New Scientist - 07.09.2019

| New Scientist | 7 September 2019

Wind economics

What is the carbon payback period
for a large wind farm, taking into
account the energy and resources
used for materials, manufacture
and the construction of supporting
infrastructure? If it is long, say
30 years, are they worth it?

Angela Cotton
Southampton, UK
In 2006, turbine manufacturer
Vestas studied the carbon payback
period for various turbines. This
took into account extraction and
manufacturing of raw materials,
production of the turbines, their
transport, erection, operation,
maintenance, dismantling and
disposal, and the same for their
foundation and the transmission
grid. The figure was between seven
and nine months, depending on
the type of turbine. Other analyses
have come up with similar figures.
Even taking into account the
carbon emitted in transportation
and installation of turbines, the
payback period is nothing like the
30 years the questioner suggests.
It is also worth noting that wind
turbines can be recycled at the
end of their lives.

Linda Latham
Biggar, South Lanarkshire, UK
The question is both easy and
difficult to answer. Easy because
it can never just be about the
cost in financial terms. Difficult
because the exact time is subject
to many influencing factors
including wind, weather and
pollution rates from industry.
Wind farms reduce the amount
of power needed to be produced
from other carbon producing
sources. And they are less costly
to build and maintain than
other low-carbon systems,
such as hydroelectric and
nuclear power plants.
They may look an eyesore
and seem to be on the march,
but remember when power
lines sprang up across our
countryside allowing us all
to access electricity? Now we
hardly notice they are there.

Daniel Baird

Cirencester, Gloucestershire, UK

Several wind turbine life-cycle

assessments have been

undertaken and are available

online. An onshore wind turbine

can be expected to repay this

energy debt in between about

six and nine months of operation.

Offshore wind turbines take

a little longer, their marginally

higher generation outweighed

by the extra steel needed. Beyond

30 years, even with refurbishment

if necessary, the energy return

on investment just gets better.

Alex Hromas

Sydney, Australia

This question is often based on

the premise that renewable energy

systems are built by people who

are technically and financially

naive. This is not the case.

In the UK, for example, sites are

chosen on the basis of wind data

from the Met Office. Actual wind

conditions are then measured for

several years to assess the viability

of the site. The resulting

assessment becomes a bankable

document that is used to secure

finance for the project from

bankers. There are then

negotiations with grid operators

and power consumers, among

whom there is no mention of

saving the planet or tree hugging.

The embodied energy of the

project and associated carbon

is represented in the capital

expenditure of the build. If

this cost cannot be covered,

the project is a no-go.

It is also worth bearing

in mind that once such an

installation is paying its capital

cost and covering its maintenance,

any energy generated in excess

of that has a very low marginal

cost – an extremely important

economic consideration.

Find yourself

This tree, in the grounds of

Anglesey Abbey, Cambridgeshire,

UK, has a branch growing in

a loop, apparently reabsorbed

by the tree. Is this common,

and how can it happen?

Mike Challen

Singleton, West Sussex, UK

This is a common sight in planted

woodland. A plantation of trees

will have a nurse crop, usually of

fir trees, planted quite close to the

main crop to encourage straight,

upward growth of the trunks. This

nurse crop is removed over time.

While the dark firs still stood,

this branch turned away from

them, towards the light the main

trunk is growing in. After a while,

the increasing canopy has shaded

the rest of the branch out, leaving

this stub. The expanding trunk

has formed around it exactly

like a rose or fruit tree graft.

I have cut large beech trees

in plantations where the whole

branch has been totally absorbed,

but is still live wood in the trunk.

There is obviously a size at which

the expanding trunk cannot

push the branch aside, and most

absorbed branches are of this

size or bigger.

This week’s new questions

Nettle effect How is it that stinging nettles don’t seem

to affect my dog’s sensitive nose and ears or his relatively

fur-free belly while I respond rapidly with a very painful

skin rash? Jan Jones, Bramcote, Nottinghamshire

Star quality With the enormous pressure and temperatures

within Jupiter, what’s the chance that one day it could ignite

and turn itself into a star? Darko Kojic, Banja Luka,

Bosnia and Herzegovina

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SPRINGTIME78/ALAMY STOCK PHOTO

Why don’t dogs’ noses

appear to be hurt by

stinging nettles?

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