Were the conditions in the Pacific in March 2010 exceptional? During the winter of 2009-2010 a rare combination of known factors in earth’s climate variability systems ................(AccuWeather.com). According to records going back to 1950, this winter saw one of the strongestEl Nino events, combined with the most negative Arctic Oscillation(and also with a negative North Atlantic Oscillation) yet seen during a winter.
Can we link this to climate change? Yes and no Individual weather events cannot be directly attributable to climate change – but With the warming of the ocean temperatures we can expect a greater occurrence of extreme weather (Hadley Centre) Forecast for 2nd April 2010
What can we do to limit carbon dioxide emissions? The world is heavily dependent on energy from fossil fuels: coal, gas, oil Approximately 80% of the UK electricity grid is still powered by fossil fuel http://www.ecotricity.co.uk/our-green-energy/energy-independence/uk-grid-live UK government target to reduce carbon emissions by 80% by 2050 to limit temperature rise to 2o C How can we achieve this?
Moving towards a low carbon economy More efficient use of energy: transport, heating, electricity Replace fossil fuel energy with renewable energy sources: Solar, wind, bio-energy, tidal, wave, hydro Build a new generation of nuclear power stations Fusion power The task is huge so all of the above have a part to play!
The sun radiates more than enough energy onto the Earth in just one day to provide enough energy for the population of 5.9 billion people for 27 years In Wales enough solar energy radiates onto just 1 square kilometre over a year to supply 10% of our electricity needs
This X-ray image of the Sun, taken by the SOHO satellite, shows numerous active regions in the Sun's atmosphere. The Sun is by far the largest object in our solar system, containing more than 99% of the total mass. The sun is composed of 75% hydrogen and 25% helium The sun’s energy comes from a thermo-nuclear reaction where the nuclei of hydrogen are converted into helium releasing huge amounts of energy atmospheric temperature of 5500 oC and a luminosity of 4x1020 megawatts
When solar radiation arrives at the Earth it can be converted to heat heat Solar radiation
But how can we generate electricity from solar radiation?
Our modern understanding of light and colour begins with Isaac Newton (1642-1726) and a series of experiments that he published in 1672.
It wasn’t until 1901 with the publication of Planck’s black body theory that we started to understand how light interacts with matter Low energy photons High energy photons Planck had to assume that light carried “quanta” of energy that we now call “photons”
To make electricity we need a flow of electrons. Einstein was the first to explain how electrons could be released from a metal in a vacuum by light (photons) beamed at the surface People are also aware of his theories of relativity: the Special Theory of Relativity (published in 1905) and the General Theory of Relativity (published in 1915). What many people do not know is that Einstein was the second person to make a major contribution to the quantum revolution, in a paper also published in 1905 . In fact, this paper won him a Nobel prize. Only blue light would release electrons and not red light, no matter how intense the red light.
How are photons absorbed in a semiconductor? photon Conduction band electron Band gap energy Valence band energy For absorption Ep > Eg Silicon cells can now convert up to 20% of the sun’s radiation into electrical energy
For the electron to become an electric current it must pass across a junction from electron depleted to electron rich semiconductor materials Unlike metals where electricity can only be conducted by electrons, semiconductors can conduct electricity with negatively charged electrons and positively charged “holes”
The Sharp silicon PV module factory in Llay is producing around 300 MW of PV panels a year (increasing to 500 MW) this year CIS tower, Manchester
What are the components of a grid-connected PV system? Inverter Export Meter Import Meter PV Modules On-site Load To Grid
Examples of grid connected silicon PV modules installed by Dulas Ltd
Market price and predicted capacity for PV solar modules Potential to drive down cost with thin film PV Solar Buzz September ‘10 minimum prices Thin film PV (a-Si, CdTe and CIGS) will be a quarter of the market by 2013 Materials cost becomes the major cost factor for high volume manufacture EPIA Report
The structure of a CdTe thin film solar cell Glass substrate Front contact TCO n- CdS junction p- CdTe Back contact
PV modules can be made much cheaper if the semiconductor was just a thin film on a sheet of glass First Solar Inc Wurth Solar
First solar is leading the way with high volume thin film CdTe PV manufacture
The PV façade at OpTICGlyndwr Campus, StAsaphdemonstrates novel thin film CIGS technology 1000 m2 generating up to 85 kWp of completely clean energy. Largest of its kind outside US In the first 12 months of operation a total of 65,000 kWh of clean electricity was generated, saving 28 tonnes of carbon emissions from fossil fuelled power stations
Variation of energy output from OpTIC PV facade through the year
What are the limits to efficiency of PV solar cells? The optimum efficiency is a compromise between the proportion of the solar spectrum that can be absorbed and the amount of energy captured per photon absorbed Potential for 30% efficient cells based on single junction PV
For greater than 30% efficiency need to go to multi-junction cells
The cost/ performance trade-off The highest performance solar cells (triple junction gallium arsenide are over 30% efficient) are too expensive for building integrated PV but used for powering satellites. Very low cost dye-sensitised solar cells (DSC) may be suitable for large areas such as industrial roofs (Tata- Dyesol piloting DSC onto sheet steel (approx 5% efficient) Crystalline silicon is still a good compromise between efficiency and cost (15-20% efficient) Thin film silicon, cadmium telluride and CIGS are moving towards crystalline silicon but with inherently lower cost.
