New concept may meet human resource needs of 'full Earth'

Using different parts of sunlight's spectrum to produce crops, generate electricity, collect heat and purify water could provide food, energy and water resources for the world's growing population, a team led by an Indian origin scientist has proposed.

The world's human population is expected to grow from seven billion to more than 10 billion over the next two to three generations, leading to a "full Earth" scenario.

"This increase in population, coupled with rising per capita income and associated change in consumption habits, will put unprecedented stress on food, energy and water resources," said Rakesh Agrawal, professor at Purdue University in the US. "The grand challenge before us is to sustainably meet the needs of a full Earth using scarcer resources, and the sun is the key energy source to achieve this goal," said Agrawal.

He led a team which proposes a system that would use the entire solar spectrum to maximise resource production from a given land area. The concept, described in the journal Scientific Reports, works by separating and harvesting the three specific segments of the solar spectrum that are best suited to facilitate the production of food, energy and clean water.

In current practices, much of this spectrum is wasted because all of the sunlight falling on a given spot is used solely for one purpose, such as agriculture, energy production or water purification. The new approach would instead use the same land mass for all three purposes simultaneously through innovative technologies that split the spectrum into three segments and efficiently harvest sunlight.

A typical photovoltaic panel, when installed on farmland, casts a shadow and dramatically reduces plant growth and crop yield from the shadowed area. The proposed photovoltaic designs transmit photons responsible for plant growth while reflecting remaining photons in the solar spectrum to specially-designed solar cells to generate electricity and collect heat for energy recovery and water purification. "The advantage of our proposed solution is clear," Agrawal said.

"With the three-way split, the entire spectrum is judiciously used for the production of food, energy and water resources," he said. Solar spectrum splitting to maximise electric power generation and heat recovery is well known, said Muhammad Ashraful Alam, Professor at Purdue.

The proposed system could create solar-powered, self- sufficient communities - a major step towards full-Earth preparedness, Peter Bermel, an assistant professor at Purdue said. "Implementing this approach across agricultural land areas could supply extra electricity to the power grid, as well as freshwater supplies to other areas in need, thus improving global resilience," he said.