Sizing optimisation of stand-alone photovoltaic generators for irrigation water pumping systems

This paper mainly presents an efficient non-conventional direct method for sizing optimisation of stand-alone photovoltaic (PV) generators for supplying AC-motor-based irrigation pumping systems. The efficiencies of various elements comprising a PV pumping system and the effects of PV-array tilt are taken into account. The strong impact of the tilt angle on the optimal sizing of a PV generator is demonstrated. Extensive analysis of the meteorological conditions of the study site is performed. An appropriate solar correlation model for the design site is determined. The optimality of the determined capacity and tilt angle for a PV generator is evaluated by calculating several optimality indicators. The proposed method is compared with the Kenna and Gillett method and the RETScreen method for suggesting the nominal power for PV generators. The results show the capability and accuracy of the proposed method in optimally sizing stand-alone PV generators for irrigation water pumping systems.     

A simple model for sizing stand alone photovoltaic systems

We consider a general model for sizing a stand-alone photovoltaic system, using as energy input data the information available in any radiation atlas. The parameters of the model are estimated by multivariate linear regression. The results obtained from a numerical sizing method were used as initial input data to fit the model. The expression proposed allows us to determine the photovoltaic array size, with a coefficient of determination ranging from 0.94 to 0.98. System parameters and mean monthly values for daily global radiation on the solar modules surface are taken as independent variables in the model. It is also shown that the proposed model can be used with the same accuracy for other locations not considered in the estimation of the model.     

A general multivariate qualitative model for sizing stand-alone photovoltaic systems

We considered a general model for sizing a stand-alone photovoltatic system, using as energy input data the information available in any irradiation atlas. The parameters of the model are estimated by multivariate linear regression. The results obtained from the numerical loss of load probability size method (LOLP) were used as initial input data to fit the mode. For this fit we have used daily global irradiation data taken from 222 US meteorological stations for the period 1961–1990. The expression proposed allows us to determine the photovoltatic array size, with a coefficient of determination to 0.96. This coefficient is independent of the used LOLP value. System parameters and mean monthly values for daily global irradiation on the modules surface are taken as independent variables in the model. It also shows that the proposed model can be used with the same accuracy for other locations not considered in the estimation of the model. We also propose a model which would allow us to calculate optimum tilts for the array surface taking the latitude into account as well as the variability of the incident irradiation.     

Systematic procedures for sizing photovoltaic pumping system,using water tank storage

In this work, the performances of the photovoltaic pumping destined to supply drinking water in remote and scattered small villages have been studied. The methodology adopted proposes various procedures based on the water consumption profiles, total head, tank capacity and photovoltaic array peak power. A method of the load losses probability (LLP) has been used to optimize sizing of the photovoltaic pumping systems with a similarity between the storage energy in batteries and water in tanks. The results were carried out using measured meteorological data for four localities in Algeria: Algiers and Oran in the north, Bechar and Tamanrasset in the south. The results show that the performance of the photovoltaic pumping system depends deeply on the pumping total head and the peak power of the photovoltaic array. Also, for the southern localities, the LLP method shows that the size of the photovoltaic array varies versus LLP on a small scale. On the other hand, for the northern localities, the sizing of the photovoltaic array is situated on a large scale power. Because of the current high crud-oil price, the photovoltaic pumping still to be the best adopted energy resource to supply drinking water in remote and scattered villages.     

Loss-of-load probability of photovoltaic water pumping systems

This paper presents a method for estimating the loss-of-load probability (LLP) of a photovoltaic water pumping system. The study has been carried out for a constant profile, using a tank with a two day autonomy capacity and two pumping heads applied to a centrifugal pump. The method developed in this paper gives a simple tool for LLP calculation. The procedure can also be used to draw LLP maps with normalised parameters using long term observed or generated sequences of meteorological data. This technique gives a generalised and practical graphical tool for systems sizing. Some examples from Algeria are used. But the method can be applied to any geographical area.     

