String Inverter
Hardware Components
A string inverter is a solar PV (PLTS) inverter that converts the DC power from a series-connected set of solar panels (a string) into ready-to-use AC current. One inverter unit serves one or two strings at a time, with a single MPPT point per string.
Under normal irradiance conditions, the peak efficiency of a mainstream string inverter is in the 97-98% range [Huawei SUN2000 / Sungrow SG series datasheet, 2024-2026].
In a string topology, several panels — generally 8-20 units per string depending on the string voltage the inverter allows and the nominal voltage of each module — are connected in series so that their cumulative voltage can reach 600-1,500 V DC. This high voltage benefits DC cable transmission efficiency, but it gives rise to one critical consequence: because MPPT works at the string level (not per panel), the weakest panel in the string pulls the output of the entire string down to its capacity. Partial shading on one panel — even the size of a single leaf or a ventilation pipe — can disproportionately reduce the production of the entire string.
String inverters are available across a wide capacity range: residential models from 3-6 kWp, medium commercial 10-50 kWp, up to utility-grade string inverters exceeding 100 kWp per unit [IEC 62109-1, Safety of power converters for use in photovoltaic power systems, Ed. 2022]. For systems with a clean roof free of shading obstacles and a uniform panel orientation, this topology delivers the best cost-per-watt ratio among all inverter topologies.
Indonesian PLTS Application Example
A 5 kWp residential system in Surabaya (PSH 4.9 kWh/m²/day [NASA POWER 1984-2023]) with a south-facing roof and no shading commonly uses a single 5 kWp string inverter. Estimated daily production: 5 × 4.9 × 0.80 (performance ratio) = 19.6 kWh, equivalent to bill savings of ~Rp 28,300/day at the non-subsidized R-1 tariff of Rp 1,444.70/kWh [PLN tariff adjustment Q1 2026]. For a medium-scale factory with a 50-100 kWp system and a uniformly sloped roof, a multi-input string inverter remains the default choice because installation and maintenance costs are simpler than a per-panel solution.
Sources & References
- IEC 62109-1, Safety of power converters for use in photovoltaic power systems — Part 1: General requirements, Ed. 1 (2010), updated Ed. 2 (2022) (2010)
- IEC 61727, Photovoltaic (PV) systems — Characteristics of the utility interface (grid connection requirements including anti-islanding)
- Datasheets of mainstream string inverters in the Indonesian market: Huawei SUN2000 series, Sungrow SG series, SolarEdge string series — peak efficiency and MPPT specifications (2024-2026) (2024-2026)
- NASA POWER LARC, Surface meteorology and Solar Energy data set, climatology 1984-2023 (1984-2023)
See Also
Microinverter
A microinverter is an inverter rated at 250-400 W installed one unit per solar panel to convert the panel's DC current directly into AC at the point of production [IEC 62109-1].
MPPT
(Maximum Power Point Tracking)MPPT, or Maximum Power Point Tracking, is an electronic algorithm inside a solar inverter or charge controller that continuously tracks the maximum power point of the panel's voltage-current curve so that DC-to-AC conversion occurs at the highest efficiency. Mainstream inverters in the Indonesian market generally have an MPPT efficiency of 96-99% — a ~3% spread that directly affects the system's realized Performance Ratio.
BOS
(Balance of System)BOS, or Balance of System, is every component of a solar PV (PLTS) system other than the solar panels themselves: the inverter, mounting structure, DC and AC cabling, electrical protection, combiner box, export-import kWh meter, and installation labour. In an Indonesian residential on-grid system, BOS typically accounts for 25-40% of the total system cost.