Air quality and health – a few thoughts now the dust has settled

Last week a cloud of Saharan dust swept across the UK, and as a result stories about air quality settled with similar ubiquity across the country’s media. As soon as we could see the choking cloud in front of our faces, we all wanted to talk about a problem that has in fact been with us every day for decades. No metaphor could have made the point more clearly that ‘out of sight is out of mind’.

Woman coughingJust last week, the World Health Organisation (with perfect timing) released new data suggesting that one-in-eight deaths around the world can be linked to air pollution. There’s no need for me to re-hash arguments made very well in the better quality media last week (see John Vidal’s piece in the Guardian, ref below). The one thing I’d like to pick up on is just what all those people in the WHO data are dying of, and perhaps why we and our politicians seem incapable of seeing the problem except when it paints the streets red.

The media reports during an air pollution ‘episode’ like the one we just had invariably focus on coughing, asthma, stinging eyes – the sort of thing you’d expect. I saw one paramedic interviewed on the BBC saying, ‘Yes, we’ve seen a 14% rise in cases of acute respiratory illness over the last two days.’

The thing is, if you read the WHO report, it summarises the deaths linked to outside air pollution by cause, and this is the run-down:

  • 40% – ischaemic heart disease;
  • 40% – stroke;
  • 11% – chronic obstructive pulmonary disease (COPD);
  • 6% – lung cancer; and
  • 3% – acute lower respiratory infections in children.

That’s 80% caused by heart disease and stroke, before you get to the ‘obvious’ stuff, the ‘lung’ stuff. I’ll be honest and admit that it made me sit back and think. So I went looking for a little more explanation, and found some great references from the American Heart Association (hardly radical) and then the penny dropped, because they reference the many studies on second-hand cigarette smoke.

We all know smoking is bad for us, and we know that it massively increases the risk of heart disease and stroke, two of our society’s biggest killers. And we’ve enacted smoking bans in public places because we realised that inhaling smoke puts you at risk even if you’re not a smoker.

Step out onto the street in London, and the air may not be pleasant, but you’re not immediately thinking about people dying from it. You may well know someone with breathing problems, or asthma, but they probably manage it. But I’m guessing most of us have been touched by the death of a friend or relative from stroke or heart disease, and not necessarily a smoker. Was the air they were breathing the final straw? Quite possibly.

Our current controls on smoking have taken decades to enact, and smoking is regarded as much more of a choice than the presence of buses, trucks, taxis and cars on our streets. In the case of smoking, it took a culture change – the public had to internalise the evidence of health risk, and the politicians reacted (eventually) to that change, some of the braver ones even helped it along.

Action is being taken on air quality, but much too slowly (another post on that soon). If we want a quicker pace of change, I think one component will need to be a greater recognition of the true health impacts, and just how much the invisible cloud is affecting us, our friends and our relatives.

So here’s a thought – next time you step outside in a major city, look at the traffic and picture every exhaust pipe as a giant cigarette. I’m talking about a six-foot Gauloises, smoked by an elephant with a 200-a-day chain-smoking habit. See if that changes your perspective on air quality.


WHO press release:

John Vidal’s piece in the Guardian:

Information from the American Heart Association:


The elephant in the room part 3: Making time to slow down

So, to recap parts one and two. If we make transport more efficient, less polluting, or generally more pleasant, then people just travel more and wipe out the benefits. We need to manage the overall demand for travel. We can do that by changing planning so that the things we need are closer to us, and by reallocating space and resources to the modes we prefer, like walking, cycling and buses.


Are we nearly there yet?
© Jonaldm | Stock Free Images &Dreamstime Stock Photos

But, and it’s a big but, even if we created perfect towns and cities, with everything nearby, we might still all travel just as much. That’s because we also have to think about the time people spend travelling, and the fact that humans are mostly creatures of habit.

Ever since Tanner suggested the idea in 1961, there’s been an ongoing academic debate about the idea of ‘travel time budgets’. In the 1970s empirical research by the likes of Szalai and Zahavi backed up the idea that all over the world, people spend roughly the same amount of time per day travelling – about an hour.

