The term efficiency can be defined as the ability to achieve an end goal with minimal waste, effort, or energy. Being efficient means using available resources in the most optimal way possible. Simply put, a system is efficient when nothing is wasted and processes are well optimised.

The use of solar power is a strong example of efficiency within renewable energy. It demonstrates how innovation can generate clean energy while supporting sustainability. With the rising demand for renewables, improving the efficiency of photovoltaic (PV) systems has become inevitable.

Maximising PV efficiency serves two clear purposes:

• It strengthens overall energy production

• It makes solar power more affordable and sustainable

Like all energy systems, PVs cannot operate at 100% efficiency. The goal is to minimise losses in order to realise their full potential.

At first glance, it may seem logical that more heat leads to more solar power, but the reality is more complex. While hot weather can coincide with higher solar output, excessive heat actually reduces PV efficiency.

This happens due to basic thermodynamic principles. Electricity generation in solar panels relies on the movement of electrons. As temperatures rise, electrons move more erratically, which reduces voltage output. In practical terms, solar panel efficiency drops by around 0.5 percentage points for every 1°C rise in temperature.

Research led by Dr. Ansar Khan from the University of Calcutta, co-authored by Prof. Mattheos (Mat) Santamouris of UNSW Sydney, used mesoscale climate simulations to study rooftop photovoltaic solar panels (RPVSPs) at the city scale. Due to limited observational data, modelling was used to assess their climatic impact.

The study found that with 100% rooftop PV coverage, urban daytime temperatures could increase by up to 1.5°C during peak summer, while nighttime temperatures could decrease by up to 0.6°C. These findings, published in Nature Cities, highlight the need for integrated rooftop solutions that balance benefits with unintended urban heating effects.

The researchers observed a linear relationship between rooftop PV coverage and daytime temperature increase. In cities like Sydney, estimates suggest that nearly 40% of the electricity generated by PV systems may be offset by the additional cooling demand caused by PV-induced overheating.

This heating effect is linked to the low albedo (reflectivity) of PV panels and airflow patterns above and below them, which intensify heat accumulation. During peak summer periods, PV surface temperatures can reach up to 70°C, eliminating any daytime cooling benefit at the urban scale.

At night, however, PV panels release heat through radiation, often resulting in lower surface temperatures than surrounding urban areas. This nighttime cooling effect is significant, especially as climate models predict nighttime temperatures may rise by around 4°C over the next century.

In this context, roof paints offer a powerful complementary solution. Prof. Santamouris advocates the use of highly reflective cool roof materials to reduce heat absorption and improve PV performance.

Combining cool roofs with PV systems can:

• Increase photovoltaic capacity by 6–7%

• Significantly lower roof and surface temperatures

Increasing the albedo of roofs and urban surfaces helps in two key ways. Reflective roofs maintain surface temperatures up to 10°C lower than conventional roofs during peak summers. Under clear-sky conditions, reflective materials can be up to 40°C cooler than dark surfaces, releasing up to 72% less heat into the surrounding environment.

Higher roof reflectance also increases solar irradiance reaching PV panels. For monofacial PV modules, reflected radiation contributes around 1–3% of total effective irradiance. For bifacial PV systems, this contribution is significantly higher—averaging around 10%.

Real-world data supports this impact. In Shanghai, increasing rear-side radiation from 50 to 250 W/m² raised bifacial PV output by 17%, while higher front-side irradiance boosted energy production by 200–360% across monofacial and bifacial modules.

Solar panels are a critical tool in decarbonising energy systems, but improving their efficiency is essential to accelerate the energy transition. Reflective roof coatings provide a low-cost, high-impact solution—boosting PV output while mitigating overheating effects.

Recent advancements in super-cool roof materials, capable of achieving sub-ambient surface temperatures, present enormous potential. By delivering very high albedo values and reducing ambient heat, these materials can significantly enhance rooftop photovoltaic performance, making solar energy both more efficient and more climate-resilient.