Optimisation and economic modeling of micro hydropower plant integrated in water distribution system
Introduction
Considering the growing worldwide energy demand, climate change, environmental consequences of conventional energies, and the principles of sustainable development, several countries are looking for alternative energy resources. They aim to develop technologies, laws, rules, and principles to improve the quality of life, avoid environmental disorders, and preserve the planet. Energy saving and renewable energies are becoming the best solutions for these countries to consider.
Energy and water are inevitably interconnected within a pipeline. An intensive amount of energy is consumed during the pumping of water; while an interesting amount of energy can be harnessed in the kinetic and potential energy embedded in the flow of water. For water delivery systems, this energy is not being exploited and is currently wasted in canal falls. The installation of small hydro-electric plants at multiple locations of water distribution networks can generate interesting amount of energy which could be beneficial to surrounding communities. A water distribution system consists of a set of reservoirs, electrical equipment, pipes, and valves which transport and distribute water to end-users. An appropriate hydraulic head is required for the movement of water. This latter is provided by the use of pumps or gravity. The use of energy to treat and pump water results in high operating costs for water suppliers (Fayzul et al., 2014). Interest in the use of small hydro power has been renewed due to the many potential benefits it provides compared to other renewable energy technologies. These include less power output fluctuation and higher energy efficiency compared to its counterparts. Small hydro power plants are classified into mini, micro, and pico hydro systems depending on the plant power production. If this latter is less than 2 MW, the installation is considered a mini hydro system. For a power production that is strictly inferior than 100 kW, the system is classified as micro–hydro power plant. Finally, for small power generation that is less than 5 kW, the installation is categorized as pico hydro power plant (Mishra et al., 2015). Even for small power output, hydro-electric installation results in interesting economic and environmental benefits (Fecarotta et al., 2015). (Hosnar and Kovac-kraj, 2014) developed a model with an aim to optimize the construction of a hydropower plant. This proposed model enables the identification of maximum economic and eco-profit from selling energy produced from hydro system. Optimal installation capacity of small hydropower system has been tackled by (Hosseini et al., 2005). The approach used by the authors involves a comparison of technical, economic, and reliability indices. The economic profitability of small hydropower plants in various regions has been investigated by (Kaldellis et al., 2005). Simulations results demonstrate that the predicted values of internal rate of return are higher than 18% for most evaluated small hydropower cases. Some literature such as (Soffia et al., 2010) have shown that the economic viability of installing a micro hydro plant results in a negative net present value. However, this analysis is significantly dependent on the support and incentives offered by the state. In Piemonte, such investment can be profitable if the power production varies between 9 and 35 kW. Depending on the incentives offered, the NPV can be in the range of 8–80 M€ (Soffia et al., 2010). A study to investigate the benefits of installing renewable energy resources in the eco-design of conventional drinking water plants has been conducted by (Ahmadi et al., 2016). The obtained results show that both economic and environmental benefits are multiplied by five when considering renewable energy resources.
The interrelationship of water supply, energy production, and demand has been evaluated by a number of researchers (Kucukali, 2011). analysed the use of existing hydropower potential in water distribution networks in Turkey. The water supply system of Edremit has been examined as a case study. This potential installation is considered as an opportunity in Turkey because of the new economic aspects and energy laws of the country (Gallagher et al., 2015). have demonstrated that there is an economic benefit in the use of micro-hydropower in water supply systems. A case study has been conducted at a regional scale, with an aim to identify reservoirs characterized by interesting energy recovery potential (Samora et al., 2016). estimated the hydropower potential in water supply networks in the city of Fribourg, Switzerland. An optimization algorithm has been proposed by the authors to determine the energy production and maximize the installation economic value. Investment in such installation has been done in some countries such as Switzerland, while others are still far behind the development of such systems (Van Dijk et al., 2018). proposed a model to study the development of a conduit hydropower plant and offer an optimal, sustainable, and resilient solution to water utilities. A review of existing hydro-turbine systems that fit a number of in-conduit applications has been discussed by (Ayu Sari et al., 2018). The authors have found that new turbines as well as the conventional ones can be utilized for diverse type of water conduits. A number of studies have discussed different aspects of hydro power plants (Finardi and Scuzziato, 2013, Williamson et al., 2014, Ahmadi et al., 2015a, Ahmadi et al., 2015b, 2015). Additionally, several models have been proposed and analyzed in literature (Norouzi et al., 2014, Aghaei et al., 2015, Sharma et al., 2015).
