Technical, Economic, and Environmental Investigation of Pumped Hydroelectric Energy Storage Integrated with Photovoltaic Systems in Jordan
4. Conclusions and Future Work
Nowadays, energy storage is attracting researchers across the world in general and to Jordan specifically. One of the main fields that has high potential for implementing such systems is pumped hydroelectric energy storage (PHES) systems. Even though an enormous number of PHES systems have been built and operate across the world, they have not been implemented in Jordan. The main reason can be attributed to the scarcity of water in Jordan, which led to the water in the dams principally being used for drinking and irrigation purposes. However, this paper can attract the attention of research and energy policy-makers in Jordan regarding the significance of such energy storage systems and how they can be implemented to solve energy problems and increase the percentage of renewable energy in the energy mix.
Based on a previous survey conducted on 10 dams in Jordan, it was found that six sites have great potential for implementing PHES systems based on meeting specific criteria. Some of these criteria include the possibility of constructing a natural or semi-natural upper reservoir and an upper reservoir location such that the difference in height and distance between the upper and lower reservoirs is practical. In this study, we carried out a technical, economic, and environmental investigation of those six sites. In order to increase the attractiveness of such PHES systems, a renewable energy resource was considered for system integration to pump water to the upper reservoirs (instead of using electricity) during off-peak hours. For every site in this study, a 1 MWp off-grid photovoltaic (PV) system was built near the lower reservoir (which is the original dam in these cases) to pump water to an upper reservoir that was placed at practical distance and elevation. In order to simulate the water flow rate for pumping to the upper reservoir, a software package named PVsyst (Version 7.3.4) was used. The water stored in the upper reservoir was assumed to flow back into the lower reservoir (dam) through a turbine for three hours at night (the peak hours) to power a 1 MW load. The power generated through the turbine was estimated using another software package called HOMER Pro® (Version 3.15.3).
Based on the results from PVsyst (Version 7.3.4), it was found that the Al-Walah site had the largest quantity of water raised to the upper reservoir (per 1 MWp PV station), hence the largest upper reservoir size due to the smallest height difference and the shortest distance between the upper and lower reservoirs. Within the head range in this study, it is noticed that the relationship between the water pumped and the height difference is inversely linear. Based on Jordan’s conditions, it was found that each 1 MWp PV station yields almost 2 GWh annually. In addition, the performance ratio (PR) for each PV system in this study is within acceptable values; it is around 80%, except for Al-Tannur site, which has a lower PR due to the long distance and large difference between the heights of the upper and lower reservoirs.
The results from HOMER Pro® (Version 3.15.3) show the energy generated for every month of the year in addition to the energy exported to the electricity grid in summer months, as well as the energy imported from the grid during winter months. It is noted that those sites with a low difference in height between the upper and lower reservoirs have high amounts of water in the upper tank and vice versa. Therefore, a high amount of water has a positive effect on the generated energy, but a low difference in heights has a negative effect on the generated energy. Because these two factors (height and water amount) have an inverse relationship for all sites, it was noticed that the energy generated is almost the same for all sites. It was found that the energy generated from turbines is almost 1.1 GWh (except for the Al-Tannur site, which is almost 0.9 GWh), with a hydro penetration value close to 100% (except for the Al-Tannur, where it is 84%).
In addition to the technical study carried out for all sites, an economic feasibility investigation was carried out. The net present value (NPV), internal rate of return (IRR), simple and complex payback periods (SPP and CPP), and cost of electricity were estimated for all sites. The results are encouraging from a financial point of view; the NPV is larger than the initial cost, the IRR is larger than the discount rate, the SPP and CPP are relatively short, and the electricity cost is cheaper than the electricity tariff. These findings are applicable to all sites in this study. From an environmental point of view, PHES integrated with PV systems might greatly reduce CO2 emissions in Jordan. It is estimated that for a PHES system with a 1 MW PV station under Jordan’s conditions, almost 1300 metric tons of CO2 might be reduced annually. This is a very small fraction when compared to global emissions, but it is an action in the correct direction.
In this study, PHES using a 1 MWp PV system is considered. However, based on the quantity of water in the dam reservoir that is allowed to be pumped from a technical and/or legislative point of view, scaling up the size of the PV and hydropower systems can be carried out easily by taking into consideration the modular nature of such systems. Implementing such systems in Jordan might surely make the energy sector sustainable, increase renewable energy in the energy mix, stabilize the grid, and balance the loads, especially during peak periods. In order to make the PHES systems more attractive financially, in the near future, it is planned to investigate the effect of employing pumps and turbines as a single unit (the same device can work as a pump (to raise water up to the upper reservoir) and a turbine (to produce power from the discharged water from the upper reservoir)). This might greatly reduce the initial cost because the combined pump/turbine is cheaper than the individual cost for pumps and turbines. In addition, using the combined pump/turbine units might reduce the length of pipes to half, which positively affects economic feasibility. For the Al-Tannur and Al-Mujib sites, re-examining the location of the upper reservoir relative to the lower reservoir to allow for a smaller height difference, and a shorter distance might enhance the technical performance of these sites, resulting in an increase in their feasibility.
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