Mahmoud Ammous

Algorithm for Optimum Sizing of a Photovoltaic Water Pumping System

ABSTRACT A sizing algorithm for a photovoltaic water pumping installation composed of photovoltaic panels, battery’ bank, DC/AC converters and a water pump is presented. Considering criteria related to the battery’ bank safe operation, fulfilling the water volume needed by the crops and ensuring a continuous operation of the pump, the algorithm decides the size of the installation’ components. The installation’ cost using the presented and the basic algorithms are compared. Obtained results confirm that the water demand is covered during the crops’ vegetative cycle with a minimum use of the battery’ bank and minimum cost. General Terms Sizing, Photovoltaic Energy. Keywords Photovoltaic energy, sizing algorithm, water, pumping. 1. INTRODUCTION The need to save water and energy is a serious issue that has increased in importance over the last years and will become more important in the near future [1]. The low price of fuel is the reason why renewable energy sources are not used in several applications, including water pumping. So, pumping systems based on renewable energies are still scarce, even though it has clear advantages, namely, low generating costs, suitability for remote areas, and being environmentally friendly. Nowadays, the price of electric energy is rising constantly, and water and energy companies are investing in more efficient solutions [2]. Renewable Energies have been used in water pump applications, especially in remote agricultural areas, thanks to the potential of renewable energies. The renewable energies’ use depends on the user’s propensity to invest in renewable based pumping systems, his/her awareness and knowledge of the technology for water pumping, and also on the availability, reliability, and economics of conventional options [3]. Moreover, the evaluation of the groundwater volume required for irrigation and its availability in the area is also relevant in determining the profitability of using renewable energies. Some installations combine solar panels and wind turbines to compensate the solar radiation and the wind velocity fluctuations. These sources act in a complementary way, since, generally, when the solar radiation is high, the wind velocity is low. This combination may result in a more reliable but complex water pumping, since electric power generated by wind turbines is highly erratic and may affect both the power quality and the planning of power systems [4]. In fact, dHence, there is a multitude of systems based on renewable energies. However, the choice of the energy source for the pump’ supply depends essentially on the site characteristics and the water needed by the crops. As Tunisia’s climate is considered semi-arid and it is good insolated country [5], the use of a photovoltaic autonomous installation for water pumping in remote areas is required. Thus, since the sizes of the photovoltaic installation components affect its autonomy [6, 7], it is necessary to define some adequate values for the components’ parameters, such as the photovoltaic panel surface and the number of batteries [8, 9]. In this sense, researchers have established various methods to optimize the components’ sizes of these installations, essentially the photovoltaic panels’ surface and the battery bank’ capacity [10]. For instance, some works have focused on developing analytic methods based on a simple calculation of the panels’ surface and battery bank capacity using the energetic balance [11-13]. Other works have concentrated on the cost versus reliability question [14]. Moreover, some researchers have proposed sizing algorithms based on the minimization of cost functions, using the Loss of Load Probability (LLP) concept [15]. This LLP approach has also been combined with artificial neuronal networks and genetic algorithms [14]. However, these methods may result in an oversized system for one location and an undersized one for another location [16]. The oversized case results in high installation costs. With an undersized case, the system is unable to supply the load with the energy needed. Moreover, the system’s lifetime is shorter, due to the excessive use of batteries. Hence, the component sizes must be carefully selected for each specific application and location [16]. Some tools have been designed to optimize the size of the PV installation components, by taking into account the energetic, economic and environmental aspects [17]. However, some softwares (such as COMPASS) does not include batteries. Hence, water pumping installations are limited to pumping over the sun. HOMER is a good tool for sizing. Despite it guarantees the installation’ autonomy, it may give an oversized sizing, since it concentrates in the system’ autonomy and it uses data base of 20 years of Nasa. RAPSim focuses on modeling alternative power supply options, using costs calculation throughout the lifespan [18]. RETscreen assists the user to determine the energy production, life-cycle costs and greenhouse gas emission reductions for various types of renewable energies [18], using statistical sizing [17].Hence, these tools may give a good sizing for the installation’ autonomy. However, they may result in oversized components. In this context, this paper presents a development for a previous published work in which, an algorithm for the optimum sizing of the photovoltaic pumping installation destined to tomatoes’ irrigation is developed [19]. uring the months that correspond to the crops’ vegetative cycle, the selected values must guarantee the water volume needed for the crops’ irrigation, the system’s autonomy and the battery bank’s safe operation [8]. Knowing

Design of a PV/T based desalination plant: Concept and assessment

The use of solar energy is promoted for water pumping and desalination especially in remote areas. For a reverse osmosis desalination plant, an increase in brackish water temperature allows an improvement in the recovery ratio, a saving in the required electrical energy, and a reduction in salt rejection. In this paper a conception of a reverse osmosis standalone desalination plant powered by Photovoltaic Thermal panels is established. A plant model is developed in order to assess the plant performances. Simulation results evince economic and ecologie advantages of the use of Photovoltaic Thermal panels in a standalone reverse osmosis desalination plant.

