India’s target for achieving net-zero emissions hinges wholly on large-scale adoption of renewable energy. Currently, coal accounts for more than 80 per cent of the country’s energy production, and this emits more than 2.4 billion tonnes of carbon dioxide annually.
Energy from the sun currently powers most renewable resources worldwide, due to widespread availability, but conventional solar photovoltaic (PV) units require a huge investment. PV modules also have a significant ecological impact and their effectiveness declines at high temperatures.
One alternative to PV cells is solar thermal power, where solar energy is converted into heat to generate electricity. When combined with thermal energy storage devices (TES), it offers several advantages over conventional PV systems, such as lower investment and increased reliability.
In a paper titled ‘Techno economic feasibility study of solar organic Rankine cycle in India’, submitted to the Physics and Society journal last week, the authors point out that TES devices are a sound alternative in solar power harvesting, vis-a-vis the environmental impact of solar panels.
The study — conducted by researchers from the Indian Institute of Engineering Science and Technology, Shibpur; Imperial College, London; and the Indian Institute of Technology, Kharagpur — evaluates the performance and cost-effectiveness of solar organic Rankine cycle (ORC) technology under Indian climatic conditions.
The paper notes that India aims to generate 40 per cent of its electricity from renewable sources by 2030. The country has achieved a 226 per cent increase in renewable energy installation, now accounting for about 25 per cent of total installed capacity.
‘Optimal fluid’
Solar ORC technology converts heat into electricity. Compared to traditional steam-based Rankine cycle technology, it generates heat at lower temperatures, making it suitable for low-power electricity generation (up to 100 kWe). The system uses solar energy to heat an organic fluid, which then expands to generate mechanical power and, in turn, electricity.
The study evaluated seven fluids. The findings suggest that ‘R 1233zd (E)’ is the optimal fluid, in terms of cost and environmental impact. This organic fluid belongs to the category of hydrofluoro-olefin refrigerants.
In the ORC system, heat from a solar collector is transferred via the fluid to an evaporator. The fluid is pumped to a high pressure, where it absorbs the heat in the evaporator, turning into a superheated vapour. This vapour then expands in an ‘expander’ to generate mechanical power, which drives a generator to produce electricity. Finally, the fluid cools in a condenser to repeat the cycle.
Competitive costs
The study shows that ORC systems are competitive compared with solar PV technology and their cost is significantly lower than that of biomass-based ORC systems across various power targets. For instance, the cost for a 100 kW S-ORC unit is $895-1,122 per kWh. A comparable solar PV system would cost $988 per kWh.
Developing countries, including India, would likely benefit from investing in this efficient, low-cost solar thermal option. But not all is rosy yet. There is still work to be done on the thermal solar front, too. The authors point out that there is further scope to reduce costs by optimising components such as the solar collector and expander, and improve efficiency even further.
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Published on November 28, 2025