High-Level Block Diagram of a Typical Rooftop PV System

Anatomy of a Rooftop Solar PV System: How Individual Components Work as One

A rooftop solar photovoltaic (PV) system may appear simple from the outside—rows of panels mounted on a roof—but behind this apparent simplicity lies a carefully integrated set of electrical, mechanical, and safety subsystems. Figure 1.9 presents a high-level block diagram of a typical rooftop PV system, offering a system-wide view of how sunlight is converted into safe, usable electrical energy for buildings and the grid.

At the front end of the system are the PV modules, which serve as the primary energy-generating units. Mounted at a defined tilt and orientation, these modules convert solar radiation into direct current (DC) electricity through the photovoltaic effect. The electrical characteristics of the array—voltage, current, and power—are determined by the number of modules and how they are interconnected in series and parallel strings.

Supporting the modules is the mounting structure (MMS). Although often overlooked, this mechanical subsystem is critical to long-term system performance and safety. Mounting structures ensure correct tilt and azimuth, withstand wind and seismic loads, prevent water ingress into the roof, and maintain adequate ventilation for thermal management. Poor mounting design can compromise both energy yield and structural integrity.

DC power generated by the modules is routed through DC cabling and protection devices, typically housed in a DC distribution board (DCDB). This stage includes isolators, fuses, and surge protection devices (SPDs). These components protect the system from overcurrent conditions, lightning-induced surges, and maintenance hazards. Proper DC protection is especially important due to the high voltages involved in modern rooftop systems.

The heart of the rooftop PV system is the inverter. As shown in Figure 1.9, the inverter receives DC power from the array and converts it into alternating current (AC) that matches grid voltage and frequency. Beyond simple conversion, modern inverters perform maximum power point tracking (MPPT), system monitoring, fault detection, and grid synchronization. In many systems, the inverter also serves as the primary data source for performance analysis and diagnostics.

On the AC side, power flows through an AC distribution board (ACDB) before supplying building loads or exporting electricity to the grid. The ACDB contains circuit breakers, isolators, and surge protection to ensure safe operation and compliance with electrical codes. For grid-connected systems, a net meter or bidirectional meter measures both imported and exported energy, enabling net-metering or feed-in tariff arrangements.

Collectively, these elements form the Balance of System (BOS)—a term encompassing all components other than the PV modules themselves. BOS design strongly influences system cost, reliability, and safety. In fact, as module prices have declined, BOS optimization has become one of the most important areas for improving overall project economics.

Figure 1.9 also highlights system classifications. Grid-tied rooftop systems operate in synchrony with the utility grid and shut down during outages for safety. Off-grid systems rely on batteries and operate independently, while hybrid systems combine grid connectivity with energy storage to provide backup power. Although the block diagram remains broadly similar, the presence of batteries and charge controllers significantly alters system behavior and control logic.

From an operational perspective, the rooftop PV system functions as an integrated whole. A failure or mismatch in one component—such as undersized cables, inadequate protection, or poor inverter placement—can degrade performance or create safety risks. Effective system design therefore requires holistic thinking rather than isolated component selection.

For technicians and engineers, the block diagram in Figure 1.9 serves as a mental map for installation, commissioning, and troubleshooting. It clarifies energy flow, protection boundaries, and interface points, enabling systematic diagnosis and maintenance.

As rooftop solar adoption accelerates globally, understanding this system-level architecture becomes increasingly important. Rooftop PV is no longer an experimental add-on; it is a distributed power plant operating on millions of buildings. Figure 1.9 captures the fundamental structure that makes this possible—turning rooftops into reliable generators within modern power systems.