This caused quite a bit of excitement, suggesting as it did that maybe the amount of time we’re prepared to spend travelling is somehow ‘hard wired’ into human beings. Since that original paper various theories have been suggested, and plenty of other researchers have questioned the data, saying there’s more variation within and between populations than has been suggested.

What does seem to be agreed on however is that at the individual level, we do tend to be quite resistant to changing how much time we spend travelling. A look at the national travel survey for the UK (2010) shows that travel time has remained static for the last 15 years, at just over an hour per day, while the number and length of trips has varied. And if you think about it, that has some pretty far-reaching consequences for how we think about managing the overall demand for, and impact of, travel.

Suppose we drastically shorten many of our journeys, or provide really fast, efficient trains, or use the internet to eliminate journeys altogether? Well, the evidence suggests that on an individual level, we’ll probably just make other journeys to use the travel time we saved. The likelihood is that if we shorten ‘essential’ travel, to work, or that hospital appointment, it will be replaced with leisure trips, maybe occasional longer trips to see friends or relations.

Here’s another thought, transport economics is almost entirely based on the idea of time savings. The case for a new road will typically be based on the idea that, for example, (a) each motorist will save 30 seconds off their journey time, (b) the average person’s time is worth £12 per hour to the economy, and (c) 200 million journeys per year will be made on the road. So, each 30 seconds is worth 10p, and the road is therefore worth £20 million per year to the economy.

You might think this is nonsense, because when you boil it down to the individual motorist, that 30 seconds is unlikely to really make any significant difference at all to their productivity. And I would agree with you. However, that hasn’t stopped government using the same method to justify investing billions in high speed rail.

But that logic is weakened still further if you assume that for each person, travel time per day will probably remain constant.

The upshot of all this is that we need to sustainably ‘reallocate’ any travel time that we save by speeding up or eliminating trips. It’s just the same as the need to reallocate road space if we want to ‘lock in’ the benefit of some motorists switching to other modes.

What might this look like? Well, having freed up time, if people are going to make extra ‘discretionary’ trips to use that time, we need to make sure they don’t choose to make those trips by car. We can make it attractive to walk and cycle for pleasure, to visit friends and leisure facilities. We can invest in extra capacity on the railways, rather than speed – given that you can now work, watch a film or surf the net on a train journey, why do we need to spend billions making that journey slightly shorter and massively more expensive? And we can stop chasing our tails building new roads.

Ultimately, perhaps what we need is a ‘slow travel’ movement, a bit like the ‘slow food’ movement? A shift in the focus of transport strategy, away from speed, and towards making travel healthy, low impact, and fun.

[P.S. One thing not addressed here is the impact of ‘outsourcing’ our shopping trips to delivery vans, via internet shopping. I think that will have to be the topic of another post.]

The elephant in the room part 2 (of 3): A journey through space (… and time)

So, to recap part one, if we try to ‘fix’ transport without thinking about overall demand, we’re running to stand still. If we make cars more efficient they use less fuel, and emit less pollution, but since they’re cheaper to run we drive more miles, and we’re back where we started. If we ease congestion, people drive more. Even making public transport better has a similar effect.


‘It’s gridlock around here.’
‘Just be glad there aren’t any more elephants!’
© Roadbully | Stock Free Images & Dreamstime Stock Photos

So what’s the answer? Well, like it says in the headline, this is about space and time. If we want people to travel less, thinking about where we put things is a no-brainer. But, and it’s a big but, we also have to think about time – because it turns out human beings are not the ‘utility-maximising’ decision makers that economists like to think we are.

So, the obvious factor first … space.  There are two elements to this – putting stuff closer together, so we don’t need to travel so much, and how we allocate space on the road, to ‘lock in’ changes in travel behaviour.

