Balance of System — BOS
Hardware Components
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.
Many residential customers budget for a PLTS system based only on the panel price and are surprised when the EPC quote arrives — the cause is BOS, often dismissed as a "hidden cost." Yet BOS components are no less important: the inverter determines DC-AC conversion efficiency and system durability, the mounting determines structural safety during high-wind seasons, and low-quality cabling is frequently one of the earliest points of failure in a system's service life.
On a 5 kWp residential on-grid system with a total CapEx of ~Rp 12.5 million per kWp [docs/data-kalkulator.md], a rough breakdown is: panels ~Rp 6.5 million/kWp (52%), inverter ~Rp 1.8 million/kWp (14%), mounting ~Rp 1 million/kWp (8%), cabling and protection ~Rp 1 million/kWp (8%), installation and EPC services ~Rp 2 million/kWp (16%), and SLO permitting ~Rp 200 thousand/kWp (2%). Total non-panel components fall in the 30-35% range.
For off-grid systems, the BOS percentage shifts sharply because the battery becomes a dominant, separate cost component.
Indonesian PLTS Application Example
On a 5 kWp residential rooftop solar (PLTS Atap) system with a total investment of Rp 62.5 million [docs/data-kalkulator.md], the non-panel components (BOS) fall in the Rp 24-30 million range, covering a mainstream string inverter, tile-roof mounting, PV1-F DC cable and NYY AC cable, DC/AC protection, the export-import kWh meter, and certified EPC labour.
Sources & References
- SolarPlanner.id Calculator Data, SECTION 1.4-1.8 (CapEx breakdown per kWp for residential and industrial on-grid) — SolarPlanner.id (2025)
- Cost estimate for Indonesian residential rooftop solar — AESI (2024)
See Also
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.
On-Grid
On-grid, or grid-tied, is a solar PV (PLTS) scheme that is connected in parallel with the PLN grid and uses no battery. The inverter synchronizes its output to PLN's voltage and frequency; when the panels produce more than the load, the surplus flows to the grid, and when production is insufficient, the load draws from the grid.
BOO
(Build-Own-Operate)BOO, or Build-Own-Operate, is a solar PV (PLTS) financing scheme in which a developer builds, owns, and operates the installation on land or rooftop belonging to the tenant, while the tenant pays for electricity per kWh over the contract term — typically 10-25 years. There is no upfront capital outlay on the tenant's side.