While the world’s eyes are glued on solar PV power plants, and for justified reasons, the other component of sunlight’s energy - its thermal component - has significant potential as a renewable energy source for decarbonization.
Most know about solar thermal through the simple solar water heaters, but there’s a lot more to solar thermal than just these. Simple solar thermal systems such as solar water heaters can provide temperatures only up to about 70 degrees C. Modified water heaters could perhaps take this close to 100 degrees C, making them more useful for some industries where there could be many low temperature processes (in industries such as food, dairy, chemicals etc.). Such low temperature uses of solar thermal alone could result in a reasonable amount of decarbonization, given the large potential available cumulatively for such low temperature industrial and commercial processes.
The full potential of solar thermal can however be realized only if we are also able to use it for high temperature processes, and to generate power. Solar energy can be used to achieve high temperatures through the use of concentrating solar technologies in which, instead of just simply capturing the heat of sunlight, the sunlight is concentrated through different mechanisms to produce temperatures as high as, or even higher than 500 degrees C. Such high temperatures can be used for industrial process heating or for power generation.
Some low temperature solar thermal systems such as solar water heaters represent mature technologies. However, solar dryers and solar cookers are yet to scale to the real potential that they offer.
Concentrating solar is still an evolving sector, with multiple technologies competing for dominance, economics still challenging, and with very few operational plants at large capacities (above 500 MW). But given its potential, concentrating solar - for both power and heat applications - could be seeing significant innovations and growth during the 2020-2030 period.
Similar to solar PV, solar thermal can be deployed in many regions around the world, and more so in countries in the tropical regions.
Solar thermal has a significant advantage over solar PV, and that is in storage. Storing thermal energy is easier and cheaper than storing electricity. Solar thermal is however not as modular as solar PV. This is especially true for concentrating solar power, where small scale systems are not very efficient at the current stage of technology development.
Global solar water heater capacities alone are about 500 GW thermal, an equivalent of about 1250 GW of solar PV for heating. Assuming that a large portion of these substitute for electric water heaters, the CO2 emissions saved by the current installation of solar water heaters alone are a massive 750 million tons per year under suitable assumptions.
Industrial processes using temperatures upto 400 degrees C emit about 2 billion tons of CO2 emissions every year, a large portion of this in the 150-400 degrees segment. The potential for much higher CO2 emission savings from solar thermal can thus be through the use of concentrating solar for thermal (and for power) applications. While currently, contributions from these two are negligible for decarbonization, improvements in technology and economics could see orders of magnitude increased capacities of high temperature solar applications used for power generation and industrial heating. Concentrating solar displacing fossil fuels for about 10% of total energy requirements of high temperature processes alone could help achieve CO2 emissions reductions above 100 million tons of CO2 per annum by 2030.
Use of concentrating solar for power generation, in addition to being a standalone system, can also work along with the conventional thermal power plants as a hybrid unit, as both these technologies use the same rankine cycle for power generation. Thermal power plants (coal and natural gas) alone emit about 11 billion tons of CO2 every year. Effective scaling of concentrating solar power thus not only has significant CO2 emissions savings potential but it could also provide a transition pathway that utilizes the massive thermal power generation infrastructure.
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Solar Thermal Decarbonization Avenue
