Solar inverters are the operational brain of photovoltaic (PV) systems, making them one of the most important components of a solar system. Since solar panels generate power in DC, which is not useful for most home appliances, you will generally need a solar inverter.
In this article, you will learn about solar inverters, the different types available, and the pros & cons of each one of them. Finally, we will give you some important tips to help you choose the best solar inverter for you.
Basics: What is a solar inverter? How does it work?
Understanding what a solar inverter is and its importance
When your solar panels are exposed to sunlight, photons hitting the surface of the modules will release electrons by a phenomenon called the photovoltaic effect. While solar panels generate electricity, this does not mean that you can directly use it on your appliances since solar panels generate DC power and not AC.
Most electronics and appliances (with a few exceptions) operate directly with AC energy. This means that you need to convert the DC power into AC, which is where the solar inverter comes in.
So, what is a solar inverter? Long story short, the solar inverter is the electronic component responsible for converting DC into AC energy, using solar panels or solar batteries as the energy source.
How does a solar inverter work?
The solar inverter for homes, connects directly to the solar panels on the DC side, while on the AC side is connected to the home and the grid (for grid-connected homes). Homes with a battery backup system, also have the batteries connected to the DC side of the inverter.
The inverter operates by stepping up or down the DC voltage, depending on the operating voltage of the solar array and the input voltage of the inverter. During the stepping process, this device usually takes the voltage to 145V DC considering voltage losses due to the operation of the circuit, but this might vary depending on the solar inverter manufacturers and models.
Once the solar inverter reaches the right voltage, it uses a complex MOSFET circuit to create a sine wave that simulates the 120V AC sine wave coming from the grid (the standard in countries like the United States, Canada, etc.). High-quality Inverters for solar panels, create a Pure Sine Wave (PSW), while older or cheaper models, might create a Modified Sine Wave (MSW).
What are the different types of solar inverters? (Pros and cons)
There are different types of solar power inverter options suiting PV systems. Depending on several factors like the type of solar system, budget, and the performance you want to get from it, you might choose one or another. In this section, we explain the different types of solar inverters, alongside their pros and cons.
Standard String Inverters
Most PV systems use standard string inverters. For this inverter, panels need to be wired into strings, by connecting the positive end of the first panel to the negative of the second one, and so on. PV systems often have several strings in parallel, increasing the power rate of the system.
The solar array is then directly plugged into the inverter for DC-AC conversion. This option is more commonly used as a solar grid-tied inverter, for homes with no battery backup systems. Solar inverter pricing for these models is generally the lowest, which is why they are the most used technology PV applications.
Standard string inverters include one or several Maximum Power Point Tracking (MPPT) inputs for the PV system. This technology pinpoints the ideal voltage (Vmpp) and current (Impp) in the I-V curve of solar panels, to optimize power output from the PV system.
The main disadvantage of standard string inverters is that they are subject to the shading effect. With the shading effect, a solar panel in a string that is partially shaded, will have lower performance and drag down the performance of the whole system. The reason for this is that a string can only perform as best as the lowest-performing solar panel in the string. An example can be seen in the figure below. This is why systems using standard string solar inverters will have lower performance under shading conditions.
- Robust and matured technology
- Cheapest and most conventional option
- Simpler installation
- Lower performance against partial shading
- Low performance against multiple orientations conditions
- Higher mismatch losses
- Minimum system size requirements
- Lower reliability of system upon failure on a single panel
- Higher DC voltage systems (not as safe)
- Future expansion of the system may need inverter replacing
- No battery compatibility
- Exposed to PID losses effect
Optimized String Inverters
Optimized string inverters are among the best options for solar systems with partial shading. This type of inverter is similar to the standard string inverter, except that in this case a power optimizer is included for each panel.
The power optimizer is a Module Level Power Electronics (MLPE) device connected to each solar panel. This device performs the MPP tracking individually for each panel and monitors their performance. This allows isolating low production modules under partial shading avoiding further impact on the rest of the array. MLPE device can also turn off the panel in case of a fire. The MLPE power optimizer is an excellent device to optimize and make your PV system safer.
- Highly reduces shading effect
- Monitors the system at module level
- Better performance against multiple orientations conditions
- Higher reliability upon a single panel failure
- Lower mismatch losses
- Generally includes rapid shutdown NEC 2017 requirements
- More expensive than standard string inverters
- DC voltage can still be high.
- Exposed to PID losses effect
- Expanding the PV system may require inverter change
The solar micro-inverter is considered a distributed inverter system installed at each solar panel, meaning is another type of MLPE device.
The solar micro-inverter is a very small solar inverter connected directly to the output of each panel, converting DC into AC energy right at the output of the panel. This inverter allows you to monitor each panel and optimizes the performance of solar systems by reducing the effect of shading.
