Not sure if this is what you are looking for? Here are a few competitions from my Great Links page at Hopebuilding wiki. Sorry, but it doesn't seem my links will copy here.
Ashden Awards for Sustainable Energy
An annual competition to identify and reward organisations which have carried out truly excellent, practical, yet innovative schemes, demonstrating sustainable energy in action at a local level, including solar, wind, hydro, biomass, biogas, fuel-efficient stoves, and energy efficiency. Ashden also runs seminars to raise awareness of these technologies and to encourage others to follow. The Awards are transforming the prospects of sustainable energy through substantial cash prizes that help winners advance their work; actively publicizing the work of winners; and bringing winners together with key decision makers to help change thinking and policy among governments and non-governmental agencies. Ashden also carries out research into the potential of local sustainable energy to meet the world's energy needs and tackle climate change, including ways of overcoming barriers to its adoption.
Goldman Environmental Prize
Created in 1990 by San Francisco civic leaders and philanthropists Richard N. and Rhoda H. Goldman, the Prize is awarded annually to honour grassroots environmental heroes from the six inhabited continental regions: Africa, Asia, Europe, Islands and Island Nations, North America, and South and Central America - individuals who make sustained and significant efforts to protect and enhance the natural environment, often at great personal risk. Each winner receives an award of $150,000, the largest award in the world for grassroots environmentalists. Through recognizing these individual leaders, the Prize seeks to inspire other ordinary people to take extraordinary actions to protect the natural world. The work of Goldman Prize winners often focuses on protecting endangered ecosystems and species, combating destructive development projects, promoting sustainability, influencing environmental policies and striving for environmental justice.
The St. Andrews Prize for the Environment
The prize is an initiative by the University of St Andrews in Scotland and the international integrated energy company, Conoco Phillips, launched in 1998, that attracts entries from all over the world. Winning ideas have included: an Indian proposal to train ‘barefoot engineers’ to install and maintain solar power equipment in remote Himalayan villages; encouraging North Vietnamese rice farmers to stop spraying harmful insecticides; and using song, dance and drama to make rural communities in Kenya more aware of environmental problems affecting Lake Victoria. Several winners and runners-up have secured funding for the projects as a result of their initial success at St Andrews: a South African project about environmental degradation caused by mining has now become a community-based rehabilitation project supported by local government and the mining industry, and a project to turn olive oil production waste into valuable by-products received grant aid from a Middle East bank. Submissions are assessed by a panel of eminent trustees representing science, industry and government with the award going to the project the Trustees consider displays the best combination of good science, economic realism and political acceptability.
Environment Program Sasakawa Awards
The $200,000 UNEP Sasakawa Environment Prize is one of the most prestigious and valuable environmental awards in the world. The 1972 UN Conference on the Human Environment held in Stockholm recommended that such a prize be created. This prize, then known as the Pahlavi Prize, was first awarded in 1976. In 1982, the Japan Shipbuilding Industry Foundation provided UNEP with an endowment of US$1 million to finance the Sasakawa International Environment Prize, which would be administered by UNEP. The UNEP Sasakawa Environment Prize is awarded annually to “individuals who have made outstanding global contributions to the management and protection of the environment". The prize’s value was increased in 1990. For award winners, see here.