Ever since geographers first started thinking about urban sprawl in the sixties, we’ve been debating its effects on transport. Hardly a week goes by without a media story about out of town supermarkets, which we all drive to, killing off the high street. But equally, there are more and more stories about urban renaissance, high density living, and those out of town supermarkets coming back into town centres with ‘metro’ stores.

Essentially, a key element in constraining our demand for transport is to change planning, to favour denser communities, that can then economically support localised services. Lots of people have written about this, but for a good discussion try this chapter from Carbon Zero by Alex Steffen. The problem with changing spatial planning is that it takes a long time to have an effect.

A less discussed side of the ‘space’ debate is how we allocate road space to different modes of transport. Reallocating road space is the often forgotten key step in creating ‘modal shift’ – i.e. getting people out of cars and into cycling, walking or buses.

Let’s say you live in a city where all the main roads in are gridlocked from 8-9am. What happens if the council launches a big push for people to use park-and-ride, or cycle in to work. A year later there are thousands of people riding the bus, or cycling in, but the gridlock is just as bad – so what happened?

Well, the answer’s simple, as some drivers switched to other modes, other drivers took their place. Congestion usually means pent up demand – there are always people who choose to make some trade off to avoid a certain level of congestion (e.g. by driving to work really early, or not travelling at all), and if the congestion level falls, they re-evaluate that decision.

If our aim is to have fewer drivers, and so less pollution, then the uncomfortable truth is that gridlock is our friend. If we succeed in getting some drivers to switch to the bus or bike, we have to reallocate the road space they were using to those modes, by putting in bus and/or bike lanes, changing priorities at junctions, removing parking or whatever. The net result will be the same level of congestion for the remaining drivers, but that means they won’t be joined by any more.

The big problem is that promoting cycling, or investing in bus services, can be seen as promoting ‘choice’, but taking space away from cars is less of a vote winner. So elected councils only tend to do half the job. Note that the thing that will actually decrease the congestion level is to increase the monetary cost of travelling at that time, with a congestion charge. That’s because the driver’s decision on whether to travel is based on both time/stress and money. Of course congestion charges haven’t exactly proved an electoral favourite either.

So, there are things we can do to decrease transport demand, and lock-in modal shift, by thinking about space, but they take time and may not be popular. However, in part 3 I’ll explain why we also have to think about travel time and human psychology, because even changing the layout and roads of our cities may still see us running to stand still.

The elephant in the room part 1: Running to stand still

There are lots of ways we can reduce the emissions from transport, and many of them will also make getting around more pleasurable, more efficient and easier. And therein lies the rub – because if something gets easier, we’ll probably do more of it.

The elephant in the room

It makes him scratch his head too!
© Tjenner | Stock Free Images & Dreamstime Stock Photos

Let’s take a really simple example – you replace your petrol car with an electric one. Great, now the pollutant emissions for each mile you drive have been reduced (by how much is a debate for another post). And you save money too, because electricity is much cheaper than petrol.

Now you’ve invested all this money in buying your electric car, you can drive around for next to nothing, and feel pretty smug about it too. So, all other things being equal, you’ll probably drive more miles. In the jargon it’s called a ‘rebound effect’.

Of course it’s not quite that simple. In reality, our travel behaviour is influenced by all sorts of complex factors, but the simple fact is, travelling has costs and benefits. If we reduce the costs – time, money, stress – then people are likely to travel more to grab more of the benefits. That might mean buying a nicer house that’s further from your job, or making more leisure trips.

None of this is rocket science (now that would really increase total miles travelled). But when the solutions to our transport problems are debated, how often do you hear serious debate about reducing, or at least managing, the overall demand for transport?

Whether it’s hard-shoulder running on the M6, biofuels for aviation, high-speed rail or electric cars, the implicit assumption is that we can reduce the impacts of our current transport patterns. But time after time, we find that by the time the latest ‘solution’ is implemented, its benefit has already been negated by an increase in total miles travelled.

