Since most clean-energy projects have a payback period of more than five years, the system thus fails to encourage green investment.

既然大多数清洁能源项目的效益回报期都在5年以上，那么“配额-贸易”制度并不能鼓励环保投资。

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The website lists rebates and other subsidies that help to defray installation costs and provides a calculator for figuring out the cost of electricity, the payback period and the return on the investment from installing small wind turbines, which refer to those that are under 100-kilowatt in size and engineered for residential and business properties, including farms and government agencies.

FORBES: A Web Tool For All You Need To Know About Small Wind Energy

Since most clean-energy projects have a payback period of more than five years, the system thus fails to encourage green investment.

ECONOMIST: Climate change