BEIJING (Reuters) - It's been billed as the "Green Olympics," but do the showpiece venues that will host the Games' key events live up to the theme?
The record is mixed, experts say, with the best venues for the Beijing Games setting a standard for energy-efficient building while others betray the promise of environmental sustainability.
In the end, much was left to the developers, with few mandatory guidelines set by Olympic organizers, meaning they had little leverage to impose consistent standards.
"The intention is always positive, but if you don't give people some mandatory parameters on which they have to work, then you allow them to make shortcuts," said Theodore Oben, head of the sport and environment programme at the United Nations Environment Programme.
"A lot of the building and facilities are developed by contractors ... If the parameters are not mandatory, then the contractors will have either to do as much as you want or more, or they may make shortcuts if they want to save money," he said.
The National Stadium, known as the "Bird's Nest" for its latticework of interwoven steel, and the National Aquatics Centre, or "Water Cube," the rectangular swimming venue that sits by its side, are considered among the world's most architecturally adventurous new buildings.
But are they the most green?
"It's an iconic structure, but a green building it ain't," Robert Watson, CEO of green building consultancy EcoTech International, said of the Bird's Nest.
The stadium features non-flush toilets equipped with sewage treatment systems, a rooftop photovoltaic system with a capacity to generate 130 kilowatts of power, and facilities to collect 58,000 cubic meters of rainwater annually.
But to Watson the structure itself, which used some 42,000 tonnes of steel, is the problem.
"The fact that it uses 10 times the materials of a normal stadium, any green virtue is inundated by that," he said.
"Ninety percent of the structure does nothing but hold itself up," said Watson, who founded the Leadership in Energy and Environmental Design (LEED) rating system for green buildings.
Experts say the Water Cube fared better.
The $143 million venue's playful facade, which evokes giant soap bubbles, is made of ETFE, a durable plastic that allows natural light into the building and is a better insulator than glass.
"It's super lightweight, so it allows us to cut a lot of the structural load out of the building as a result," said Haico Schepers, leader of the sustainable buildings group at Arup, the engineering firm that was a partner in the Cube's design.
The daylight that the material conducts into the building is also harnessed to heat the swimming pool, reducing the pool enclosure's energy consumption by 30 percent.
Part of the building's success, said Schepers, was that its green aspects were not afterthoughts, but integrated into the design.
"What we tend to find with sustainability is if you make it an add-on item, there's a large risk it gets costed out through the process," he said.
Premier Wen Jiabao himself has urged energy efficiency in the Olympics venues as environmental sustainability becomes a theme of China's leadership, keen to ward off civil discontent sparked by widespread degradation.
"There will be no talk of extravagance or ostentation in organizing the Olypmic Games. We should save every drop of water and every unit of electricity in the construction of the Olympic venues," local media quoted Wen as saying last year.
For its part, Beijing's organizing committee has stressed the environmental aspects of the Olympic village, which include solar heating to supply hot water to its more than 16,000 residents, a rainwater collection system and a heating and cooling system that will cut electricity by 40 percent by using recycled water.
But experts say there have also been near-misses and lost opportunities.
One of the buildings where Chinese athletes are training was built with timber from an uncertified source -- meaning it could have come from protected forests -- because Beijing's organizing committee had little control over the contractor, Oben said.
The design for the basketball venue initially included giant LED screens on each side, a plan Watson said would have used as much energy in one project as several thousand Chinese families.
Still, despite some missed opportunities, environmentalists hope where things went well they will provide a template for what rapidly growing China could do in future.
"I think the ability to point at some of the innovations in these facilities, or the mistakes, will have some impact down the road," said Watson.
"Certainly the best buildings in China are equivalent to the best buildings anywhere."
Editing by Jerry Norton