BBC News by the Reality Check team
It is well known that painting the roof of a building white will reflect sunlight and reduce its temperature.
But how many disadvantages does this have?
In a recent BBC interview, former UN Secretary-General Ban Ki-moon stated that this drop could be as high as 30 degrees Celsius and the internal temperature of the building dropped by as much as 7 degrees.
So where do these numbers come from, and does broader research support this?
Mr. Pan is talking about a pilot project in Ahmedabad, western India, where summer temperatures can reach 50 degrees Celsius.
In 2017, more than 3,000 urban roofs were painted with white lime and special reflective coatings.
Simply called "cold roof", this process aims to reduce the absorbed solar radiation, which in turn means less heat is transferred into the building.
The cool roof also emits some of the heat normally retained by the building, further cooling it.
The Gujarat project’s planning documents stated that reflective roof coverings “can help lower the roof temperature by as much as 30 degrees Celsius and reduce the indoor temperature by 3 to 7 degrees.”
But this is not the actual discovery of the project itself.
"Compared with traditional roofs, cool roofs can help reduce indoor temperatures by 2 to 5 degrees Celsius, depending on the environment," said Anjali Jaiswal of the US Natural Resources Conservation Commission, which oversees the Ahmedabad project.
This range is slightly lower than Mr. Pan’s building temperature reduction figure, but it is still a significant drop.
Another pilot in Hyderabad, southern India, used a cool roof coating film and found that the indoor air temperature had dropped by an average of 2 degrees Celsius.
As for Mr. Pan’s claim that the temperature of the roof itself has dropped by 30 degrees, the Gujarat pilot did not provide an answer, but we can refer to the results of a study by the Berkeley Laboratory in California for some guidance.
Studies have found that a clean white roof can reflect 80% of the sunlight, and the temperature will remain around 31 degrees Celsius in the summer afternoon.
The situation in California is of course very different from the situation in India-more than 60% of the roofs in India are made of metal, asbestos and concrete. Even after white coating, these roofs will trap heat in the building.
However, the pilot projects in the Indian cities of Ahmedabad and Hyderabad have been successful enough that they launched an expanded cool roof plan this year.
This idea is certainly not new. In southern Europe and North Africa, white roofs and walls have been a typical sight for centuries.
New York City recently painted more than 10 million square feet of roof white.
Other places such as California have updated building codes to promote cool roofs, which are seen as an important way to save energy.
A cool roof can save up to 40% of air-conditioning costs.
An experiment in Bhopal in central India found that solar reflective coatings on low-rise buildings can save 303 kWh of energy load during peak summer hours.
Some people even estimate that if cooling paint is used on the roof of every major city in the world, global carbon emissions may be reduced.
Berkeley Lab said that the use of reflective roofs on a global scale can produce a global cooling effect equivalent to offsetting 24 gigatons of carbon dioxide-equivalent to reducing 300 million cars on the road in 20 years.
This is of course a low-cost option, especially in poorer countries.
Ms. Jaiswal said that the lime wash coating "could be as low as 1.5 rupees (£0.017; US$0.02) per square foot to more expensive reflective coatings or films."
The differences in personal comfort and cooling energy savings can be quite large.
However, in the end, “political will and implementation played an important role,” Ms Jaiswal said.
There are also possible disadvantages to consider.
For cities with colder winters, reflective roofs may increase heating requirements, and roof condensation is a risk of mold.
This is why a team at University College London decided not to use white paint in the colony resettlement project in New Delhi.
"Residents are also opposed to painting the roof white because the roof has other uses," said Renu Khosla of the Delhi City and Regional Center of Excellence.
She said that this highly reflective paint makes it difficult for people to walk on the roof to use the space to store objects and do daily housework.
A team from the University of Chicago also conducted research in the same area near Delhi.
They painted the roofs of a group of buildings and found that although the indoor temperature has only dropped moderately, the people who live in them have indeed adjusted their behavior to save energy and water bills.
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