Table of Contents:
Sustainable development has been defined as “.. development that meets the needs of the present without compromising the ability of future generations to meet their own needs” (WCED, 1987). In the process of transition from a fossil fuel to a renewable energy system, it is very important to ensure that the future renewable energy system will be sustainable, considering both economic, social and environmental sustainability. The sustainability issue is of particular importance for hydropower, since it depends on and can have significant impact on an equally important resource: Water.
Besides economic sustainability, which always will have high priority, other important aspects to be assessed, evaluated and documented in a sustainability analysis are as follows:
Hydropower has many advantages compared to other sources of electrical energy, especially compared to those based on fossil fuels: it is renewable, clean, largely carbon-free and well suited for integration into the grid, often supporting the stability of the grid. But hydropower can also have negative impacts, especially on the local level, where dams and reservoirs, weirs, diversions and changes in river flow may disturb ecosystems and create problems.
Hydropower schemes will often modify the flow regime in rivers and the water levels regime in lakes and reservoirs and can, therefore, have negative consequences for ecosystems and biodiversity. RoR projects usually do not change the flow regime, while storage hydro projects typically lead to changes in the seasonal flow regime, for example by decreasing spring and summer flows and increasing winter flows in Nordic rivers.
The natural transport of sediments may also be altered, creating problems both in the reservoir and intake pond where sediments are deposited, and downstream of dams where reduced sediment concentrations may lead to increased bank and riverbed erosion, and decreased stability.
Table 4. Median life-cycle carbon equivalent intensity (IHA, 2018B).
The energy payback ratio (EPR) is the ratio of total energy produced during a system’s normal lifespan to the energy required to build, maintain and fuel that system. Other metrics that refer to the same basic calculation include the energy returned on energy invested (EROI). A high EPR indicates good performance. Lifecycle energy payback ratios for hydropower plants reach the highest values of all energy technologies, ranging from 170 to 267 for ran-of-river, and from 205 to 280 for reservoirs (IPCC, 2011).
A few observations of high greenhouse gas (GHG) emissions from tropical hydropower reservoirs has been raising doubt about the low GHG emission levels for hydropower, but it is still not clear if these observations represent a net emission or emissions that occur naturally, for example from a wetland (Prairie et al., 2018).
The comparison of typical carbon emission caused by various electricity production sources is shown in Table 4. One can see that the life-cycle emission of hydropower is very low compared to fossil fuel-based sources, lower than for Solar PV and in the same range as nuclear and wind power.
In order to assess the long-term sustainability of hydropower projects, it is necessary to assess all relevant social, economic and environmental consequences of the project. Sustainability issues are becoming increasingly important for hydropower developers, and the International Hydropower Association (IHA) has, therefore, developed the Hydropower Sustainability Assessment Protocol, containing tools to guide in planning, implementation and operation of hydropower projects (IHA, 2019). The protocol includes between 19 and 23 relevant sustainability topics, depending on the development stage of the project. It is the result of a long process involving many different stakeholders: Social and environmental NGO's, governments, commercial organizations, development banks and the hydropower sector. Some of the topics included are biodiversity, indigenous people, infrastructure safety, resettlement, water quality, erosion and sedimentation and downstream flow regimes. Hie tools can be downloaded from IHA web pages (IHA, 2019).
Integration into Water Management System
Water, energy and food production are closely linked. On the one hand, water availability is crucial for many energy technologies, including hydropower and cooling water for thermal power plants, and on the other hand, energy is needed to secure water supply for agriculture, industries and households, particularly in water-scarce areas. This mutual dependence, the ‘water-energy-food nexus’, has led to the understanding that water, energy and food production must be addressed in a holistic way, also considering impacts of climate change and project sustainability. The challenge to provide energy, water and food for an increasing population in a sustainable way, will require improved regional and global water governance.
Since hydropower projects often include large water storage facilities (reservoirs), hydropower can play an important role in providing both energy, water and food security (Killingtveit, 2014: IEA Hydropower, 2018). Out of 45000 large dams and water reservoirs in the world, about 11000 (25%) har e hydropower capacity. Therefore, hydropower development is often also part of water management systems, as much as energy management systems, both of which are increasingly becoming climate driven.
