Answer the questions below. Then discuss your answers in groups. 1 What information is given on each axis? What do the colours refer to? 2 What two scenarios does the graph show? 3 Which three energy sources will continue to have the highest share in worldwide electricity generation if policies do not change? 4 Which two fuel sources should be used less if countries develop sustainably? 5 Choose three fuels and compare the projected scenarios, once with current policies and once with sustainable development. 6 Which sources of energy do you think are the three most important and the three least important in Austria today? 7 Which sources should be used more in the future and how do you think this could be done? Read the article and make a list of technical terms. Compare them in class and clarify their meaning. Example: efficiency of solar cells b 33 a Breakthrough approaches for solar power With climate change, the amount of sunny days is rising. As much as this is a global problem, the solar power industry benefits from this. One major area has been problematic: the efficiency of solar cells. All around the world, companies are taking part in the race to produce an efficient solar cell. On average a commercial solar panel converts about 19% of the light energy hitting it into electricity. In 2019, the world’s installed solar power jumped to about 600 gigawatts. Most solar cells are made from wafer-thin slices of silicon crystals. A solar cell made from silicon has a maximum efficiency of only 30%. However, combining six different materials into what is called a multi-junction cell can push efficiency as high as 47%, under concentrated light. Another way to break through this limit, is to use lenses to focus the sunlight falling on the solar cell, which is very expensive. The fastest improving solar technology is called perovskites. These have a particular crystal structure that is good for solar absorption. Thin films, around 300 nanometres (much thinner than a human hair) can be made inexpensively – allowing them to be easily applied as a coating to buildings, cars or even clothing. Perovskites also work better than silicon on cloudy days or for indoors. They can even be printed using an inkjet printer. With such a cheap, flexible, and efficient material, you could apply it to street furniture to power free smartphone charging, public wifi, and air quality sensors. In 2020, already 10 startups were working on perovskite technology. The silicon absorbs the red band of the visible light spectrum, and the perovskite the blue bit, giving the tandem bigger efficiency than either material alone. A Swiss startup has taken a different tack – embedding a grid of hexagonal lenses in a solar panel’s protective glass, thus concentrating light 200 times. To follow the sun’s motion, the cell array shifts horizontally by a few millimetres throughout the day. What they did was miniaturise the expensive sun tracking mechanism and integrate it within the module. This way they managed to reduce production costs and reached an efficiency of 29% within a short period. Current silicon technology is not quite dead, though, and there are approaches to make tiny, quick wins in efficiency. One is to add an extra layer to a cell’s back to reflect unabsorbed light back through it a second time. This improves efficiency by 1-2%. Another is to add an outside layer, which reduces losses that occur where silicon touches the metal contacts. From such small gains – to the use of concentrated solar and perovskites – solar tech is in a race to raise efficiency and push down costs. Discuss these questions in pairs. 1 What is the problem with silicon solar cells? How can they be made more efficient? 2 What alternative methods to silicon are mentioned in the article? How do they work? Media task. Work in small groups. Go online and research the latest solar technology. List your findings and present them in class. 1 Writing guide: How to write a handout, p. 153. b 34 36 Language skills Extras Explore 3 Success Nur zu Prüfzwecken – Eigentum des Verlags öbv
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