The roads protesters of the 90’s understood this, a central part of the case against the ‘roads for prosperity’ programme was that new roads just lead to more traffic. But that argument rarely strayed beyond the professional transport community – the media were only interested in tree-houses and Swampy, and the politicians only axed the programme because they realised it was going to cost a fortune in security guards. (It looks like we’re about to see a re-run of that scenario, but I doubt the debate will have moved on much.)

So what’s the answer? Will we forever be running to stand still? Transport emissions remain stubbornly high, and I would argue that rebound effects are a large part of the reason. Without a serious debate about overall transport demand we’ll never make progress.

There is work going on to address the issue, but it’s hardly part of the mainstream. At an event recently I found myself talking to someone from the Department for Transport, and I was delighted (and surprised, I admit) to discover that she was part of a team looking at overall demand management. It’s a good sign, but the cynic in me doubts whether they’ll ever be listened to seriously by the ministers.

In part two I’ll go on a journey in space and time, to consider how it might be possible to make transport better without making us want more of it!

Two pints of lager and a packet of crisps – the problem with reporting freight emissions

Working out the greenhouse gas (GHG) emissions of a truck ought to be pretty easy, right? If you know how much diesel it used, you know how much carbon it emitted. So far so good – but what if you want to know the carbon emissions per unit of product delivered? It gets a little trickier, but that’s not the real mind-bender…

Mmmmnnn... beer

© Duel | Stock Free Images & Dreamstime Stock Photos

Let’s say you go to the pub (by the end of this post, you’ll probably want to). You buy your beer and crisps, and then start to wonder what the associated GHGs are. (OK, you don’t, but humour me here.) The giant brewer BigBrew might have made your pint, and as of next April they’d be required by law to report their GHG emissions. But if a third party haulage company, let’s call them A2B, was contracted to deliver the beer to the pub, the truck’s emissions would probably not be reported by BigBrew. And what about your crisps? CrispCo, the manufacturer, would have reported their emissions, but A2B might have delivered those crisps to the pub too.

This is the first issue when deciding on how to report company emissions – where do you draw the line? In general, the global standard says that if you’re a business, you report emissions just on the stuff that’s directly ‘yours’. These are called ‘scope 1’ emissions (except electricity you buy, but we’ll leave that for now). How do you decide what’s ‘yours’, well, generally by whether you have ‘financial control’ of that thing – e.g. a building, a factory, or a vehicle. Financial control usually means you own or lease it, and you profit from its operation.

Lots of big companies don’t own the trucks that transport their goods – they outsource freight to other people. So it’s these hauliers that own the trucks, and profit from them, and the emissions from those trucks are the hauliers’ to report as scope 1.

So far so good, but what if the haulier isn’t really free to do anything that could reduce their emissions? In some cases, contractors provide vehicles and drivers, but the client specifies the vehicles, and decides what they’ll carry and what route they’ll take. In this case, it is possible to decide that the client has ‘operational control’ of the vehicles, and should count the emissions as theirs.

Of course, if I want to know the emissions associated with my pint of beer, I need to include transport in that. Let’s say BigBrew report the emissions from making the beer as their scope 1, and A2B claims the delivery truck’s emissions as their scope 1. In order to calculate the total emissions for the single pint of their product in my hand, BigBrew might ask A2B to give them a report on the emissions created by delivering each barrel of their beer. These emissions are described as BigBrew’s ‘scope 3’, i.e. emissions that are from another company’s operations, but which are ultimately associated with their product.

This could give A2B a bit of a headache. If they’ve got trucks which just deliver BigBrew’s beer, then no problem, they just calculate all the fuel/emissions from those trucks, and divide it by the number of barrels they delivered. However, they may well deliver beer from different companies, to a range of pubs, on the same truck. They could come up with a good estimate by allocating some of the truck’s emissions on the basis of the weight of beer delivered, and some on the basis of the distance travelled, or the number of stops made.

Now, I think you’d better pour yourself a stiff drink for the next bit. What if the truck isn’t just delivering beer? The amount of beer you can get on a truck is limited by weight. So you divide up emissions by the weight of each customer’s product. But what if you’re also delivering crisps? If you fill a truck with crisps, the load will be limited by volume. And if you have a mix of crisps and beer … don’t think too hard about it.

