Solar Inverter Glossary
Every technical term used across this database, defined. Specification terms link to the models that publish them.
AC Output Classification DC Input Efficiency Grid & Safety Physical Power PV Array Storage & Backup System Design
AC Output
- AC Output Frequency Specification
- The nominal frequency of the alternating current the inverter delivers, in hertz — 50 Hz across most of the world and 60 Hz in North America and parts of Asia and Latin America. A grid-tied inverter synchronises precisely to the grid's own frequency.
- AC Output Voltage Specification
- The nominal alternating-current voltage the inverter produces at its output terminals, matched to the grid or load it serves. It is quoted per phase or between phases depending on whether the unit is single-phase or three-phase.
- Output Wave Type Specification
- The shape of the alternating-current waveform the inverter produces: either a pure sine wave, matching what the utility grid supplies, or a modified sine wave, a stepped approximation. Grid-tied equipment is always pure sine wave.
- Total Harmonic Distortion (THD) Specification
- A measure of how far the inverter's output waveform departs from a clean sine wave, expressed as the percentage of total signal energy sitting at harmonic frequencies rather than at the fundamental. Lower is better.
Classification
- Hybrid Inverter
- A grid-tied inverter that also has a battery port and the control logic to charge and discharge storage, deciding moment by moment whether solar energy goes to the loads, to the battery or to the grid. Many hybrids can additionally supply a protected circuit during an outage.
- Inverter Type Specification
- The architectural class of the unit: string inverter, microinverter, hybrid or off-grid. The type determines where it sits in the system, what it can be connected to, and whether it can work without a grid present.
- Microinverter
- A small inverter mounted behind an individual solar module that converts that module's DC output directly to grid-frequency AC. Modules are then connected in parallel on an AC trunk cable instead of being wired into a DC string.
- Number of Phases Specification
- Whether the inverter delivers single-phase or three-phase alternating current on its output. It must match the building's supply, and above a certain power level the network operator normally requires three-phase connection.
- Off-Grid Inverter
- An inverter that creates its own AC network from a battery bank rather than following an existing grid, supplying loads in an installation with no utility connection. It is also called a standalone or battery-based inverter.
- Transformerless Inverter
- An inverter that converts DC to AC without a galvanic isolation transformer between the array and the grid. Removing the transformer raises efficiency and cuts weight and size, and it is the dominant design in modern residential equipment.
DC Input
- MPPT Voltage Range Specification
- The band of DC input voltages within which the inverter can actively track the array's maximum power point and convert at full capability. Outside this window the inverter either cannot start, or runs at reduced output.
- Maximum DC Input Current per MPPT Specification
- The highest direct current each MPPT channel can accept from the strings connected to it, in amperes. It limits how many strings may be paralleled on one tracker, since parallel strings add current while voltage stays the same.
- Maximum DC Input Voltage Specification
- The absolute highest DC voltage that may be applied to the inverter's input terminals without risk of damage. It is a hard limit, not an operating recommendation, and exceeding it can destroy the input stage and void the warranty.
- Maximum Power Point Tracking (MPPT)
- The control algorithm an inverter uses to continuously adjust the voltage it draws from a PV array so the array delivers the most power available under the current light and temperature. The point moves constantly, so the tracker searches for it many times a second.
- Number of MPPT Channels Specification
- How many independent maximum power point trackers the inverter has, each able to optimise a separate group of strings at its own voltage and current. More channels allow strings on different roof orientations or with different shading to work without dragging each other down.
Efficiency
- European Efficiency Specification
- A single weighted efficiency figure that averages an inverter's efficiency at several load levels, with the weights chosen to reflect a typical Central European irradiance profile. It is always slightly lower than peak efficiency and is the fairer number for comparing models.
- Maximum Efficiency Specification
- The best conversion efficiency an inverter reaches at any single operating point, given as the percentage of DC input power that leaves the unit as usable AC power. It is a peak value measured at the most favourable combination of load and input voltage.
Grid & Safety
- Arc-Fault Detection (AFCI)
- A protective function that monitors the DC circuit for the electrical signature of an arc caused by a damaged conductor or a loose connection, and shuts the inverter down when it detects one. It is required on PV DC circuits above a defined voltage in several jurisdictions.
- Curtailment (export limiting)
- The deliberate reduction of an inverter's output below what the array could deliver, in order to respect an export limit set by the network operator. Zero export means the system is curtailed whenever generation exceeds on-site demand.
- Feed-In / Export
- The energy a PV system sends to the public grid when generation exceeds on-site demand. It is measured by a bidirectional meter and remunerated or netted according to the local regulatory scheme.
