The fluid that splits sunlight: how NANOSPLIT turns the sun into electricity and heat + test

• Electricity and heat from the same sunlight
• The problem with hot solar cells
• A light filter made of zinc oxide and gold
• Presented to the research community
• The work continues after the project
• Smart optics for solar power
• Summary
• Five questions: how do you use energy? (test)

⇑Electricity and heat from the same sunlight

The EU-funded NANOSPLIT project was launched in 2021 to enhance concentrated photovoltaic-thermal (PV-T) systems. These hybrid designs generate electricity and high-temperature heat at the same time.

They work by using lenses or mirrors to concentrate sunlight onto a small solar cell area, while the excess heat produced in the process is captured instead of being wasted.

⇑The problem with hot solar cells

Traditional PV-T systems have a weak spot. At high solar radiation intensities, temperatures rise too – and hot photovoltaic cells lose efficiency.

NANOSPLIT tackled this by creating nanofluid-based spectral splitters. These filter the incoming sunlight, directing the most useful wavelengths to the solar cells and absorbing the unused, heat-generating wavelengths. That heat can then be used for thermal applications such as domestic hot water or space heating.

⇑A light filter made of zinc oxide and gold

The project’s breakthrough lies in hybrid nanofluids composed of zinc oxide sheets and gold nanoparticles. Together, they act as intelligent light filters.

Inside the filter, sunlight is split into two paths:

• visible and near-infrared light passes through to reach the photovoltaic cells,
• ultraviolet and heat-carrying infrared wavelengths are directed to the thermal components,
• the solar cells stay cooler, which is exactly what conventional systems struggle with.

In short, each part of the solar spectrum goes where it is most useful, instead of being lost as unwanted heat in the cells.

⇑Presented to the research community

The team presented its findings at the ECOS 2024 conference in Rhodes, Greece. Sharing results at an international meeting is an important step for any new energy technology, as it puts the idea in front of other experts working on similar problems.

⇑The work continues after the project

NANOSPLIT was completed in 2023, but the story did not end there. The team has been collaborating with European and Indian partners on further development.

One line of research focuses on carbon dot nanofluids that can be “tuned” to specific light wavelengths. At the same time, Solar Flow, a spin-out company from Imperial College London, is exploring higher-temperature industrial heat applications.

This shows how a research project can lead to several new directions at once: new materials in the lab and a company looking at industrial uses.

⇑Smart optics for solar power

Christos Markides, project coordinator at Imperial College London, sums up the result: “NANOSPLIT has successfully demonstrated how advanced optical and thermal management solutions unlock next-generation solar technologies.”

For students of physics, materials science or energy engineering, NANOSPLIT is a good example of how optics, chemistry and thermodynamics come together in a single device.

Hybrid PV-T systems already outperform stand-alone photovoltaic or solar thermal systems, because their overall efficiency is higher. By splitting the spectrum, NANOSPLIT pushed this advantage further, making use of the full solar spectrum while keeping the cells at lower temperatures.

⇑Summary

NANOSPLIT found a way around the main weakness of concentrated PV-T systems: overheating solar cells. Its hybrid nanofluids made of zinc oxide sheets and gold nanoparticles split sunlight, sending visible and near-infrared light to the cells and ultraviolet and infrared wavelengths to the thermal components. The project ended in 2023, and work on carbon dot nanofluids and industrial heat applications continues.

⇑Five questions: how do you use energy? (test)