Environmental Impact of Solar Photovoltaic Installations on Urban Heat Island Effect
Energy, in the form of fossil fuels, is the driving force of human life; therefore, renewable energy sources such as solar energy are seen as the answer to the energy crisis. However, these are relatively new technologies and might affect the environment negatively. In this article, Khushal Matai discusses the possible negative effects of SPV installations, which need further research.
Climate Change and Renewable Energy
Climate change has become a highly critical issue as the repercussions have started manifesting all around the world with melting glaciers, fluctuating weather conditions, crop deterioration, etc.
A major transformation is required to address these challenges and to avoid catastrophic future consequences. Large-scale conversion to clean, perpetual, and reliable energy at low cost can be a solution to such problems as well as the energy crisis. A move towards cleaner and greener renewable energies, such as solar, wind, geothermal, etc. has been initiated with an understanding of these issues.
It has been predicted that the share of renewable energy in global primary energy sources could increase from the current 17% to between 30%–75%, and in some regions exceed 90% by 2050.
Solar energy has been at the forefront due to its abundance and various technical advancements. Recent estimates of achievable solar power in the world ranges from 400–8,800 TW given: the current system performance; topographic limitations; and environmental and land use constraints.
In 2010, the average global power consumption was about 17.5 TW, so harvesting a few percent of the achievable solar power should be able to provide enough energy for all. It is also one of the few renewable energy sources that can be implemented on a large scale within cities itself.
If compared with solar farms, individual rooftop solar panels are a convenient and cost-effective means of increasing renewable energy generation and decreasing GHG emissions.
Solar Power and India
On a worldwide level, awareness about the renewable energy wave is resulting in huge investments in this field. India itself has ambitious targets for harnessing solar energy. India’s solar market, especially solar photovoltaic, has seen significant growth after the launch of the Jawaharlal Nehru National Solar Mission in 2010, with installed capacity of over 3 GW in just 4 years.
According to the Ministry of New and Renewable Energy (MNRE), India has an ambitious target of 100,000 MW by 2022, out of which 40,000 MW shall be rooftop. MNRE has also announced the Rooftop PV and Small Solar Power Generation Programme (RPSSGP) under phase I of the solar mission to encourage grid connected projects. Driven by various national schemes and the rising energy crisis, solar panels have now started becoming an integral part of rooftops in the urban areas. Solar panels absorb solar energy to produce energy, either in the form of heat (in case of solar thermal panels) or as electricity.
Thus, they modify the energy balance of the urban surface in contact with the atmosphere and thus possibly influence the urban microclimate. They also change the radiation received by the roof and influence the overall heat fluxes (radiative and convective) to the atmosphere.
Urban Heat Island Effect and SPV
Rapid urbanization and industrialization have resulted in warmer cities. The urban heat island effect (UHIE) is defined as the rise in temperature within man-made areas.
The UHIE intensity is an indicator of urban heating, which is the maximum difference between urban and rural air. It varies between 5 °C to 14 °C within climate zones. Increased temperatures have a negative effect on the health and microclimate, such as increased air temperature, decreased humidity, changed wind patterns, formation of ground-level ozone, heat-related mortality, etc.
In this solar rush, the possible adverse effects of solar PV installations are being overlooked. One of such negative impact is the effect on the temperature in the urban areas due to SPV installations. Few studies looking into the relation of SPV and heat island effect in deserts as well as urban areas have produced a mixed bag of results.
Turney and Fthenakis investigated 32 impacts from the life stages of solar farms which are broadly divided into five sections: land use, human health and well-being, wildlife and habitat, geo-hydrological resources, and climate and GHG emissions.
