Pumped Hydro-Energy Storage System in Ethiopia: Challenges and Opportunities

The shares of RE sources are rising because of global warming concerns and the depletion of fossil fuels. However, due to its intermittent nature sustainable power supply depends on the proper energy mix and energy storage. By 2025, Ethiopia has planned to export 24 TWh of energy. Accordingly, its power generation is incorporating different RE sources dominated by hydropower. This paper has reviewed the global up-to-date status of PHES and Ethiopia’s current energy situation and potential PHES. The objective of this paper is to show Ethiopia’s potential for PHES and serve as a “Green Battery’’ for the East Africa Power Pool (EAPP). The review shows that PHES can easily replace backup diesel generators used as a backup during a blackout. Moreover, it showed the Policy barrier for energy storage in the Ethiopian National Energy Policy proclaimed in 1994 and its 2012 updated policy. Thus, Ethiopia’s energy policies need to consider PHES in its energy storage strategy while expanding its generation

Nations Economic Commission,2011). Ethiopia is following a green economy strategy and its economy is categorized as one of the fastest economies growing in the world (Seid,2016).
The study by Atems and Hotaling (2018) shows that electricity generation from renewable sources has a positive relationship with economic growth. Accordingly, analyzed the coefficient on renewable electricity generation of Ethiopia by using a two-step System Generalized Methods of Moments (GMM) and found it positive at 0.03. Figure   there is no grid-scale energy storage facility incorporated in this plan to stabilize the grid system to accommodate wind and solar resources into the energy mix. Experience of some countries, like China, had shown about one-fifth excess power of the installed wind power output in the system was curtailed. This was considered as loss of investment and revenue and this loss could be significant if the curtailment is during high wind speed period. Some of this curtailment is due to the lack of pumped-hydro energy storage capacity (PHES) (International Hydropower Association,2017), or any other grid-supported energy storage system.  This implies large scale storage is a need to have stabilized power on the grid system. Thus, using detailed modeling of wind and solar power system to evaluate wind integration issues found that transmission and energy storage can both reduce wind curtailment (Jorgenson, Denholm, and Mai,2018).

The Need for Energy Storage
According to the International Energy Agency (IEA) around 80 GW additional energy storage capacity is needed worldwide by 2030 to meet the Sustainable Development Scenario (SDS) (McLarnon and Cairns,1989).
In the context of Ethiopia, the purpose of this paper is to review the situation of the electric power sector with its abundant but untapped resources and opportunities of PHES. In addition, it identified the barriers that hinder the implementation of PHES from the experience of other countries.
Dawit, A. T., Asfafaw, T. H and Muyiwa, S. A (MEJS)  Ethiopia's blackouts are affecting industrial productivity adversely, from 2011 to 2015 alone, and caused the firm's operating cost to increase by 15% due to expansion of diesel backups (Barrie and Mathews,2010). The challenge to fulfill the optimum power demand and supply is a linear algorithm. Besides, unless consumed, electricity cannot stay on the grid. Figure   5 shows Ethiopia's active load for 24-hourelectricity consumption of May 1 from 2013 to 2016 (Africa, Powering, 2014). As the pattern of the graphs shows the demand is generally low from midnight 24:00 to 06:00 in the morning. Due to combination of many reasons regarding consumption and production, the demand and supply of electricity change frequently and there is a need for a supply and grid system to respond to these changes on time to avoid unnecessary load shedding. The unplanned load shedding could be significant in situations where the generation of electricity is dominated by intermittent renewables and if the grid system is not designed to handle this like the case in Ethiopia. Figure 5 shows that there is a gradual increase in peak load on May 1 from around 1200 MW in 2013 to about 1600 MW in 2016 in the country.

