Solar Balance of System (BOS)

Balance of system (BOS) refers to the non-module, non-battery components that enable a solar power system to be installed, protected, interconnected, monitored, and operated safely. BOS is where real-world reliability, maintainability, and code compliance are often won or lost.

What is included in BOS

BOS includes the mechanical, electrical, and controls hardware surrounding PV modules and power electronics. The exact set varies by system size, architecture (string vs microinverter vs optimizer), and whether storage is present.

• Mechanical: racking, mounting, structural attachments, grounding and bonding hardware
• Electrical: conductors, connectors, junctions, combiner boxes, disconnects, protection devices
• Interconnection: metering, service equipment interfaces, transformers as required, switchgear interfaces
• Controls and monitoring: sensors, communications, monitoring gateways, rapid shutdown devices
• Safety and compliance: labeling, conduit and raceways, arc-fault and ground-fault protection as required

Why BOS matters

PV module wattage and inverter specs get attention, but BOS drives many practical outcomes: installation quality, downtime risk, fire and shock protection, inspection success, and long-term operations and maintenance (O&M) cost.

• Reliability: connector quality, weather sealing, strain relief, and cable routing reduce failures
• Safety: proper disconnecting means, grounding and bonding, and protection devices reduce hazards
• Performance: voltage drop, thermal derating, and mismatch losses are strongly influenced by BOS choices
• Serviceability: accessibility, labeling, and standardized parts reduce O&M time and cost
• Compliance: BOS is where many electrical-code requirements are implemented and verified