Two years ago I was the lead author on guidance for the freight industry on how to report its GHG emissions. I was one of a team of consultants working for the Department for Transport, with an industry steering group, to draft guidance to supplement the government’s general guidance to all companies, itself based on the Greenhouse Gas Protocol. That guidance is available on Defra’s website, and on my site here.

Working with Nick Gazzard of CILT, and Jaques Leonardi of Westminster University, we came up with simple(ish) mathematical answers to most of these problems. And we put them into a spreadsheet tool that’s also available on the Defra website.

But if you’re a haulier unlucky enough to be delivering crisps and beer on the same truck, for two different customers, I’m afraid we didn’t come up with a solution. I’m afraid that mathematically, you pretty quickly disappear down the rabbit-hole – and the only way to really solve the problem is to measure each truck’s emissions in the lab at different weights, and calculate it’s co-efficient of drag, and then model each individual stage of each truck’s journey.

Nobody’s suggesting hauliers should go that far. You just need to make a reasonable guess …

or maybe persuade pubs to stop selling crisps?

The US mandate for ethanol production pushes up corn prices – doesn’t it?

In a year that saw the worst drought in decades in the US, the ‘food vs. fuel’ debate is highlighted once more. The corn crop has been badly hit, pushing up prices, so farmers are urging the government to drop the requirement to make ethanol from corn. However, the Environmental Protection Agency (EPA) has just refused (again – they also refused in 2008).

© Rdodson | Stock Free Images & Dreamstime Stock Photos

The interesting thing is that the EPA says dropping the ethanol blending mandate wouldn’t make any difference to corn prices. Which seems rather counter-intuitive doesn’t it? In 2007, a little over 10% of US corn was used for ethanol production, whereas now that figure is 40%. Surely that must have an impact on price?
Specifically, the EPA said:

“EPA examined a wide variety of evidence, including modeling of the impact that a waiver would have on ethanol use, corn prices, and food prices. EPA also looked at empirical evidence, such as the current price for renewable fuel credits, called RINs, which are used to demonstrate compliance with the RFS [Renewable Fuel Standard] mandate.

“EPA’s analysis shows that it is highly unlikely that waiving the RFS volume requirements will have a significant impact on ethanol production or use in the relevant time frame that a waiver could apply (the 2012-2013 corn marketing season) and therefore little or no impact on corn, food, or fuel prices. We analyzed 500 scenarios, and in 89% of them we see no impacts from the RFS program at all.”

To my mind, this is just another good example of how hard it is to draw a direct link between food prices and biofuels. That’s not to say I think using food crops for fuel is generally a good idea, just that I think looking at food prices is going to be a tough way to argue against it.

In a 2008 report, the International Energy Agency pointed out that estimates of biofuel impact on food prices can vary somewhat. They cited an estimate by the Council of Economic Advisors, who estimated that biofuels accounted for 3% of that year’s rise in food prices, compared to a World Bank estimate that biofuels accounted for 75%! The CEA had used only data on corn markets, and extrapolated it out to all food crops, while the WB had simply looked at the impact of oil price on food prices, and then assumed that all of the remaining increase was due to biofuels.

So, back to the EPA’s decision – how can they say that using all this corn won’t have an impact on price? Well, there are two broad reasons.

First off, they’re not really saying that using corn for ethanol doesn’t impact on price, they’re just saying that removing the Renewable Fuel Standard for this year won’t help. In fact, there are several other forces that determine how much ethanol is blended into gasoline in the US, such as:
• Ethanol has been cheaper than gasoline for the last few years
• Gasoline sales have been declining in the US, this year down 5% on last year, which means less ethanol is needed to hit the target
• Demand for ethanol is driven just as much by the Clean Air Act, which requires an ‘oxygenate’ to be blended into fuel to lower emissions of carbon monoxide, and ethanol is the cheapest oxygenate

The second reason is that although more corn is being used in ethanol, it’s compensated for in other ways. For one thing, that huge 40% figure doesn’t allow for the fact that the by-product of ethanol production, Dried Distiller’s Grains (DDG), is itself a high grade animal feed. Allowing for this, it’s actually about 27% of corn which is used for ethanol. For another, US corn exports have fallen by over half since the food price spike of 2008 because those high prices caused much more land to be put into corn production elsewhere in the world.

