Asphalt and Battery: The future of the London Bus (part 2)


In the comments following part 1 of The Future of the London Bus we saw how controversial just about every single aspect of a London bus can be. Size, style, configuration, means of procurement and many other aspects are hotly debated. Given that these aspects are interrelated it is not entirely surprising that it seems no two people can agree on what the London Bus ideally should be like. Nevertheless we will take a bold attempt at looking at the new technologies that might be underneath a future new bus for London.

Possibly one of the few things that can be agreed on is that there is no single bus design that is ideal for all routes in London, and that we will continue to see a variety of single and double deckers of different designs and different lengths with different numbers of doors supplied by different companies. We can probably identify little in common on the outside other than they will all be predominately red and all have the same style of blinds.

Even the history of London’s bus service clearly has different interpretations and the reasons for why we are where we are seem to be disputed. If what happened in the past is hotly disputed then it is almost inevitable that a look at what the future either will, or should, look like is going to ensure almost complete disagreement. In attempting to just look at one aspect of that – future technology and how the London Bus of the future will be powered – one can immediately see the traditionalists being pitted against those who want to embrace new technology, even if it hasn’t yet proved its worth.

The limits to growth

One surprising thing about the predicted growth of bus services in this time of rapid population increase is that there seems to be virtually no growth in the centre and only limited growth in the suburbs. Financial austerity and lack of road space in central London have been seen as possible explanations. One partial solution is to make buses bigger but people have recognised the downside in that solution because of the way buses struggle with our relatively narrow roads and the way they block junctions. Even the issue of long dwell times was raised. In a Oystercard society one would have thought such an issue would have been banished from a discussion about buses – but clearly not and it must be a genuine potential problem otherwise why go to such trouble to introduce a bus with three doors?

It comes back to air quality again

One reason given for the lack of any increase in bus service in central London is the concern over air quality. This does seem to be focusing the minds of TfL and the mayor and it is certainly the case that hybrid buses aren’t cheap and would have to save an awful lot of fuel to justify their existence purely on an economic basis. If one assumes that a London bus burns around 50,000 litres of fuel per year, takes into account that bus services don’t pay tax on fuel and that hybrid batteries only last for a few years anyway, one can see that the accountant does not have a particularly easy job producing a financial case for the hybrid bus. So one could argue that the money that one would expect to be spent on improving bus services is actually being spent in improving air quality.

Non-electric alternatives

When you are responsible for a fleet of over eight thousand diesel buses it is only right and proper that you investigate alternative options and this TfL has done. At one stage hydrogen looked very promising. In the past few years TfL have experimented off and on with hydrogen buses on route RV1 but, whilst the latest buses are still in service, there does not seem to have been any effort made to extend them beyond this one route. This is probably because they are very expensive indeed. It is also the case that, although hydrogen can be seen as a solution for getting rid of tailpipe emission at the point of use, it does not solve any energy issues because more energy in the form of electricity is required to extract the hydrogen from water than can be obtained from burning it as a fuel (and creating water). As such, hydrogen is merely an alternative to the battery.

There are of course various other gases apart from hydrogen that can be burned. The problem with these are that they are still hydrocarbons but in gaseous rather than liquid form. The main attraction of these fuels for taxis and other vehicles is that they don’t attract fuel duty – something that bus operators don’t pay anyway.

The answer’s electric

It does seem that the only current viable alternative to the diesel-engined bus is an electric, or a partially electric, vehicle in some form or other. There are various methods of getting electricity to the electric motor but ultimately it either comes from a battery aboard the vehicle or from a wire or two dangled above the vehicle or, exceptionally in the past, from an electrified conduit buried in the road.

MleEndLook no wires! This is Mile End tram change pit where trams changed over from an overhead wire to a conduit system in the road. The conduit system might have been aesthetically more pleasing but was not maintenance free and work to repair or renew the conduits would have been enormously disruptive. It would be hard to envisage such a system being installed today.

The Diesel-Electric Spectrum

One feature about the modern debate is that it should no longer be polarised as a diesel bus v trolleybus/tram debate. In the past they were the only options available. There was a very early attempt to introduce an electric bus in 1906 but sadly it was mainly done as a fraudulent scam to fleece investors.

Diesel Heater Fill

It might be an electric bus without a diesel engine but it may still need diesel fuel!