Small-scale irrigation with photovoltaic water pumping system in Sahara regions

Several photovoltaic applications, specially the water pumping systems, are installed to contribute in the socio–economic development in Algerian Sahara. About sixty pumps are installed in remote regions to supply water for drinking and irrigation. The centrifugal pumps present the state-of-the-art for most applications. This paper presents the electrical and hydraulic performance of a surface centrifugal pump versus total water heads and versus a size of PV array. Also the area irrigated by this solar surface pump is calculated under Sahara climate conditions for four crops, namely wheat, potatoes, tomatoes and sunflowers. These were selected to meet with food standards of the sites. Two application sites were chosen to test the developed model. The first is Bechar station and the second is Tamanrasset station. In both, the recorded solar radiation data were used. The results, which are illustrated by tables and curves, are analysed. The analysis of the performance concluded that this surface pump is suitable for installation in the Sahara regions with low water head.     

Optimal sizing of photovoltaic pumping system with water tank storage using LPSP concept

This paper recommends an optimal sizing model, to optimize the capacity sizes of different components of photovoltaic water pumping system (PWPS) using water tank storage. The recommended model takes into account the submodels of the pumping system and uses two optimization criteria, the loss of power supply probability (LPSP) concept for the reliability and the life cycle cost (LCC) for the economic evaluation.With this presented model, the sizing optimization of photovoltaic pumping system can be achieved technically and economically according to the system reliability requirements. The methodology adopted proposes various procedures based on the water consumption profiles, total head, tank capacity and photovoltaic array peak power. A case study is conducted to analyze one photovoltaic pumping project, which is designed to supply drinking water in remote and scattered small villages situated in Ghardaia, Algeria (32°29′N, 3°40′E, 450 m).     

Economic viability of photovoltaic water pumping systems

A comparison of the economic viability of photovoltaic and diesel water pumping systems is presented for system sizes in the range 2.8 kW_p to 15 kW_p. Actual performance data from installed systems are employed for the base case. Sensitivity analysis is carried out to generalize results for other locations and conditions. The effect of system oversizing due to mismatch of water supply and demand patterns on the economic viability of PV water pumping system is illustrated based on real data and three-year operational experience of eight installations. Investment prospects in PV water pumping applications for different selling price scenarios of water have been investigated.     

A new approach for sizing stand alone photovoltaic systems based in neural networks

Several methods for sizing stand alone photovoltaic (pv) systems has been developed. The more simplistic are called intuitive methods. They are a useful tool for a first approach in sizing stand alone photovoltaic systems. Nevertheless they are very inaccurate. Analytical methods use equations to describe the pv system size as a function of reliability. These ones are more accurate than the previous ones but they are also not accurate enough for sizing of high reliability. In a third group there are methods which use system simulations. These ones are called numerical methods.Many of the analytical methods employ the concept of reliability of the system or the complementary term: loss of load probability (LOLP). In this paper an improvement for obtaining LOLP curves based on the neural network called Multilayer Perceptron (MLP) is presented. A unique MLP for many locations of Spain has been trained and after the training, the MLP is able to generate LOLP curves for any value and location.     

Utilisation of solar photovoltaic pumping for aeration systems in aquaculture ponds

This research pertains to solar photovoltaic (PV) pumping for aeration of aquaculture ponds and evaluates it economically. A stand-alone photovoltaic aeration system based on recycling of water at 10 cm under the water surface, at the surface (0 cm) and above the surface (30 cm) on a perforated tray was evaluated. The effect of pump discharges (35, 50, 65 L/min) on standard oxygen transfer rate (SOTR) and standard aeration efficiency (SAE) was investigated. Results revealed that the daily averages of PV energy output, PV efficiency and load energy were 0.844 kWh/d, 9.87% and 0.615 kWh/d, respectively, at 65 L/min and 42.7°C PV temperature. Water flow upward at 30 cm over the perforated tray in the radial direction proved to be better since it gave an opportunity for the exchange of gaseous between the water and the atmosphere. The SOTR and SAE for the third position were 0.025 kgO₂/h and 0.1 kgO₂/kW h, respectively.     

