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Special effects
The back pages Almost the last word Why don’t dogs’ noses appear to be hurt by stinging nettles?
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?
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. 56 | New Scientist | 7 September 2019
SPRINGTIME78/ALAMY STOCK PHOTO
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.
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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
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.
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.
Want to send us a question or answer?
Email us at [email protected] Questions should be about everyday science phenomena Full terms and conditions at newscientist.com/lw-terms
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?
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. 56 | New Scientist | 7 September 2019
SPRINGTIME78/ALAMY STOCK PHOTO
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.
Find yourself
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
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.
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.
Want to send us a question or answer?
Email us at [email protected] Questions should be about everyday science phenomena Full terms and conditions at newscientist.com/lw-terms