The EconomistNovember 30th 2019 Science & technology 792
O
n the principlethat no news is
good news, the fact thataidshas
dropped out of the headlines is surely a
good thing. Nevertheless, it does no
harm for the world to be reminded from
time to time that the illness has not gone
away. To that end,unaidsand the World
Health Organisation, the international
agencies charged with dealing with the
epidemic, promote December 1st as
WorldaidsDay.
This year is the last before the target
date for the success of the latest of the
agencies’ campaigns to roll out the anti-
retroviral drugs that both keep those
already infected withhivalive and stop
them passing the virus on. This partic-
ular campaign is called 90-90-90. Its
aims are that, by the end of 2020, 90% of
all those around the world who are in-
fected will know they are infected; 90%
of that group will be receiving sustained
antiretroviral therapy; and 90% of those
receiving therapy will have had the virus
effectively suppressed.
The 90-90-90 campaign follows the 3
by 5 initiative, begun in 2003, to put 3m
people on the drugs by 2005, and the
subsequent target of 15 by 15. The latest
estimate is that 38m people are infected
withhiv, so 90-90-90 implies 28m being
treated successfully. As the chart shows,
doing this by 2020 is unlikely. Whether
that is seen as a failure, though, depends
on your point of view. Had the target
been reached easily is would surely have
been criticised as unambitious.
Regardless of when 90-90-90 is
achieved the next aim, 95-95-95, is al-
ready pencilled in for 2030. This is also
the year set by theun’s Sustainable De-
velopment Goals for the end ofaidsas a
public health threat.
The exact meaning of that phrase is
unclear. But in principle eliminatinghiv
is possible with existing technology. As
has happened with smallpox and polio,
the identification and treatment of allwho are infected would stop new cases
arising. The slogans for this are “zero
newhivinfections”, “zeroaids-related
deaths” and (aidsbeing an illness that
has always been surrounded by preju-
dice) “zero discrimination”.
Unlike smallpox and polio, however,
there is no vaccine againsthiv. If this
state of affairs continues, eliminating
the virus will mean giving drugs to all
those infected until they have died of
other causes. It will also mean someone
paying for those drugs. And, in the case
of those living in the poorest parts of the
world, that “someone” is often going to
be taxpayers in rich countries, who
already contribute about $8bn a year to
the anti-aidseffort. Exterminatinghiv,
then, will be a huge undertaking and an
expensive one. But not, with luck, an
impossible one.Remember, remember
AIDSSlowly, AIDS is being beaten backDispatches from the battle frontSource: UNAIDS 2019 estimatesNew cases of HIV,worldwide, m2000 05 10 15 1843210Aware of HIV status2000 05 10 15 18 20100
80
60
40
20
0Viral load
suppressedUN AIDS 90-90-90
targets for 2020Receiving
antiretroviral
treatmentTreatment status
% of HIV-positive population3 by 5UN AIDS initiatives launched:
15 by 15 90-90-90run 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