Review on the externalities of hydropower: A comparison between large and small hydropower projects in Tibet based on the CO2 equivalent

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Abstract

Both large hydropower projects (LHPs) and small hydropower projects (SHPs) have environmental and societal externalities, which have not been taken into account in their construction costs and operation benefits. These externalities are becoming an increasingly important issue in hydropower development policy making; as a result, it is essential to perform a systematic assessment of them among different hydropower patterns.

The purpose of this paper was to establish a general externalities inventory for hydropower development through reviewing worldwide. This inventory allowed these externalities to be classified into three categories: externalities due to civil works, due to reservoir impoundment and due to cumulative impacts. Meanwhile, as these inventories were all related to greenhouse gas (GHG) activity, they could be transformed into the CO2 equivalent (CO2-e), either directly or indirectly. This transformation method not only enables a feasible comparison of the externalities between different hydropower patterns but also enriches the carbon footprint assessment for hydropower.

In the case study of 5 LHPs (>50 MW) and 10 SHPs in Tibet, China, SHPs have reduced externalities compared to LHPs, with SHPs and LHPs representing a burden of 5.1 and 29.2 gCO2-ekW h−1 on average, respectively. This extra carbon emission burden indicates that the present low-carbon potential of hydropower has been overestimated. Meanwhile, this reduced externality makes SHPs perform better in terms of environmentally friendly development and low-carbon energy than LHPs for Tibet. The externality caused by reservoir impoundment and occupation is the primary component of the total externality of a LHP; therefore, increasing the power density is an efficient way to decrease its externality.

Introduction

Externality is an inefficiency that appears when part of the costs or benefits of an activity are external to the decision maker’s calculations. In other words, part of the benefits shared by or part of the costs threw to those who play no part in the decision [1]. When it comes to hydropower development, the plant construction cost and hydroelectricity benefit, which are imposed on the hydropower enterprise directly, are the main costs and benefits in the general cost–benefit assessment; however, little attention is paid to many of the costs imposed on the environment [2], [3], [4]. To conduct a complete assessment of the externalities, this paper defines which as the costs and benefits that impose a burden on the environment and external community (Fig. 1).

An installed capacity of 10 MW is often set as the demarcation between large hydropower projects (LHPs) and small hydropower projects (SHPs) [5], but different countries set different upper limits to classify hydropower [6]. 50 MW is the latest hydropower classification norm in China [7]. A hydropower project exceeding 50 MW is often involved with a high dam (>30 m) construction to form an artificial reservoir, while hydropower below 50 MW is often in the form of run-of-river or a low dam (weir) with flow diversion [8]. Therefore, this paper adopts 50 MW as the standard by which to differentiate LHPs and SHPs. Both LHPs and SHPs are bracing for a new round of construction as energy demands increase and technologies develop. In this context, the installed capacity of them will also increase. For example, geographic information systems (GIS) and remote sensing (RS) have been introduced into the process of exploring hydropower sites and their maximum hydropower potentials [9], [10]. Generally, LHPs generate greater electrical power than SHPs as a result of its greater installed capacity. However, high dam removal efforts are receiving increasing support from a public concerned with river ecosystem restoration in recent years [11]. In this context, LHPs face significant challenges from issues regarding environmental and societal externalities, which has led to greater appreciation of SHPs [12], [13]. However, SHPs also face many doubts from issues regarding cumulative environmental problems when SHPs are put to widespread use [14].

Because of the issues described above, a comparison of the externalities between LHPs and SHPs is required. Many countries around the world make a high priority in developing hydropower under the increasingly tense circumstances of traditional fossil energies [15], [16], and the low-carbon economy requirement also trigger the development of hydropower [17]. As a result of the different operational approaches, different levels of externalities are embodied in LHPs and SHPs [5]. Therefore, a comparison between the externalities of LHPs and SHPs can clarify which approach contributes more to environmentally friendly hydropower development.

To conduct a quantitative comparison, it is essential to transform the quantification of the different externalities into the same units. Considering that these externalities all directly or indirectly contributed to GHG activity, it is feasible to transform them into CO2-e. For example, hydropower reservoir emits GHG directly via the decay of flooded vegetation, meanwhile, its flood control function can offset some other shadow flood control projects, and then offset GHG emission by shadow project construction indirectly.

Section snippets

Review of the externalities of hydropower

Cascaded hydropower development will cause a one-time impact from each individual hydropower plant and a cumulative impact from the cascaded hydropower plants. The civil works and reservoir impoundment are the two main sources of environmental and societal impact for a single hydropower plant. Therefore, this paper reviewed the inventory of externalities for hydropower by civil works, by reservoir impoundment and by cumulative impacts, and then established a general externalities inventory for

Externalities transformation based on CO2-e

Externalities inventory of hydropower has been established in the form of different dimension, and it is necessary to uniform the different dimension for the comparison. Transforming the externalities into CO2-e activity is a fresh attempt to link the environmental issues and carbon footprint calculation of hydropower. CO2-e activity includes carbon emission, carbon reduction and carbon neutral, which depends on the own features of the impacts. Therefore, the total externalities of hydropower

Study area and data source

As a hydropower reserve base for China, the hydropower theoretical potential and technical potential are 2.01×105 MW and 1.10×105 MW, respectively, in Tibet, ranking them first and second place among the provinces in China, respectively [58]. Tibet is very likely to be the main hydropower development area in China after 2020, and hydropower development in Tibet will contribute to the “west-to-east power transmission” policy and contribute to the achievement of the low-carbon goals in China [59].

Conclusions

Transforming the externalities of hydropower into CO2-e values is a new approach that enables the efficient assessment of the externalities, which allows a feasible overall comparison of different externalities among different hydropower patterns, and proposes a new attempt to perfect the carbon footprint calculation of hydropower.

Low-carbon potential of hydropower has been overestimated when combining with net carbon emission by externality. Externality and carbon activity is intrinsically

Acknowledgement

The work reported in this paper is funded by the National Science & technology Pillar Program, China (no. 2012BAC05B02), the Fund for Innovative Research Group of the National Natural Science Foundation of China (Grant no. 51121003) and the State Environment Protection Commonweal Special Program, China (no. 201209032). The author gratefully acknowledges the funding support.

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