Concentrators might just prove to be a winner for terrestrial triple junction cells Whitfield Solar – trough type concentrators
concentration up to 500x the amount of expensive solar cell material can be reduced
but the array has to track the sun so not suitable for building facades
Circadian Solar – plastic Fesnel lens concentrators
The opportunity for the UK to generate substantial amounts of solar electricity is by incorporating into the fabric of buildings (BIPV) Thin film PV offers the cost advantage but how can we get higher efficiency without the cost going through the roof? Thin film can be either on rigid surfaces such as glass or on flexible surfaces such as steel or even on plastic. Opportunity for designing or even disguising PV in buildings.
Solar glazing Polysolar partially transmitting thin film silicon modules
Solar tiles Solar Century solar tiles to replace roof slates and tiles
Solar facades Examples of PV facades from Green Coast Solar
What do we know from our current knowledge of materials science that can improve on these solar energy materials? Improve light capture – if it reflects we are losing energy! Need to work with a wider range of materials to integrate PV into buildings Improve the efficiency of low cost PV such as thin film and organic Photon management to capture more of the spectrum Hybrid solar cells
Research in the CSER lab at the OpTIC campus of Glyndwr University, applying materials science to develop new thin film PV technology
Development of a research thin film deposition process to be compatible with production processes
From single batch to continuous process
Batch process flows chemical vapour over the substrate
In-line process flows the chemical vapours onto the surface that moves underneath the injector
SPARC inline process outline (15×15 cm2 ) for experimental PV modules Buffer TCO CdS CdTe CdTe p+ CdCl2 Exhaust Loading & pre-heating zone Annealing & Cooling zone
Thin film PV materials are complex and uniformity is everything! Scanning electron microscope (SEM) image of plan view of cadmium telluride thin film PV cell Scanning electron microscope (SEM) image of a cross section of the cell
New laser scanning method to understand defects in PV cells - Micro-LBIC Areas of thin CdZnS window layer Blue red infrared
Plasmonic down conversion to enhance short wavelength response CSER in collaboration with Markvart and Lefteris, Southampton University Comparison of external quantum efficiency plot (EQE) of CdTe cell (Glyndwr) with a PMMA blank luminescence down shifting (LDS) layer, a single dye and a two dye mixture LDS layer. An inset of a simplified structure of the LDS + cell structure is shown. Observed increased EQE efficiencies are for the single dye ~9.8% and two dye ~ 12.5%
Nano-materials for down conversion Blue laser on nano-material film Blue laser on polymer Polymer + nano-material Polymer film
Conclusions Solar energy has enormous potential but we have to improve ways of capturing it Capturing more of the solar spectrum can be very challenging and expensive! Solar electric modules in the future will become part of the fabric of a building – so you might not even recognise them Materials Innovation needed at all levels of PV module manufacture – improve efficiency and reduce cost. Will we be able to reduce our carbon emissions in time? What will the climatic conditions be like in 2050?
Acknowledgements Members of the CSER team Pilkington Group for supply of NSG TEC glass Financial support from the EPSRC energy programme, funding through PV21 –SUPERGEN consortium. Financial support from the Low Carbon Research Institute (LCRI) EU Convergence programme http://www.cser.org.uk
CSER Team Dr Vincent Barrioz Dr Dan Lamb Dr Louise Jones Dr Andy Clayton Dr GirayKartopu Dr Sarah Rugen-Hankey Dr Graham Sparey-Taylor Garth Lautenbach Eurig Jones William Brooks Steve Jones Simon Hodgson Peter Siderfin Fraser Hogg Emma Dawson