Simulation of grape culture irrigation with photovoltaic V-trough pumping systems

In large areas of the Northeast of Brazil, the population is faced with the severe problem of water shortage aggravated with the lack of electric power. However, some places, like the area next to the river São Francisco, near the city of Petrolina, in the state of Pernambuco, have become quite prosperous with the cultivation of grape crops, either for wine production or to be consumed as fruits. Wine exports have grown as an important economic activity in the region. On the other hand, in areas far from the electric network, photovoltaic pumping systems have contributed to the supply of water for local rural communities. Production of fruits, with water supplied by photovoltaic systems, might, then, become a good alternative in terms of local economic activities. The viability of this proposal depends strongly on the market value of the crop. Taking advantage of some significant technical benefits provided by low concentration tracking devices we propose to use those systems to drive local irrigated crops. Among the large family of concentrators available, V-troughs are particularly adequate for photovoltaic applications since, for certain combinations of the concentration ratio (C) and vertex angle (Ψ), they provide a perfectly uniform illumination in the region where the modules are located (absorber region). A drip irrigation system, located in the city of Petrolina, has been simulated and the maximum surface that can be irrigated by a V-trough photovoltaic pumping equipment was estimated by performing a water balance on a monthly basis. With an array of 1.3 kW_p it was found that the system is able to irrigate, without deficit, 2.11 ha. A fixed photovoltaic pumping equipment, with the same photovoltaic array, is able to irrigate an area of 1.20 ha. In both cases, the water stored in the soil contributes with an increase of 33% to the irrigated area, as compared to the case where that contribution is not considered.     

Sizing and modelling of photovoltaic water pumping system

With the decline in price of the photovoltaics (PVs) their use as a power source for water pumping is the most attractive solution instead of using diesel generators or electric motors driven by a grid system. In this paper, a method to design a PV pumping system is presented and discussed, which is then used to calculate the required size of the PV for an existing farm. Furthermore, the amount of carbon dioxide emissions saved by the use of PV water pumping system instead of using diesel-fuelled generators or electrical motor connected to the grid network is calculated. In addition, an experimental set-up is developed for the PV water pumping system using both DC and AC motors with batteries. The experimental tests are used to validate the developed MATLAB model. This research work demonstrates that using the PV water pumping system is not only improving the living conditions in rural areas but it is also protecting the environment and can be a cost-effective application in remote locations.     

Optimal sizing of array and inverter for grid-connected photovoltaic systems

Optimum PV/inverter sizing ratios for grid-connected PV systems in selected European locations were determined in terms of total system output, system output per specific cost of a system, system output per annualised specific cost of a system, PV surface orientation, inclination, tracking system, inverter characteristics, insolation and PV/inverter cost ratio. Maximum total system output was determined for horizontal, vertical and 45° inclined surfaces for a low efficiency inverter for sizing ratios of 1.5, 1.8 and 1.3, respectively; and for a medium efficiency inverter with sizing ratios of 1.4, 1.5 and 1.2. PV surface orientation and inclination have little impact on the performance of a high efficiency inverter. For different PV tracking systems and for different inverter characteristics, the optimum sizing ratio varied from 1.1 to 1.3. The PV/inverter cost ratio and the PV and inverter lifetimes have significant impact on the optimum PV/inverter sizing ratio. A correlation relating optimum sizing ratio and PV/inverter cost ratio has been developed; the correlation coefficients were found to be functions of insolation and inverter type. The impact of PV/inverter sizing ratio on PV array performance was less when PV array has a much higher cost than the inverter. The optimum sizing ratio for PV/inverter cost ratio of 6 and low efficiency inverter system varied from 1.4 to 1.2 for low to high insolation sites. For a high efficiency inverter system, the corresponding variation was from 1.3 to 1.1.     