One final piece of the puzzle is the RINs (Renewable Identification Numbers). These are certificates that fuel companies get to show how much ethanol they’ve blended into their fuel. For the last few years, most fuel companies have blended more than they had to, because ethanol was cheaper than gasoline, so now they’ve got spare RINs, which they can use to meet some of this year’s mandate. Which means if the price of corn ethanol goes up, they can use RINs instead, lessening the RFS’s impact on corn prices.

So what do we learn from all this? Well, like I said, drawing a direct link between food price and biofuel policies is never going to be easy – there are a lot of different factors to take account of. But let’s face it, using all that corn for ethanol still sounds like a bad idea, in a year when the US corn crop fried and the European wheat crop was flooded. So what’s the real argument against?

Well, in the US, the RFS could have been challenged on environmental grounds. In fact, the last time the RFS was challenged, by the Republican Texas Governor Rick Perry in 2008, it was also on economic grounds, after Perry considered but rejected the idea of a challenge on environmental grounds. Of course, an environmental challenge would have led to questions about the greenhouse gas emissions associated with corn production, and that would have opened up a can of worms within Perry’s own party.

The thing is, by challenging the RFS on purely economic grounds, the farmers of America have probably let the EPA right off the hook. Because there are some pretty serious questions that need to be asked about what land has been used to increase corn production in the rest of the world, and, within the US, where’s the water going to come from for next year’s crops?

Reuters, EPA, EPA Insider, Ethanol Producer, Dairy News, International Energy Agency

Is ‘range anxiety’ a problem for running trucks and buses on compressed gas – and does it need to be?

[This post is based on part of a presentation I gave to the Global Biomethane Congress in Brussels this October. The full presentation is available here.]

There are lots of advantages to running trucks and buses on gas, compared to diesel. Gas is cheaper (half the duty of diesel), cleaner (no particulate emissions), and if you use biomethane, i.e. gas from waste, then you can get up to huge reductions in greenhouse gas emissions. Vehicles even run more quietly on gas.

There are downsides of course. The main one is the initial cost of switching, but that goes for any new technology. But, as with electric vehicles, another big issue is how much fuel you can get in the vehicle, and therefore its range.

The problem is that gas is, of course, a lot less dense than diesel. In fact, most other fuels have a lower energy density than diesel, as illustrated by the chart below. (All data from the Oak Ridge National Laboratory in the US.)

The easiest thing to do with your gas is compress it, and for vehicles in Europe this usually means compressing to 200 bar. As you can see from the bar chart above, looking at the bars for CNG (Compressed Natural Gas), that means your fuel will take up much more space than diesel. The gas tanks are heavy too, so you may lose some of your payload. In practice, this usually means you can’t have as much fuel on the vehicle, and you have to accept a cut in range.

But is the drop in range really that much of a problem? I thought I’d do a few quick calculations to figure this out.

The typical set up for putting gas cylinders on mid-size trucks, and refuse collection vehicles, is in two banks of four 80 litre tanks, like in the picture below. This can of course be modified if requested, and buses often have a different arrangement with gas cylinders on the roof, but it seems that 640 litres of gas (2 x 4 x 80) is fairly standard. So how far will this get you?

Well, 640 litres of gas at 200 bar pressure has the same energy as about 150 litres of diesel. However, diesel is used in a compression ignition engine, whereas gas needs to be burned in a spark ignition engine, and compression ignition is about 25% more efficient than spark ignition. So, our 640 litres of gas will actually get us as far as about 120 litres of diesel.

