Meeting the energy mix challenge

The debate over how to reduce the environmental impact of energy usage in the UK is riddled with inconsistencies, hyperbole and misunderstanding. While one group of people will say we need a massive expansion of wind power, for example, another will say it will lead to the whole country being covered in wind turbines. Others say that nuclear power is the only answer.

What is needed, according to many environmental scientists and energy specialists, is a clear understanding of where we are now, where we’re likely to be and the technologies and techniques that can be used to get us there.

The key target date is 2050, which is likely to be benchmarked by the Copenhagen protocol next month. By that time, the UK will probably have to reduce its carbon emissions by 80 per cent — a daunting total and one that cannot be met merely by looking for ways to reduce energy wasted in current processes (see backstory below).

‘There’s no point in greenwash,’ said David McKay, the chief scientific advisor to the Department of Energy and Climate Change, at a recent seminar at Cambridge University. ‘You have things like electricity companies asking you to click on a green tariff on their website, when they generate 98 per cent of their electricity from fossil fuels and no amount of clicking will change that. That’s the kind of twaddle that motivates me.’

His calculations put all energy into two different units: kilowatt hour (kWhr) for consumption and watts per metre squared (W/m²) for generation. ‘A kilowatt hour is a familiar unit,’ said McKay. ‘Put a kettle on for 20 minutes and you’ll use 5kWhr. In the UK, we use 125kWhr per day per person; you can visualise that by all of us carrying around 125 normal 40W light bulbs that are on all the time.’

When looking at renewable electricity, the crucial statistic for each method is the amount of energy it generates per unit area. McKay starts with the population density of the UK, which means that we all have 4,000m² — about half the area of a football pitch — from which we can generate energy. He then looks at each different method.

‘Wind, for example, generates an average of 2W/m²— it’s higher on top of mountains in Scotland, lower around Cambridge,’ said McKay. ‘So, if we were to cover 10 per cent of the UK in windfarms, we’d have 400m² per person and we’d generate 800W per person, which equates to 20kWhr per day.’

That is a lot less than the total 125kWhr per day, but it is still more than the current daily electricity consumption per person (17kWhr). However, it is a huge expansion of wind power. ‘To get that, we’d need to have double the total number of wind turbines in the world today,’ he said. ‘And that’s just physics; it’s not pro or anti wind power.’

Other renewable sources produce similar amounts of energy. Tidal pool power, for example, produces 8W/m². ‘So to get a good contribution from that, you’d need a country-sized tidal pool, not an estuary-sized one,’ added McKay. ‘Fortunately, God in his wisdom gave us a country-sized tidal pool. It’s called the North Sea and we could conceivably populate it with underwater turbines.’

He believes that the energy landscape in 2050 will have to take in technologies from many sectors: ‘We need to take in as many efficiency improvements as we can, such as switching cars to electricity and making them four times as efficient as they are now; insulating all buildings effectively; and using ground-source heat pumps for low-grade energy to heat buildings, rather than burning stuff for that, which is a thermodynamic crime.’

This will reduce overall energy use but increase electricity demand. This will be met by ‘four times as much nuclear as we have today, renewables, clean coal and other people’s renewables, such as electricity generated from concentrating solar power in deserts in Libya or Algeria and transmitting it across France’, said McKay. The UK would still need 40 times as much windpower to meet this demand, he added. ‘There is an exchange rate for this: 2,000 wind turbines is equivalent to one Sizewell B.’

The other vital information for a realistic view of energy and how it can be conserved is how it is actually used. Julian Allwood, director of Cambridge University’s low-carbon and materials processing group, has analysed energy flows, going from their original source as a fuel ofsome sort through their various conversion devices into the final service that is actually consumed. So, for example, the energy source of oil, through refining into petrol, diesel and kerosene, is converted by internal combustion engines into passenger and freight transport. In much of the world, biomass is the major source of energy and it is converted for thermal comfort and to cook food.

The resulting chart, which Allwood refers to as his ‘Map of the World’, shows the energy at each stage as a line whose thickness is proportional to the amount of energy used. At the source side, oil and coal are thick lines, with gas slightly thinner, nuclear rather slender and renewable very narrow. Conversion into steam systems and heated or cooled space shows up heavily, while aircraft, ships and trains are thinner. On the services side, we see that the largest amounts of energy are used for sustenance and thermal comfort, with communication and illumination making up the smallest proportion.

Some of the truisms revealed by the map are surprising. For all the discussion of electricity generation, this only accounts for a third of worldwide energy use. Various forms of transport account for a third of converted energy; more than half the converted energy is used to heat things up or cool them down. What the energy is converted into is also a surprise: transport and structure — that is, industrial production — account for less than a third, while the neglected areas of sustenance, hygiene and thermal comfort account for almost half.

‘We want to produce a version of the chart for 2050, but to do that we’ll have to print it on rubber and stretch the nuclear bit of the energy sources considerably,’ said Allwood.

In practical terms, the chart is helping him to understand where energy savings can be made. For example, while energy-converting devices are highly developed, there are still big losses whenever we use energy at a high temperature in cool applications, such as burning gas to heat a house. ‘The greatest energy savings would occur through better design of “passive systems” to provide more final services for each unit of useful energy,’ said Allwood. ‘For example, most fuel used in vehicles is to propel the vehicle itself, not its contents.’

Reusing materials, rather than recycling, could also lead to significant savings; the less you process something, the less energy you use. Allwood’s team is looking into lower-energy methods of processing scrap metal (see box), but another process that could lead to energy savings is ‘un-photocopying’ — designing a method to remove the toner from unwanted photocopied or printed documents, leaving the paper clean so that it can be reprinted.

One of his PhD students, Thomas Counsell, has calculated that the consumption of paper and board accounts for one to two per cent of all climate-change gas emissions — a small proportion, but a staggering amount of CO₂. The paper energy chain includes forestry, pulping, papermaking, printing and landfill; the industry is in the top five contributors to carbon emissions. Although reusing a printed sheet, rather than throwing it away and starting with a fresh one, might appear the sort of behavioural change that is often written off as trivial, it could have a major effect. Counsell believes it could replace more than 60 per cent of new paper, consume less than 40 per cent of the energy of recycled paper and cost less than half a penny per sheet, as long as a good enough method of un-photocopying can be found.

He has tried three methods of removing toner from printed paper: abrasion, laser treatment and solvents. Solvents were effective, but environmentally unfriendly to the extent that there was no net gain over recycling; ablation reduced the quality of the paper too much; and lasers showed promise but caused yellowing of the paper. He is now looking into the use of cheaper high-efficiency semiconductor lasers and seeing whether a laser can remove the toner without heating up the paper, as he believes this is what causes the yellowing. ‘We have to look at all the options for removing or reducing processes that use heat,’ said Allwood. In the end, he added, that is the only sure-fire way to reduce our impact on the planet.