【易伯华出品】雅思阅读机经真题解析--Sunny Days For Silicon

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Sunny Days For Silicon

You should spend about 20 minutes on Question 14-26 which are based on

Reading Passage below.

AThe old saw that "the devil is in the details" characterizes the kind of

needling obstacles that prevent an innovative concept from becoming a working

technology. It also often describes the type of problems that must be overcome

to shave cost from the resulting product so that people will buy it. Emanuel

Sachs of the Massachusetts Institute of Technology has struggled with many such

little devils m his career-tong endeavor to develop low-cost, high-efficiency

solar cells. In his latest effort, Sachs has found incremental ways to boost the

amount of electricity that common photovoltaics (PVs) generate from sunlight

without increasing the costs. Specifically, he has raised the conversion

efficiency of test cells made from multi-crystalline silicon from the typical

15.5 percent to nearly 20 percent—on par with pricier single-crystal silicon

cells. Such improvements could bring the cost of PV power down from the current

$1.90 to $2.10 per watt to $1.65 per watt. With additional tweaks, Sachs

anticipates creating within Four years solar cells that can produce juice at a

dollar per watt, a feat that would make electricity (rum the sun competitive

with that from coal-burning power plants.

BMost PV cells, such as those on home rooftops, rely on silicon to convert

sunlight into electric current. Metal interconnects then funnel the electricity

out from the silicon to power devices or to feed an electrical grid. Since solar

cells became practical and affordable three decades ago, engineers have mostly

favored using single-crystal silicon as the active material, says Michael Rogol,

managing director of Germany- based Photon Consulting. Wafers of the substance

are typically sawed from an ingot consisting of one large crystal that has been

pulled like taffy out of a vat of molten silicon. Especially at first, the

high-purity ingots were left over from integrated-circuit manufacture, but later

the process was used to make PV cells themselves, Rogol recounts. Although

single-crystal cells offer high conversion efficiencies, they are expensive to

make. The alternatives- multi-crystalline silicon cells, which factories

fabricate from lower-purity, cast ingots composed or many smaller crystals—arc

cheaper to make, but unfortunately they arc Jess efficient than single-crystal

cells.

CSachs, who has pioneered several novel ways to make silicon solar cells less

costly and more effective, recently turned his focus to the details of

multi-crystalline silicon cell manufacture. The first small improvement concerns

the little silver fingers that gather electric current from the surface of the

bulk silicon," he explains. In conventional fabrication processes, cell

manufacturers use screen-printing techniques ("like high-accuracy silk-screening

of T-shirts," Sachs notes) and inks containing, silver particles to create these

bus wires. The trouble is that standard silver wires come out wide and short,

about 120 by 10 microns, and include many nonconductive voids. As a result, they

block considerable sunlight and do not carry as much current as they should.

DAt his start-up company—Lexington, Mass- based 1366 Technologies (the number

refers to the flux of sunlight that strikes the earth's outer atmosphere: 1.366

watts per square meter)—Sachs is employing "a proprietary wet process that can

produce thinner and taller" wires that are 20 by 20 microns. The slimmer bus

wires use less costly silver und can be placed closer together so they can draw

more current from the neighboring active material, through which free electrons

can travel only so far. At the same time, the wires block less incoming light

than their standard counterparts.

EThe second innovation alters the wide, flat interconnect wires that collect

current from the silver bus wires and electrically link adjacent cells.

Interconnect wires at the top can shade as much as 5 percent of the area of a

cell. "We place textured mirror surfaces on the faces of these rolled wires.

These little mirrors reflect incoming light at a lower angle--around 30

degrees-—so that when the reflected rays hit the glass layer at Lire top, they

stay within the silicon wafer by way of total internal reflection,” Sachs

explains. (Divers and snorkelers commonly see this optical effect when they view

water surfaces from below.) The longer that light remains inside, the more

chance it has to be absorbed and transformed into electricity.

FSachs expects that new antireflection coatings will further raise

multi-crystal line cell efficiencies. One of his firm's future goals will be a

switch from expensive silver bus wires to cheaper copper ones. And he has a few

ideas regarding how to successfully make the substitution. "Unlike silver,

copper poisons the performance of silicon PVs," Sachs says, "so it will be

crucial to include a low-cost diffusion barrier that stops direct contact

between copper and the silicon." In this business, it's always the little

devilish details that count.

GThe cost of silicon solar cells is likely to fall as bulk silicon prices

drop, according to the U.S. Energy information Administration and the industry

tracking firm Solarbuzz. A steep rise in solar panel sales in recent years had

led to a global shortage of silicon because production capacity for the active

material lagged behind, but now new silicon manufacturing plants are coming

online. The reduced materials costs and resulting lower system prices will

greatly boost demand for solar-electric technology, according to market watcher

Michael Rogol of Photon Consulting.

Questions 14- 18

Use the information in the passage to match the people or companies (listed

A-C) with opinions or deeds below. Write the appropriate letters A-C in boxes

14-18 on your answer sheet.

NB you may use any letter more than once

A. Emanuel Sach

B. Michael Rogol

C. Solarbuzz

14. Gives a brief account of the history of the common practice to

manufacture silicon batteries for a long time.

15. Made a joint prediction with another national agency.

16. Established an enterprise with a meaningful name.

17. Led forward in the solar-electric field by reducing the cost while

raising the efficiency.

18. Expects to lower the cost of solar cells to a level that they could

contend with the traditional way to generate electricity.

Questions 19-22

Do the following statements agree with the information given in Reading

Passage 2?

In boxes 19-22 on your answer sheet, write

TRUE if the statement is true

FALSE if the statement is false

NOT GIVEN if the information is not given in the passage

19. The Achille’s heel of single-crystal cells is the high cost.

20. The multi-crystalline silicon cells are ideal substitutions for

single-crystal cells.

21. Emanuel Sachs has some determining dues about the way to block the

immediate contact between an alternative metal for silver and the silicon.

22. In the last few years, there is a sharp increase in the demand for solar

panels.

Questions 23-27

Summary

Complete the following summary of the paragraphs of Reading Passage, using No

More than Three words from the Reading Passage for each answer. Write your

answers in boxes 23-27 on your answer sheet.

Emanuel Sachs made two major changes to the particulars of the manufacture

23. One is to take a 24 in the production of finer wires which means more

current could be attracted from the 25 . The other one is to set 26 above the

interconnect silver bus wires to keep the incoming sunlight by 27 .

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