Why Do Solar Cells Need an Inverter?
The earliest known use of an inverter can be traced back to the early 20th century. Inverters were then used primarily in industrial settings to convert direct current (DC) power from batteries and generators to alternating current (AC) for use in machinery.
One early example of the practical use of inverter was in the electric arc welding process where DC power from a generator was converted to AC power to operate the welding equipment. Another example comes from the early telephone exchanges where batteries provided DC power which needed to be converted to alternating current to operate the switching equipment. Inverters were also used in early electric vehicles to convert the power for the electric motor.
As technology progressed, inverters became handy in a wider range of applications. They gained their role in renewable energy systems as well as in power grid stabilization. They also convert the backup energy in case of power outages. And this is where we are getting to our question: Why do solar cells need an inverter, and is an inverter really a necessary piece of equipment?
What is a solar inverter?
A solar inverter is a key component in a solar energy system. This little box is responsible for converting the direct current (DC) output of the solar panels into alternating current (AC) electricity. It is the AC power that runs our homes and businesses, or is fed into a utility grid.
There are two main types of solar inverters: string inverters and microinverters. String inverters are typically used in large-scale solar systems where multiple solar panels are connected in series (or “strings”) and the DC electricity is passed through a single inverter for conversion.
Microinverters work the best for smaller and decentralized solar energy systems where each individual solar panel has its own dedicated inverter. This helps to maximize the performance of a small system.
Solar inverters are classified as grid-tied or off-grid (based on their connection to the grid). Grid-tied inverters are connected to the utility and allow excess energy to be fed back into the grid. While off-grid inverters are not connected to the grid and are typically used in remote locations where a grid connection is not available.
Solar inverter efficiency
Efficiency rating of inverters describes how effectively they convert DC to AC electricity. Inverters with a higher efficiency rating convert more power to usable electricity and waste less energy in a form of heat. Most solar inverters have an average efficiency rating of around 96 to 98 percent.
Another useful characteristic you should know about is the Maximum Power Point Tracking (MPPT). MPPT tracks the operating points (Voc and Isc) that yield maximum power output from your solar panel.
Maximum Power Point Tracking improves the overall efficiency of a whole solar system.
Voltage open circuit (Voc) and current short circuit (Isc) are two key parameters that describe the electrical characteristics of a solar panel. These values determine the maximum output of a solar panel, as well as the size of the inverter and other electrical components.
Voc expresses the maximum voltage that a solar panel can produce, while Isc is the maximum current. Voc is measured with no load on the solar panel. Isc is measured with a short circuit across the terminals of the solar panel.
Why do solar cells need an inverter?
A solar inverter is a must-have component in majority of solar systems. Solar cells generate electricity through the photovoltaic effect, during which sunlight gets converted into direct current power.
An inverter is a necessary piece of equipment to convert this DC energy from the solar cells into alternating current power that powers homes or is fed to the utility grid. Without an inverter, solar energy would be incompatible with most electrical devices we use.
As mentioned in the previous section, solar inverters also have a Maximum Power Point Tracking (MPPT) capability.
MPPT is an algorithm that allows the inverter to optimize the power output from solar panels by adjusting the voltage and current to match their maximum power point (MPP). Thanks to this feature, the inverter can extract the maximum amount of energy possible from solar panels, which in turn improves the performance of the whole setup.
How does a solar inverter work?
A solar inverter converts the current through a process of electronic switching and voltage transformation.
How solar inverter works can be broken down into the following steps:
- Solar panels convert sunlight into DC power, which is sent to an inverter.
- The inverter converts the energy it has received into a low-voltage DC power.
- A device called an inverter bridge switches the low-voltage DC into AC. This is done by rapidly switching the DC voltage on and off, which creates an AC waveform.
- The inverter is equipped with a transformer to precisely synchronize with the frequency and phase of the grid. The transformer increases or decreases the voltage of the AC to match it with the electrical system.
- The AC electricity is then sent to the electrical system for use or fed into the grid.
