An SMA central inverter.
Solar inverters are the hardest working component of a solar field, as described by PV Evolution Labs (PVEL) in its first “PV Inverter Scorecard”.
According to the report, inverters alone are responsible for more operational functions than any other PV system component. These tasks have continued to grow as systems become smarter and improve how they interact with the utility grid.
What exactly does an inverter do? In its report, PVEL set out five important tasks for solar inverters.
1. Convert direct current to alternating current
The basic function of an inverter is to convert the direct current generated by solar modules into alternating current that can be used in households and companies or fed directly into the grid in on-site projects (solar systems on a supply scale).
2. Maximize performance
Inverters are responsible for continuously tracking the voltage of the solar array in order to determine the maximum power with which the modules can be operated according to PVEL. If there is shadowing from environmental factors or if modules are degraded, the inverter can inadvertently identify the wrong spike in the chain, reducing the overall energy production of the system.
3. Interface with the grid
Smart inverters, the new frontier of solar inverters, have developed from one-way communication to two-way communication with the grid and support grid support functions. Thanks to advanced software, intelligent inverters can perform certain grid-supporting functions with regard to voltage, frequency, communication and control.
One of the most important grid support functions of intelligent inverters is the ability to overcome small disturbances (e.g. voltage changes). When the voltage changes, intelligent inverters can switch to standby mode and monitor how long the fault has been occurring. You can then only switch it off if the disturbance continues for too long. This ensures that there are minimal voltage fluctuations in the grid, as distributed resources are completely switched off and power generation is stopped. Read everything about intelligent inverters here.
4. Report on power generation
Inverters allow solar owners to track the performance of their solar systems. Most inverters have communication functions via hard-wired Ethernet, Bluetooth or Wi-Fi, according to PVEL. This communication link can put inverters at risk for cyberattacks, but scientists are working on solutions to reduce this possibility. Read more about inverter cybersecurity here.
Solar owners can view fault codes, diagnostic and power generation information from inverters on their computers or even on dedicated smartphone apps like the one from SolarEdge. Large solar owners may also want to invest in advanced monitoring services to diagnose and troubleshoot multiple-inverter array issues through a third-party provider like Solar-Log.
5. Ensure safe system operation
According to PVEL, inverters must shut down in the event of an electric arc caused by system aging and material deterioration. They are programmed to identify these arcs, but PVEL has determined that not all inverters do this effectively. The top performers in the PVEL earth and arc fault tests were Delta and Fronius inverters.
Because inverters are made up of so many electronic parts and perform so many tasks, PVEL says they are more likely to fail than any other component in a PV system. String and central inverters have different advantages and disadvantages. However, string inverters are easier to service when a failure is inevitable. Read more about how installers should prepare for inverter failure here.
Inverters are an integral part of any solar system, and their roles are constantly evolving as both the grid and solar projects get smarter.