Water management sen-ices consists of both qualitative and quantitative functions, such as:
Integration into Broader Power System
In addition to providing capacity to meet electricity demand, hydropower has several characteristics that enable it to provide other important sen-ices to make power systems operation more reliable:
The ability to rapidly change output in response to system needs without suffering large decreases in efficiency, makes hydropower plants well suited to providing the balancing sendees called regulation and load-following. The almost instantaneous regulating of production of electricity from hydro generators make hydropower very cost-attractive for balancing purposes (IEA Hydropower, 2018).
The need for balancing arises from the time lag between planning the production and the actual consumption. Demand may be stochastic due to the influence of varying weather, and there may also be stochastic events on the producer and transmission side, like accidents within generators and transformers, mishaps on the transmission lines and other disturbances.
Because the physical balance between supply and demand must be continuous, access to regulating supply up or down is essential if short-term physical restriction of demand or blackout is to be avoided. It is believed that the introduction of more intermittent energy will increase the profitability of hydro in the balancing market (EASE EERA, 2018; IEA, 2014).
Today's electricity system is changing rapidly, creating new opportunities for hydropower to contribute to system resilience, reliability, and affordability. Therefore, interest in PSH is increasing, particularly in regions where solar PV and wind power are reaching high levels of penetration or are growing rapidly. PSH is among the most efficient and flexible large-scale means of storing energy available today. It is highly cost-effective when compared with other sources of energy storage, like a battery, on life cycle basis (Krueger et al., 2018). It allows not only the production of electric energy, as hydr opower plants do. but also the storage of energy in the form of the gravitational potential energy of the water. During periods with high demand or high energy prices, the water, stored in an upper reservoir, is released through turbines to a lower reservoir in order to produce electricity. During periods with low demand or energy prices, the water is pumped back from the lower reservoir to the upper reservoir in order to store it. PSH technology can ramp up to frill production capacity within minutes, providing a quick response for peak-load energy supply and making it a useful tool for many grid sendees (EASE/ EERA, 2018; IEA, 2014):
The majority of existing pumped storage capacity, 176 GW, is found in Europe, Japan and the United States of America. According to data from IHA, this is expected to increase rapidly in the future. There are now more than 100 projects in the pipeline around the world, totaling 75 GW of new capacity. This is expected to increase the world total PSH capacity to 250 GW. The majority of the new projects will be operational by 2030 (IELA, 2018A).
Future Deployment of Hydropower
The transition from a fossil (carbon-based) electricity system to a renewable system has high political priority, and all possible renewable sources needs to be developed. So far. hydropower, wind power and solar PY have given the largest contribution to a “greener” power system. Also, in the future, these three seem to have to take the lion’s share in the process. Hydropower will have a special role, as the only renewable technology (beside bioeuergy) that can provide energy storage and dispatchable power. Increasing the share of wind and solar power is expected to increase the demand for such services from hydropower.
Based on information about hydropower potential (Table 3) and what has already been developed (Table 1), it is possible to get an estimate of remaining resources. This information is summarized in Table 5 for six main regions and globally. As seen in the table, the remaining economically feasible potential is still well above 5000 TWh. Not all of this will be possible to develop, mainly due to social and environmental restrictions, but the figure still shows a large potential for further development, much more than what has already been developed. Furthermore, if the cost limit is increased, we can see that the technically feasible resources are very large, up to nearly 12000 TWh or 2.5 times the existing development.
Looking at the different regions, one can see that, for economically feasible projects, there are three distinct classes: Europe and North America both have about 30% left to develop, Africa over 90% and the rest of the world around 55-60%.
Considering hydropower’s moderate cost, long lifetime, high energy payback ratio, low GHG emissions and important energy management sendees, combined with manageable social and
Table 5. Remaining (undeveloped) hydropower resources by 2016.
Figure 10. Annual hydroelectncity generation till 2050 in the Hydropower Roadmap vision (IEA, 2012).
environmental impacts, it seems safe to assume that hydropower will continue to be developed up to a level of at least twice the current generation by 2050, possibly before.
One example of projections for future deployment is given in Figure 10. This projection was based on data from 2009, and has been surprisingly good up to 2018, though slightly too low.