Too much heat is bad news for solar panels and can hurt energy generation

The frequency and duration of heatwaves have been increasing in India due to global warming. This year too, the month of April recorded some of the hottest days. Some northern and eastern states in India recorded maximum temperatures above 44 degrees Celsius. Heatwaves were also reported from other South Asian countries such as Bangladesh, Thailand and Laos.

An Intergovernmental Panel on Climate Change report mentions that climate change is likely to be accompanied by an increase in the frequency and intensity of heat waves. More than 90% of India is at extreme risk of being adversely impacted by heatwaves, according to a study published early this year. This poses significant risks to the energy sector.

A 2022 report by the World Meteorological Organization says that changes in climate, increase energy demand by putting pressure on the fossil fuel sector, making the net-zero transition even more urgent. The reality, however, is that even the clean energy sector is not spared of the adverse effects of heatwaves.

Impact of heatwave on solar energy

The solar energy sector in India mostly uses photovoltaic solar technology which converts sunlight into electricity, using panels made of semiconductor cells. Large solar power plants are often built on vast arid lands where sunlight is available in abundance.

For example, Pavagada taluka in Karnataka which has the world’s second-biggest solar power plant in terms of efficiency (at 2,050 megawatts), receives solar radiation of 5.35 kWh (kilowatt-hour) per square metre per day. While this abundant sunlight is good for a photovoltaic system, too much heat is bad news.

Solar panels are designed to function optimally at 25 degrees Celsius and operate at their peak efficiency at temperatures between 15 and 35 degrees Celsius. Higher temperatures result in a drop in voltage as electrons that generate electricity “bounce too much”, not moving efficiently between the electrical circuit, affecting power generation, explained Saksham Nijhawan, manager of Responsible Energy Initiatives at an international sustainability organisation, Forum for the Future. Studies have suggested that there is a 0.5% drop in efficiency, for every 1 degrees Celsius rise in temperature.

“During the summer in India, the temperature often crosses 40°C. Moreover, solar cells that convert sunlight into electricity, absorb heat during this process. If the ambient temperature is 40°C, it would be about 70°C inside a solar cell,” said Goutam Samanta, head of PV technology at renewable energy developer, Juniper Green Energy. It is also documented that the efficiency of some solar panels goes down by 10%-25% when it is exposed to such elevated temperatures for a longer duration.

A heatwave is a period of abnormally high temperatures, more than the normal maximum temperature. According to the Indian Meteorological Department, it is likely a heatwave when the maximum temperature of a station goes above 40°C in the plains and 30°C in the hilly regions.

Solutions for solar sector

With heatwaves becoming a frequent feature of Indian summers, is it time for the solar energy sector to find long-lasting solutions to the decline in solar power efficiency?

Subrahmanyam Pulipaka, CEO of the National Solar Energy Federation of India said that the renewable energy sector is at risk of extreme weather events which are not only limited to heatwaves. “Though theoretically, a high-temperature results in a decline in solar power generation, there is no data from India to conclusively prove it is happening here,” he said.

Solar developers, however, are feeling the heat. In case of extreme temperatures, the decline in power efficiency coupled with the natural wear and tear of the infrastructure is a matter of concern.

Samanta said that at the end-of-the-life stage of a solar installation, which is estimated to be 25 years, the power output of the PV modules naturally falls to 85%-87%, depending on the modules and the technology used. To compensate for the loss, the developers have to install more PV modules and take up more land area which increases the capital investment, he added.

Infrastructure modification

World Resources Institute, in a study on the role of decentralised solar in climate-vulnerable areas, noted that future climate considerations are not reflected in solar installations. The report suggests a need to go beyond conventional implementation models that have specific, often siloed responsibilities and choose innovative models that take future climate change scenarios into consideration.

Bharath Jairaj who leads the Energy Programme at World Resources Institute in India said that even before we come up with engineering solutions, we need to focus on region-wise infrastructure modifications that are climate resilient. “The demands of a solar infrastructure in a flood-prone Assam will be different from that of one in Rajasthan which witnesses extreme temperatures,” he said.

A 2013 study points to the need to consider geographical changes when it comes to choosing photovoltaic modules. The study says that generally the performance ratio of photovoltaic modules decreases with latitude because of temperature. “However, regions with high altitude have higher performance ratios due to low temperature, like, southern Andes, Himalayan region, and Antarctica,” the paper reads. The study suggests using photovoltaic modules with less sensitivity to temperature for high-temperature regions and those that are more responsive to temperature for low-temperature regions.

Experimenting with new materials

While ground-mounted solar panels have the advantage of convective airflow cooling the plants naturally, this is missing in most roof-top installations which are more affected by the increase in temperature, explained Samanta. He added that floating solar is a good response to heat.

“It performs better in increased heat conditions because water vapour acts as a natural coolant and power generation is not as affected,” he said. It also has the additional advantage of not needing land, thereby reducing land-use conflicts and environmental degradation. Floating solar has no shadowing effect either, making them more efficient in power generation.

He also suggested replacing the existing technology used in the photovoltaic sector with TOPCon technology which is more efficient. The tunnel oxide passivated contact solar cells, also known as TOPCon, is the latest buzzword in the solar sector. In this technology, tunnel oxide and polysilicon layers are added to the rear side of the solar cells to improve efficiency and these cells are said to have better resistance to high temperatures. Solar manufacturers have only started using TOPCon since 2019.

Studies have also suggested the application of phase change material as a viable strategy for reducing and managing the temperatures of PV panels and for increasing the electrical energy efficiency of the system. Phase change materials are used in energy systems to provide cooling. A 2023 study finds that phase change material cooling has a positive short-term influence on the performance of photovoltaic panels, with an improvement in predicted efficiency.

Other well-discussed solutions include constructing panels with light-coloured materials to reduce heat absorption and moving components like inverters and combiners into shaded areas.

Apart from the infrastructure and engineering challenges, heatwaves also impact the health and safety of the workforce, which is not often addressed. World Health Organization has warned that global population exposure to heat is increasing due to climate change. Continuous exposure to excessive heat can lead to heatstroke with fatal outcomes and the people installing solar panels and those working in solar farms are also at risk. “Heatwaves have a wider impact on communities living in these (high temperature) areas, resulting in temporary or permanent out-migration or significant impact on health,” said Nijhawan.

The International Labour Organization, in a 2019 report, states that temperatures above 24-26 degrees Celsius are associated with reduced labour productivity and at 33-34 degrees Celsius, 50% of a labourer’s work capacity is lost. Projections based on a global temperature rise of 1.5 degrees Celsius by the end of the 21st century, and also on labour force trends, suggest a productivity loss of 2.2%, equivalent to 80 million full-time jobs in 2030. In South Asia, which is estimated to be one of the most affected sub-regions, the loss is 5.3%, corresponding to around 43 million full-time jobs.

While the country steers ahead in its goal to achieve its clean energy targets, experts say that it is important to consider the health of both the human and the machine in the changing climate, to ensure that solar energy productivity is long-term and sustainable.

This article was first published on Mongabay.