In today’s class, we learnt about the Urban Heat Island (UHI) effect. Personally, I’m quite surprised how big a difference urban forms can have on surface and atmospheric temperatures. Dr Coleman mentioned that in some cities, the difference between surface and atmospheric temperatures can go up to 20 to 50 degrees!
In view of these, I wonder how the use of solar panels contribute to UHI. The Singapore government is pushing for increased utilization of solar energy, and by 2020, the goal is for solar panels to be installed at 5,500 HDB blocks – more than half of all blocks here! Knowing that these many buildings in Singapore will have their rooftops fitted with solar panels, I thought it would be interesting to know how these things differ in absorbing heat, compared to our usual rooftops.
The albedo – or reflection coefficient – of the earth is about 0.30 (on average). That means, 30% of light hitting the earth is reflected into space. Apparently, solar panels also fall into this range. On the other hand, the value for new concrete is about 0.5, while that for asphalt ranges from 0.04 to 0.12. Since many rooftops are composed of concrete, it seems that based on albedo values alone, solar panels do not seem that promising…
However, other than the albedo, other factors that are involved include the reduced absorption of heat by the building, due to the buffer space created by the solar panels. These help reduce air-conditioning energy consumption, which accounts for around 50-70% of our energy needs in our hot climate. And of course, don’t forget that solar panels themselves are also a source of clean energy! Numerous studies have also pointed out the benefits of solar panels on reducing global warming and UHI (links below).
In conclusion, in addition to methods such as urban greening, solar panels may be a possible way to reduce UHI in cities. In fact, solar cooling technology has been developed and is currently being tested at the United World College (UWC) in Singapore. This is the first and only school that uses renewable solar energy to run both the air-conditioning and hot water system using a hybrid system. This development will be an interesting one to watch. Find out more about it here.
Ask Pablo: Do Solar Panels Contribute To The Heat Island Effect?
Masson, V., Bonhomme, M., Salagnac, J. L., Briottet, X., & Lemonsu, A. (2014). Solar panels reduce both global warming and urban heat island.Frontiers in Environmental Science, 2, 14
5 thoughts on “Do solar panels reduce UHI?”
Very interesting ! And thanks for providing a link to an article i’m keen to read ! I would recommend you check out the Academy at BCA – it’s a bldg that goes beyond zero energy and actually produces more than it uses. I visited it – very cool.
Wow, I checked out your blog post you mentioned on the BCA Academy & CDL’s South Beach Project, and I must say that I’m very impressed with Singapore’s progress in introducing green buildings to our cityscape. I also have a strong interest in design, and how we can merge it with new technologies to solve problems. It’s good to know that there are more of such buildings in the works!
There’s another project I know of that seeks to integrate agricultural technologies with high-density housing – called the Home Farm by SPARK Architects. It’s still in its conceptual stage, but it has been winning numerous awards since I attended their press release last year. They’re trying to tackle a different problem from the one we’re talking about, but I thought it might be interesting to share as well.
Link to blog post:
More about the Home Farm:
Hi Xiao Ping,
Thanks for the interesting post! I have a few thoughts about tapping on solar power as an alternative source of energy in the context of Singapore, albeit a slightly delayed reply:
Having solar panels installed in 5,500 HDB blocks in Singapore by 2020 is a pretty impressive number! Initially I, too, thought that it was a great idea because Singapore has so many high-rise buildings and rooftops are generally unused spaces in this heavily urbanised city. Plus, it is an alternative to rooftop gardens that might possibly help ameliorate the UHI.
I’m wondering, though, how economical is it to install solar panels since Singapore experiences high cloud cover throughout the year? While a lot of solar energy reaches Earth’s surface (could amount to 100 000 terawatts), and civilisation is using only a small percentage of energy for all its purposes today (around 17 terawatts/ less than 0.0002% of total solar energy reaching Earth), cloud cover can significantly limit the amount of electricity generated. Plus, there are several reasons why this might not be a practical idea to carry out, and for one, cost is likely to be an issue.
Perhaps a more practical goal Singapore could consider striving towards would be to produce and build solar panels cheaply? I came across an interesting case study about a Chinese solar company, Suntech power, using scientific innovations to cut the costs of using solar energy by increasing the efficiency of the panels* (e.g. one way is to move the metal lines closer together to that the electrons do not have to travel so far). Here they’re combining science with business, which if successful, might help bring us closer to being a sustainable city, ideally speaking!
*hyperlink to the press release: http://www.suntech-power.com/news/news160.html
Think solar panels are only well-suited to the sunniest locations ? Think again.
Whether solar panels would have a positive/negative impact to UHI depends on the actual conversion of solar radiation to IR. Assuming that a solar panel is able to convert 25% solar radiation to electrical energy, there would be 75% solar energy that could either be reflected or absorbed. Because solar panels are dark, I tend to suspect a large part of the remaining solar radiation would be absorbed. So unless a solar panel has built in reflective coating that would reflect the spectrum of radiation that it is unable to use to convert to electrical energy, it is likely to aggravate UHI than reducing UHI.
I searched through the internet and indeed there are studies that indicates that solar panels would increase surrounding temperatures.
So solar panels are really not that great for cities.