8/13/2019 2013 49 Winter Wiring Matters Solar Energy

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IF THE PRICEIS RIGHTIs it really possible that solar energy

could meet almost one-third of the

worlds energy demand by 2060?

THERE ARE two mainkinds of solar energy solar photovoltaic (PV)and concentrating solarpower (CSP). PV directlyconverts solar energy intoelectricity using a PV cell

made of a semiconductormaterial, while CSP devicesconcentrate energy from thesuns rays to heat a receiverto high temperatures.This heat is transformedfirst into mechanical

energy (by turbines orother engines) and theninto electricity solarthermal electricity (STE).

Over the period 2000-11,solar PV was the fastest-growing renewable power

technology worldwide.Cumulative installed capacityof solar PV reached roughly65GW at the end of 2011, upfrom only 1.5GW in 2000. In2011, Germany and Italyaccounted for over half the

global cumulative capacity,followed by Japan, Spain, theUnited States and China.

In its SunShot strategy theUS Department of Energypredicts that when the priceof solar electricity reaches

about $0.06 per kilowatt-hourover its lifetime, it will becost-competitive with othernon-renewable forms ofelectricity. This in turn willenable solar-generatedpower to grow.

The drive to reducecosts encompasses theentire value chain from theefficiency of individual cellsto manufacturing costs aswell as complementarytechnologies such as

energy storage andeffective planning.

Black and dyeOne approach is to developcells that can convert agreater percentage of the

WiringFeature#49

By Sean Davies

8/13/2019 2013 49 Winter Wiring Matters Solar Energy

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suns spectrum. Around aquarter of the spectrumis made up of infraredradiation, which cannotbe converted by standardsolar cells. One way toovercome this loss is to use

black silicon, a material thatabsorbs nearly all of thesunlight that hits it, includinginfrared radiation, andconverts it into electricity.Researchers have recentlysucceeded in doubling

their overall efficiency.Black silicon is produced

by irradiating standardsilicon with femtosecondlaser pulses under a sulphur-containing atmosphere,says Dr Stefan Kontermann

of the Fraunhofer Institutefor Telecommunications,Heinrich-Hertz-Institut(HHI). This structures thesurface and integratessulphur atoms into the siliconlattice, making the treated

material appear black. Ifmanufacturers were to equiptheir solar cells with blacksilicon, it would significantlyboost the cells efficiency.

By using black silicon,Dr Kontermann and his teamat HHI have now managedto double the efficiency ofblack silicon solar cells.We achieved that bymodifying the shape ofthe laser pulse we use toirradiate the silicon, enabling

us to solve a key problemof black silicon, saysDr Kontermann. In normalsilicon, infrared light doesnot have enough energy toexcite the electrons into theconduction band and convertthem into electricity, butthe sulphur incorporated inblack silicon forms a kindof intermediate level.

You can compare thiswith climbing a wall,Dr Kontermann adds. Thefirst time you fail because

the wall is too high, but thesecond time you succeedin two steps by using anintermediate level. However,in sulphur this not onlyenables electrons to climbthe wall, it also works inreverse, enabling electronsfrom the conductionband to jump back viathis intermediate level,which causes electricityto be lost once again.

By modifying the laserpulse that drives the sulphur

atoms into the atomic lattice,researchers can change thepositions that these atomsadopt in the lattice andchange the height of theirlevels in other words, theirenergy level. We used thelaser pulses to alter theembedded sulphur in orderto maximise the number ofelectrons that can climb upwhile minimising the numberthat can go back down.

The researchers havealready successfully built

prototypes of black siliconsolar cells and their next stepwill be to try to merge thesecells with commercialtechnology.

An even more radicalapproach to delivering

solar power would be todispense with the costly andfragile semiconductor solarpanel that uses crystallinesilicon. Researchers at theUniversity of Turku believethat they can do this byusing flexible, lightweightand inexpensive dyes.

It is hoped that dye-sensitised solar cells (DSCs)can become a ubiquitoussource of energy without thecomplex and expensive

clean-room manufacturingprocesses associated withcurrent solar panels,Jongyun Moon, researcher atthe University of Turku, says.

In a DSC, sunlight hits alayer of the white pigmenttitanium dioxide, the solarenergy absorbed then suckselectrons from dye moleculesin a layer beneath thiscoating, thus generating aflow of electrons andproducing a current.

However, Moon suggests

that despite the maturityof the silicon technologyDSCs could ultimatelydisplace it simply becausethey are easier and cheaperto manufacture. That said,current DSCs are lessefficient than silicon devicesand much developmentwork is needed.

Anti-ageing solarIt is not just the high costof a solar module that isof concern, but also its

longevity. Given the high costof solar power installationsit is critical that the moduleslast as long as possible.Fraunhofer researchers in theUS are developing materialsto protect solar cells fromenvironmental influencesto extend their lives.

Silicone is a promisingprotective material. It isneither inorganic crystalnor organic polymer, butis related to both. WhilePV modules have been

encapsulated with silicones,until now they were notwidely used for laminatingsolar modules. Laminationis a protective coating thatsurrounds the fragile siliconwafer. Today, most >

The Gemsolar CSPpower plant in southernSpain employs 2,650

heliostats, each 120m2and distributed in

concentric rings aroundthe central power tower

8/13/2019 2013 49 Winter Wiring Matters Solar Energy

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8/13/2019 2013 49 Winter Wiring Matters Solar Energy

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