The EconomistNovember 30th 2019 Science & technology 71
2
O
n theprinciplethatnonewsis
goodnews,thefactthataidshas
droppedoutoftheheadlinesissurelya
goodthing.Nevertheless,it doesno
harmfortheworldtoberemindedfrom
timetotimethattheillnesshasnotgone
away.Tothatend,unaidsandtheWorld
HealthOrganisation,theinternational
agencieschargedwithdealingwiththe
epidemic,promoteDecember1stas
WorldaidsDay.
Thisyearisthelastbeforethetarget
dateforthesuccessofthelatestofthe
agencies’campaignstorollouttheanti-
retroviraldrugsthatbothkeepthose
alreadyinfectedwithhivaliveandstop
thempassingtheviruson.Thispartic-
ularcampaigniscalled90-90-90.Its
aimsarethat,bytheendof2020,90%of
allthosearoundtheworldwhoarein-
fectedwillknowtheyareinfected;90%
ofthatgroupwillbereceivingsustained
antiretroviraltherapy;and90%ofthose
receivingtherapywillhavehadthevirus
effectivelysuppressed.
The90-90-90campaignfollowsthe 3
by5 initiative,begunin2003,toput3m
peopleonthedrugsby2005,andthe
subsequenttargetof 15 by15.Thelatest
estimateisthat38mpeopleareinfected
withhiv, so90-90-90implies28mbeing
treatedsuccessfully.Asthechartshows,
doingthisby 2020 isunlikely.Whether
thatisseenasa failure,though,depends
onyourpointofview.Hadthetarget
beenreachedeasilyiswouldsurelyhave
beencriticisedasunambitious.
Regardlessofwhen90-90-90is
achievedthenextaim,95-95-95,isal-
readypencilledinfor2030.Thisisalso
theyearsetbytheun’s SustainableDe-
velopmentGoalsfortheendofaidsasa
publichealththreat.
Theexactmeaningofthatphraseis
unclear.Butinprincipleeliminatinghiv
ispossiblewithexistingtechnology.As
hashappenedwithsmallpoxandpolio,
theidentificationandtreatmentofall
whoareinfectedwouldstopnewcases
arising.Theslogansforthisare“zero
newhivinfections”,“zeroaids-related
deaths”and(aidsbeinganillnessthat
hasalwaysbeensurroundedbypreju-
dice)“zerodiscrimination”.
Unlikesmallpoxandpolio,however,
thereisnovaccineagainsthiv. If this
stateofaffairscontinues,eliminating
theviruswillmeangivingdrugstoall
thoseinfecteduntiltheyhavediedof
othercauses.It willalsomeansomeone
payingforthosedrugs.And,inthecase
ofthoselivinginthepoorestpartsofthe
world,that“someone”isoftengoingto
betaxpayersinrichcountries,who
alreadycontributeabout$8bna yearto
theanti-aidseffort.Exterminatinghiv,
then,willbea hugeundertakingandan
expensiveone.Butnot,withluck,an
impossibleone.
Remember,remember
AIDS
Slowly,AIDSisbeingbeatenback
Dispatchesfromthebattlefront
Source:UNAIDS 2019 estimates
NewcasesofHIV,worldwide,m
2000 05 10 15 18
4
3
2
1
0
AwareofHIVstatus
2000 05 10 15 18 20
100
80
60
40
20
0
Viralload
suppressed
UNAIDS90-90-90
targetsfor 2020
Receiving
antiretroviral
treatment
Treatmentstatus
%ofHIV-positivepopulation
3 by 5
UNAIDSinitiativeslaunched:
15 by 15 90-90-90
run for their money: liquid air.
At a temperature of -196°C, all of air’s
component gases will liquefy. Doing this is
a routine, electrically driven industrial
procedure. Storing liquefied gases in bulk
is also a routine piece of engineering. The
result occupies a 700th of the volume of
those gases at room temperature—so,
when liquid air is warmed and allowed to
expand, it does so forcefully. Using a device
called a Dearman engine (after its inventor,
a Briton named Peter Dearman), that force-
ful expansion can be employed to spin tur-
bines, and thus generators, thereby recov-
ering part of the electricity used to liquefy
the air in the first place.
Expanding possibilities
Such cryogenic energy storage’s main pro-
ponent, a firm in London called Highview
Power, has been running a pilot grid-scale
plant in Bury, near Manchester, since April
- This can store 15 megawatt-hours
(mw-hr) of energy, which is enough to pow-
er about 5,000 homes for three hours.
At the moment, the plant in Bury recov-
ers as electricity just over half of the power
used to liquefy the air in the first place.
With design tweaks, that could probably be
increased to 60%. Moreover, the technol-
ogy’s inventor, Ding Yulong, sees a path to
yet greater efficiency. As head of an energy-
storage group at the University of Birming-
ham, Dr Ding has spent years experiment-
ing with a small test plant. The trick, he
says, is to capture, probably in oil or salt,
the heat generated as the air is compressed
prior to its liquefaction. Some of this heat
can then be used to boost the warming of
the liquid air as it enters the Dearman en-
gine. This adds oomph to the expansion,
thereby increasing the power output.
The rest of the heat from the compres-
sion can be used to power a piece of refrig-
eration kit called an absorption chiller. The
cold this chiller creates would reduce the
amount of electricity needed to liquefy the
air in the first place. Dr Ding reckons that
recycling waste heat in this way will in-
crease the efficiency of biggish cryogenic-
energy-storage plants to at least 69%. That
is close to the figure obtained by banks of
lithium-ion batteries.
Having proved the technology, and
raised the money to do so, the firm now
plans to build a commercial-scale British
plant. According to Highview’s boss, Javier
Cavada, this will have almost twice the
storage capacity of the world’s largest exist-
ing lithium-ion battery, the Hornsdale
Power Reserve in South Australia, which
can squirrel away a mere 129mw-hr (though
Hornsdale has a maximum power output
of 100mw, which is twice that of Highview’s
proposal). Construction should begin early
next year at an as-yet-undisclosed site in
northern England.
Over the next two years Highview also
hopes to announce additional 250mw-hr
plants, including two it plans to build in
America for Tenaska, an energy company
in Nebraska. And Enel Group, Italy’s largest
electricity firm, is interested as well. Ac-
cording to Gianluca Gigliucci, who is lead-
ing Enel’s study of the technology, the com-
pany will soon build a grid-scale plant if
the business case for doing so appears at
least reasonable.
To take on lithium-ion batteries in a se-
rious way cryo-batteries—as Highview
dubs the technology—will have to show
that they are able to respond rapidly to fluc-
tuating demand in the way lithium-ion
cells can. They will also have to be able to
match, in future, the fall in price over the
years that such cells show every sign of
continuing to demonstrate. If they can do
these things, though, they could well
emerge as competitors in the grid-scale-
storage stakes. 7