The impacts have been categorized as either beneficial or neutral, with the exception of the ‘local climate’ effects for which they concluded that research and observation are needed. PV panels have low reflectivity and conversion efficiency variation between 13%–20% which results in conversion of most of the incident solar radiation, that is 80% into heat which can alter the air flow and temperature profiles near the panels. Such changes may,
Global climate CO2 emissions Reduces CO2 emissions Beneficial High Strong benefit Other GHG emissions Reduces GHG emissions Beneficial High
Strong benefit Change in surface albedo Lower albedo Neutral Low The magnitude of the effect to low Local climate Change in surface albedo Lower albedo Unknown Moderate Need research and observation Other surface energy flows Unknown Unknown Low Need research and observation subsequently, affect the thermal environment of nearby living organisms. In Tokyo, the effect of largescale rooftop PV installations on heat island effect was investigated and was found to be negligible, provided PV systems are installed on black roofs.
However, black roofs are a significant factor/ assumption in this study, and if white roofs are considered, then the result could be different altogether. Another study shows that the annual average of air temperatures in the centre of a PV field can reach up to 1.9 °C above the ambient temperature, and that this thermal energy completely dissipates at a height of 5–18 m. Analysis of 18 months of detailed data showed that in most days, the solar array was completely cooled at night, thus it is unlikely that a heat island effect could occur.
Although daytime effects will also have some impact on the microclimate of the areas, these cannot be ignored. Aixue Hu, a climate change research scientist at the National Centre for Atmospheric Research, conducted a study attempting to predict the climatic effects of solar arrays.
He assumed a future scenario by 2100 wherein around 40% of the urban and desert regions will be covered with equally distributed solar panels in the sunny regions all over the world. Their results suggest that idealized, massive-scale installations of solar panels redistribute the incoming solar radiation and change the local radiation balance, resulting in changes in atmospheric circulation, thus aﬀecting regional and global climate. Overall, regardless of its capacity (as large as ∼800 TW or a more realistic projection of 45 TW), the potential global mean climate changes induced by the use of solar panels are small in comparison to the expected climate change owing to fossil fuel consumption, which, relative to pre-industrial climate, could raise the global mean temperature by a few degrees by 2100.
However, some of the regional climate changes induced by solar panels could be much greater than the global mean. For example, India and the West coast of North America warm up by 1 °C. The warming in India is associated with a precipitation feedback on land.
SPV and Their Effects on Buildings Energy Consumption
A scenario of large but realistic deployment of solar panels on the Paris metropolitan area has shown that solar panels, by shading the roofs, slightly increase the need for domestic heating by 3%. In summer, however, the solar panels reduce the energy needed for air-conditioning (by 12%).
The air temperature of the study area also reduces by 0.2 K during day and up to 0.3 K at night. In this study, the solar panels affect the indoor temperature by shading and decreasing the energy consumption of cooling/heating.
According to Masson et al., the deployment of solar panels is good both globally, to produce renewable energy (and hence to limit the warming of the climate), and locally, to decrease the UHI, especially in summer when it can constitute a health threat. 15 Researchers at UC, San Diego, determined that during the day, a building with rooftop solar installations had a ceiling temperature 2.5 °C cooler than that of a roof exposed to sunlight. At night, the panels helped retain the heat absorbed by the roof material, thereby reducing heating costs in winters.
For the building, the researchers analysed that the panels reduced the amount of heat reaching the roof by about 38%.16 All these studies shed light on the absence of such a study in the highly diverse Indian conditions. With MNRE’s ambitious targets, the relation of SPV installations and UHI has become significant so that the move to control GHG emissions does not trigger another climatic cataclysm. It has become critical to analyse whether the two objectives of mitigating climate change and global warming, that is, solar panel installation for cleaner energy and attenuating UHIE, are compatible.
According to a few research projects mentioned above, installation of SPV on buildings impacts the temperature of the urban areas to some extent. Mostly, all such studies have been done in colder climates (refer to Figure 2), which shows the necessity of conducting such research in tropical countries such as India.
The move towards renewable energy is inevitable due to the shortage of non-renewable resources and GHG emissions. Such a large number of solar panels redistribute the incoming solar radiation and change the local radiation balance, resulting in changes in atmospheric circulation, thereby affecting regional and global climate. So, it is of utmost importance to understand how SPV installations impact the urban climate of Indian cities.
source- GRIHA Shashwat Magazine