Today we have the non-hybrid diesel bus at one end of the spectrum and include the current hybrid in both its forms. Nowadays we can also put the battery bus very near the other end of the spectrum as something that is almost pure electric. However, it seems that one still has to have a diesel storage tank on board to provide heat in winter as the batteries aren’t up to the task of heating the interior and probably never will be. One could probably make a case in London to argue that passengers will already be wearing a coat when it is cold and the bus quite warm with the heat of the passengers aboard but even then one has to consider the driver and give him/her a reasonable working environment.

The diesel bus

The diesel bus uses a diesel engine to power the bus and an alternator to generate what electricity it needs which is then fed into a battery (generally lead-acid) which provide electricity for electrical functions such as powered doors, lights and possibly some kind of air-conditioning. The diesel bus is actually fairly energy efficient providing one does not have to brake a lot. Obviously in central London one does brake a lot so it is not ideal here being both the worst polluting form of fuel at the point of use and one where a lot of energy is wasted.

The diesel bus with regenerative braking

The trouble with hybrids is that they are expensive. The large battery is expensive and the revised power train with electric motors is also expensive. At the same time capturing the energy from regenerative braking is not such a cost liability and a bus tends to use a lot of electricity just in ancillary functions – air-conditioning, powered ramps, lights, doors, CCTV, iBus and even (not in London) Wifi. A fairly obvious thing to do for urban routes is to add regenerative braking and a reasonably sized battery, and use the regenerative braking to provide all the electrical power required. This is really a case of picking the low-hanging fruit and generally produces fuel savings around 10%.

Wrightbus market the idea of using regenerative braking to power the electrical requirements as “micro hybrid”. Of course it is not a hybrid anything but the term is less of a mouthful than a more correct name as well a convenient marketing term that helps position the product in the marketplace.

It is probably the case that if the objective was to reduce air pollution by buses in all of London then it would probably make far more economic sense just to specify that each new bus in London must be a “micro-hybrid” or better. Or rather specify maximum emissions permissible that require at least a micro-hybrid to achieve compliance. Of course a blanket reduction of emissions isn’t the objective, the objective is to get air pollution down in central London so this neat simplistic solution isn’t good enough.

The Parallel Hybrid Diesel Bus

The Parallel Hybrid Diesel Bus is a bit of a curious beast. It has additional weight and design restrictions compared to its series cousin but really comes into its own when largely used in conventional mode because, as it can behave like a conventional diesel bus, there are no electrical transmission losses and no needless charging/discharging of the battery. The problem is that, if it is used in conventional mode most of the time because there is limited braking going on, the need for an expensive hybrid is in fact questionable as the traffic conditions don’t really warrant it.

The Series Hybrid Diesel Bus

As stated in part 1 the series hybrid bus runs on pure electricity. The downside is that it has to lug around a diesel generator to create that electricity. There is clearly going to be a limit to its potential efficiency saving. Some expenditure of energy is just not recoverable – air resistance, tyre resistance, air-conditioning, door opening and closing – as well as losses within the system itself converting diesel energy into electrical energy. Around 40% energy saving is currently supposed to be achievable but it is hard to see how this really can be improved other than by a few percentage points.

The Conventionally Rechargeable Battery Bus

The fairly obvious dream situation is the battery bus. It runs all day on batteries and at night in a few hours it is plugged into the mains and completely recharged. The basic problem today is that the batteries are either heavy and/or expensive and/or liable to catch fire and take up a lot of space. One can trade off one against the other but right now there is not a perfect solution. To provide a bus with the most lightweight batteries available that would last all day would probably cost in the order of £500,000. In other words, for the price of three New Routemasters you could by sufficient batteries for two electric buses. It is entirely possible that a large part of the difference in price between an ADL Enviro 400H and a New Routemaster is largely down to the more generous battery capacity on the latter.

What does look promising is that there are multiple areas of technology development that appear to suggest that battery development is not only improving rapidly but will continue to do so for many years to come. This includes the battery’s close cousin, the supercapacitor which achieves the same function by different means. One must not forget that the proposed new trains for the Piccadilly Line due in service from 2022 onwards are relying on battery development to be sufficiently advanced to get a train to the next station in the event of a power failure.

