1. 2024 PV Market Overview: Rooftop Solar Is in Full Swing

2024 marks another year of rapid growth for China’s PV industry. Data show that in 2024, China added 277.57 GW of new PV capacity, a 28% year-on-year increase, bringing cumulative installed capacity to 886 GW, accounting for 26.5% of total power generation capacity. Among this, distributed PV added 118.18 GW, up 23% year-on-year, representing 43% of new capacity. By the end of 2024, cumulative distributed PV capacity reached 375 GW, accounting for 42% of total PV capacity.

From a global perspective, 2024 saw over 600 GW of new PV capacity added worldwide, a year-on-year increase of more than 30%, with total global operational PV capacity exceeding 2.2 TW. China continues to dominate the global market, accounting for nearly 60% of new installations. The U.S. PV market also maintained strong demand, with total solar investment reaching a record $41.05 billion in 2024 and new installations of about 50 GW, up 21% year-on-year.

Notably, the center of gravity for distributed PV in China shifted significantly southward in 2024. Jiangsu, Zhejiang, and Guangdong surpassed the traditional leading provinces of Shandong, Henan, and Hebei to become the top three in distributed PV installations. In 2024, the National Energy Administration (NEA) also released the Distributed PV Power Generation Development and Management Measures (Draft for Comments) to further standardize distributed PV management. Meanwhile, 70 localities across the country still maintain PV subsidy policies, covering residential and commercial & industrial (C&I) projects. Zhejiang, Guangdong, and Jiangsu offer the most subsidies, with upfront installation subsidies as high as RMB 1.8/W.

2. Roof Material Determines Installation Method: Detailed Guide to Five Major Types

Different roof materials have a direct impact on the choice of installation methods and accessories. Adopting the correct installation plan is key to ensuring the safety and efficiency of a PV system.

2.1 Asphalt Shingle Roofs

Asphalt shingle roofs are the most common residential roof type in North America and the easiest for solar panel installation. They offer simple installation and cost-effectiveness. Installers can drill directly into the shingles to mount brackets, creating a stable foundation.

When installing solar on asphalt shingle roofs, a specialized racking system is typically used. Installers locate the rafters, secure roof hooks to the rafters or roof beams using lag bolts, then attach aluminum rails and finally the solar panels to the rails. One important note: asphalt shingles typically last 15–20 years, while solar panels last about 25–30 years. Therefore, if the roof is older than 15 years, it is advisable to replace the shingles before installing solar to avoid having to remove the panels later for a roof replacement.

2.2 Metal Roofs

Metal roofs, with their excellent durability and smooth surface, are considered one of the best roof types for solar panel installation. Their advantage lies in the use of clamp‑based fastening systems that require no roof penetrations, better preserving the roof’s waterproof integrity.

For standing seam metal roofs, installers can use clamps that attach directly to the raised seams of the metal panels, then secure the racking system above the roof. This non‑penetrating installation method not only protects the waterproof layer but also greatly improves installation efficiency. Metal roofs typically have stronger load‑bearing capacity, supporting over 30 psf, much higher than the 15–20 psf of asphalt shingles.

When installing solar on metal roofs, proper grounding is essential. Because metal conducts electricity, the electrical grounding system must be complete to mitigate lightning‑related hazards.

2.3 Tile Roofs

Tile roofs (including clay and concrete tiles) require careful handling to avoid damaging the tiles. Traditional tile roofs generally use specially designed penetrating brackets, installed with minimal tile damage.

During installation, installers carefully lift some tiles, attach bracket hooks to the roof deck or rafters, lower the tiles back over the hooks, and then attach the PV rails to the hooks. Each penetration point must be meticulously sealed to ensure no leakage. At the same time, the weight of the PV modules must be checked to ensure the tile roof structure can support the additional load.

In recent years, solar tiles (building‑integrated PV or BIPV) have emerged as a new option. Solar tiles combine power generation and roofing functions, providing weather protection while generating electricity. Unlike adding solar panels to an existing roof, solar tiles require a full roof replacement, offering higher integration but at a higher cost.

