Quick Facts
What a string inverter is
A string inverter is an electronic power converter that takes the direct current (DC) output from a series-connected group of solar panels and converts it into alternating current (AC) at the voltage and frequency of the local electricity grid. It is the most common inverter architecture in Indian solar, used in homes, factories, commercial rooftops, and smaller utility plants.
The “string” in the name refers to the series chain of solar panels wired together. A typical residential system has one or two strings of 6 to 14 panels each. A commercial system has multiple strings feeding into a single inverter through its DC inputs.
A string inverter is more than a simple AC/DC converter. It manages Maximum Power Point Tracking, monitors string voltage and current, synchronises with the grid, detects faults, communicates with monitoring portals, and shuts itself off during a grid outage for safety.
How a string inverter works
Solar panels generate DC electricity whose voltage varies with sunlight intensity and temperature. The string inverter performs several functions to deliver useful AC power.
Maximum Power Point Tracking: The inverter measures the I-V curve of each MPPT input thousands of times per second and adjusts the operating voltage to the point that gives maximum power.
DC-AC conversion: A power electronics bridge (typically IGBT or SiC MOSFET) switches the DC at 16 to 20 kHz to produce a pulse-width-modulated waveform that, after filtering, becomes a sinusoidal AC waveform.
Grid synchronisation: The inverter senses grid voltage and frequency and matches its output exactly. Any mismatch would cause large fault currents.
Anti-islanding protection: If the grid fails, the inverter detects the loss within milliseconds and disconnects, preventing the system from feeding power into a “dead” line.
Communication and monitoring: Most modern inverters connect to wifi or cellular networks to report energy, voltage, current, temperature, and faults to a cloud monitoring portal.
Common ratings and topologies
Single-phase residential string inverters range from 1 kW to 6 kW with 1 or 2 MPPT inputs.
Three-phase commercial string inverters range from 5 kW to 100 kW with 2 to 6 MPPT inputs.
Three-phase utility-class string inverters range from 100 kW to 350 kW with 8 to 12 MPPT inputs, designed for ground-mount installations.
All three categories are sold in India through MNRE-empanelled or ALMM-aligned vendor lists for government-subsidy projects.
Sizing a string inverter
The two key sizing decisions are AC rating versus DC kWp, and string voltage versus inverter MPPT range.
AC rating: Indian designs typically use 75% to 90% of the DC kWp as the inverter’s AC rating. A 5 kWp residential plant pairs with a 4 kW to 5 kW inverter. A 100 kWp commercial plant pairs with an 80 kW to 100 kW inverter. The slight DC oversizing improves morning and evening capture and trims summer peak clipping.
String voltage: The number of panels in series multiplied by the panel’s Voc (at the lowest expected ambient temperature) must stay below the inverter’s maximum input voltage. For an inverter rated 600 V max, with panels at 50 Voc cold, the limit is around 11 to 12 panels per string. Designers use site-specific temperature-corrected Voc calculations.
MPPT count: Each MPPT input can host one or two strings. Diverse string orientations (east-west or different tilt) work best when each goes to its own MPPT.
String inverter compared with alternatives
| Inverter Type | Best For | Pros | Cons |
|---|---|---|---|
| String inverter | Most rooftop and commercial systems | Lowest cost per Wp, mature supply chain | Shading on one panel affects the whole string |
| Microinverter | Complex roof shapes, partial shading | Panel-level optimisation, safer DC voltages | Higher upfront cost, more devices to fail |
| Power optimiser plus string inverter | Partial shading, panel-level monitoring | Best of both worlds for many sites | Moderate cost premium |
| Central inverter | Large utility plants above 1 MW | Lower cost per kW at scale | Single point of failure |
For most Indian rooftops and commercial sites, the string inverter is the right choice. Microinverters become attractive for sites with complex shading or where panel-level diagnostics matter.
Leading string inverter brands in India
International brands with strong India presence include Sungrow, SMA, Solis (Ginlong), Goodwe, Huawei, Solaredge, Growatt, Delta, and Fronius.
Indian manufacturers and assemblers include Havells, Qbits (Heaven Green Energy’s own inverter brand), Servotech, Microtek, Statcon Energiaa, Su-Kam, and Polycab.
For residential and small commercial under 10 kW, Solis, Growatt, Goodwe, Havells, and Qbits dominate by volume.
For commercial above 10 kW, Sungrow, SMA, Huawei, and Solis are the most common choices.
For utility-class three-phase, Sungrow, SMA, and Huawei lead. Indian assemblers are growing presence under the PLI scheme for inverters.
Common mistakes when specifying string inverters
Oversizing the inverter relative to the array. Inverters operate at their best efficiency at high load. A heavily undersized array forces the inverter to run at low load most of the time, where efficiency is worse.
Undersizing the inverter relative to the array. Heavy DC oversizing beyond 1.3 to 1.4 times causes significant clipping in summer, throwing away annual energy.
Ignoring MPPT count when planning multi-orientation arrays. Two strings on different roof faces should not share one MPPT.
Mounting the inverter in direct sun or in a poorly ventilated location. Overheating reduces efficiency and shortens inverter life.
Failing to verify inverter compatibility with the cell technology. Some older inverters do not support n-type modules without configuration changes.
Choosing on price alone. The cheapest inverter often has shorter warranty, slower after-sales support, and lower efficiency.
Best practices
For Indian sites, prefer inverters with at least IP65 rating for outdoor use and an operating temperature range up to 60 deg C ambient.
For commercial projects above 25 kW, choose inverters with at least 4 independent MPPT inputs to manage shading and orientation flexibly.
Look for inverters that support reactive power (Q) control for high penetration zones, which DISCOMs increasingly mandate.
Buy from brands with verified Indian after-sales presence. A 10-year warranty is only valuable if there is a service network to honour it.
Match inverter polarity to the cell technology (especially for n-type). Confirm with the supplier before contract.
Standards and compliance
String inverters sold in India must comply with IEC 62109 (safety), IEC 61727 (grid-interactive characteristics), and where relevant, IEEE 1547. Anti-islanding behaviour is tested under IEC 62116. CEA Connectivity Regulations 2019 apply to all grid-tied inverters. MNRE maintains an empanelled inverter list for government rooftop projects.
Related glossary terms
- Microinverter
- Hybrid Inverter
- MPPT
- DC Oversizing
- Anti-Islanding Protection
- Grid-Tied vs Grid-Interactive
- String Combiner Box (SCB)
- ACDB
- DCDB
Key takeaways
A string inverter converts DC from a series of solar panels into grid-quality AC. It is the most common inverter type in Indian solar from residential rooftops to mid-size utility plants. Modern units deliver 97% to 99% peak efficiency, support multiple MPPT inputs, include anti-islanding protection, and integrate with cloud monitoring. Correct sizing (slight DC oversizing, sufficient MPPT count, voltage compliance) and brand selection from a reputable manufacturer with Indian service support drive long-term reliability.