October 3, 2005  -  

You may be in the dark as to when the next bus will come along, but from October stored solar energy will keep London’s bus stops shining through the night.

Some 7000 of the city’s 17,500 bus stops are scheduled to be retrofitted with solar-powered panels over the next five years. The panels will power lights that illuminate the sign, timetable and passenger waiting area.

The scheme will be rolled out in October and by Christmas, London will have the largest network of solar-powered bus stops in the world. But according to Ivan Bennett, head of research and development at Transport for London, this is despite the solar industry’s apathy to the project.

“I was surprised at how backward the industry was in coming forward with solutions when we first approached them,” he says. But the company that did come up with the good, Canadian firm Carmanah Technologies, has been awarded a £1.5M contract, their bigest contract to-date outside North America.

A canopy holds the photovoltaic cells.

Solar bus stops appear to be big business. Carmanah reports Q2 revenues of $6.5M, an 87% increase over Q2 2004.

A 30-watt solar array on top of the canopy (see pic) captures light energy. Two light-emitting diodes under the canopy provide illumination and an energy management system monitors input and output and safeguards the battery, a 96 watt lead-acid Hawker cell battery.

The system is based on Carmanah’s solar-powered marine lights. Marine lights are used to mark hazards and have a range of several miles. “They have to be robust and reliable”, says Bennett, “which is what we need at bus stops in the middle of winter”.

Older photovoltaic (PV) panels would have had to be the size of a filing cabinet to cope with UK weather. The new panels are much smaller and include sufficient by-pass diodes to prevent shading. On small panels, even a leaf could confuse the system into assuming it was dark and switching on the lights.

PVs generate electricity from sun light. Certain materials, in this case silicon, can be adapted to release electrons when they are exposed to light, thereby producing electricity that can be stored in rechargeable batteries for night-time use. The technology contains no moving parts, releases no emissions and is independent of any grid system.