Since the voltage output for solar panels with a solar micro-inverter is generally 240V AC, solar arrays with this type of inverters are connected in parallel. By using this type of inverter, homeowners can increase or reduce the size of their system, without changing other components.
- The solar micro-inverter delivers a higher performance against shading
- Monitors the system at module level.
- System expansion can easily be done by adding another micro-inverter
- Mismatch losses are reduced to minimum
- No PID effect
- DC voltage is maintained low (safer)
- Built-in rapid shutdown system
- High system reliability upon single panel failure
- Highest cost
- Compatibility with battery systems is exclusive to some models
Hybrid Inverter Systems
A commonly used inverter for battery-backed homes and off-grid homes is the hybrid inverter system. This inverter combines the solar grid-tied inverter with a battery inverter, controlling the whole solar system in one single component.
A hybrid solar inverter has the capacity of powering the load directly, by converting energy from either the solar panels or the batteries. On top of that, when panels generate excess energy, the inverter will charge the batteries, keeping them charged for later usage.
- Especially designed to install battery backup systems
- Multiple components combined into a single one
- Most cutting-edge technology
- Smart-home energy management generally included
- Low performance against shading effect
- Low performance for multiple orientations PV systems.
- Hybrid inverters are the most expensive options after microinverters
- Expansion of the PV system or the battery bank, may require a re-sizing of the inverter
- Minimum system size requirements
- Low reliability of the system upon failure of a single solar panel
How do the different types of solar inverters compare?
Each of the inverters for solar panels has unique features setting them aside from the other options, while some might share some aspects. In the following table, we compare them all and highlight the best features for each category.
|Standard String Inverters||Optimized String Inverters||Microinverters||Hybrid Inverter Systems|
|Aesthetics||Simple box design||Simple box design||Not visible||Simple box design|
|Cost||Cheapest option||Medium cost||Most expensive option||Medium cost|
|Ease of System Maintenance||Hard to detect failure of a single panel||Performing maintenance is easier, since you can detect failure in a single panel||Performing maintenance is easier, since you can detect failure in a single panel||Hard to detect failure of a single panel|
|Shade Mitigation||Does not mitigate the shade effect||Mitigates shade effect||Mitigates shade effect||Does not mitigate the shade effect|
|System Monitoring||You can monitor the system as a whole||You can monitor each panel||You can monitor each panel||You can monitor the system as a whole|
|Battery Control||Not included||Not included||Not generally included||Included|
|The best option for grid-tied solar systems under a budget||Best cost-performance relation for grid-tied solar systems||Best performing option for grid-tied solar systems||Best for off-grid homes and grid-tied homes with battery backup|
Which type of solar inverters should I choose? (Things to consider)
When looking to get the best solar inverter for your home, it is important to consider some aspects to choose the right inverter type. Here are some details to consider.
Rated Power and Peak Efficiency
If you are looking to get a centralized inverter like the hybrid, optimized, or standard, you should consider the rated power of your solar system. In any case, the PV system rated power must be below the maximum input power of the inverter. If you are looking to get microinverters, you must verify that the micro-inverter can handle the rated power of the solar panel.
In addition, looking at the inverter’s rated efficiency is also important to compare among similar options. Inverters should have efficiencies above 95% to be considered good.
To connect to the grid and to operate your appliances properly, you need to have the right inverter frequency. For systems in the U.S., you will need an inverter operating at a frequency of 60 Hz, while in Europe you would need 50 Hz.
Maintenance and Monitoring
Like everything, PV systems require maintenance. Using standard or hybrid solar inverters will make maintenance harder, since you cannot pinpoint a problem on a single solar panel.
With optimized string Inverter or microinverters, you can monitor the performance for each panel, meaning that you can easily spot any solar panel that is performing poorly or that is malfunctioning.
Grid-tied or Battery-Based
For grid-tied systems, you will need to choose among standard inverters, optimized inverters, or microinverters.
On the other hand, if you are installing a battery-based PV system, you will need to go with a hybrid inverter system, since this inverter allows you to keep batteries charged and monitor the whole system with a single component.
Will you need shade mitigation?
If your solar system does not get shaded at all and the strings only have panels from a single orientation, then you will do just fine by installing a standard string inverter. However, if your solar system performs poorly at certain hours due to shading or has multiple orientations, it might be better off to get an optimized inverter or microinverters.
The solar inverter is one of the most important components of your solar system. Choosing the best solar inverter is key to getting the best performance for your PV system.
We recommend you pick your inverter according to your budget, type of solar system, and which features you want to get from the system. Standard solar inverters are the cheapest option, while optimized and solar microinverters, will make your system perform at its best. For battery-based solar systems, we recommend going with a hybrid solar inverter, which controls both your batteries and solar panels.
When getting a new solar inverter for your home, consider the aspects we told about you in the last section of this article. These will help you choose the right inverter for you and help you get the best value for your money.