Energy Live News report on the electric buses in London. For a more critical report there is this alternative.

Despite an ideal battery not yet being available, the battery bus is already present and operational in London as TfL is now running two electric buses in service. They run on lithium ion batteries but not the most expensive and energy dense type. At least with the conventional engine gone there is more space for these to be located. The batteries are the Lithium Ferrophosphate type which have the alleged advantage of being able to last for up to ten years. Like the New Routemaster, there have had to be design sacrifices made to fit in equipment necessary to provide propulsion.

The bus is loaded with an incredible 3 tonnes of batteries. This reduces its passenger carrying capacity. It is also difficult to find sufficient storage for this quantity of batteries and as a result the passenger forward view is rather limited due floor-to-ceiling battery storage and, like the New Routemaster upstairs, there is no rear window.

It is perhaps telling how little publicity TfL have given to the electric bus. They do not provide a timetable for their operation or even what route they will be on what day so they are difficult to try out. From the comments on the youTube clip above it appears that TfL are investigating all their options with an open mind but do not yet feel that with the current product available they are onto a game-changer. It is notable that there has been very little said about the initial cost of the vehicle which is not known.

The Trolleybus Battery Hybrid

Included for completeness in a look at what is technically possible is the the Trolleybus Battery Hybrid. This would probably not be quite like a diesel hybrid in that it makes little sense to store electricity in a battery when one can connect it directly from the overhead wire to the electric motors that power the vehicle. For that reason it would be a trolleybus and not an electric bus recharged using two overhead wires. This would be a very attractive proposition if one had an existing trolleybus network and wanted to extend its range without having to build a lot of new infrastructure.

It is difficult to see how this would be attractive in London, which would have to start again from scratch with overhead trolleybus wires and all the opposition that is likely to encounter. It would be expensive and an planning nightmare to implement – almost certainly needing a Transport and Works Act Order.

It should be noted that having a dual-mode trolleybus is nothing new either with batteries or an appropriately sized diesel-engine. It is obviously fairly simple to switch from wired to unwired. In reverse it currently requires the vehicle to be stationary and accurately positioned with the trolley poles below guides attached to the wire to ensure correct contact.

A youtube video showing a diesel hybrid trolleybus in Solingen switch to and from trolleybus mode. Thanks to Graham Feakins for providing the link.

With technology in such a state of flux it is hard to be sure that this would not rapidly become obsolete. If the technology had been around a few years ago it might have been an attractive proposition for East London Transit with the trolleybus charging the batteries on the reserved sections and running off the wires in places like Barking town centre. As it is, with money tight and this not yet being a cheap solution – remember those batteries are still extremely expensive – it is difficult to see how this would be attractive to TfL or the mayor.

The Induction Charged Bus

Finally we come to what many see as the most promising development yet for the future bus. Whilst it is recognised that the battery-powered bus is considered the ultimate goal, currently a requirement for a battery to power a bus all day is just not practical for various reasons, the most significant of which is the current cost of the batteries.

Electric Bus MKElectric inductively rechargeable bus in Milton Keynes. Note that lack of space on the low floor bus means that one of the three batteries is on the roof. Although clearly not in public service on this occasion, one route is normally entirely operated by eight of these buses.

It is long been recognised that if, by some means, one could recharge the bus either by small but frequent recharges at busy stops or a bigger recharge at the terminus stand then one could ensure that the drain on the battery was more gradual. The goal would be to keep the battery sufficiently charged so that it could run all day without the battery getting depleted to the extent that the life of the battery was reduced. An electric bus is typically recharged at around 20kW and it needs six to eight hours overnight to fully recharge it. Clearly, even ignoring all the Health & Safety implications, the idea of plugging in a bus to a conventional recharging point at the terminus wasn’t really going to be very practical as the benefit would either be tiny or the time required to recharge would make the bus very unproductive.

