are perpendicular to the sun and can dramatically increase the amount of electricity produced.

    There is a drawback, though, because at the moment tracking systems are expensive, usually prohibitively so. The cost of the tracking system can be greater than the extra electricity generated, so few home systems use trackers. Solar tracking systems are an emerging technology with much promise for the future.


    the mounting of a solar array is simply the aluminum racking on which solar panels are mounted. On rooftop solar installations, this mounting usually cleaves a space between roof tiles and panels as temperature control to keep the panels cool.


    the different elements of a solar system are connected by cabling to transfer electricity. Cables are made from either copper or cheaper and less efficient aluminum. Because exterior cables are exposed to extremes of weather and temperature, their casing is made from special moisture and heat-resistant thermoplastic (THWN)

    DC Isolator

    A DC isolator is an important safety component of a home solar system. It is simply a switch that disconnects the solar array from the electricity network for servicing and maintenance.

    Generation Meter

    Generation meters show us how much electricity is being produced by the solar array. These provide valuable information that we can use to monitor the performance of our solar system and calculate precisely how much power our panels are generating.

    Charge Controller (not essential)

    We use a charge controller in solar systems that have battery storage. It monitors the current going into the batteries from the solar panels and ensures that the batteries don’t overcharge.

    Battery (not essential)

    Batteries are one of the ways that your home solar system stores the electricity it generates. Batteries are used in off-grid solar systems where they are the only storage mechanism for solar electricity. We charge the batteries with solar electricity and then use them to power devices in the home.

    On-grid solar systems often don’t include batteries because the solar system connects to your main electricity supply. However, batteries can be added to provide backup power in case of grid outages. Electricity is transferred backward and forwards through this network connection so any excess electricity you generate is made available to the grid as a whole.

    In hybrid solar systems, batteries are added to an on-grid connection to provide backup power in case of power outages.


    solar panels generate direct current DC electricity, but our homes use alternating current AC electricity. The inverter is where DC electricity is converted into AC electricity, making it compatible with the grid power supply and suitable for use in most household appliances.

    Fuse Box

    home solar systems, like all other home electrical systems, have a fuse box. This is a vital safety device where power surges or other problems trip a fuse, cutting power to the system and keeping it safe.

    AC Isolator (not essential)

    An AC isolator is a crucial safety element used only in grid-connected solar systems. It is a switch that you can turn off to isolate the AC power supply from the rest of the solar system for maintenance purposes.

    Electricity Meter (not essential)

    Your electricity meter connects to your home solar network in on-grid and hybrid solar systems. The meter monitors and records your electricity usage, the difference being that with your solar array connected, you are likely to see times when you’re giving more electricity into the system than you’re using and the meter will run backward.

    How a home solar system comes together

    Our last diagram provides a helpful summary of how all the components of a home solar system connect.

    In the first stage of the process, we can see how our solar modules generate DC electricity. This DC electricity is cabled through to the second stage, where an inverter converts it into alternating current AC electricity.

    After this conversion, the electricity is transferred through a fuse box for safety and then networked to our home appliances which receive power from the system.

    In an off-grid system, the fuse box also connects to a battery which is where any extra electricity is stored and used to power the network at times when the sun isn’t generating electricity.

    Things are different with an on-grid system where the fuse box connects through our electric meters to the power network, taking energy from the grid when solar production is low and giving it back when we have an excess.

    Hopefully, these diagrams have given you a clearer understanding of how solar systems work and the individual elements that make them up. If you are considering solar energy for your home or business, it might be helpful to understand the pros and cons of solar energy. If you have any questions, Комментарии и мнения владельцев, or suggestions, please share them with us below.

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