Capture tidal energy
There was a major omission in the article “Soaring Twenties”.
Energy in the form of electricity generated from wind and solar will, as described, probably dominate. Missing is the third gift of nature – tidal energy from a barrage across the Bristol Channel where tidal rise is up to 11m in four hours.
An Aberthaw-to-Minehead barrage could produce for a short time over 9,000MW on particular spring tide days. More usefully, it could produce 4,000MW for 16 hours a day, every day, using predictable tidal energy. Using batteries with a peak limited to 6,500MW (all from tides) will give 4,000MW continuously.
Construction must be based on technology that is well-proven. Examples are oil/gas rig steel structures (thus avoiding the mass use of concrete), wind-turbine sectional main support columns, and batteries in 20MW arrays located close to water turbines.
Channels for marine life and shipping must be incorporated in the design. Seismic events up to 6.0 must be accommodated.
All new power-generation coastal projects must address the possibility of increases in sea level caused by climate change.
One way of addressing all the above is shown in www.aberthawtidalps.co.uk.
Edward Grist, Congleton, Cheshire
Heavyweight planes just won’t take off
I write in response to the article “Rising to the carbon challenge”. The plan seems to be to store energy required by the aircraft in the battery rather than in liquid fuel whose energy density is 70 times higher.
Even a short-haul plane like the Embraer 135 carries around 5,100 litres of fuel or 50MWh of fuel energy. A battery to store that much energy would weigh around 14 times the maximum take-off weight of the plane. So what is the thinking behind this, given that weight is such an important issue in aviation?
Even if the electricity to charge these batteries comes from completely CO2-free sources, there is another important source of CO2 from the manufacture of batteries, which could be as high as 200kg/kWh of battery capacity. Currently, a substantial portion of this embedded CO2 originates in countries where the metals required are mined and processed and the energy sector in these countries will not be decarbonised for a long time to come. In addition there are serious issues of human health associated with the mining of metals which cannot be ignored as the size and number of batteries increase. So batteries are not zero-emission devices and putting them on planes will not make aviation free of CO2 in any honest assessment on a lifecycle basis.
As for direct air capture of CO2 – is this really a serious proposition, given that CO2 concentration in air is only around 0.042%?
Making electro fuels is energy intensive – the energy conversion efficiency starting with fully renewable electricity is around 44%. The daily global demand for aviation fuel is 7.5m barrels of oil equivalent or 0.046 exajoules. The world will need to build the equivalent of 400 nuclear power stations (of 3GW) to produce CO2-free electricity to make enough electro fuels to meet the global aviation demand.
Biofuels are also not strictly suitable for aviation since their gravimetric energy density is 16% lower than that of aviation fuel – the fuel weight on the aircraft would be 16% higher.
In summary, it is very unlikely that aviation could be decarbonised. So if the UK wants to go to zero carbon by 2050, the aviation industry will have to be shut down by that time along with the steel and cement industries.
Gautam Kalghatgi, Oxford
Limit motorway speeds to save energy
We have an environmental lobby who are saying urgent action needs to be taken to avoid catastrophic climate change. At the same time we have a public who are happy to purchase large, heavy SUVs for no better reason than fashion, status or ego, blissfully ignorant of the impact.
Most frustrating is the push for electric vehicles. I have no objection to electric vehicles in principle, but when car manufacturers produce battery or hybrid versions of large, heavy SUVs the point has been missed!
Dealing with climate change has as much to do with reducing energy consumption as where it comes from. Energy reduction is sometimes an easy win. A blanket speed reduction on motorways to 60mph or even 50mph would make an immediate impact for little outlay.
A more elegant solution would be to govern a vehicle’s speed as a function of its mass, drag coefficient and frontal area. This would “normalise” the energy consumed over a given journey. If you feel you need a 4x4 truck, fine, but you accept it will only go at 50mph. If you have a modest family saloon then you can do 70mph. The impact on energy consumption would be significant and it would provide a real incentive for the public and car manufacturers to drive smaller, lighter vehicles. It would also take away the incentive for the wealthy to buy large vehicles simply because they can.
It’s not a perfect solution but, if the public think they can tackle climate issues without any compromise, they are wrong.
Jamie Keyte, Woodborough, Nottinghamshire
Let’s go it alone
I found surprising the range of views expressed in the article “How can the government support UK manufacturing?”
All six of the respondents supported direct government intervention in contrast to conventional wisdom, which advocates a laissez-faire attitude. Automation,
investment, planning, training and reviews are all activities best conducted by private companies and universities without interference from ministers.
The government should concentrate on the areas private companies are powerless in, such as building infrastructure and keeping energy prices low.
David Walker, Cambridge
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