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One of the key decisions when installing solar panels on your roof is the type of inverter you are going to use. The solar inverter or power inverter is one of the most important elements of a self-consumption installation, and probably the most unknown.
What is an inverter? A solar inverter is a converter that transforms the direct current received from the photovoltaic panels into alternating current, which you can use in your home, store in batteries or feed into the grid. When purchasing an inverters for your home, cabin, or RV, you’ll quickly find there are two main types solar inverters, you can easily distinguish the pure sine wave inverter from modified sine wave inverter.
What types of solar inverters are there?
In the case of residential solar self-consumption, three main types of solar inverters are used: string inverters, microinverters and power optimizers. In the solar industry, microinverters and power optimizers are referred to as “module level power electronics” or MLPEs (Module Level Power Electronics).
Today, string inverters and power optimizers are the most widely used residential inverters worldwide, with a high market share. However, microinverters are starting to make inroads, as they have managed to reduce many manufacturing costs.
How do photovoltaic inverters work?
When our photovoltaic panels receive sunlight, electrons begin to move inside the solar cells, producing continuous electricity. The circuits inside the photovoltaic cells collect that energy for use in our home or business.
This is where the solar inverter comes into play. Most homes use alternating current electricity, not direct current, so the energy produced by the solar panels is not useful on its own. When the solar panels collect the sunlight and convert it into energy, it is sent to the inverter, which receives the DC electricity and converts it to AC power.
This is when the solar electricity can power appliances and electronics. If we are producing more electricity than we need, we can also store it in batteries or feed it into the grid to receive financial compensation in return.
Main functions of the solar inverters
Energy conversion: The solar photovoltaic inverter converts direct current into alternating current, which is used by all our electrical appliances at home.
Energy optimization: Maximizes the power generation of the solar panels. To do this, the panels are isolated individually in order to increase energy production, and therefore improve the overall performance of the installation.
Monitoring and protection: A solar inverter tracks the PV system’s energy yields, electrical activity and signals when problems arise. This information can be viewed at the device itself or from another location if the appropriate communication technology and online services are implemented.
Which solar inverter to choose for your self-consumption system with solar panels?
Surely you have doubts about what type of solar panel inverter is best for your home or business. They all have the same function, however, there are some differences between them.
String inverters are currently the most widely used option worldwide. If your house has a roof that is not affected by shading and has only one direction, they are a good choice.
For example, if your house has a gable roof, it will be a good solution if you only put solar panels on one of the skirts, but if you put them on both you will be facing a bad solution.
Most small-scale solar power systems use a string inverter, also known as a “centralized” inverter. In a self-consumption system with a string inverter, each panel is connected in series. When they produce power, it is all sent to a single inverter, which is usually located on the side of the house, in the garage or in the basement. The inverter converts all the green energy your solar panels generate into electricity you can use in your home or business.
Pros: String inverters are the lowest cost option and are a proven technology. They are also easy to maintain, as they are located in easily accessible places.
Cons: If our system uses a string inverter, it will only produce as much useful electricity as the solar panel that produces the least. Electricity generation in a string inverter installation can suffer from the “bottleneck” effect, or be drastically reduced, if only one or two of the panels are shaded or not working properly.
Ideal for: Homes with “unobstructed” roofs that receive radiation consistently throughout the day, and for homeowners looking for photovoltaic systems at the lowest cost.
How string inverters work
Solar panels are connected in series with each other and grouped in strings. Each string is connected to a single solar power inverter, which is responsible for converting the direct current from the panels into alternating current. The string inverter was developed decades ago, so it is a mature, proven and efficient technology, but it is not suitable for certain types of installation.
Due to its principle of operation, a string inverter draws as much electricity as the least efficient panel in the string, i.e. if a single panel in the string is affected by a shadow at any time of the day or in a stationary manner, the entire string power is reduced to the power of the panel in the shaded area. As a consequence, the string inverter is not a good solution when your panels face in several directions or are affected by shadows.
These shadows caused by surrounding objects are one of the main reasons why a panel significantly decreases, or even cancels, its production. Therefore, a good solution to avoid a shaded area of your roof is to remove the shading object or not to install in the shaded area.