The perceived solution to the recharging problem on buses is the induction recharger. Think of a wireless recharger for an iPhone but on a much larger scale. A coil in the road rapidly creates a magnetic field and then collapses it. Meanwhile a similarly size coil on the bus takes advantage of this to create electricity to recharge the batteries. The technology isn’t really new. It is basically what happens in a traditional transformer except that the coils are intertwined for maximum efficiency. By separating the coils there is energy loss – but not that much providing the coils are close together. Clearly, getting the coils close together is not a major problem if designing an iPhone recharger but a bit more difficult if designing a bus recharger.

recharging plateAt the time of taking this photo this must have been the most photographed bus stop in the world. The charging plate is quite substantial but there is little to show for it at the bus stop itself

One might have intuitively thought that an induction recharger for a bus just would not be practical given that it takes six to eight hours to fully charge a battery bus. Here the advantage of an induction charger comes in. Instead of charging at 20kW it potentially recharges at 120kW. Or to put in in simple terms, if one ignores energy transmission losses, ten minutes charging at the bus stand is equivalent to an hour’s recharge at the bus garage. In
the induction chargers recharge at 200kW.

There are energy losses in induction recharging but these are reported to be well under 10%. Unfortunately this is actually more of a problem than might initially be thought. The energy lost is given out as heat and though it is small in as a proportion of the total it still amounts to a few kilowatts, which means that cooling has to be built in to the charger so that it is dissipated. Of course, if an induction charger is only used for a short time, such as at an intermediate bus stop, one may be able to avoid the need to provide cooling but then one has a big investment for a very short period of use.

Roadside cabinetsRoadside cabinets for recharging plate

Induction charged buses are certainly not new but most implementations so far have been fairly experimental. South Korea even does induction recharging on the move but it is notable that reports indicate that they only have two buses.

Of far more interest to us is a route in Milton Keynes that is running today with induction recharged buses. It shows that it does work but it also shows that there are potential problems that might not be such an issue in Milton Keynes but may be more of one in London.

Space is needed for the batteries and that is not easy to find in a bus. In Milton Keynes, with its single door single decker buses, two of them can be hidden under a step leading to the rear of the bus, but such a solution would probably not work well in London with the vast majority of routes operated by buses with separate entrances and exits. Worse still, in Milton Keynes they have resorted to putting a third battery on the roof. Judging by the pictures it looks as if the same is the case in South Korea. The unsatisfactory situation probably comes about because they are adapting a bus chassis and body for use as induction recharged bus rather than going to considerable expense of designing a few buses for what is still only a long-term trial.

Positioning markersPositioning markers on the bus door and the kerb to enable the driver to position the bus accurately over the recharging plate. Crude but effective.

A lesser issue with induction charging is that one has to position the bus pretty accurately over the recharger. This means that one has to select where this is done quite carefully so that the bus can be parked exactly where it is required (and not blocked by conventional buses for example) and it can stand there for around ten minutes. The latter condition would mean that somewhere like Victoria bus station, where buses pull forward as the one in front leaves, would not be ideal even if it was equipped with multiple chargers. There is also the issue that one needs somewhere to install the roadside cabinets associated with recharging.

bus rechargingThe collector plate on the bus is lowered so that the batteries can be recharged.

One To Look Out For?

As this video makes clear, induction rechargeable buses are still experimental and need to be fully evaluated. Despite that, the physics behind it is sound and with the expected future developments in battery technology it is hard to see how they will not be at least one of the potential candidates for the London bus of the future. It is not a foregone conclusion though and, apart from not yet being a mature technology, there is the problem that all the development so far has been on single deckers. The main reason TfL would want to look at this would probably be because of air quality targets. This would mean buses in central London. As it is highly unlikely any future mayor would endorse a return to bendy-buses this would mean double deckers. This would be in contrast to the bus manufacturers and other interested parties who would probably be more cautious and initially develop the technology using single decked vehicles.

As this presentation shows, London Buses are taking emission reduction extremely seriously and are already intending to trial induction charging. If TfL went down the induction charging route they would probably want to use this technology on double deck buses. The problem would be that in all probability there is no suitable double decker in existence. A new bus would have to be designed from scratch in order to accommodate suitable space for batteries and one wonders if any manufacturer would take the risk on their own given the limited guaranteed market. So it could be a case, yet again, of TfL specifying their own requirements and not buying off-the-peg buses. That means they would also have to deal with the bad publicity of all the failures and design issues encountered in a product that was pushing the limits of current technology. And, if the induction recharged double decker bus became a reality in central London in a few years time, one then asks what would happen to those iconic New Routemasters?

Thanks to London Transport Museum for permission to use the photograph of the Mile End tram change pit.

Written by Pedantic of Purley