There are two types of electrical current: direct current (DC) and alternating current (AC). Both types of current power electrical and electronic devices, but both have intrinsically different properties and advantages. Our homes and offices use alternating current because AC is safer and more manageable.
But electricity generated by solar panels comes in the form of direct current (DC). So, what do we do to make it usable for our homes and offices where AC electricity is used?
That is where solar inverters step in. Read on as we explain what is a solar inverter, different types of inverters , how solar inverter works, and which type of inverter is best for your home.
What is a solar inverter?
A solar inverter is an electrical device that converts direct current (DC) electricity to alternating current (AC) electricity. It is a key component of the solar panel system, without which the electricity generated by solar panels would not have the kind of utility it has today.
If solar panels are considered the heart of a solar system, the inverter can be called its brain.
A solar energy system can also work without inverters, but its functions would be limited only to running a few devices, such as fans, and not your whole home. If you want to use solar energy for your entire home and connect your solar system to the grid, you must use inverters.
In addition to converting DC to AC, solar inverters also perform other functions, such as regulating voltage, monitoring performance, optimizing power output, and keeping a record of electricity produced.
How does a solar inverter work?
Solar panels generate electricity when sunlight falls upon them. This is due to the flow of electrons, but this flow is unidirectional, moving in a straight line with a 0 Hz frequency. It is called direct current (DC), which needs to be switched to alternating current (AC)—alternating current is in the form of sine waves, with ups and downs and a frequency of 50 to 60 Hz.
All our domestic appliances work on alternating current (AC).
When direct current is passed through an inverter, it goes through multiple electronic components such as transistors, transformers, and frequency oscillators. These components convert 12-volt direct current to the desired voltage and frequency. 120V AC at 60 Hz frequency is standard in the United States, but other combinations, such as 230V at 60 Hz, also exist. In much of the world, the AC voltage is 230V at 50 Hz.
Types of solar inverters
There are three types of solar inverters: string inverters (also known as central inverters), micro-inverters, and power optimizers. The latter two are called “Module-Level Power Electronics (MLPEs).” They all have the same task of converting DC electricity to AC electricity, but for one homeowner, one type of inverter would be more suitable than the others. The key difference lies in their working and performance monitoring.
Let’s break each solar inverter technology down.
- String inverters
String inverters are the oldest type of inverter, where DC electricity is collected from each panel and then fed into a centralized inverter. The central inverter converts the total DC coming from all panels to the total AC output.
In solar systems where string inverters are used, a set of solar panels are arranged into groups, with each panel connected to the other, forming one string. Multiple strings can be made (usually, not more than three) and connected to your central inverter. String inverters are best for properties with no shading and simple roofs where all panels receive the same amount and intensity of sunlight.
Pros of string inverters
- A string inverter is the most cost-effective option, as you need only one inverter to convert all the DC output to AC output.
- It also helps property owners easily monitor the performance of their systems.
- String inverters are also easy to maintain, repair, and replace.
Cons of string inverters
- If an individual solar panel has issues (shading or malfunctioning), it will affect the performance of all panels.
- You cannot track the performance of or diagnose issues in individual solar panels in string inverters.
- String inverters are unsuitable for complex roofs, where panels face the sun at different angles.
- Micro-inverters
String inverters had certain issues—for example, the performance of all solar panels gets compromised due to one panel. Micro-inverters were introduced in the market to address this issue and give solar shoppers more control over the optimization of their solar systems.
Unlike central inverters, micro-inverters are connected to each solar panel and convert DC to AC at the source right at the modular level. The AC electricity coming from each panel is fed to the main electrical distribution box, from where it goes to your home.
Micro-inverters work best for homes with uneven and shaded roofs, where some panels get more exposure to the sun than others. The DC/AC conversion takes place right at the panel, ensuring that the performance of other panels is not affected due to an issue in one panel.
Pros of micro-inverters
- Shading or malfunctioning does not affect the power output of the whole solar system.
- Best for uneven rooftops where panels face different directions.
- Micro-inverters allow solar owners to track the performance of individual panels.
Cons of micro-inverters
- Micro-inverters have a higher upfront cost. But if there is shade on your roof, the higher initial cost would be worth the improved performance of your system.
- Since inverters are installed on roofs, it is difficult to maintain, repair, and replace faulty inverters.
- Power optimizers + string inverter
Think of power optimizers as a middle ground between string inverters and micro-inverters. Like micro-inverters, power optimizers are attached to individual panels. But they don’t convert DC to AC; instead, they “condition” the DC electricity by optimizing the performance of individual panels.
The conditioned DC electricity is then sent to a central inverter, where it is converted to AC electricity.
Installing power optimizers in combination with a central inverter is a cost-effective option for homes with shaded and uneven roofs. Since the output of each panel is optimized at the modular level, any issue in an individual doesn’t affect the performance of the whole system.
Note that power optimizers are not inverters. You will always have to install them in combination with string inverters.
Pros of power optimizers
- Less expensive than micro-inverters
- More efficient than using only a central inverter. Unlike in a simple string inverter setup, the impact of shading is offset by the ‘conditioning effect’ of power optimizers.
- You can monitor the performance of individual solar panels.
Cons of power optimizers
- Power optimizers cost more than installing only a string inverter. But if there is a shade on the roof or the roof is uneven, you will have to install power optimizers with a central inverter.
- Like micro-inverters, they are installed on the roof and hence, more difficult to maintain and replace.
Which type of inverters is best for me?
There is no one-size-fits-all answer to this; it all depends upon the specifics of your property and roof structure.
We have discussed different types of inverters, with their pros and cons. As a rule, if you have shade above your property, it is better to go with micro-inverters. You can also go for power optimizers with a string inverter if you find micro-inverters expensive.
The same goes for uneven roofing. If solar panels installed on your rooftop do not get uniform sunlight, or if they face the sun from different directions, we would recommend micro-inverters or power optimizers + central inverters.
In contrast, if your roof is clear of shading and where panels can be installed in such a way to get uniform sunlight, choosing a central inverter would be the best option.
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