Thin-film solar power
The modernist box that won this year’s Solar Decathlon, a contest for solar-powered houses sponsored by America’s Department of Energy, had solar panels of the conventional, crystalline sort on its roof. But the walls were covered in solar cells made with thin coatings of silicon and other materials in the place of expensive slices of crystal. Thin film, as this technology is known, is still less popular than crystalline cells and its move to the mainstream has been a year or two away for a decade. But its time may have come at last.
There are many exotic ideas involving thin film, from the solar shingles recently unveiled by Dow, a big chemical company, a roof’s worth costs $27,000, to experimental prototypes of power-generating clothes, roads and cars. However, most thin film comes in the form of panels that resemble crystalline ones. They are roughly half as efficient, meaning that a panel must be twice as big to generate the same amount of power, but a third cheaper, watt for watt. So in places where there is no shortage of space, they are the natural option.
Thin-film cells are also more versatile, since they can be mounted on a variety of materials including flexible plastics and fabrics. Like all solar cells, they are becoming more efficient: the decathletes of Team Germany, who designed the winning house, bragged that its north facade was covered in panels that could convert even indirect sunlight into electricity.
Over the past year or so, thanks to a crash in demand tied to the recession and falling subsidies in big markets, the price of crystalline panels has fallen by 30-40%, undermining thin film’s relative advantage. Nonetheless, thin film’s share of the market has continued to rise: it is now almost half, compared with just 10% in 2004.
The biggest force in the industry is a firm called First Solar, based in Arizona, a sunny American state. Like that of virtually all alternative-energy firms, its share price has suffered in the recession. But it has nonetheless performed considerably better than Standard & Poor’s clean-energy index over the past three years. Its gross margins in the first half of the year were over 50%, on sales of $944m. This month the firm was added to the S&P 500 stockmarket index of America’s biggest firms.
First Solar looks likely to continue to grow. Last month it signed a memorandum of understanding with China to install two gigawatts’ worth of panels in Inner Mongolia-a place with plenty of space. That is enough to power 3 million homes. Installation is due to begin next year and finish in 2019. That and other projects should consume all its output for several years to come.
First Solar’s rivals are much smaller. But technological advances may yet catapult one to the fore, says Steve Milunovich, an analyst at Bank of America Merrill Lynch. First Solar makes its cells from a chemical called cadmium telluride. But firms such as Nanosolar, which is building factories in California and Germany, believe that a combination of copper, indium, gallium and selenium known as CIGS will prove cheaper to produce on a mass scale. Researchers at the University of California, meanwhile, hold out great hopes for cells made of organic chemicals.
For the moment, however, the cheapest form of solar power is none of these, but the less glamorous solar-thermal power, which involves heating water with sunlight to make steam. Utilities are also keen to use lenses to increase the amount of sunlight hitting solar panels-a technique known as concentrating solar power. They still need subsidies or a high price on carbon emissions to make investments in any sort of solar power profitable. But the gap between solar and conventional power sources is becoming, well, thinner.
Based on its contract with China, it seems probable that First Solar will further. However, it does face competition from several sources. First, there are a number of using the potentially CIGS production process. In addition, power, though perhaps not as as the alternatives is still the cheapest. And despite a narrowing , solar’s biggest competitor is still .
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Question Focus: Inference from contract details - future growth
Correct Answer: grow
Why this is correct: The summary says it is probable First Solar will do something further. The passage clearly says it looks likely to continue to grow, based on long-term projects that will use all its output.
Passage Reference: s. First Solar looks likely to continue to grow. Last month it signed a memorandum of understanding with China to install two gigawatts' worth of panels in Inner Mongolia-a place with plenty of space. That is enough to power 3 million homes. Installation is due to begin next year and finish in 2019. That and other projects should consume all its output for several years to come.
Common Mistake: Students may write expand or increase, but you must copy the exact word from the passage. This is a synonym trap.
Paraphrasing: Passage: 'looks likely to continue to grow' = Summary: 'it seems probable that First Solar will ___ further'
Tips: When the summary uses probability words like 'seems probable', look for phrases like 'looks likely' in the passage.
