Caitríona Farrell reports on new solar energy techniques that borrow from Mother Nature’s own energy systems
“Chlorophyll? More like bore-ophyll.” Chlorophyll has come a long way since it was described by Adam Sandler in the 1995 movie Billy Madison.
Oh yes, this green puppy might soon be making an appearance in the B&Q catalogue, or even Homebase!
No clue what I’m on about? Read on my friend. There’s ongoing research into how viable and efficient it would be to use the green pigment, i.e. chlorophyll, in solar panels, and it’s good, really really good.
A molecular electronics group at the University of Sydney, led by Professor Max Crossley, have investigated the possibility of adapting aspects of natural photosynthesis into a solar cell design. The researchers have developed a synthetic chlorophyll molecule in the design of the shape of a soccer ball, or – as it is known in the scientific world – a molecule of Buckminsterfullerene C60.
The structure has a dendrimer scaffold, a highly branched nanosized polymer made of carbon, hydrogen and nitrogen. Attached to the dendrimer are synthetic versions of the light-harvesting pigment, porphyrin. Spherical carbon molecules are perched between the porphyrin and absorb electrons from the photons of collected light.
A leaf is about 30-40 per cent efficient at converting light to electricity, in comparison with as little as 12 per cent efficiency for conventional silicon-based solar cells. “In the long term what we’re trying to do is have something we can simply paint on a roof, like a thin layer”, explained Prof. Crossley.
Barack Obama’s inauguration speech highlighted how even world leaders are supporting the development of cutting-edge technologies with the goal of finding a renewable energy. “We will harness the sun and the winds and the soil”, he said, “to fuel our cars and run our factories.”
Ireland itself, renowned for being the Emerald Isle, is presently in dire need of restoring its ‘greenness’. Our government, though, seems still to be crying over the spilled champagne of the Celtic Tiger’s extravagant soirées. Suffocated by financial matters and public services crises, we are forgetting more long-term issues such as the quest for clean energy.
Faraway hills are green at the moment, and the Green Party could do with a boost of chlorophyll in Government buildings to wake up and realise once again the underpinning principles they had when they entered power two years ago. No other western country would be jade with envy of Ireland as a green country any more.
The aim of reaching Ireland’s 2020 targets – of having 40 per cent of electricity generated through renewable sources – looks out of focus. Manipulating nature, and the science we currently understand, is the key answer to reaching these goals. It is still theoretically possible for Ireland to meet this goal if we put our minds to it.
Solar energy is definitely the most abundant renewable energy source in our world. Extraordinarily, more light energy falls on the planet in one hour than is used by humans in one year. In the cruel light of day (pardon the pun), this statistic sheds light (sorry) on how we aren’t using our resources wisely enough.
Another exciting breakthrough is an electronic device that uses spinach to convert light into electrical charge, developed by US researchers. Zhang Shuguang and research collaborators at the Massachusetts Institute of Technology have combined a protein complex extracted from spinach chloroplasts, with organic semiconductors, to make a solar cell that could be incorporated with solid state electronics. “Nature has been doing this for billions of years,” Zhang says, “but this is the first time we’ve been able to harness it.”
With nanotechnology and the minimalist idea of ‘less is more’, thinner and lighter panels are making way to a more efficient design of a solar panel.
Zhang’s team artificially stabilised the protein complex at the heart of their system, consisting of 14 protein subunits and hundreds of chlorophyll molecules, using synthetic peptides to bind small amounts of water to it, within a sealed unit.
Photons then ‘excite’ coupled pairs of electrons within chlorophyll, causing an electron to transfer to a nearby receptor molecule. Plants use this transfer to complete photosynthesis. Zhang has fostered this principle into his device, feeding electrons into organic semiconductors aligned on top of a layer of glass.
Zhang encountered difficulties with the use of organic materials in system. The protein complex is kept stable for about three weeks by the peptides, and the cells convert only twelve per cent of light to electrical charge. The solution seems to point towards layering numerous cells atop each other, so that a certain amount of light can pass through.
Interestingly enough, in New Zealand other researchers are on a similar wavelength. Solar cell technology developed by Massey University’s Nanomaterials Research Centre will enable New Zealanders to create electricity from sunlight 90 per cent cheaper than the current silicon-based, photo-electric solar cells.
Dr Wayne Campbell and researchers in the Centre have developed a prototype range of coloured dyes for use in dye-sensitised solar cells. These synthetic dyes are made from very basic organic compounds closely linked to those found in nature, such as chlorophyll and haemoglobin. They can also be effectively incorporated into tinted windows that trap light to generate electricity.
The green solar cells are more environmentally friendly than silicon-based ones, as they are made from a chemical called titanium dioxide. This white mineral derived from New Zealand’s black sand is in an abundant supply, is renewable and non-toxic, and already has economic benefits used in such consumer products as toothpaste, white paints and cosmetics.
Refining pure silicon is an energy-consuming task, and is quite expensive despite its plentiful supply. Another disadvantage of the silicon-based cells is that they require direct sunlight, whereas the green cells also work well in low diffuse light conditions.
The Centre claim that they now have the most efficient porphyrin dye in the world, and aim to optimise and improve the cell construction and performance before developing the cells for the commercial market.
The ultimate aim of using nanotechnology to develop a better solar cell is to convert as much sunlight to electricity as possible. There can surely be little doubt in this light (again, sorry) that the leaf itself is one of life’s most crucial structures.