How Inverters Enhance Small-Scale Solar Results and Drive Grid Reliability

While inverters clearly do not get the attention solar panels do, and they’re often almost unknown to solar energy users, they are critical to system performance and even grid reliability. New technologies are enabling far better performance.

How Inverters Work

At a fundamental level, inverters convert direct current (DC) electricity generated by solar panels or other renewable energy sources into the alternating current (AC) electricity that homes and businesses use. AC and DC are two types of electric current that differ in the direction of the flow of electrons. AC alternates its direction periodically, while DC flows in one direction only. AC is more efficient for transmitting power over long distances, while DC is more stable. Historically, electrical power has been predominantly generated by burning fuel and creating steam, which spins a turbine generator to creates AC power. Home appliances were designed to use AC voltage from the local grid and cannot run on the DC provided by solar panels.

Solar inverters are DC-to-AC power conversion devices, so they can solve this problem. Inverters are thus one of the most important pieces of equipment in a solar energy system.

Small-scale Solar Inverter Solutions

Also known as on-grid systems, grid-tied solar setups are directly connected to the utility power grid. The solar panels on homes or businesses generate DC electricity from sunlight, and the inverter converts DC power into AC. Since inverters synchronize with local electrical grids which use AC, homeowners or businesses can export surplus energy to the grid when solar generation is higher than usage. Access to backup power from the utility grid or from solar batteries is available when needed.

For individuals and businesses, MarketWatch explained, there are four main types of inverters:

  1. String inverters: Solar panels are wired in a “string” series that connects to a central inverter, which connects to home wiring and converts the combined output of the panels into AC power. While string inverters cost less to install, the string leads to system output being lower or being down if one panel malfunctions, even if the other panels are still working.
  2. Microinverter: The system has small inverters installed on each solar panel. While it costs more, a dedicated conversion device for each solar module enables better performance.
  3. Power optimizers: Optimizers installed on each solar panel regulate the voltage and current of each panel, which increases total electricity output. They increase the cost of the system, though, because there is one for each panel.
  4. Hybrid inverter: Along with converting DC to AC, EENE said, hybrid inverters also manage energy storage in batteries and support grid interactions, which means these inverters can support off-grid or backup power configurations and enable grid resilience and energy independence. Since hybrid inverters have a built-in controller for battery systems, they cost more than string inverters.
    While solar power installers will usually recommend or select the inverters to be used, individuals or businesses who understand inverters can ask better questions and make sure the system that’s installed actually meets their needs.

Traditionally, grid-connected inverters must shut down for grid powerline worker safety when grid power goes down. This process prevents the inverter from feeding electricity back into the grid and harming workers during maintenance. Unlike standard grid-tie inverters, which disconnect from the grid during outages, hybrid inverters can switch to off-grid mode and draw power from an attached battery. Hybrid inverters are more complex and typically costlier than standard grid-tie inverters. However, they provide peace of mind by offering backup power when needed.

A new development, IQ8 microinverters, will continue to produce energy and meet the demands of a home or business as long as there is sufficient sunlight, even if the grid fails.

Grid Operators Require Different Solutions

Grid operators such as utilities operate at a different scale than a residence or a business, so they benefit from different solutions.
In the past, spinning turbines generated AC electricity for utilities at 60 hertz, according to the National Renewable Energy Laboratory. Those synchronized machines can have the capability to correct frequency fluctuations automatically.

Large renewable energy installations also use inverters to convert DC to AC, and most inverter-based resources installed to date use grid-following inverters. If a large amount of generation goes offline, causing the frequency to fall below 60 hertz, generators that use grid-following inverters “try to keep online and inject power and keep the frequency stable,” Ben Kroposki, organizational director of the UNIFI Consortium, told PV Magazine. The problem is that the way to save the system when the frequency drops below 59.5 hertz is to drop some load to keep the rest of the system online, resulting in a partial blackout. As renewable energy generation grows, PV Magazine explained, demand is rising for grid-forming inverters.

Whereas traditional “grid-following” inverters require an outside signal from the electrical grid to determine when switching will occur, the Department of Energy (DoE) explains that grid-forming inverters can start up a grid if it goes down. The power from the grid provides a signal that the inverter tries to match. More advanced grid-forming inverters generate the signal themselves, respond much more quickly to a frequency disturbance to maintain the frequency within range, and deliver essentially the same functions as traditional rotating synchronous generators.

One challenge, though, is that the US does not have unified comprehensive standards requiring grid following inverters, which took 20 years to develop in Europe. The UNIFI Consortium is now taking the lead in advancing the development of this new inverter technology, according to PV Magazine. One example is Hawaii, which Kroposki said already requires grid-forming inverters for their large-scale energy storage projects.

Inverters are getting More Advanced

Along with the development of grid-forming inverters, other innovations are leading to inverters having greater capabilities.

As digitalization progresses, Intersolar noted, it is also becoming easier to install, operate and maintain inverters. Using digital tools for planning and system design as well as artificial intelligence and cloud-based energy management apps that visualize energy consumption and self-generated energy is becoming common practice. Because modern inverters have high scalability and are designed to adapt to changing requirements, users will often not have to replace their inverter when their energy demand increases or when they upgrade their solar installation. A growing number of manufacturers now offer retrofit options for their systems to protect against events such as power grid failures.

Many solar inverters now come with built-in monitoring systems that collect real-time data on energy production, system health and overall performance that is invaluable for identifying potential issues early, EENE said, which allows for optimization of system performance and helps ensure that the solar power system operates at peak efficiency. This data can be accessed remotely, providing insights into the system's efficiency and allowing for timely maintenance.

Inverters with maximum power point tracking (MPPT) technology ensure that solar panels work at their maximum efficiency regardless of the weather and can optimize power production even when panels are partially shaded or when sunlight fluctuates. These inverters are designed to operate at high efficiency levels, ensuring that as much of the solar energy as possible is converted into usable electricity.

Communication and interconnection capabilities such as multiple digital switching outputs and LAN ports allow integrated WIFI interface and additional digital interfaces such as Modbus TCP and SG-ready, Intersolar said. These inverters can then offer easy commissioning and system configuration, connection to a smart meter for measuring and visualizing self-consumption, and quick monitoring data exchange.

Leveraging Information and Technology is Essential

While inverters may seem like an obscure technology, they are an essential component of solar system and are critical to optimizing renewable energy performance. Individuals, businesses and even grid operators can all benefit by leveraging the newest technology to make sure they optimize the performance of their system.

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