Harvesting Solar Energy - Artificial Leaves

Having had a quick look at solar energy already, one of the key issues is the efficient production of energy from solar cells using widely available materials. Scientists at Harvard University have been addressing this.

The Artificial Leaf 

This carries out the same processes as in nature but it allows for collection of oxygen and more importantly hydrogen which can be used as a fuel. The leaf is made of a silicon wafer: one side produces oxygen and the other produces hydrogen from photosynthesis. The the important break through with this research is that cheap and widely available metals have been used as catalysts in the reaction, instead of platinum which how it was originally achieved (Reece et al, 2011, Science). As it really highlights in the paper, the most important development is the cheap and widely available materials that are used in the process.

Harvard Professor and one of the main authors on the paper, Daniel, Nocera, explains the process in this Horizon clip. 

No external wires or controls are needed, the silicon chip just has to be placed in water. This is what it actually looks like, with some real leaves in the background in case you hadn't seen them before... More information can be found on the MIT News Site

The artificial lead - image from MIT news

'Here comes the sun'

Before university I spent a year working with a chemical engineering company making ink. I was a little disappointed to discover that this did not involve farming squid but instead mixing up various combinations of chemicals. I specialised in conductive inks and by far our the fasting growing demand was for solar cells. This hardly makes me an expert but means I have an interest in the area!

Firstly, some basics. Solar cells (or photovoltaic cells) generate energy by the photovoltaic effect. Light from the sun, made up of photons, hits the semiconductor in the solar cells. This excites electrons in the atoms which make up the semiconductor and releases them from the shell. There is a electrical gradient in the semi conductor which attracts the released electrons which then flow: generating electricity (physics online).

Potential energy - image from Solar Spark

The potential solar energy available is enormous: 120,000 TW per day compared to the global energy use of 15 TW per day (solar spark). However, this is the total sunlight hitting the earth so if we wanted to use it we would have cover the earth in solar cells and have them all work with 100% efficiency. This is not possible but it does demonstrate just how much we could utilise solar energy.

Now back to those squid...