Pushing at the Boundaries of Solar Power Proves Illuminating for London’s Bus Users

October 21, 2005
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By 2010, 7,000 bus stop flags and timetable cases across the capital will be lit by the rays of the sun, whilst many other conventional shelters will be lit far more efficiently. Robin Bennett spoke to London Buses’ Ivan Bennett (no relation) on the results of the in-depth research conducted in the capital to make this rollout possible

If waiting passengers at some of London’s darkest bus stops think they have cause to be grateful from the spread of solar technology to light up their journey, they should also think themselves lucky that they don’t have to do a bit of hard labour to make it possible. When London Buses commissioned a product design consultancy to investigate all manner of alternative technologies for lighting up its stops, one of the suggestions – aside from windmills and piezo-electric strips in the road activated by passing buses – was an adaptation of clockwork radio technology. Passengers would have to wind up the stop in order to produce sufficient energy to light the flag and timetable display until the bus came.

“It would have been fun for a few days, but they would soon have got tired of it,” reflects London Buses’ research and development manager Ivan Bennett, who has been involved with the project for the past five years. Amongst some weird and wonderful power sources, however, solar power soon stood out as offering the best opportunities, despite limitations on the area available for the panels, and the fact that none of London’s 17,500 stops face south at a 70-degree angle.

The quest for sustainable stop lighting goes back to the mid-nineties when all the capital’s bus stop flags were being replaced. In Kingston town centre, a year-long trial saw 30 stop flags and timetable cases lit by mains power. Although it proved popular, the fact that on average one bus stop in the capital is lost each day due to a road accident, having a mains power supply was seen as a logistical and a safety problem. In addition, the electricity providers were not terribly keen on going out of their way for such a small project. Although each stop used only £2.75 worth of electricity each year, the £28 standing charge per stop made the cost unsustainable.

So the idea was put to one side, only to be dusted off and examined again in 2000. Just what viable, sustainable alternative power options were there?

“The heart of the matter is the use of energy to illuminate the timetable and sign face,” says Bennett. “This gives passengers the reassurance that the bus driver can see their stop, which is often difficult in a yellow sodium environment.

“Yellow sodium is designed for road traffic users, to reduce glare for drivers, but doesn’t help pedestrians. The clarity of graphics is compromised, and our red and white bus stop logo becomes brown and yellow, and disappears against harsh retail lights in town centres.”

What London Buses was looking for was not to maximise brightness, but to have sufficient light to correct this contrast from the stop’s surroundings. This would also aid partially-sighted bus users and help promote the expanding night bus network.
“We didn’t need a huge amount of light, as the streets are never black. You can see your hand in front of you, you just can’t read something very well,” says Bennett.

London Buses was convinced that solar power could be harnessed to produce the lighting required, and found that although there were stops in underpasses, under bridges and alongside south-facing elevations that would never be converted, these were few in number. A number of trial stops were built in 2001, to compare different solar products over a 10-month period and to give reassurance over its suitability.

The trials proved the solar photo-voltaic system, and comparison of different types of crystal management proved that mono-
timetable display was more stable. “Amorphous thin film works, but you need twice as much area, and the panels need to be twice the size,” Bennett points out. “This product is also only available from one supplier which caused us concern.”

He would dearly loved to have used electro-luminescence solar technology, used in fighter planes and other military hardware, but which requires more energy to run. “It can also take a kicking on a Friday night,” he adds. “You can even slash the material with a knife and it will still work.” The energy was used to internally illuminate the roundel on the existing vitreous enamel bus stop flags and to power a 12mm-thick backlit panel which fitted within existing timetable cases. The canopy design for the solar panels is integral to the bus stop and designed to minimise complaints over aesthetics. The process is aided by the fact that illumination of transport displays is permissible within planning acts without need for separate consent, unlike commercial advertising.