Previous studies focused solely on the optimal implementation or economic analysis of small hydro plant. This paper presents an energy, economic, and environmental analysis to investigate the feasibility and viability of small-hydroelectric installation. The topic of investigating the technical, economic, and environmental aspects of installing micro hydro plant in water distribution reservoirs has never been explored in literature. These studies are conducted in this work to facilitate precise estimation of the benefits of integrating such installation. The design of this small hydro installation is modelled to investigate the system practicability. Both technical and economic studies of are performed and discussed. This is done by estimating revenues and costs of such project over the plant lifetime operation. Economic indexes are considered to evaluate and compare the profitability of different scenarios. These include the system net present value (NPV), the kWh average cost price, and the payback period. In this study, we propose a methodology to assist investors in developing strategies about the integration of hydropower plant in existing water supply. The proposed model attempts to explore the feasibility and investment revenues obtained by such installation. This approach does not provide the optimum placement of the installed turbine within the water supply network. In addition, hourly variation of flows throughout the year is not considered by the model. An optimization problem which considers both water flow variation as well as the adequate location for installing the turbine could be developed. To understand the contribution of this research paper, the main objectives of this work are summarized as:
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An optimization model is formulated to properly size the hydro plant with an aim to maximize its economic gain.
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To perform the dimensionality problem of the system components, a technical model is developed using Matlab/Simulink with a case study.
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The simulation obtained results demonstrate that the economic gain is doubled to achieve 1,800,000 € for a CF of 80%.
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The proposed models obtain satisfactory results in different scenarios, providing a new methodology to evaluate the practicability and profitability of implementing micro hydro-plant in a water distribution system.
This paper is organized as follows. Section 2 gives the mathematical model of the sizing optimization problem. A methodology to model the different components of the hydro plant is presented in section 3. This is followed by a case study applied to investigate the feasibility of real-world micro hydropower system in Morocco (Section 4). Section 5 presents a discussion of the obtained results. The environmental impact of this installation is also discussed in this section. A conclusion is provided in Section 6.
Section snippets
Plant sizing optimisation
To determine the optimum sizing of a small-scale hydro plant integrated in water distribution system, an optimization model has been proposed. The design of small hydropower installation is cost-driven. Therefore, maximizing the plant net present value is necessary, as it enables it to become more appealing compared to other energy production systems. The aim of this optimization model is to find the optimal sizing of this installation that minimizes the overall cost of the system, while
Modeling of a hydropower plant
Energy is generated by passing water from the upper reservoir to the lower one through a turbine. The amount of energy produced depends on the vertical height through which water falls; this is known as pressure head. It represents also the difference in elevation between the upper reservoir and the turbine located in the lower reservoir. The net effective head at the nozzle is lower than the calculated head known as the gross head due to friction and other factors.
The net head (HN) is the
Case study
A land survey was performed to determine the case study site characteristics. This latter is located in Azrou, a Moroccan city in the province of Ifrane. The population of the city of Azrou is about 82,000 inhabitants. It is divided in two major districts: The first one is AHADAF, located in the plains. It has about 45,000 households. They are supplied by low and very low voltage electricity. The second district is Azrou center which includes suburbs of Mohammadie, Tizi, Kachla and Sabah among
Optimal sizing and economic analysis
To optimally size the hydro plant, it is necessary to determine the optimal net mechanical power, the plant net head, as well as the pressure losses. These latter would be used in the dimensioning of the plant conduit, turbine, and generator; all in accordance with the norms and the availabilities of the market.
The plant gross head used in this case study is 174 m, while the estimated net head is about 95 m with the use of a 0.13 m pipe diameter. There is a large pressure drops in pressure head
Conclusion
As concerns about climate change have grown, there has been a raising demand to shift from fossil fuels to renewable energy sources. Micro hydropower is a crucial component in meeting the local demand for renewable energy. Energy production from water supply systems is an environmentally friendly solution, as it is based on exploiting the water conduit excess pressure for generating energy. Additionally, the integration of micro hydropower plant in water distribution system has several
Nomenclature
B bucket size
- capital cost
- Period payment for year i
- hourly costs
- operation and maintenance cost
- diameter of the jet
- runner diameter
- D′
- inside diameter of the pipe (m)
- E
- is the relative roughness
- hourly produced energy
- annual energy produced
- f
- frequency
- F
- jet force
- f’
- friction factor
- g
- gravitational acceleration (m/s2)
- G
- optimization factor
- HN
- net head
- HG
- gross head
- HL
- head losses
- Minor losses
- loss coefficient
- head losses coefficient
- L
- longitude of the pipe (m)
- M
- torque
- n
- number of years of operation
- n’
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