绿色PPP项目组合的最优契约:经济与环境效应的福利视角

绿色PPP搭配高收益项目的激励方式是吸引社会资本参与环境治理的举措之一。本文基于经济与环境的双重福利效应,从理论上研究了该激励方式的契约设计问题,阐释了博弈均衡的存在性以及最优特许期的形成逻辑和关键决定因素。研究表明:第一,绿色PPP搭配高收益项目能够提高企业利润,激发社会资本参与环境治理来应对环境风险。第二,政企双方博弈决策模式决定了契约能否订立。如果独立决策,使企业利润最大的特许期也能够带来最高的环境效益,但此时博弈结果展现为“刀刃上的均衡”,契约难以建立;如果合作博弈,双方最优特许期选择达成一致,契约得以订立,政府向企业让渡经济利润而收获环境效益,最终实现经济与环境福利的双赢。第三,绿色PPP搭配高收益项目优于传统政府补贴的激励方式,在收获同等环境效益的基础上,能够带动社会总福利的提升。研究结论为绿色PPP搭配高收益项目激励方式的推广实施、从而助力实现碳达峰和碳中和战略目标提供了契约设计理论依据和相关框架。

The Optimal Contract for Green PPP Project Portfolios: A Welfare Perspective for Economic and Environmental Effects

Green finance serves green investment, which serves the green economy. In practice, there is a huge demand for funds to develop green finance and promote environmental protection. In addition, it is unsustainable to rely solely on government financial support. Therefore, an important solution for this problem is public-private partnerships (PPP), in which the government and enterprises work together. However, enterprises are not enthusiastic participants of pollution prevention, green, and low-carbon PPP projects because they generally experience problems such as high investment thresholds, competition homogeneity, and high market risk.
Although the direction of the new incentive method is clear, relying only on the traditional PPP contract framework is insufficient to manage the complex problems that arise when managing project portfolios. Thus, the contract model for traditional single-commercial PPP projects cannot be directly adopted. The key issues involved in the green PPP project portfolio are as follows: What elements must be considered when concluding the contract？ What coordination mechanism must be selected to ensure that the contract is signed？ Is there an optimal concession period for green PPP projects？ Is the green PPP project portfolio better than the traditional incentive mechanisms of direct government subsidies？ Exploring these issues will provide a good theoretical basis and technical support for the promotion and implementation of the combination of green PPP and high-yield projects.
This paper uses the net present value method to propose a decision-making model for the optimal concession period of green PPP project portfolios based on the win-win goal of economic and environmental benefits. Our model differs from those of the literature in three dimensions. First, we introduce environmental benefits and extend the optimal concession period model for a single PPP project to the green PPP project portfolio. The goals of combining green PPP and high-yield projects include social welfare, environmental benefits, consumer surplus, and economic profits of enterprises and the government. Second, we compare the different game modes between the government and the enterprises, demonstrate the existence of an equilibrium, reveal the internal logic and key determinants of the optimal concession period, and provide a basic framework for the contract design of the green PPP project portfolio. Third, through a scenario analysis, we show the superiority of the green PPP project portfolio over the traditional incentive mechanism of direct government subsidies. The results provide theoretical support for promoting the combination of green PPP and high-yield projects.
We obtain three important results. First, the combination of green PPP and high-yield projects can improve enterprise profits and stimulate social capital to participate in environmental governance and deal with environmental risks. Second, whether the government-enterprise contract can be signed successfully depends on the game decision-making mode. If the decision is made independently, although the concession period that maximizes enterprise profits can also achieve the highest environmental benefits, the game results are shown as “equilibrium on the edge” and it is difficult for both parties to enter into a contract. Therefore, it is necessary to study the behavioral restraint mechanism to promote coordination and cooperation between the government and enterprises. PPP stakeholders can then decide from a global optimal perspective and achieve a win-win situation of mutual economic profit and environmental protection. Third, compared with direct government subsidies, the combination of green PPP and high-yield projects not only increases consumer surplus and improves social welfare, but also copes better with the fisical burden. Therefore, policy guidance could be strengthened to manage the reasonable bundling of projects with strong correlation, upstream and downstream links, or adjacent sub-projects. Some direct government subsidies will gradually be replaced by the combination of green PPP and high-yield projects. The diversified funds can then be used to provide continuous support for environmental protection, achieve the goals of emission peak and carbon neutrality, and better serve the green economy and sustainable development.