Last year I wrote the final report on a trial of a gas refuse collection vehicle (RCV) by Leeds City Council. Their RCVs get about 3.3 mpg, which means that 120 litres of diesel would give a range of 86 miles. Urban RCV routes are about 50 miles in Leeds, with the longest routes into the surrounding area getting up to around 100 miles. So, a range of 86 miles shouldn’t present a barrier to cities all over the country running these fuel thirsty vehicles on gas.

What about buses? Well, a conservative estimate would suggest a bus getting 8 mpg, in which case 120 litres of diesel (equivalent) would give a range of 210 miles – which is plenty for an urban bus. Hardly surprising then, that cities all over the world are switching their buses to run on gas, mainly driven by the desire to improve air quality, although financial savings are also welcome.

Are trucks a different story, hauling up and down the motorway all day? Well, yes and no. For big articulated 44t trucks there currently isn’t really a 100% gas option (the reasons for which I’ll cover in another post soon). However, for the smaller, rigid trucks in the 7.5 – 26t range, gas is an option. An 18t truck, for example, might get around 12 mpg, so 120 litres of diesel would give a range a little over 300 miles. Department for Transport figures show that vehicles of this type make very few trips over this range.

There is no doubt that one of the things fleet operators worry about, when considering gas, is the drop in range of their vehicles. But as with electric cars, we’ve become so used to the incredible energy density of diesel and petrol, and the huge range it gives our vehicles, that it can be hard to swallow a reduction – even if the reality is that we don’t really need it most of the time.

[For those few applications where we do need greater range, gas vehicles can use liquefied gas, which you may have noticed from the graph has a much higher energy density. And indeed one of the big debates in the gas vehicle community is on the relative merits of compressing vs liquefying gas. But that’s a story for another post.]


Who’d have thought running an electricity grid and running a railway would have so much in common?

I was at a transport industry networking event the other night, chatting to Peter White of the University of Westminster. He was outlining strategies for reducing emissions from rail travel, and I was explaining the potential role of electric vehicles in grid balancing, and we realised that both problems were surprisingly alike.

The problem with running a railway is that you have to invest in loads of rolling stock to meet rush hour demand, and then it sits there idle most of the day. Here’s the total number of passengers in and out of London stations, hour by hour, on average (DfT stats):

That’s a lot of unused capacity outside the rush hour. If we could just spread out that morning rush, by employers allowing (or even encouraging) employees to have staggered start and finish times, the railways would be a whole lot cheaper to run – and more pleasant to travel on.

Turns out, that’s just what happened during the Olympics. As well as encouraging businesses to promote home-working during the Olympics, the ODA and Transport for London asked them to stagger shifts.

One of the most striking successes was with City trading firms. They’d always maintained there was no way they could allow flexible working, because of trading times, but with the Olympic spirit behind them they tried out an ‘early’ and ‘late’ shift. Turns out it worked beautifully, because the early traders were clued up on the Eastern markets, and the late traders got to see how things played in the US. How many other types of business could benefit from this approach?

So how’s all this like running the electricity grid? Let’s say you’re National Grid, and you’re responsible for supplying us all with electricity. Your biggest problem is variable demand – everyone wants power at 5.30pm, and nobody wants it at 4am. Here’s the graph of demand on the UK grid through one day (1st January 2012 as it happens, data from National Grid):

So you have base-load generators, like coal and nuclear, which are cheap but hard to turn on and off, and you have peak-load generators (usually gas), which are only turned on when you need them, but which are therefore more expensive.

Just as with the railways, if we could spread demand more evenly, or store electricity, we could generate our power more efficiently. Grid operators call it ‘filling the bath-tub’. This is one reason why the electricity companies are so interested in electric cars – they all come with an energy storage device (i.e. the battery).

If we all went and bought electric cars tomorrow, and charged them overnight, it would allow for a much more even load on the grid. This would allow the energy companies to run more base load generation, and therefore provide cheaper electricity.  Of course, the opposite is also true – if everyone put their car on charge when they got home from work, we’d need even more peak capacity, making power more expensive.

