I. Ensuring Power Generation Efficiency and Preventing Power Reduction Due to High Temperatures

Photovoltaic modules exhibit a significant negative temperature coefficient; the higher the operating temperature, the lower the power generation efficiency. In summer, enclosed rooftops have extremely poor heat dissipation, and internal temperatures can exceed 60°C—far surpassing the standard operating temperature for modules—which directly inhibits photovoltaic power generation performance.

If the bottom ventilation gap is omitted, heat from the back of the modules cannot dissipate through convection. The continuous accumulation of heat will trigger the manufacturer’s high-temperature derating mechanism, resulting in sustained power generation losses; the overall annual power generation of the project may decline by as much as 8%–15%.

Reserving a standardized ventilation gap allows natural air convection to continuously remove accumulated heat from the back of the modules, stabilizing their operating temperature and ensuring the power plant’s sustained, high-efficiency power generation in a cost-effective and high-return manner.

II. Delaying Module Aging and Extending Service Life by 25 Years

PV backsheets, sealants, and frame gaskets are all weather-resistant consumables designed for outdoor use, and they have strict requirements for temperature and humidity conditions. Prolonged exposure to high temperatures, high humidity, and an enclosed environment can significantly accelerate the rate at which these materials age and fail.

A sealed installation structure without ventilation gaps is highly prone to heat and moisture buildup on the back of the modules. Over time, this can lead to issues such as yellowing of the backsheet, delamination and blistering, and water ingress between layers. These problems can in turn trigger core issues like the hot-spot effect and hidden cracks in the solar cells, resulting in a year-on-year decline in power generation and an inability to meet the 25-year design service life of the solar power plant.

Roof-mounted photovoltaic mounting systems feature standardized ventilation gaps that allow natural air convection to continuously dissipate heat accumulated on the back of the modules, thereby stabilizing their operating temperature and ensuring the power plant’s sustained, high-efficiency power generation in a cost-effective and high-yield manner.

III. Eliminating the Risks of Roof Water Accumulation, Mold, and Leaks

Roof leaks and mold growth or deterioration of the waterproofing layer are the most common post-installation issues resulting from the omission of ventilation gaps. When solar panels are installed directly against the roof, they completely block the roof’s drainage and moisture-ventilation pathways, creating multiple potential hazards.

On rainy days, water accumulates beneath the modules and cannot drain quickly; moisture from the roof remains trapped for extended periods and cannot evaporate. This causes the waterproofing layer to develop mold, peel, rot, and eventually detach, ultimately leading to roof leaks and damp, moldy interior walls.

This is particularly true for older roofs and color-coated steel sheet roofs, where sealed, non-ventilated conditions make it extremely easy for mud and water to accumulate and for moss to grow, causing continuous damage to the roof structure. At the same time, prolonged exposure to moisture at the base of the mounting brackets accelerates rusting and loosening, creating safety hazards for the roof structure.

IV. Reducing the Risk of Hot Spots and Enhancing Power Plant Operational Safety

Dust and moisture buildup on the underside of modules, as well as obstructed ventilation, can lead to uneven heat dissipation across the module surface and excessive local temperature differences. Over the long term, this can easily trigger dangerous phenomena such as localized overheating and hot spots.

Hot spots represent a core safety risk for photovoltaic power plants; at best, they cause individual module failures and reduced power generation; at worst, they can scorch cables due to high temperatures and trigger fires. Standard ventilation gaps ensure uniform heat dissipation across the entire module surface, mitigating the risk of hot spots at the source and comprehensively enhancing the operational safety of the power plant.

V. Standards and Guidelines: What Is the Optimal Ventilation Clearance?

In accordance with domestic photovoltaic construction standards, the requirements for ventilation clearances on different roof types are clearly defined and categorized as follows:

1. Standard flat concrete roofs and glazed tile roofs: Bottom ventilation clearance ≥ 100 mm;

2. Color-coated steel sheet factory buildings, high-temperature and stuffy areas, and rainy and humid regions in southern China: A clear space of 150–200 mm is recommended.

It is strictly prohibited to omit ventilation gaps or use roof-flush, sealed installations in an attempt to blindly increase installation density. Non-compliant construction practices that compromise the long-term performance and safety lifespan of the power plant must be strictly prohibited.