2.4 Flat Roofs (Concrete Roofs)

Flat roofs are common on C&I buildings and some residences. They offer large available areas and flexible installation methods. There are two mainstream solutions for flat‑roof PV installation:

Expansion Bolt Fixing Method: Installers use a hammer drill to make holes in the concrete roof deck, insert expansion bolts, then mount the brackets and solar panels. Quality‑conscious contractors apply sealant and then a waterproof asphalt coating around each bolt.

Ballasted Concrete Block Method (Non‑Penetrating): This approach combines the racking system with concrete ballast blocks, using weight to hold the PV system in place without penetrating the roof membrane. Its significant advantage is that it does not damage the existing waterproofing, but the roof’s load‑bearing capacity must be evaluated.

The concrete‑ballast method offers strong load capacity and reliable wind resistance, does not damage the concrete roof, and is simple to install. However, disadvantages include increased roof load, a large amount of reinforced concrete required, a longer construction period, and higher overall cost.

On flat roofs, solar panels can also be arranged at an optimal tilt angle to maximize sunlight exposure and power generation. Additionally, converting a flat roof into a pitched roof (a “flat‑to‑pitched” retrofit) before adding solar is another option worth considering, especially for older buildings – it can slow down aging and improve generation efficiency.

2.5 Color‑Steel Tile Roofs (Profiled Steel Sheet Roofs)

Color‑steel tile roofs are widely used in industrial plants and commercial buildings. PV installation on such roofs mainly uses clamp‑based mounting, with materials such as aluminum profiles, hot‑dip galvanized steel, aluminum alloy, or stainless steel. This method is lightweight, low‑cost, highly reliable, and quick to install.

Special attention is needed for several aspects: check purlin spacing and direction to ensure secure bracket attachment; waterproofing – if drilling through the steel sheet is necessary, use waterproof adhesive or gaskets; and load calculation – generally, adding solar to a steel‑structure plant roof increases the load by about 15 kg per square meter, so the original design load margin must be verified.

3. Key Considerations for Rooftop PV Installation

3.1 Structural Load Assessment Is Essential

Before installing a PV system, a structural load capacity verification is indispensable. Different roof types have significantly different load‑bearing capacities. It is necessary to confirm that the building’s roof can meet the PV system’s design requirements. When in doubt, a structural engineer should perform load calculations.

3.2 Waterproofing Is Critical

Drilling during PV installation inevitably penetrates the existing waterproof layer. If not properly treated, leaks can easily occur. Therefore, ensuring proper sealing of each penetration point, or applying a waterproof membrane after installation, is key to long‑term reliability.

3.3 Sunlight Conditions Must Be Fully Evaluated

PV generation efficiency is directly related to sunlight exposure. Before installation, evaluate potential shading from nearby buildings, trees, exhaust vents, parapets, etc. The ideal orientation for solar panels is true south, and the optimal tilt angle should be calculated based on local latitude to maximize annual generation efficiency. Also, adequate ventilation space should be left between the panels and the roof to meet module operating temperature requirements.

3.4 Safety Regulations Must Be Strictly Followed

Rooftop PV installation involves electrical work and working at heights, which carry risks. It is advisable to choose a certified installation team and ensure that the system design complies with local building codes and electrical safety standards. For large C&I projects, fire protection design must also be considered to mitigate fire risks from electrical faults or lightning strikes.

4. Basic Installation Process Overview

Regardless of roof type, PV system installation generally follows this basic process:

(1) Needs Assessment: Determine required power generation and energy independence goals; evaluate roof size, orientation, and sunlight exposure.

(2) Choose Panel Type: Select monocrystalline (highest efficiency), polycrystalline, or thin‑film panels based on budget and efficiency needs.

(3) Obtain Permits: Contact the local building department to determine specific permit requirements for solar panel installation.

(4) Prepare the Roof: Inspect for any damage or issues that need repair; ensure the structure can support the panel weight.

(5) Install the Racking System: Installers assemble a sturdy mounting frame according to roof type and design, using appropriate attachment hardware.

(6) Mount the Panels: Attach the solar panels to the racking system, ensuring proper alignment and spacing for optimal sunlight exposure.

(7) Electrical Connections: Connect the panels to the inverter (converting DC to AC), then connect to the building’s electrical system.

(8) System Testing and Grid Connection: Perform thorough testing and inspection to ensure safe and efficient operation; complete grid interconnection procedures.