Bypass Diodes in Solar Panels

In solar panels, bypass diodes are connected in parallel with solar cells or panels to provide a current path around them in case a cell or panel fails or is open circuit.

This use of bypass diodes allows a series of connected cells or panels to continue to provide power at a low voltage, rather than having no power at all. Bypass diodes are connected by reverse polarity between a solar cell (or panel) positive and negative output terminals and have no effect on the output.Ideally, there would be a bypass diode for each solar cell, but this can lead to quite high costs, so usually one diode is used per small group of serial cells.

A "solar panel" is built using single solar cells, and solar cells are made of layers of silicon semiconductor material.A layer of silicon is processed with a substance to create excess electrons.This is a negative or N-type layer.The other layer is processed to create an electron deficiency and becomes a positive or P-type layer similar to transistors and diodes.

When combined with conductors, this silicon editing becomes a light-sensitive PN-link semiconductor.In fact, photovoltaic solar cells, or more commonly called PVs, are nothing more than large, flat light-sensitive diodes.

Photovoltaic solar cells convert photon light around the PN connection directly into electricity without any moving or mechanical parts.PV cells generate energy not from heat, but from sunlight.Interestingly, when they are cold, they are in the most efficient working range.

When exposed to sunlight (or any other intense light source), the voltage generated by a single solar cell is about 0.58 volt DC and the current flow (amperage) is proportional to light energy (photons).In most photovoltaic cells, the voltage is almost constant, and the current is proportional to the size of the cell and the intensity of light.

Bypass Diodes in Solar Panels

The equivalent circuit of a PV shown on the right is the circuit of a battery with an RINTERNAL series of internal resistor, similar to any conventional battery.However, due to changes in internal resistance, cell voltage and therefore the current present will vary between photovoltaic cells of equivalent size and structure, depending on the same load and the same light source, so this should be taken into account in solar panel assemblies.

The silicon plate of the photovoltaic solar cell facing sunlight consists of electrical contacts and is covered with an anti-glare coating that helps to absorb sunlight more efficiently.Electrical contacts provide the connection between semiconductor material and external electrical charge, such as light bulbs or batteries.

When sunlight shines on a photovoltaic cell, light photons hit the surface of semiconductor material and free electrons from their atomic bonds.During manufacturing, certain doping chemicals are added to the semiconductor composition to help create a pathway for released electrons.These pathways create a stream of electrons that generate an electric current that begins to flow over the surface of the photovoltaic solar cell.

Metallic strips are placed on the surface of a photovoltaic cell to collect the electrons that make up the positive ( + ) connection of the cell.The back of the cell, away from the incoming sunlight, consists of a layer of aluminum or molybdenum metal that forms the negative ( – ) connection to the cell.Then a photovoltaic solar cell has two electrical connections, one positive and one negative, for traditional current flow, as shown.

Photovoltaic Solar Cell Structure

Bypass Diodes in Solar Panels

When exposed to sunlight, photovoltaic (PV) solar cells produce the same DC power as those obtained from a battery or cell.Without any external circuits or loads connected to its terminals, that is, I O = 0 , most photovoltaic solar cells produce a maximum "no load" open circuit voltage (V OUT) of approximately 0.5 to 0.6 volts, much lower than a standard battery (1.5V).But just like batteries, higher voltages can be achieved by serially connecting several PV cells.

When exposed to sunlight, a photovoltaic cell produces a current (I) proportional to the level of sunlight falling on its surface.Short circuit current represents the maximum short circuit current that a PV cell called ISC can produce. It occurs when cell terminals short-circuit each other, but under these maximum current conditions the terminal voltage is zero, V OUT = 0. Then the output voltage of a photovoltaic cell largely depends on the demands of the load current from I SCto I O.This means that a PV cell is essentially a low-voltage, high-current device.

The current (and power) output of a photovoltaic cell is proportional to the intensity of sunlight hitting the surface of the cell.For example, cloudy or dull days reduce the effectiveness of a PV cell, so the maximum current it can provide to a certain load is low, but the cell can still provide full output voltage.To increase the current requirements of the payload, a brighter, larger amount of solar radiation will be required to provide full power.

However, no matter how intense or bright the solar radiation, there is a physical limit to the maximum current that a single photovoltaic solar cell can provide due to its size (surface area).This is called maximum deliverable current and is symbolized as I MAX.

Therefore, when choosing blocking diodes or bypass diodes to connect to solar cells or panels, this maximum current value I MAX should be taken into account.

Diodes in Photovoltaic Sequences

The PN-connection diode acts as a solid state one-way electric valve that allows the electric current to flow through itself in only one direction.The advantage of this is that diodes can be used to block the flow of electric current from other parts of an electrical solar circuit.When used with a photovoltaic solar panel, this type of silicon diode is often called Blockage/Blocking Diodes.

Bypass Diodes are used in parallel with single or several photovoltaic solar cells to prevent current(s) flowing from solar cells exposed to sunlight from overheating and burning weak or partially shaded solar cells by providing a current path.Blocking diodes are used differently from bypass diodes.

Bypass diodes on solar panels are "parallel" to a photovoltaic cell or panel to shunt the current around them, while blocking diodes are "serially" connected to PV panels to prevent the current from flowing back.Therefore, blocking diodes differ from bypass diodes, although in most cases the diode is physically the same, but they are installed differently and serve a different purpose.

Bypass Diodes in Photovoltaic Arrays

Bypass Diodes in Solar Panels

Diodes, as we have said before, are devices that allow the current to flow in only one direction.Above, green diodes are "bypass diodes", which are parallel to each solar panel to provide a low-resistance path.Bypass diodes in solar panels and arrays should be able to safely carry this short-circuit current.

Two red diodes are called "blocking diodes", which are serialized with each series of branches.Blocking diodes are different from bypass diodes, but in most cases the two diodes are physically identical.But they are set up differently and serve a different purpose.

These blockage diodes, also called serial diodes or isolation diodes, allow the electric current to flow to the external charge, controller or batteries in the direction of only one "OUT".

This is due to preventing the current generated by other parallel connected PV panels in the same array from flowing back over a weaker (shaded) network, as well as preventing full-charge batteries from draining from the array at night.Therefore, when multiple solar panels are connected parallel, blockade diodes should be used in each branch that connects parallel.

Generally speaking, blocking diodes are used in PV arrays when there are two or more parallel branches, or when there is a possibility that part of the array will be partially shaded during the day while the sun moves through the sky.The size and type of blocking diode used depends on the type of photovoltaic array.

There are two types of diodes as bypass diodes in solar panels and arrays: PN-connected silicon diode and Schottky barrier diode.Both are available with a wide range of current ratings.The Schottky barrier diode has a much lower forward voltage drop of about 0.4 volts, as opposed to the 0.7 volt drop of PN diodes for a silicon device.

This lower voltage drop saves one full PV cell in each branch of the solar array, so the array is more efficient because less power is expended on the blocking diode.Most manufacturers use both blocking diodes and bypass diodes in solar panels that simplify the design.