PUMPED HYDRO STORAGE PLANTS
PHES generates power from stored water as a form of potential in the upper reservoir previously pumped from a lower reservoir. The basic principle of PHES is to store water in the form of potential energy in the high-level reservoir (1) (Fig 6) when there is an availability of excess energy generated from any of the renewable sources, typically during off-peak periods, used to pump water from lower reservoir (2). This stored energy be used when there is peak energy demand. The water stored at higher elevation will be released to flow back kicking the turbine and generating electricity (3), and the water be dispatched to the lower reservoir like conventional hydropower. Two basic parameters required as vital resources are the head or elevation and amount of water in the reservoirs.

Global Pumped Hydro Energy Storage Status
Pumped

OPPORTUNITIES FOR PHES IN ETHIOPIA
Ethiopia has the opportunity to develop a large-scale pumped-hydro energy storage system and the largest PHES project in the world at the Danakil Depression. This is on the northern part of the Afar and can generate electricity of nearly 6 TWh. According to the assumption made by (Solomon, 2014) Permitting an extensive 10-meter swing top to bottom between completely charged and completely released states, as it is distinctive dedicated pumped storage reservoirs today. The other assumption is an average depth below sea level of the Danakil Sea of 50 meters, and an average surface area of the lower reservoir that is half the total area of the depression.
Hence, if one meter per day is allowed a maximum swing in the level of the Danakil Sea, corresponding to the typical swing of natural tides, this would imply a daily cycle round-trip capacity of about 600 GW. For 12 hours charging, 12 hours generating, this would mean 46 GW maximum output, 57 GW maximum input, which would be by far the largest pumped storage project in the world (Solomon, 2014). Another opportunity is the low resource risk in Ethiopia than numerous nations in the region. This will ease investment in PHES. Ethiopia has turned into an eager accomplice, offering liberal motivations and supporting the investment with the fast development of pertinent infrastructure. Since 2017, the government has provided an opportunity to invest in the energy market to worldwide investors (Gordon, 2018). ISSN: 2220-184X

Existing Infrastructure
PHES facilities require a relatively small reservoir as related to the conventional hydropower facilities. This is because the required working time of PHES is on average 4 to 20 hours (Antal, 2014). Hence appropriate PHES spots can be identified at some of the seventeen (17) existing and under construction hydropower plants in Ethiopia. And this can be done without affecting the ecosystem and dwellers. In addition, Ethiopia could be a potential for electricity storage, "Green Battery'' of East Africa, with its large potential for electricity storage from hydropower reservoirs. The existing hydropower and the potential of hydropower, PHES can be applied, as a breakthrough for synergies with other water uses, such as freshwater demand from desalination and irrigation (Hülsmann et al., 2007). Besides, it is remarkably less difficult to change the existing conventional hydro reservoir to PHES than constructing a new PHES facility. After analyzing the economic feasibility of an existing hydropower plant, it is possible to transform it into a PHES site that can store energy for weeks and even months .

Wind and Solar power plants
In the past few years development of new power generation from renewable energy sources, especially solar and wind was growing in Ethiopia. This is a due combination of more factors, such as various national incentives and support schemes, climate change, and international commitment to reduce consumption of fossil fuel-based energy resources, as well as energy security and reducing dependence on imported energy resources by net energy importer countries. Ethiopia's wind farms cumulative installed capacity is projected to increase to 5,200 MW by mid-2020. This new development creates a good opportunity for PHES investment (Council of Representatives, 2013).

The Market in the Neighboring Countries
The establishment of the East Africa Power Pool (EAPP) in 2005 by seven nations, Burundi, DRC, Egypt, Ethiopia, Kenya, Rwanda, and Sudan, was a new era for the power-sharing zone.
EAPP has discharged all-inclusive strategies and regional power framework planning and anticipating being completely operational within some time. The EAPP has released master plans and regional power system studies and is projected to be fully operational within several years (Avila et al., 2017). One advantage of the power pool is to accelerate the economic growth of the region by creating a regional network of power-sharing and available resources (Avila et al., 2017). Ethiopia is currently selling power up to 250 MW and 90 MW to Sudan and Djibouti ISSN: 2220-184X respectively and planned to sell up to 2,000 MW power to Kenya by the end of 2019 (Ministry of Water Irrigation and Electricity, 2017). To accomplish these targets, which could bring extra revenue to Ethiopia, reliable energy generation system complimented with a large-scale energy storage system would be essential.

