The world's five coolest solar projects

Solar bridge, Blackfriars station, London

Fitting the 6,000 square metre array over 2012 has been no mean feat - installers Solarcentury had to battle some of the worst weather on record while maintaining the 126 year old bridge.

One other solar bridge is known to exist, the Kurilpa footbridge in Brisbane, Australia, although 16,000 solar panels were laid on the top of a train tunnel in Belgium at the beginning of 2012, generating enough power to run all of the country's trains for one day of the year.

Narmada canal network, Gujarat, India

Building over canals also means land is not lost for agriculture or development, while developers Sun Edison, which funded the £2m project, estimate the cooling effect of the water underneath will boost panel performance by 15 per cent.

Gujarat is already leading India's solar efforts and if the canal network reaches its projected 85,000km length the sky is the limit.

Narmada canal network, Gujarat, India

In April 2012, Gujarat's chief minister Narendra Modi opened what could be the first step in one of the most replicable green energy projects anywhere in the world.

The 1MW solar array near Mehsana, 45km from Ahmedabad, is thought to be the world's first "canal top" installation - and if successful could pave the way for a huge network of similar systems.

It has been built on a stretch of the Narmada canal network, which extends for around 19,000km across the north-western Indian state. Covering just 10 per cent of this distance with solar panels could produce 2.4GW of clean energy each year at a fraction of the current cost, as well as saving two billion litres of water each year currently lost in evaporation.

Solar powered office complex, Dezhou, China

It probably comes as no surprise that China is host to reputedly the largest solar-powered office building in the world.

Known as the Sun-Moon Mansion, this office block located just outside the city of Dezhou in the north-east of the country, was designed to "underline the urgency of seeking renewable energy sources to replace fossil fuels.

Inside the 75,000 square metre sundial-shaped structure are offices, research facilities and even a hotel, all of which run almost entirely on solar power provided by a 5,000 square metre solar panel array.

Solar powered office complex, Dezhou, China

There are other green credentials too - a geothermal system provides hot water, cooling in summer and heating in winter, while an advanced roof and wall insulation systems enables the building to save 30 per cent more energy than the national standard. During construction, the building required only one per cent of the amount of steel used to build the Bird's Nest stadium in Beijing.

But the Mansion is far from a one-off - it is in fact the centre piece of a new industrial zone known as the "Solar Valley" being built in Dezhou in the style of California's famous Silicon Valley. The 330ha site hosts one of the world's largest solar water heaters, solar-powered traffic lights, and also has plans for an enormous spa known as the Solar Egg.

One word: cracking.

Solar bridge, Blackfriars station, London

One of the world's most innovative projects is taking shape right here in the UK - 4,200 panels have been fitted along a new roof of London's remodelled Blackfriars station, which itself has been extended across a Victorian rail bridge spanning the Thames.

When complete, the world's largest solar bridge is expected to generate 900,000 kilowatt hours of electricity, providing up to half of the station's annual energy needs, while saving almost 500 tonnes of CO2 when working in conjunction with other energy saving measures, such as rain harvesting systems and sun pipes for natural lighting.

Crescent Dunes project, Nevada

SolarReserve's flagship development could prove the Holy Grail for solar energy - renewable power without intermittency. And it looks pretty impressive too.

But don't take our word for it. A $737m Federal loan guarantee shows just what high hopes the government has for the 110MW Crescent Dunes plant, currently under construction at Tonopah in the Nevada desert midway between Reno and Las Vegas.

ACS Cobra and Santander have also injected finance into the project, which is estimated to cost in the region of $1bn and supply around 75,000 homes when complete at the end of 2013.

Crescent Dunes project, Nevada

Around 17,500 mirrors focusing the sun's rays onto a receiver sat atop a 200 metre high tower filled with molten salt - thought to be the world's highest.

The salt is pumped up the tower at 260°C (500°F) where it is then heated by the sun to more than 565°C (1,050°F), before being stored in a tank. When needed, the thermal energy is released through a heat exchanger to create steam and power a turbine - meaning the site can continue to produce power in the evening when demand peaks.

But there is more to come. SolarReserve now holds the exclusive worldwide license to commercialise the technology, originally developed by Pratt & Whitney Rocketdyne, the company that lends NASA a helping hand with its rockets.

And, in November 2012, SolarReserve received final Approval for the larger 150MW Crossroads project, set to use the same technology along with 65MW of solar PV panels, which should be up and running at Gila Bend, Arizona, in 2016.

Solar Ark, Gifu, Japan

Sanyo's famous Solar Ark is well worth a mention given the extraordinary story that lies behind it. The Japanese electronics giant intended this remarkable building to be a celebration of its 50th anniversary - but it ended up as an exercise in contrition.

Plans to build a 3.4MW installation - then the world's largest - made up of its best solar technology, a hybrid system of crystal silicon and thin-film amorphous silicon with around 15 per cent efficiency, hit the buffers when Sanyo was forced to recall a raft of monocrystalline cells, the preceding technology, due to lack of output.

Rather than dumping the cells, Sanyo used the recalled cells in the Ark's construction "to show our sincere regret that this problem has occurred and to express our willingness and determination to both remember what happened and how important it is to maintain quality".

Solar Ark, Gifu, Japan

Eventually completed in 2001, the Ark sits next to Sanyo's semi-conductor factory in Gifu and can be seen from the adjacent bullet train.

Its 5,000 solar panels now produce around 530,000kWh per year, while the 315 metre façade is covered in over 75,000 LED lights that are used to show images and messages. Inside the earthquake-proof building is a solar museum and a lab where Sanyo, now part of Panasonic, is working on new solar technology.