Nanofluids and the sun: Illuminating the way to clean energy

The sun is an attractive source of renewable energy, yet we use hardly any of it. In 2010, just 17 terawatts of solar energy was harvested worldwide – less than 0.02% of the amount available.

Despite the sheer magnitude of energy available, solar energy reaching the earth’s surface is typically considered ‘low grade’.

Fortunately, a number of solar concentrating devices are available to help convert solar energy into a more potent form. But once that energy is so concentrated, we need to be able to capture and store it.

Current methods of capturing solar energy typically use flow receivers. The concentrated solar energy falls on a tube through which a fluid is flowing. It heats the fluid, which can then pass that heat on elsewhere, and eventually be used to generate electricity.

A more promising capture method for concentrated solar power plants, called volumetric absorption, uses the material both to capture and transport concentrated energy.

Because of this dual function, volumetric absorption presents an opportunity to reduce the energy losses and improve energy efficiency above that of current flow receiver methods.

The challenge is how to get the volumetric absorption material to absorb as much energy as possible, without impinging on its other necessary functions.

Nanoscience offers some enticing possibilities. Nanofluids – suspensions of nanoparticles in fluids – have great potential as volumetric solar absorbers.

The nanoparticles, if selected correctly, can convert light energy from the sun to thermal energy within the fluid that contains them. Even very small quantities of nanoparticles are able to absorb nearly all of the incident solar radiation.

Employing nanofluids in volumetric receivers would provide flexibility in that the optical properties can be tuned to ensure optimum absorption of light energy.

As part of my thesis research at the Masdar Institute of Science and Technology, I am exploring ways to optimise nanofluid-based volumetric solar receivers.

Volumetric receivers can be separated into two broad components: the absorbing medium, and the housing that contains it.

We are looking to improve energy efficiency in both by assessing the impact of various alterations.

In the housing component, we are looking at how changing the shape and changing the materials affects the overall performance.

We also have found improvements when we tune the optical properties by adjusting the fraction of nanoparticles within the absorption material.

It is our hope that this research will contribute to enhancing humankind’s ability to capitalise on the ready supply of solar energy our planet receives.

We are continuing our research in this regard with experimental characterisation to find the best nanofluid for solar absorption with the goal of providing insight into properties that current theories can’t predict.

We are also looking at developing nanofluids that can efficiently absorb solar energy, as well storing the resulting thermal energy.

Our vision is to use nanofluids to harness and store the immense energy presented by the sun, thereby contributing to Abu Dhabi’s renewable energy goals, and the clean energy needs of the world at large.

Luqmaan Habib is a master’s student of mechanical engineering at the Masdar Institute. Dr Yousef Shatilla is professor of mechanical engineering and dean of academic programmes at the Masdar Institute. Dr Mohamed Ibrahim Hassan Ali is an assistant professor of mechanical engineering.