Modern inverters that are meant to be connected to the grid would actually not produce power if they do not detect the grid. This is an important safety measure to prevent injuries to utility workers or solar technicians.
What are the main components of a solar inverter?
The main components of a solar inverter depend on the inverter type and its application. For example, additional battery charge controllers are needed in off-grid systems. Grid-tied inverters include grid management and communication systems to match the grid.
As one of the most important pieces of equipment in your solar system, an inverter is composed of these important components.
Power electronic switch: The electronic switch, also known as an inverter bridge, is responsible for switching the direct current from solar panels into alternating current. It uses a process known as pulse width modulation (PWM) to rapidly switch the DC voltage on and off which creates an AC waveform.
Microcontroller: The microcontroller is a small computer that controls the operation of the inverter, including the power electronic switch. It also monitors the performance of the system and sends data to monitoring and control system (see below).
Transformer: The transformer matches the voltage of the AC electricity with the electrical system.
Maximum Power Point Tracking (MPPT): It is an algorithm that allows the inverter to optimize the power output from the solar panels by adjusting the voltage and current to match the system’s maximum power point (MPP).
Cooling system: A cooling system dissipates the heat produced during the operation and protects electronic components from overheating.
Monitoring and control system: This system monitors the performance of the inverter as well as of the entire solar array. It is has the function of controlling and adjusting the settings of the device if needed.
How does a solar inverter synchronize with grid?
A solar inverter needs to synchronize with the utility grid to make sure that the electricity it generates is in phase and at the same frequency as the grid. This function is important if you want to feed excess solar energy to the grid but also draw energy from the grid when solar panels do not produce enough power to sustain your needs.
The process of synchronization can be broken down in a few steps:
- The inverter monitors the grid voltage and frequency. Based on the obtained values, it adjusts its own output to match.
- A device called a phase locked loop (PLL) locks the phase of the inverter’s output.
- A grid-tie controller keeps the voltage and frequency output within certain limits.
- The inverter utilizes also a grid-tie inverter interface to communicate with the grid operator to ensure that the feed-in power is in compliance with the grid codes and regulations.
- The inverter has protection devices such as anti-islanding protection, to disconnect the inverter from the grid in case of grid failure or maintenance.
Grid-tied solar inverters use various devices and algorithms to lock the phase and communicate with the grid operator, as well as to ensure the safety and compliance with grid codes.
Further reading: Best Solar Panels for Homes in 2023
Are there safe alternatives to solar inverters?
The inverter is a necessary component of a solar system to convert the variable DC output of photovoltaic solar panels into a utility frequency alternating current. However, there are some alternative technologies that are able to store or run on the direct current from the solar.
One option is to use batteries that store the DC energy from solar panels. The battery storage system allows for the use of energy at a later time when the sun is not shining or when the demand is higher than the actual output of solar panels.
Another alternative is the use of Direct Current loads. These are appliances or devices that operate on DC power directly. They are mainly utilized in off-grid conditions where the connection to the grid is not available.
Some examples include:
- Portable electronic devices of a daily use like smartphones, tablets, and laptops. They run on DC power from batteries.
- Small appliances, such as portable fans, portable lights, and portable heaters. Some versions could be powered directly from a small solar panel.
- Electric vehicles use DC power from the battery pack.
- LED lights and other low-voltage lighting systems use DC power.
- Small motors found in toys and other devices.
- Electric shaver, hair clipper, and toothbrush.
- Power tools such as cordless drills and saws use DC power from rechargeable batteries.
The list is quite big, right? Why do we still need the AC power then? Well, most of the household appliances and large electrical equipment run on AC power for practical reasons. Alternating current is distributed in the grid and is more efficient to transmit over long distances. However, some appliances even have DC-AC inverters built in to convert the AC power to DC power to run certain internal components.
Additionally, there are also new technologies that are being developed to convert DC electricity into AC electricity without using an inverter, such as DC-DC converters, DC-AC inverters and Solid State Transformer (SST). However, these technologies are still in the early stages of development and are not yet widely available for commercial use.
Further reading: Top-rated solar powered generators