Photovoltaic roofs
Wouldn’t it be great if you could produce all your own energy needs – at no cost? Imagine having your own personal electricity supply to run your house and your cars.
Associate Professor Ashton Partridge at work
Associate Professor Ashton Partridge working on dye-sensitised solar cells.
Associate Professor Ashton Partridge from Massey University is working on just that. His work in photovoltaics aims to produce a roof that (together with solar energy) will supply us with all the electricity we need. Ashton is not talking about having a few photovoltaic panels on your roof, but the roof itself is photovoltaic.
NIWA (National Institute of Water and Atmospheric Research) has calculated that every square metre of light shining on a roof is the equivalent to a 650-watt light bulb being shone onto it. Ashton says, “We want to harness that energy. We want to spread the photovoltaic effect over the whole roof.”
What makes this work special and different from other photovoltaic roofing projects is the use of conducting polymers. Usually silicon is used as the semiconducting material in photovoltaics. Silicon is effective but expensive. This roofing uses conducting polymers to produce the photovoltaic effect.
Conducting polymers are plastics that conduct electricity. Using plastics to conduct electricity was discovered by 3 people – 1 of them was a New Zealander, Alan MacDiarmid, who won a Nobel Prize in 2000 for his work.
OPV layers in a solar roof
A new roof is being produced where the entire roof is the solar panel. This illustrates the conducting layers, which are only 1 cm thick.
The conducting polymer (known as OPV – organic photovoltaic) works exactly like silicon. It is doped just like silicon where electrons are taken out or added to atoms of the material to enable them to move. The OPV is then sandwiched between 2 conductors. The top layer (closest to the Sun) has to be transparent so the light can shine through to the OPV. This transparent conductor is known as ITO (indium tin oxide), which is a metal oxide. The bottom layer is a metal – usually aluminium because it’s cheap.
Sunlight passes through the ITO, strikes the OPV and excites the electrons. The electrons can then move through to the metal, and electricity is produced. This is either stored in batteries for whenever the household needs it or channelled out through the power lines.
An advantage of OPV over silicon is that it doesn’t require direct sunlight. It works well on cloudy days and can be installed down the side of a building. OPV is inexpensive. It is like ink that can be printed. In the USA, OPV is printed onto sheets of supporting plastic.
The OPV panels are embedded into a roof and are not visible, so the roof looks normal – you don’t see any photovoltaic panels sitting on them. This means people can have whatever roof they want and it won’t be spoilt by having panels on it.
Having the whole roof photovoltaic means the average house will have 4 times more electricity than the average household needs. This is enough electricity for a whole house plus 2 vehicles with some left over that could be fed back into the national grid. Ashton says, if you put a photovoltaic roof on every house in New Zealand, you could generate the total amount of energy required for the country including what is used by businesses. He says, “We won’t need more hydro dams or windmills. There will be an abundance of electricity including for the running of vehicles.”
Solar roofs
On the left is an example of some photovoltaic panels installed on a rooftop. New technology means an entire house roof can be photovoltaic. Photovoltaic cells are embedded within the roof and are not visible such as in the right hand image. The roof looks like any ordinary roof.
There are environmental benefits too. To produce this electricity, you only need a roof. No one would object as they do to damming rivers or building wind farms.
Ashton is hoping that his research will lead to an OPV industry in New Zealand that will result in worldwide production of these special roofs.
Nature of science
Scientists often investigate according to need – solar energy is an alternative energy source to fossil fuels, which are becoming increasingly more limited and inaccessible.
Scientific research often leads to technological development – solar roofing is a result of exploring solar energy.
Science is evolving – “only metals conduct electricity” was once stated as scientific fact, but now scientists can make plastics conduct electricity.
Scientific research is often collaborative.
Five universities collaborate in this research. Along with Massey, there are researchers in Auckland, Victoria, Otago and Wake Forest University in North Carolina. There are about 20 researchers working on different aspects of OPV in New Zealand. Ashton heads the Massey group. He says they are all supporting a small, local New Zealand company to make solar roofing.
Activity idea
Use the activity, Exploring solar power, with your students to further explore sunlight being converted into electricity.
Useful link
Dr Nathaniel Davis from Victoria University is also experimenting with solar roof paint. Read about his research in this Newshub article.
