Over the past year, solar has been setting records at an accelerated pace -- especially in California. Consider, for example, the substantial 4.5 gigawatts of power that utility solar plants pumped into the California grid in late May. This is exclusively output from utility solar plants and doesn’t account for the more than 2 gigawatts of rooftop solar capacity installed as of May 2014.
As solar rapidly increases, the grid must be poised to manage greater output. This is where the inverter comes in, and, for utilities and grid operators, the capabilities of the inverter are vital to reliably integrating solar onto the grid. The inverter has long been considered the brain of the PV system, but advancements in inverter technologies have given rise to a new category label: the smart inverter.
The name is actually quite fitting. With balance-of-system costs now totaling more than half of all PV plant costs, manufacturers must build inverters that work smarter and drive down costs throughout a project lifecycle. This pressure has triggered consolidation in the inverter manufacturer market, as it is becoming more difficult for peripheral players to continue to add and improve upon the features built into the smart inverter, such as closed-loop control and storage integration.
On a fundamental level, the inverter converts direct current input to alternating current output, which, for a grid-tied system, enables the supply of real power to the grid. Other standard functions include power transfer optimization, voltage conversion, grid synchronization, disconnection, anti-islanding protection, and storage interfacing. These capabilities ensure that power is efficiently supplied to the grid while also providing key safety features.
Functions beyond this scope are what qualify an inverter as "smart." These include reactive power control, voltage, frequency ride-through, advanced two-way control capabilities, storage integration and data streaming.
Action VAR control (also called "power factor") provides an intelligent supply of reactive power to correct voltage and current imbalances that are inherent to the distribution system. Historically, capacitor banks and other external power-electronics-based systems, such as voltage regulators, were used for this purpose. However, integrating VAR control within the inverter results in a significant cost savings, while enabling more effective network support with improved local power quality and distribution efficiency.
Voltage and frequency ride-through are related to the inverter’s ability to respond appropriately to a temporary fault, caused by temporary grid disturbances in the host distribution line. Standard inverters can identify a fault and disconnect from the grid when faults are detected, but this reaction can destabilize the grid, especially in areas with PV penetration. Ride-through addresses this deficiency by responding to fluctuations in voltage or frequency with a supporting response; for example, providing timely voltage support or frequency suppression, thereby increasing overall grid reliability and increasing PV system uptime in the process.
Inverter advancements continue in parallel with the growth in grid-scale solar deployment, storage and data analytic innovation, along with the evolving needs of grid operators to manage energy delivery. Inverter manufacturers are providing greater functionality and better services that complement the core purpose of the inverter: power delivery. For example, Advanced Energy's inverters can provide plant-level control, as opposed to simply inverter-level control, through integrated monitoring -- a cornerstone of smart inverter technology. Advanced Energy provides a "lossless" data stream with each of its inverters; even if a network connection is lost, data collected during the outage won’t be. AE’s monitoring service also provides an online profile for each inverter so that plant operators can manage the fleet on a holistic or individual inverter basis.
As inverters continue to deliver more functionality, there is a new level of product differentiation occurring that goes well beyond traditional measurements like efficiency, kW rating and cost, because these new inverters are enabling levels of PV penetration that simply would not otherwise be possible. These advanced features are enabling the next phase of growth in the global PV industry.
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For more information on Advanced Energy's smart inverters, see the company's Reference Library, which includes the SEGIS smart inverter white paper and LVRT PG&E case study.