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PVHI & making solar energy plants "sustainable"

About the blog

Madhukar Swayambhu
Madhukar Swayambhu is a TEDx speaker, awarded by Jal Shakti Mantralaya as Water Hero, Recognized as Global Top 3 Author on Water by Smart Water Magazine (Spain), having many published articles in various Water & Environment magazines.
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  • PVHI & making solar energy plants "sustainable"

We often see people using clean, green and renewable energy being used interchangeably by people in their everyday vocabulary. There are many similarities between the terms but they are very different from each other too.

If we look at definitions:

Renewable energy is energy that is collected from renewable resources that are naturally replenished on a human timescale. It includes sources such as sunlight, wind, rain, tides, waves, and geothermal heat. Although most renewable energy sources are sustainable, some are not.” – source Wikipedia

Green power represents those renewable energy resources and technologies that provide the greatest environmental benefit. To qualify as green power, this renewable electricity must also go above and beyond what is otherwise required by mandate or requirement. In other words, green power is voluntary, or surplus to regulation. Customers often buy green power for its zero-emissions profile and carbon footprint reduction benefits.” – source US EPA (the United States Environmental Protech Agency)

The corollary is, maybe all green energy sources are renewable, but vice-versa isn’t necessarily true. The idea behind “Green and Clean” energy is to have the “least environmental impact”.

Problem Identification

Let’s understand it with some examples, which is the key focus of this project.

Why did we switch over from coal-fired plant to solar?

The reason was environmental protection. A coal-fired plant, in the process of burning coal, generates GHG (Green House Gases), which remain in the atmosphere and entrap IR (Infra-Red) rays from Sunlight, which are the reason for heat in the Sunlight. Entrapping the IR by GHG in the atmosphere leads to warming of the atmosphere – the phenomena that we know as “Global Warming” due to which the global temperature is rising by 1° ~ 2° Celsius in a century, whereas earlier for last 7000 years, there was a consistent decline in global temperature by 0.01°C per century.

But did it really change the scenario?

"Urban Heat Islands (UHI) – is a phenomenon that occurs when cities replace the natural land cover with dense concentrations of pavement, buildings, and other surfaces that absorb and retain heat. This effect increases energy costs (e.g., for air conditioning), air pollution levels, and heat-related illness and mortality.” – source US EPA (the United States Environmental Protech Agency).

The key reason behind the phenomenon is believed to be the energy impact of heat island, is associated to the high energy consumption for cooling in buildings, which increases the production of smog, contributes to high production of pollutants from power plants (SOx, COx, NOx) and acts as a trap for pollutants, reducing, therefore, the quality of life and resulting in a social - economic impact on urbanized areas.

Similar to UHI, we have another interesting term called “PVHI – Photo Voltaic Heat Island”, which is defined as the heat islands created near the PV cell deployments (i.e., Solar Plants) due to the IR rays getting reflected from PV cells and adding to the local temperatures in the vicinity, raising it by 5° ~ 8° Celsius, on daily basis.

Detailed Scientific research was conducted on this subject in the year 2016, which got published in the scientific reports section of The Nature magazine, that says “Transitions to PV plants alter the way that incoming energy is reflected back to the atmosphere or absorbed, stored, and reradiated because PV plants change the albedo, vegetation, and structure of the terrain. Prior work on the PVHI has been mostly theoretical or based upon simulated models. Furthermore, past empirical work has been limited in scope to a single biome. Because there are still large uncertainties surrounding the potential for a PHVI effect, we examined the PVHI empirically with experiments that spanned three biomes. We found temperatures over a PV plant were regularly 3–4 °C warmer than wildlands at night, which is in direct contrast to other studies based on models that suggested that PV systems should decrease ambient temperatures.”

We tried to postpone the problem of “Global Warming” by switching over from Coal Fired Plants to Solar plants, but instead we ended up preponing the issue. What coal-fired plants could harm in a century on a global scale, the Solar Plants started doing 5 - 8 times of it in a local level on a daily basis.

Resolution

MDPI (Multidisciplinary Digital Publishing Institute), is a publisher of open access scientific journals, established in June 1996, based out of Basel, Switzerland. Today, they publish over 390 diverse, peer-reviewed, open access journals and are continuously expanding their portfolio. MDPI is the largest open access publisher in the world and the fifth largest publisher overall in terms of journal paper output.

In the year 2019, they published a research paper on "Ecosystem Service Reducing Heat Island Effect by Waterbodies". The study concluded that large water bodies are broadly capable of lowering daytime temperatures, and the distance to the water bodies should be effectively utilized in microclimate regulation provided by water bodies in cities which have a larger surface water area.

The simple resolution of the problem can be addressed by creating a Waterbody next to the Solar plants, so that the heat dissipated by the solar plant due to deflection of the IR rays, can simply be absorbed by the Waterbody to restore the ambient temperature.

A water body temperature is capable of being lower than the surrounding urban environment around 2° - 6 °C. According to these findings; one may conclude that the rise of evapotranspiration in cities, that has roots in vegetation and water body, can efficiently mitigate the influence of the urban heat island.

Detailed research conducted by Centre for Study of Built Environment in the Malay World (KALAM), Faculty Built Environment, University Technology Malaysia, UTM Skudai, Johor, Malaysia, published by Canadian Centre of Science and Education, concluded that “Water has a lower temperature in comparison to its surroundings and will therefore always work as a cooling factor. Water has a role of a buffer for the daytime temperature cycle; it cools the environment over the course of day and makes it cool at night. When waterbodies reach a higher rate of temperature over the hot seasons, they are capable of acting as night warming elements too.”

We’ve seen it in everyday life too, in natural Waterbody like a lake, pond, a river or a rivulet, a canal or a reservoir, the Water is always cooler in summers and warmer in winters, which proves the point of the above-mentioned study in Malaysia.

Conclusion

Thus, we can conclude that any effort for renewable energy could be green, provided the research is done on all aspects in detail and an apt solution is arrived at. If the study is holistic, we can resolve the problems from grass root level, else we would only be postponing the problem.

References –

1- Paper on “Development and testing of photovoltaic pavement for heat island mitigation”, a study report by Group Building Environmental Physics, Physics Department, Division of Applied Physics, University of Athens, Panepistimioupolis, 15784 Athens, Greece

2- Research paper on "Water Bodies’ Cooling Effects on Urban Land Daytime Surface Temperature: Ecosystem Service Reducing Heat Island Effect" published by MDPI, on 2nd February 2019.

3- Influential factors of water body to enhance the urban cooling islands (UCIs): A REVIEW, published by International Transaction Journal of Engineering, Management, & Applied Sciences & Technologies, published on 14th November 2019.

4- Observational Study on the Impact of Large-Scale Photovoltaic Development in Deserts on Local Air Temperature and Humidity, published on 22nd April 2020 by MDPI.

5- The Photovoltaic Heat Island Effect: Larger solar power plants increase local temperatures, published by www.nature.com/scientificreports on 13th October 2016.

6- Water Bodies an Urban Microclimate: A Review, Published by Canadian Center of Science and Education on February 2, 2015.

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