Key Vocabulary:
- consume = use up
- output = production
Question Focus: Identifying competitors
Correct Answer: rivals
Passage Reference: me. First Solar's rivals are much smaller. But technological advances may yet catapult one to the
Why this is correct: The summary mentions competition from several sources. The passage directly introduces competitors by saying First Solar's rivals.
Common Mistake: Some students write companies or firms, but those words are not used here. This is a synonym trap.
Paraphrasing: Passage: 'First Solar's rivals are much smaller' = Summary: 'there are a number of ___'
Tips: If the summary uses 'competition', scan for words like 'rivals' or 'competitors' in the passage.
Key Vocabulary:
- rivals = competitors
Question Focus: Cost advantage of CIGS
Correct Answer: cheaper
Passage Reference: any, believe that a combination of copper, indium, gallium and selenium known as CIGS will prove cheaper to produce on a mass scale.
Why this is correct: The summary says the CIGS process is potentially something. The passage states it will prove cheaper to produce.
Common Mistake: Students may write less expensive, but that phrase is not in the passage. This is a synonym trap.
Paraphrasing: Passage: 'will prove cheaper to produce' = Summary: 'potentially ___ CIGS production process'
Tips: Adverbs like 'potentially' are often followed by an adjective taken directly from the passage.
Key Vocabulary:
- mass scale = large quantities
Question Focus: Identifying the cheapest power type
Correct Answer: solar-thermal
Passage Reference: als. For the moment, however, the cheapest form of solar power is none of these, but the less glamorous solar-thermal power, which involves heating water with sunlight to make steam.
Why this is correct: The passage says the cheapest form is solar-thermal power. The summary shortens this to fit the sentence.
Common Mistake: Some students write solar power, which is too general and changes the meaning. This is a partial truth trap.
Paraphrasing: Passage: 'the cheapest form of solar power is ... solar-thermal power' = Summary: '___ power is still the cheapest'
Tips: Hyphenated words count as one word in IELTS, so solar-thermal is safe here.
Key Vocabulary:
- thermal = related to heat
Question Focus: Describing image or appeal
Correct Answer: glamorous
Passage Reference: , but the less glamorous solar-thermal power, which involves heating water with sunlight to make steam.
Why this is correct: The summary says this power is not as something as alternatives. The passage calls it less glamorous.
Common Mistake: Students may write attractive or exciting, but these are not in the passage. This is a synonym trap.
Paraphrasing: Passage: 'the less glamorous solar-thermal power' = Summary: 'though perhaps not as ___ as the alternatives'
Tips: Comparative structures in summaries often remove words like 'less'. Look for the base adjective.
Key Vocabulary:
- glamorous = attractive or exciting
Question Focus: Difference between power sources
Correct Answer: gap
Passage Reference: able. But the gap between solar and conventional power sources is becoming, well, t
Why this is correct: The summary mentions a narrowing something. The passage clearly says the gap is becoming thinner.
Common Mistake: Some students write difference, but that word is not used in the passage. This is a synonym trap.
Paraphrasing: Passage: 'the gap between solar and conventional power sources' = Summary: 'a narrowing ___'
Tips: Abstract nouns like 'gap' are often repeated exactly in summaries.
Key Vocabulary:
- gap = difference
Question Focus: Main competitor of solar
Correct Answer: conventional power
Passage Reference: . But the gap between solar and conventional power sources is be
Why this is correct: The summary asks for solar's biggest competitor. The passage contrasts solar with conventional power.
Common Mistake: Students may write fossil fuels, which are not named here. This is a context shift trap.
Paraphrasing: Passage: 'conventional power sources' = Summary: 'solar's biggest competitor is still ___'
Tips: Do not add extra words like 'sources' if they are not needed in the summary grammar.
Key Vocabulary:
- conventional = traditional
General Tips:
- Summary completion questions follow passage order. Use the previous gap to help you find the next answer.
- Always copy the exact word from the passage. Synonyms are not accepted.
- Check grammar clues around the gap like 'will', 'a number of', or comparison structures.
- Watch the word limit carefully. Two words means exactly one or two, never three.
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