The London Olympics is on track to be sustainable but will fall short of its renewable energy targets, the event's sustainability watchdog has reported.
The Commission for a Sustainable London 2012 said carbon emissions from the Games was likely to be reduced by 50%.
However it said only 9% of this would come from renewable energy - falling short of the 20% target.
The Olympic Delivery Authority (ODA) said it had to find other ways to reduce the event's carbon footprint.
New safety rules and design changes led the ODA to abandon plans for a wind turbine at the Olympic Park in east London last year.
Shaun McCarthy, who chairs the sustainability watchdog, said the scrapping of the wind turbine was the main reason why renewable energy targets would not be met.
To achieve the reduction in carbon emissions, the ODA is instead investing more than £1m in measures like insulation and draft-proofing in local houses and schools.
"It is regrettable that the renewable energy industry could not come up with the answers," said Mr McCarthy. "But this is a sensible solution to reduce carbon emissions.
"We are incredibly close to our ultimate goal of a sustainable Games, which would make London 2012 a unique entry in the annals of Olympic and Paralympic history," he added.
The ODA's Richard Jackson said providing renewable energy to the site was a big challenge.
"Beyond the huge sustainability benefits already delivered, we also set ourselves challenging targets on carbon reduction and renewable energy," he said.
"Despite exhaustive efforts we have not been able to find a cost-effective solution to deliver a large percentage of renewable technology on the park."
It is now 15 months until the Games' opening ceremony.
London Assembly Green Party member Darren Johnson criticised the missing of the renewable energy target.
"This really is a miserable result, he said. "I know the organisers have had some difficulties but quite frankly this should never have been allowed to happen.
"It makes a mockery of the idea of a green Olympics," he added.