An inverter is an electronic device that converts the direct current produced by the solar panels into an alternating current. In other words, it is a low voltage current converter (12, 24, or 48 Volts) into a high voltage current (120 Volts). This conversion is necessary since almost all our electronic devices require alternating current for their operation.
The power of an inverter is a testament to the amount of direct current it can transform into alternating current. Thus, the more powerful an inverter, the greater the amount of electricity it can convert during operation. It is therefore important to properly size the inverter in a solar energy system so that it can be able to convert all the energy produced by the solar panels.
The amount of energy that an inverter converts depends on its power and the duration of its use. The powers of the most common solar inverters vary from 4 to 8 kW.
In the case of a solar energy system with a central inverter, the inverter is connected at the end of the series of solar panels. There is only one inverter for all the panels. It must therefore be powerful enough to manage on its own the transformation of the direct current from the solar panels into an alternating current. If the total power of the solar panels is greater than that of the inverter, additional inverters must be installed (until the same power is achieved as that of the solar panels). In this case, the inverters will no longer be central, but well connected in “strings”, or independent rows.
In the case of a solar energy system with microinverters, each panel is connected to a microinverter. Microinverters have the same function as regular inverters, the difference being that there are several microinverters which transform the direct current of the solar panels rather than a single centralized inverter. The goal of using microinverters is to increase the overall energy productivity of the solar energy system by optimizing the individual energy productivity of each of the solar panels.
The image below schematizes these words.
The main advantage of using a single inverter is the price. Having a single central inverter installed generally costs less than having a multitude of microinverters installed (even if their cost is less per unit). This is explained by the fact that a solar energy system with microinverters needs as many microinverters as solar panels, which increases the overall price of the system.
The downside is in terms of power generation. The central inverter does not produce less than several microinverters in normal times, but in the event of a panel failure or in the case where a cell of a panel is shaded, it is the whole series of panels who suffers the consequences. This is explained by the fact that the cells of a solar panel are connected in series (to obtain more power and thereby better production of electricity) and that the energy produced by a chain of cells is determined by the one that produces the least. When a cell is shaded, the whole series is impacted. In other words, even if a 72-cell panel has only one shaded cell, the energy produced by the entire panel will be less. Thus, having a single inverter means that in the event of failure, energy productivity is lower.
The same logic applies for inverters connected in string. When a panel in the string (or in a row) is shaded, all the following panels produce less energy.
The image below shows the effect of shading on the cells of a solar panel. In the case of the image, even if it is only the 5th cell in the series that is shaded, all the following cells in the series will not generate electricity (even if they are not shaded). This phenomenon can be observed for any type of photovoltaic solar panel, regardless of the manufacturer.
The main advantage of using microinverters is the optimization of energy production from solar panels. In the event of a panel failure, the other panels always produce optimally and are not limited by the panel which produces the least. With microinverters you do not necessarily have more energy gains, but you limit losses, which increases your overall electricity production.
The downside of microinverters is the price since you multiply the cost of microinverters by the number of solar panels. Although the energy production of solar panels is increased (by limiting potential energy losses), it up to you to judge whether the additional cost is worth it.
However, you should not forget the fact that central inverters have a 10 year warranty while microinverters have a 25 year warranty, the same warranty period as that of your solar panels. You may therefore be forced to install a second central inverter within 25 years of the life of your solar power system, which would likely offset the initial overhead of microinverters. It is up to you to decide whether you prefer to have a single inverter (buy twice in 25 years) or multiple microinverters (purchased only once in 25 years).
In the same logic as for the previous image, the image below shows the impact of near and far shading on the productivity of your solar energy system according to the type of inverter installed.
To summarize, micro-inverters optimize the energy production of your solar panels but are more expensive while central inverters (or in strings) are less expensive but are more sensitive to panels which produce less energy due to close shading. and distant or of some failure. From a theoretical point of view, the two types of inverters are equivalent.
That said, from a practical point of view, the choice of the type of inverter depends on the architecture of your house’s roof and the area where the solar panels will be installed. Indeed, when the solar panels point in one and the same direction (all facing south, for example), it is more advantageous to opt for a central inverter. This is justified by the fact that energy production takes place without any lag and that it is easier to manage centrally (the panels start and stop producing energy at the same time). However, when the panels point in several directions (ten facing south and ten facing east, for example), it is more advantageous to opt for micro-inverters since the energy production is offset and more difficult to manage by a single inverter (the panels facing east produce energy earlier than those facing south, but stop producing energy earlier than those facing south, which reduces the efficiency of the panels facing south if the panels facing east are connected in series with those facing south).
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