João Lucas de Souza Silva

Have you ever encountered losses in a photovoltaic system due to shading? Or cases where the photovoltaic modules would have to be placed at different inclinations or orientations? These are typical cases in which the photovoltaic system designer has the difficult task of proposing alternatives to reduce losses during the energy generation process. It is on these occasions that modular photovoltaic architectures with MLPE (module-level power electronics) devices stand out. This type of architecture includes microinverters, which are already widely used on the market, and power optimizers. In this article, we will talk about the advantages of power optimizers in photovoltaic systems. In short, they offer the following possibilities in a photovoltaic installation: solar panels with different angles and orientations in the same string; panels of different powers in the same string; strings with different numbers of panels in the same inverter; reduction of the effect of shadows on the photovoltaic modules; MPPT per module (maximum power point tracking); greater safety with the reduction of open circuit voltage when the system is off; total elimination of the risk of electric arcs and fires. What is a power optimizer? The power optimizer for photovoltaic systems is a device whose main function is to reduce losses in a photovoltaic system, increasing the efficiency of the system. The generic architecture of a photovoltaic system with power optimizers is shown in the following figure. The central idea of the system with optimizer is that the solar panels are not connected directly to the DC-AC inverter. Instead, the panels are connected to DC-DC converters that pre-process the energy before delivering it to the inverter. Direct current (DC-DC) converters can be interconnected in series or parallel, supplying power to a conventional inverter or to a specific inverter for use with power optimizers. The choice of connection method or type of inverter varies depending on the manufacturer and model of power optimizer, as there are several ways to carry out the optimization process. The architecture that employs series optimizers has been more common on the market, as we will see below. Figure 1: Generic photovoltaic architecture with power optimizer In general, power optimizers perform optimization by locating the maximum power point for each photovoltaic module. Thus, unlike the string or central inverter, which seeks the maximum power point considering the output of the set of photovoltaic modules, the optimizer operates individually on each photovoltaic module, increasing the precision in locating the maximum power point. Thus, in situations where a photovoltaic module limits others due to being shaded (altering the system's global IV curve), the existence of the optimizer will ensure that this limitation does not occur to a considerable extent. Although the idea of the optimizer is to act individually on each solar module, there are optimizer options on the market that work with up to two modules. Advantages of optimizers Photovoltaic systems with power optimizers have the following advantages, including some that we have already mentioned at the beginning of this article: Increased efficiency (greater energy generation) provided by the location of the maximum power point per module; Ease of maintenance due to the possibility of isolating the defective photovoltaic module from the system; Reduction of energy losses due to mismatch (losses caused by power differences between the modules of a string); Possibility of using modules of different brands and characteristics; Possibility of installing modules at different angles, orientations and shade conditions; Greater safety in the electrical installation, reducing the open circuit voltage of the strings; Option of individually monitoring the energy produced by the photovoltaic modules. Regarding the advantages mentioned in the previous paragraph, it is worth highlighting an important characteristic of photovoltaic systems with optimizers: the elimination of the risk of electric arc, which is a very frequent problem in conventional photovoltaic systems. The optimizers have an automatic shutdown system when an electric arc is detected, making photovoltaic systems completely immune to fires. Architecture with SolarEdge optimizers The figure below shows how the power optimizers operate considering the SolarEdge architecture. Figure A shows the system working without shading and Figure B with shading. In the system without shading, the output voltage of the optimizers is divided equally, bringing the value closer to the inverter's DC link. When a photovoltaic module is shaded, the optimizer output voltage for the shaded module is reduced and the other voltages are increased in order to maintain the same current at the output of each optimizer and the voltage on the DC link. Figure 2: Operation of power optimizers. Adapted from Optimizer vs. Microinverter Now that you know what a power optimizer is, you might be wondering, "What's the difference between a power optimizer and a microinverter?" Well, the main difference is in the losses during the DC-AC conversion process (from direct to alternating current). In systems with optimizers, the DC-AC conversion is done in the inverter, while in microinverters the conversion is done in each of them. In the latter case, there is an increase in conversion losses. It is worth noting that, even so, the efficiencies of photovoltaic systems with power optimizers and microinverters are really close. The line between microinverters and optimizers is very thin, but optimizers can be more advantageous. The economic viability of using optimizers, compared to using microinverters, increases as the power of the photovoltaic system increases. In short, in very large systems the optimizer ends up being cheaper than the microinverter. Considerations: Optimizers are very interesting and offer many advantages, as we mentioned earlier. If the solar system is subject to shadows, optimizers are undoubtedly an excellent option. However, in any type of system (even without shadows), optimizers increase energy generation, because even in homogeneous solar irradiation conditions there are always modules with different characteristics in the strings. The presence of individual MPPT systems for each photovoltaic module is a factor that increases the efficiency of photovoltaic systems in any case. This is especially true when modules are installed at different angles and inclinations, conditions in which traditional string inverter systems do not perform well. If the safety of photovoltaic installations is an important aspect for the designer or owner of the photovoltaic system, the use of optimizers is very attractive. It is worth highlighting that the best solution for reducing losses is a well-designed photovoltaic system, even in problematic scenarios. Therefore, before opting for systems with MLPE (optimizers and microinverters), the designer must check the positioning of the photovoltaic modules in the best possible way. That is why it is very important to use photovoltaic system simulation software such as PVsyst, Helioscope or SolarEdge Designer. There are advantages and disadvantages to all photovoltaic system architectures. The objective of this article was to present the advantages of optimizers, not only in relation to optimizing energy generation in systems with shadows and modules in different operating conditions, but also in terms of safety. If we mainly analyze the safety aspect of photovoltaic electrical installations, optimizers become a good choice for any type of photovoltaic system, as they eliminate the risks of electrical arcs and fires. Be prepared for changes in the energy sector. Access the solar energy magazine now.Canal

João Lucas de Souza Silva

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Understand optimizers for photovoltaic systems