GHG Emission Reduction
For the carbon compelled world, a novel chance to make use of and derive benefits from large intermittent wind and solar resources can be using large storages of PHES to fulfillthe electricity demand (Barnes and Levine,2011

CHALLENGES OF PHES
Although energy storage is one of the important potential areas that could considerably affect global future energy needs, it is one of the challenging research areas (Chu and Majumdar, 2012). The challenges of building new PHES vary from the environmental legislation (Environmental Impact Assessments) to the duration of permitting procedures. According to the United States' National Hydropower Association (NHA,2018), PHES development has some degree of complexity and risk significant regulatory, market and financing hurdles that other energy storage technologies typically do not encounter (NHA, National Hydropower Association, 2018). However, when it comes to the developing countries, the development of PHES has additional barriers, such as lack concrete policy, investment cost and retail price of electricity as well as political uncertainty, which could repelce potential investors. ISSN: 2220-184X

Fixed Electricity Tariff
According to Deane et al. (2010) for a PHES to be economically viable, the price for pumping (or charging) should be at least 25-30% less than the selling price. However, in Ethiopia, where electricity tariff is fixed, irrespective of Time of Use, there is generally no differentiated rate during low or peak demand periods. Hence, the cost of charging the PHES and generating electricity is the same and considering inefficiency in the pumping and generating systems, this would result in economic or financial losses to the operator of PHES in Ethiopia. However, sustainable availability of power is a great concern and this could be solved by integrating large energy storage to the power sector. In this view, PHES becomes a feasible large scale storage technique that is fit to the economic development of the country and will address the tariff based economic feasibility ones Ethiopia become a key player in the east Africa Power Pool.

Financial Constraints
The huge initial financial investment required to develop power plants from renewable energy sources is the major barrier of energy development in Ethiopia like other developing countries.
This is due to the broadly disseminated nature of allocation these resources need more innovation and intellectual property turn out to be more imperative in relative terms than the convection fossil fuel resources. A secondly related constraint would be potential rivalry regarding sustainable power source foundation with the existing well-established infrastructures from fossil fuel. In Africa, acquiring the source of global financing is the principal real hindrance for some renewable energy projects. Reaching a financial close can reach over five years longer for African projects than for their counterparts in more stable investment environments (Gordon, 2018).

Policy Barrier
In Ethiopia, the main energy policy is the National Energy Policy proclaimed in 1994. This

CONCLUDING REMARKS
To satisfy the electricity demands in a stable, reliable and balanced manner, development and implementation of energy storage systems in the country's future energy mix would be crucial.
Therefore, it is imperative to analyze the technical and economic effects of the flexible, renewable power sources on Ethiopia's energy system. With recent innovative and cutting-edge technology development of adjustable speed pump/turbine PHES, which improved their operating efficiency, implementation of PHES would greatly improve electricity supply in the country.
With all the benefits of pumped-hydro power energy storage systems especially to improve quality of power supply, no potential assessment of PHES has made so far to the authors' knowledge in Ethiopia. Unless planned wisely, the desire of the country to have renewable energy-based power system in the future might not be achieved and would likely be replaced with backups mostly diesel generators, as an alternative the source of power by industrial and commercial sectors. This can slow down the economic growth due to hard currency in importing the crude oil and affecting the green economy growth with the CO2 and GHGs. Therefore, the responsible government agencies and departments should consider the potential of PHES in Ethiopia sustainable energy plan. Besides, there must be the provision of incentives as a regulatory framework to support electricity storage systems with mechanisms like time-of-supply variable as feed-in tariffs.