London Buses now uses backlit film, similar to that used for high value retail shop displays, rather than encapsulated paper for printed information in its 28,000 cases, due to the fact that it works better with the backlighting, but also that it is now cheaper and is being used at all locations regardless of their power source.

Now that the light source had been identified, a 48-stop trial in Sutton began in 2002. Stops on poorly-lit roads and at sites prone to vandalism were deliberately chosen to put the technology through its paces.

900 questionnaires were issued, and included bus drivers along the chosen routes. The feedback was extremely positive, and referred to the “reassuring pool of light” at the stop. Of the users surveyed, 38% said they would consider travelling by bus at night solely because of this improvement. The light units attracted little vandalism even at the most notorious locations.

“There were some sites where we were going to struggle in midwinter,” says Bennett, and the system did have to prove itself in snow, a rare event in the capital. The core element of the technology being tested was each stop’s energy management system, which is essentially a self-learning piece of software. “The stop looks at how much power has come in during the day then thinks, last night I gave out so much light, so what can I do tonight?” he explains.

“It may even think to itself that I’ve had such a terrible day, I am only going to illuminate the timetable case button and flag, although there is always a glow for the timetable display.” In extreme midwinter conditions it could decide to switch the flag off, but even if the timetable display is not lit, passengers have the option of getting 20 seconds of light by pressing the button. Some power is always held in reserve, and the system could sustain itself on minimum settings for five days if need be.

The positive outcomes led to a business case submission for just under £8m of funding to convert 7,000 stops across the capital over the next five years, which was approved earlier this year. These will be concentrated in outer London, away from the distractions of retail frontage lights, although there will be some in the centre. “In busier areas, buses are more frequent anyway so the benefits are reduced,” says Bennett. The work is being done as an alteration to Trueform’s contract to supply bus stops for London, and it has teamed up with Canadian solar expert Carmanah.

A spin-off from the project has been the use of solar technology to light bus shelters. “Shelters were almost a coincidence when we got reassurance about the technology,” admits Bennett.

Five per cent of London’s 11,500 shelters are unlit, although the vast majority have mains power sources that could be tapped into. As with the stops themselves, the challenge has been to incorporate the batteries and solar panels – supplied by SolarCenrury – into the shelter without having inefficient and large battery cabinets and unwieldy panels. However, although the panels have to lie flat on top of the shelter, the energy deficiency from not pointing directly at the sun has proved to be marginal.

Trials between Enfield and Potter’s Bar, and in Eaton Square in central London, proved successful, such that 320 such shelters are now in operation across the capital and, Bennett says, are seen very much as a regular product solution. “They’re nothing special now,” he admits.

As well as stops in dark streets, many shelters could not be economically connected to the mains power supply, and so solar is seen as the obvious solution. Two shelters on Waterloo Bridge, now solar-powered, would have cost £36,000 to connect to the mains, and off-bus ticket machines at the stop are also now powered thus. Meanwhile, a shelter outside St Mary’s Hospital at Paddington is also a prime contender for solar panels – to connect it to the mains would have meant shutting the A&E department for two days, reveals Bennett.

Although he admits that there are greater business benefits from mains-powered shelters – able to support real time displays, CCTV, ticket machines and help points -there is also room for a reliable, sustainable source of power. “We’ve crossed off ticket machines already with solar,” says Bennett, “but we don’t have enough power to light poster adverts – yet.”

The experience has also given London Buses useful experience in managing lighting at its conventional shelters – the use of LEDs instead of one central light fitting has halved the energy required, often with a bigger pool of light as well. In renegotiating its advertising shelters contract with Adshel, all shelters are now being modified to make their lighting more reliable and cost effective.

Bennett is justifiably proud of the work that London Buses has done in pushing the boundaries of solar technology. So what’s his advice to other authorities thinking of following his lead? “Get competitive quotes and keep your options open,” he says, adding that those same local authorities must not neglect their responsibilities in pruning adjacent trees to make sure the sun’s rays still make it through.