Balance of System (BOS)
Balance of System (BOS) refers to all components of a solar photovoltaic (PV) system except the solar panels (modules) themselves. BOS includes everything needed to turn solar panels into a functioning, grid-connected power system.
BOS components typically include:
- Inverter(s): DC-to-AC conversion (string, micro, or central)
- Racking and mounting: Roof attachments, rails, clamps for panels
- Electrical BOS: Wiring, conduit, combiner boxes, disconnects, meters
- Monitoring system: Data loggers, sensors, communication hardware
- Engineering and permitting: Structural analysis, electrical drawings, permit fees
- Installation labor: All on-site work including trenching, roofing, electrical
- Grid interconnection: Utility application fees, interconnection equipment
BOS Cost Trends
BOS costs have become the dominant portion of solar system installed costs as panel prices have plummeted. In 2010, panels represented ~60% of system cost; today they're often 25–35%. BOS — particularly labor, permitting, and structural components — now represents the largest opportunity for continued solar cost reduction.
"Soft costs" within BOS (customer acquisition, permitting, interconnection, inspection) account for roughly 30–40% of US residential installed system cost, compared to 10–15% in more streamlined markets like Germany and Australia.
Installed Cost Benchmarks (2024, US)
- Residential: $2.50–$3.50/W installed (includes all BOS + installation)
- Commercial (100 kW–1 MW): $1.50–$2.50/W
- Utility-scale (>1 MW, fixed-tilt): $0.80–$1.20/W
These ranges vary significantly by region, labor market, interconnection complexity, and system design.