Energy costs are rising and leaps in technology make renewable power a natural choice for reduction of bills and carbon. Yes, the number of both domestic and commercial projects has increased dramatically, but speaking as a Londoner, there still aren't many innovative solar PV systems in our cities that people can recognise.

Until now

In the centre of London, crossing the Thames between St Pauls and the Southbank, 6000 square metres of photovoltaic panels are being deployed in the city's largest PV installation.

The project will make Blackfriars Bridge (built in 1869) the world's largest solar bridge, a modernised Victorian landmark capable of an annual output of 900,000 kWh, which will cover about 50% of Blackfriars station's overall power requirement. Its solar panels will save 511 tonnes of CO2, and reduce Network Rail's annual energy bill by somewhere between a princely sum and a king's ransom.

NB: The overall cost of the Blackfriars redesign is estimated at around £550 million but buying and installing the PV panels probably cost more like £7-10m. I haven't found any public information on the estimated payback period for this scale of commercial installation. Domestic solar usually doubles your money over 20 years, but commercial systems vary for a number of reasons.

In addition to the carbon reduction, other energy saving measures are being introduced, such as rain harvesting and sun pipes to let in natural lighting.

As well as generating energy and cutting carbon emissions, Blackfriars' makeover has seen its platforms being lengthened to accommodate 12 carriage trains to increase capacity on peak journeys coming into London.

All this improvement work is part of two simultaneous objectives: the Thameslink Programme, a £5.5bn investment on journeys travelling through London in a North-South direction, and Network Rail's target of 25% less carbon by 2020.

The Construction Stage

Work began in Spring 2009 when Blackfriars underground station was closed until Autumn 2011, when a Southern entrance was added, and the 12 carriage trains were able to make their first inbound trips. While these longer overground trains were ferrying commuters in and out of the station the bridge was being reinforced and widened, without any disruption to service.

As of now - July 2012 - the solar panelling is about half-way complete, and is being installed over the top of the live railway. Conditions haven't been perfect: the PV installers have had to endure the wettest 3 months on record.

The PV work's been carried out by Solarcentury, often described as the UK's leading solar company. Solarcentury was founded by industry figurehead Jeremy Leggett along with Solar Aid - a fantastic charity that replaces kerosene lamps in Africa with solar.

Frans van den Heuve, Solarcentury CEO described the Blackfriars PV project as "one of the world's great solar-power installations. Architecturally challenging, the project demonstrates just what is possible with this versatile technology in dense urban areas.

We've been working among one of the most complex building programmes in the country, at height, over water and live train lines. It's a great feeling to be halfway there."

The Verdict

Feedback from the public has mostly been encouraging, and positive about the ambitious new design of the solar roof and wider platforms. A glance at the Guardian comments section shows people want more projects of this nature, that generate rather than devour energy, and that are designed for the benefit of the people. UnShardlike projects, in other words, such as PV systems on supermarket roofs.

And there should be appreciation of the fact that Blackfriars Bridge was widened by 9 metres while trains were still running along the track, especially during a time of infrastructural inconveniences (Tottenham Court Road station, anyone?).

The logistics and solar aspects of the Blackfriars project speak for themselves, which is why they haven't really been criticised. And next to the great Olympic transport disaster that's surely approaching, the redesign of Blackfriars will look seamless.

However there have been a few words of disappointment about the facade of the building from architectural critics, because the original architects Pascall & Watson (who redesigned St. Pancas so beautifully) were replaced by utilitarian construction company Jacobs. The criticism is that this is typical interference by politicians with architectural vision: London's appearance being decided by people who have no taste!

Another sunrise please

But from a solar point of view, and personally speaking, so far Blackfriars is a success story. Most new builds are low-carbon, but this is retrofit, something Britain needs to be much better at if we're to reach our ambitious carbon targets. And, after the feed-in tariff issues that shredded our solar PV industry, solar needs some good news. If only domestic solar would get another high profile push like this!