What Is a Solar Inverter?
Your solar inverter converts the direct current electricity generated by your solar panels into alternating current that can be used at home. During this conversion, some energy gets lost, but quality inverters have low losses.
Some inverters include power optimizers installed directly on your PV modules (like microinverters). These increase panel-level productivity by doing maximum power point tracking at each module.
DC to AC Conversion
Most renewable energy systems generate DC power, which is fine for batteries or solar panels but can’t be used to run appliances that require AC. To address this, most renewable energy systems include a device called an inverter that converts the DC power to AC power. Inverters convert the one-way flow of Solar Inverter DC current into the oscillating flow of AC current required by most household appliances.
Inverters are available in a range of sizes, but all perform the same basic task: they convert the DC power from solar panels or battery storage into alternating current (AC). They can also adjust their output voltage based on the amount of sun that hits the PV modules and how much is being consumed by appliances. Some inverters can also be daisy chained together, which allows them to support larger arrays and increased surge wattage capacity.
The key to a good inverter is its DC-to-AC ratio, which is measured as the ratio of an inverter’s AC power rating to the peak output of a solar panel or array. It’s important to have a higher DC-to-AC ratio when designing a solar system because it prevents the inverter from being overloaded during the maximum power point (MPP) of a PV module, which can be capped at the inverter’s nameplate power rating.
However, a high DC-to-AC ratio will result in clipping losses, which means that the inverter will produce excess energy that it can’t use all of the time. To minimize these losses, solar designers can add extra batteries to increase the overall ampere hour (Ah) capacity of the battery set or can use a DC coupled system that combines additional inverters with the primary inverter.
Battery Storage
Battery energy storage is a great way to capture and use solar generation at night or during peak utility rates. Known as ‘peak shaving’ and ‘energy arbitrage’, it can help reduce your utility bill by shifting your consumption to the stored energy during high rate periods, or even eliminating them entirely.
The inverter converts DC electricity to alternating current (AC) electricity that powers your home’s appliances. It also monitors the performance of your PV system and battery energy storage.
A hybrid inverter with Maximum Power Point Tracking (MPPT) ensures your solar panels and batteries are always working at their optimal efficiency levels. It does this by continuously checking and comparing each panel’s output to the best available voltage on the battery. The inverter will then adjust the battery to deliver the optimum level of power.
You can also choose to install a battery storage system without a solar panel and rely on the stored energy during off-peak times. These are known as grid-tied batteries. They’re used for energy arbitrage and peak shaving, and can be connected to a utility rate tariff.
Battery storage is also a valuable option for customers on utility rates that don’t offer net metering. Grid-interactive battery inverters are able to export excess energy to the utility grid, can charge a battery using surplus energy for use during low generation, and some can supply backup power during a power outage.
Grid Interconnection
Grid interconnection is the process by which your solar panel system is granted permission to feed power back into your local energy grid. This involves setting up a bi-directional meter and allowing the energy company to measure your input and output. The process typically doesn’t cost more than a few hundred dollars to complete and should be included in your installation price by the installation company.
Your solar inverter is part of your grid-interactive system because it sucks the DC current from your solar panels into alternating current that is fed through your breaker box, the utility meter and into the grid. The inverter is also responsible for providing a mechanism to protect the photovoltaic system in case of short circuits or other grid-side faults.
Modern inverters can provide additional grid services beyond simply converting your solar power to AC power for household use. One of the most important is the ability to supply reactive power to the grid. The voltage on the grid is always switching back and forth and the current is often delayed. When this happens, some of the electricity flowing through the grid cannot be absorbed by connected devices, wasting energy.
Inverters that can provide reactive power can help keep the voltage and current synchronized, maximizing efficiency. They solar batteries manufacture can also absorb and supply reactive power to match up with other sources of this energy on the grid, like wind turbines or even neighboring solar systems.
Monitoring
Monitoring systems enable solar system owners to check on the performance of their panels and inverters remotely. These systems collect data about power output, environmental benefits & history of energy production from the panel array and send it to a web portal or smartphone app for analysis. Many of these systems also include power optimizers installed at the solar panel level that improve system efficiency and provide additional data points for monitoring.
In addition to logging data, many solar monitoring systems have an integrated UI that shows the overall performance of the system. This can help identify problems such as shade or dirt affecting performance. Those issues can then be addressed with preventative maintenance and can reduce the need for costly repairs in the future.
SolarEdge offers its MyEnlighten software for its PV systems that features both a per-panel and system overview monitoring functionality. This software is accessible via a web portal or mobile device and collects measurement data by integrating monitoring sensors and transmitters with the PV system’s power optimizer and solar inverter.
Other solar manufacturers like SMA offer a similar monitoring interface for their PV systems. Their Sunny Portal web interface and smartphone apps allow users to view total solar system output notifications, but they do not provide module-level monitoring or an impressive level of detailed data or polished user interface as seen with Enphase’s solutions.