- Grid Code
- The set of technical rules a distributed generator must comply with to connect to the public network, covering voltage and frequency operating limits, power quality, protection settings and required responses to grid disturbances. Inverters are certified against specific national grid codes.
- Islanding and Anti-Islanding Protection
- Islanding is the dangerous condition in which a grid-tied inverter keeps energising a section of the network after the utility supply has failed. Anti-islanding protection is the mandatory function that detects this and disconnects the inverter within a fraction of a second.
- Rapid Shutdown
- A safety requirement that the DC conductors of a rooftop PV array be brought down to a low, touch-safe voltage quickly once an initiator is operated, so firefighters and maintenance staff can work on the roof. It is enforced by module-level or string-level shutdown devices.
- Residual Current Monitoring (RCD / RCMU)
- The detection of leakage current flowing to earth rather than returning through the intended conductor, which indicates an insulation fault and a possible shock hazard. Transformerless PV inverters include an internal residual current monitoring unit sensitive to both AC and DC leakage.
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Physical
- IP Protection Rating Specification
- A two-digit code describing how well the enclosure resists solid objects and water: the first digit covers dust and contact, the second covers moisture. IP65, for example, means dust-tight and protected against low-pressure water jets from any direction.
- Operating Temperature Range Specification
- The span of ambient temperatures, in degrees Celsius, within which the inverter is specified to work. Within this range it functions safely, though not necessarily at full output across the whole span.
- Weight Specification
- The mass of the inverter unit itself, in kilograms, excluding mounting hardware, cabling and any external accessories. It determines how the unit is handled during installation and what the mounting surface must support.
Power
- Maximum AC Power Specification
- The highest alternating-current output an inverter can produce, usually for a limited period or under favourable temperature conditions. It sits above the nominal AC power and represents a short-term ceiling rather than a continuous rating.
- Nominal AC Power Specification
- The continuous alternating-current power an inverter can deliver to the grid or to a load under normal conditions, expressed in watts. It is the figure used to size an inverter against a PV array and the number that appears in the model designation of most units.
PV Array
- Array
- The complete assembly of photovoltaic modules in an installation, made up of one or more strings together with their mounting structure and DC wiring. It is the generating side of the system, as distinct from the inverter and the AC side.
- Open-Circuit Voltage (Voc)
- The voltage a solar module or string produces with nothing connected to it and no current flowing. It is the highest voltage the array will ever present, and it rises as cell temperature falls.
- Short-Circuit Current (Isc)
- The current a solar module or string delivers when its terminals are shorted together, which is the maximum current it can produce. It scales almost directly with irradiance and changes only slightly with temperature.
- String
- A group of solar modules wired in series so their voltages add while the current stays that of a single module. The string is the basic building block a string inverter's MPPT channel connects to.
Storage & Backup
- AC Coupling
- A storage architecture in which the PV inverter and the battery inverter are separate units connected on the AC side. Solar energy is converted to AC first, and any surplus is then converted back to DC to charge the battery.
- Backup / Protected Loads Panel
- A separate distribution board containing the circuits that a hybrid or off-grid inverter will keep supplied during a grid outage. Only the loads wired into this board stay live when the utility supply fails.
- DC Coupling
- A storage architecture in which the PV array and the battery share the same DC bus inside a single hybrid inverter, so solar energy charges the battery without first being converted to AC. Only the energy actually consumed or exported passes through the DC-to-AC stage.
- Round-Trip Efficiency
- The proportion of energy put into a battery system that comes back out again, after accounting for losses in charging, storage and discharging. A round-trip efficiency of 90% means ten kilowatt-hours in returns nine.
System Design
- Clipping
- The loss that occurs when a PV array could produce more DC power than the inverter is able to convert, so the inverter holds its output at the AC limit and the surplus is simply never harvested. It appears on production graphs as a flat plateau around midday.
- DC/AC Ratio (oversizing)
- The ratio between the array's rated DC capacity in watt-peak and the inverter's nominal AC power. A ratio above 1.0 means the array is deliberately oversized relative to the inverter, which is standard practice rather than a design error.
- Derating
- The automatic reduction of an inverter's output power to protect its internal components, most commonly triggered by high temperature but also by high grid voltage or by an out-of-range input. The unit keeps running at reduced capacity instead of shutting down.
- Power Optimiser
- A small DC-to-DC converter fitted to each module that performs maximum power point tracking at module level and conditions the module's output before it joins the string. The string then feeds a simplified central inverter that handles only the DC-to-AC conversion.
- Self-Consumption
- The share of the energy a PV system generates that is used on site rather than exported to the grid. It is the metric that most directly drives the economics of a residential installation, because avoided imports are usually worth more than exported units.
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