On fuzzy logic control of PV/T based reverse Osmosis desalination plant

Reverse Osmosis desalination process supplied by Photovoltaic Thermal collectors presents a practical method for water desalination [1]. It is shown that the control of the circulated fluid rate ameliorates the system productivity. Photovoltaic Thermal collector combines between heat and electric energy production. In addition, the fluid flow rate variation inside the collector ducts decreases photovoltaic cells temperature. Feed water temperature is increased by the produced heat in order to improve the Reverse Osmosis unit productivity. The system control serves also to prevent overheating Photovoltaic cells and stored water in the boiler. In this paper, a Fuzzy Logic Controller is designed to achieve these objectives. The controller effectiveness is validated using LABVIEW.

Photovoltaic thermal collectors: Reverse osmosis desalination system as an application

Solar energy presents one of the frequent used energy resources to desalinate water especially with reverse osmosis desalination process. Photovoltaic thermal collector (PV/T) is a hybrid generator which converts solar radiation into useful electric and thermal energies simultaneously. This paper gathers all PV/T submodels and reverse osmosis desalination model in order to form a unique dynamic model that reveals PVT based reverse osmosis desalination interactions. As the system is a multi-input/output/output system, a state space model based on energy balance equations is developed in order to analyze and assess the parameters behaviors and correlations of the system constituents. The model simulation is performed using LabVIEW software. The simulation reveals the influence of heating feed water on the process efficiency and the afforded energetic gain by the coolant fluid circulation.

Energy optimization for a photovoltaic/thermal desalination plant

Renewable Energy based systems cannot effective without control. In this paper, Fuzzy Logic Controller which aims to ameliorate the PV/T based RO process performance is proposed. The conceived control is based on varying the flow rate of the circulated coolant fluid according to feed water temperature and Photovoltaic cells temperature. Obtained results which are based on simulation using LABVIEW software prove the effectiveness of the proposed controller. Measurements show an increase on the RO unit productivity while protecting the RO membrane from overheating problem. Additionally, electric efficiency of PV/T collectors is ameliorated due to the coolant fluid circulation. Besides, permeate salinity is maintained in the standards.

Dynamic modeling and LabVIEW simulation of a Photovoltaic Thermal Collector

Photovoltaic Thermal Collector (PVT) is a hybrid generator which converts solar radiation into useful electric and thermal energies simultaneously. This paper gathers all PVT sub-models in order to form a unique dynamic model that reveals PVT parameters interactions. As PVT is a multi-input/output/output system, a state space model based on energy balance equations is developed in order to analyze and assess the parameters behaviors and correlations of PVT constituents. The model simulation is performed using LabVIEW Software. The simulation shows the impact of the fluid flow rate variation on the collector efficiencies (thermal and electrical).

PV/Batteries sizing under multi criteria consideration

Electrification of isolated area is commonly ensured by autonomous power installation including renewable energy sources. Many software tools are available to size such installations. These tools refer to the daily energy need and the site global renewable potential which leads to inaccurate and wasteful sizing. This paper presents an alternative tool based on the energy consumption and the daily loads profile to compute the size of a standalone PV/Batteries system installed in an isolated chalet in Sfax, Tunisia. Obtained results are compared to those provided by PVsyst sizing tool to confirm the proposed algorithm effectiveness. In fact, although the slight high initial cost provided by the algorithm sizing, a profit of 55% in yearly charges is offered by the proposed sizing tool.

Charcterisation of an off grid hybrid system: Modelling and simulation

In this paper, a modelling and simulation of an hybrid system composed of photovoltaic panels, a lead-acid battery bank and a diesel generator connected in parallel, is studied. A non-linear model that depends on the solar radiation and the ambient temperature is adopted to model the photovoltaic panels. The battery is characterized by the depth of discharge deduced by a non-linear model. The genset model consists in modelling its three parts: the diesel engine, the synchronous generator and the excitation system. The system characterization and simulation demonstrate that the load is supplied during the day even in case of weather disturbs.