Microinverters have recently gained popularity in residential PV self-consumption. However, microinverters tend to be more expensive than string inverters and power optimizers but have certain advantages. Over time, the cost of microinverters continues to decrease, which has a direct impact on increasing sales.
While a string inverter can be considered a “centralized” inverter, microinverters are “distributed” inverters. In self-consumption installations with microinverters, each solar panel has a small solar inverter installed. Instead of sending power from all the panels to a single inverter, microinverter systems convert DC solar power to AC power on the rooftop itself.
Pros: Microinverters are more efficient than string inverters. Solar panel installations that benefit from this technology continue to produce power even if one or two of the panels in the system are underperforming. They also allow the performance of specific solar panels to be monitored, making it easier to identify production problems should they occur.
Cons: Microinverters cost more than a string inverter, and are more difficult to maintain or repair in the event of a problem, since they are located on the roof.
Ideal for: Homeowners who are willing to pay more to increase the efficiency of their solar panel system.
How microinverters work
Microinverters are installed individually on each solar panel. Each one of them is an independent converter that transforms direct current into alternating current on site, without the need for the direct current to travel to the inverter center as is the case with string inverters. Microinverters can be integrated directly into the solar panel or located close to it, in the metal structure.
The main advantage of microinverters over string inverters is the elimination of the negative impact of partial or total shading. Consequently, production increases because the “bottleneck” effect, produced in string inverters, is eliminated. In addition, microinverters allow individual monitoring of each panel.
Power optimizers combine the best of string inverters and microinverters, but are slightly less expensive than the latter. Like microinverters, power optimizers are located on the roof next to – or integrated with – the individual solar panels. However, systems with power optimizers still send power to a centralized inverter.
Power optimizers do not convert direct current electricity to alternating current at the solar panel site. Rather, they “condition” the DC electricity by setting the voltage of the electricity as it is sent to the PV inverter. A solar panel installation with power optimizers is more efficient than one using only a string inverter.
Pros: They improve the efficiency of the installation, offer the advantage of monitoring the performance of each solar panel individually, and reduce the effect of shading on the performance of the installation. Installations using power optimizers are more affordable than microinverters and have lower maintenance costs.
Cons: An installation with power optimizers will cost more than an installation with a string inverter.
Ideal for: Homeowners who want to maximize the output of their solar panel installation and not worry about costly maintenance. Homes that have “complicated” roofs with gables, chimneys or other objects that may cause shading.
How power optimizers work
Like microinverters, power optimizers are devices attached to the back of each solar panel, allowing it to operate independently of the other modules in its row.
The main difference with microinverters is that power optimizers do not convert direct current to alternating current. They are direct current to direct current converters whose function is to modify the operating point of the I-V (Intensity-Voltage) curve of the panels that receive shading, while the rest continue to operate the same. In other words, the power optimizers follow the MPPT (maximum power point) with fixed V (fixed voltage) of each circuit, which allows the intensities of the string connected to the string inverter to be unified.
Like microinverters, they allow individual monitoring of each solar panel, reducing the effect of shadows on the operation of the solar photovoltaic system. Installations using optimizers are more affordable and have lower maintenance costs.
Summary of key concepts
1. The function of solar inverters is to transform direct current, coming from the PV system, into alternating current for domestic use.
2. There are three types of solar inverters: string inverters, microinverters, power optimizers.
3. MLPE technologies (microinverters and power optimizers) are more expensive because they have more electronic equipment.
4. If any solar panel of the photovoltaic installation is affected by shading or the installation is located in several directions (complicated roofs), MLPEs technologies are the best solution.
5. Microinverters and power optimizers make it possible to monitor the production of each panel individually.
- Microinverters and power optimizers allow your PV system to have a slightly higher production.
How to choose the best solar inverter option?
Now that we understand how solar inverters work, the next step is to decide which type is best for our electric self-consumption installation. You must analyze all the options, as not all PV inverters are good alternatives. In the end, the choice comes down to how much we are willing to pay for a higher yield, and whether we are willing to pay for possible additional maintenance.
At renogy we can help you make that decision about your solar inverter options. By registering your home, you will receive a personalized offer, and you will be able to evaluate the costs and benefits of different solar inverter options. We will walk you through the process and answer any questions you may have. Start saving on your electricity bill now by producing your own green energy.