Photonic solutions for solar bioenergy

Lead Research Organisation: University of Birmingham
Department Name: Sch of Biosciences

Abstract

We are at risk of energy poverty. Fossil fuels will last only a few more decades and nuclear power stations cannot be built quickly enough to meet the predicted shortfall. Without alternative energy, rising prices will be grudgingly accepted until the oil is exhausted. Wealthy oil/gas companies will control an energy-starved world in which our descendants suffer the long-term effects of global warming, including drought, famine, disease and flood-loss of many major coastal cities and large parts of Asia.

To avoid this we must focus urgently on renewable energy like sunlight, which is so abundant that it exceeds our requirements 10,000 times. Therefore, better ways of collecting, storing and using it could make a big difference.

All living things rely on sunlight. We are part of a food chain that starts with photosynthetic organisms. Even the oil that we rely on for energy was slowly made using sunlight over the last 60 million years, but most of the oil that can be reached easily has been burnt in just 100 years with massive CO2 release.

Growing plants for food effectively harvests solar energy and scientists have recently found ways to cultivate crops and microbes for fuels. But ?biofuels? have hit a serious problem; there is not enough land to produce both food and fuel because only about 0.1% of the energy in sunlight ends up in the biofuel or the food.

New photonic materials give us the chance to ?process? sunlight and change its composition, so that it becomes more useful to the organisms that convert it to food or fuels. By combining new photonic materials made by physicists with the biofuel technologies developed by biologists, we could shrink the land requirement so that all our energy and food needs can be met by sunlight.

Technical Summary

We are at risk of energy poverty. Fossil fuels will last only a few more decades and nuclear power stations cannot be built quickly enough to meet the expected shortfall as demand continues to grow. Without alternative fuels, rising prices will be grudgingly accepted until the oil is exhausted. Wealthy oil/gas companies will control an energy-starved world in which our descendants suffer the long-term effects of global warming, including drought, famine, disease and flood-loss of many major coastal cities.

The transition to clean, renewable energy is urgent and necessary. Biofuels such as bio-oil and bio-hydrogen offer the potential to capture solar energy in the form of convenient fuels. Once heralded as a key part of the solution, the rush towards biofuels slowed when a key issue came to light: There is not enough space to grow enough crops for both food and fuel. This is because all solar biological approaches rely on photosynthesis; they are limited by very poor efficiency (0.1-1% in practice).

To improve the efficiency of photosynthesis has been the ambition of many workers, but there has been limited success. Now, photonic materials create novel opportunities with immense potential impact. Rather than attempting to improve the biology through molecular methods we propose, instead, to modify the light itself so that it can be used more efficiently.

Efficiency is low because only small regions of the solar spectrum are well-used by photosynthesis, while the majority is absorbed but wasted. The action spectrum differs greatly among different organisms. For example, green plants, algae and cyanobacteria ?prefer? red light, while purple bacteria ?prefer? near infra-red (NIR).

This ?hop? is from biology into physics. We will investigate two approaches to increasing the efficiency of photosynthesis. Firstly, fluorescent quantum dots (Qdots) will be applied to modify a simulated solar spectrum, providing photosynthetic systems with an enhanced energy source. Secondly, selective mirrors will be applied to get a double hit from a single ?sunbeam? by dividing it between two cultures so that each receives its ideal wavelengths. A variety of suitable Qdots and selective mirrors are commercially available to support this. Test-tube scale cultures will be studied under simulated solar irradiation to evaluate the effectiveness of these two ideas singly and in combination.

Due to its potentially huge global impact, this project will seed a large collaborative study bringing in process engineers and leading to exploitation by industrial partners who urgently require efficient photobioreactors.

Publications

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Redwood MD (2012) Enhanced photosynthetic output via dichroic beam-sharing. in Biotechnology letters

 
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