Incidentally, price and greenhouse gas emissions are pretty closely linked here. If you buy an electric car in the UK right now, and charge it from midnight to 7am, you’ll be saving GHG compared to an equivalent petrol or diesel car. However, if you put your car on charge anytime from around midday to 10pm, you’ll be emitting around twice as much GHG as charging off-peak, and more than a petrol or diesel car.

Adding renewables like wind or solar to the mix is even more of a headache, because you don’t know when you’ll get the power. That’s when electric cars really come in handy – but more of that in a later post…

A bluffer’s guide to the difference between a ‘parallel’ hybrid and a ‘series’ hybrid. (And why the parallel hybrid came first.)

So, we’ve had the Prius around for a while, and that’s a hybrid – right? Then the Ampera/Volt comes along (with billboards everywhere you look), and it’s an electric car – or is it? Because it’s got a petrol engine too.

Well, when they’ve got their petrol engines running, the Prius and the Ampera represent two different ways of making a ‘hybrid’ – parallel and series, respectively. I’ve explained which technology I think is superior to many people at parties, and I still seem to have friends, so hopefully you’ll find this interesting too.

A ‘parallel’ hybrid has two complete drive-trains connected to the wheels, which operate in parallel, hence the name. Basically, you start with a regular petrol car (or a diesel, more of that in a later post) and you bolt on an electric motor and a battery that can also drive the wheels. The electric motor ‘assists’ the petrol engine when needed, allowing a car like a Prius to have a smaller petrol engine, and use less fuel, for a given level of performance.

The electrical energy in most parallel hybrids thus far has come from ‘regenerative braking’. Essentially, when you apply the brake, the wheels drive the electric motor in reverse, generating power which is stored in the battery. The new ‘plug-in’ Prius has a bigger battery, which you can charge up from a wall socket. This means that you can get a little over 10 miles on the electric motor alone, but most of the time that electrical power is still ‘blended’ with power from the petrol engine.

OK, sounds good right? Well yes, until you consider that a petrol engine is incredibly inefficient. At its most efficient, a ‘sweet spot’ of revs and load, it converts about 25-30% of the energy in the fuel into forward motion – the rest is mostly lost as heat out of the exhaust or the engine block. But that’s when you’re cruising at a steady, optimum speed. The rest of the time, when you’re accelerating, or decelerating, or in the wrong gear, the efficiency drops much lower. This means that the engine in a car has to be oversized to cope with all this variation.

Suppose you only needed the petrol engine to deliver a constant power, at constant revs? Like, say, the engine in an electrical generator. Hmmnn… and suppose you only had to have one drive train connected to the wheels, that would save a load of weight, right? Bingo! – you’re thinking of a ‘series’ hybrid. Electric motors drive the wheels, and they’re 85-90% efficient (very little heat loss), and that efficiency doesn’t vary much at different speeds. Then you charge up the battery using a small engine acting as a generator.

In theory, the series hybrid should be more efficient than a parallel hybrid, because the petrol engine only has to run at its optimum speed and load. It only has to deliver the average power requirement to the battery, which buffers this power, supplying more or less energy to the motors driving the wheels as the car accelerates, cruises etc. This is essentially what an Ampera does, although like a plug-in Prius it has a bigger battery, that you can charge up from the wall, so you can run the car on ‘pure electric’ mode for about 30 miles before the generator kicks in.

So why did we get a parallel hybrid, like the Prius, years before a series hybrid, like the Ampera? Well, it’s a simple question of what happens if it goes wrong. A parallel hybrid is in essence just a regular car with the electric motor helping out – if the electric drive train fails, you can still drive the car. But with a series hybrid, if the battery, the motor, or any of the complex systems managing them were to fail, you’re stuck at the side of the road waiting for a tow truck (or an electrician!). It’s only now, with ‘pure’ electric cars like the Leaf on the market, that big manufacturers have got enough confidence in the technology.

In my opinion, the Ampera, or cars like it, will lead the mass adoption of electric cars, for several reasons. But that’s for another post…