Inverter sizing of grid-connected photovoltaic systems in the light of local solar resource distribution characteristics and temperature

Inverter sizing strategies for grid-connected photovoltaic (PV) systems often do not take into account site-dependent peculiarities of ambient temperature, inverter operating temperature and solar irradiation distribution characteristics. The operating temperature affects PV modules and inverters in different ways and PV systems will hardly ever have a DC output equal to or above their STC-rated nominal power. Inverters are usually sized with a nominal AC output power some 30% (sometimes even more) below the PV array nominal power. In this paper, we show that this practice might lead to considerable energy losses, especially in the case of PV technologies with high temperature coefficients of power operating at sites with cold climates and of PV technologies with low temperature coefficients of power operating at sites with warm climates and an energy distribution of sunlight shifted to higher irradiation levels. In energy markets where PV kW h’s are paid premium tariffs, like in Germany, energy yield optimization might result in a favorable payback of the extra capital invested in a larger inverter.This paper discusses how the time resolution of solar radiation data influences the correct sizing of PV plants.We demonstrate that using instant (10 s) irradiation values instead of average hourly irradiation values leads to considerable differences in optimum inverter sizing. When calculating inverter yearly efficiency values using both, hourly averages and 1-min averages, we can show that with increased time resolution of solar irradiation data there are higher calculated losses due to inverter undersizing. This reveals that hourly averages hide important irradiation peaks that need to be considered.We performed these calculations for data sets from pyranometer readings from Freiburg (48°N, Germany) and Florianopolis (27°S, Brazil) to further show the peculiarities of the site-dependent distribution of irradiation levels and its effects on inverter sizing.     

Methodology for optimal sizing of stand-alone photovoltaic/wind-generator systems using genetic algorithms

A methodology for optimal sizing of stand-alone PV/WG systems is presented. The purpose of the proposed methodology is to suggest, among a list of commercially available system devices, the optimal number and type of units ensuring that the 20-year round total system cost is minimized subject to the constraint that the load energy requirements are completely covered, resulting in zero load rejection. The 20-year round total system cost is equal to the sum of the respective components capital and maintenance costs. The cost (objective) function minimization is implemented using genetic algorithms, which, compared to conventional optimization methods such as dynamic programming and gradient techniques, have the ability to attain the global optimum with relative computational simplicity. The proposed method has been applied for the design of a power generation system which supplies a residential household. The simulation results verify that hybrid PV/WG systems feature lower system cost compared to the cases where either exclusively WG or exclusively PV sources are used.     

A fuzzy global efficiency optimization of a photovoltaic water pumping system

This paper presents an on-line fuzzy optimization of the global efficiency of a photovoltaic water pumping system driven by a separately excited DC motor (DCM), a permanent magnet synchronous motor (PMSM), or an induction motor (IM), coupled to a centrifugal pump.The fuzzy optimization procedure stated above, which aims to the maximization of the global efficiency, will lead consequently to maximize the drive speed and the water discharge rate of the coupled centrifugal pump. The proposed solution is based on a judicious fuzzy adjustment of a chopper ratio which adapts on-line the load impedance to the photovoltaic generator (PVG). Simulation results show the effectiveness of the drive system for both transient and steady state operations. Hence it is suitable to use this fuzzy logic procedure as a standard optimization algorithm for such photovoltaic water pumping drives.     

Optimization of a photovoltaic pumping system based on the optimal control theory

This paper suggests how an optimal operation of a photovoltaic pumping system based on an induction motor driving a centrifugal pump can be realized. The optimization problem consists in maximizing the daily pumped water quantity via the optimization of the motor efficiency for every operation point. The proposed structure allows at the same time the minimization the machine losses, the field oriented control and the maximum power tracking of the photovoltaic array. This will be attained based on multi-input and multi-output optimal regulator theory. The effectiveness of the proposed algorithm is described by simulation and the obtained results are compared to those of a system working with a constant air gap flux.     

Renewable energy technologies for irrigation water pumping in India: A preliminary attempt towards potential estimation

Simple frameworks have been developed for estimating the utilization potential of: (a) solar photovoltaic (SPV) pumps; (b) windmill pumps; (c) producer gas based dual fuel engine pumps; and (d) biogas based dual fuel engine pumps for irrigation water pumping in India. The approach takes into account factors such as: solar radiation intensity, wind speed, availability of bovine dung and agri-residues, and their alternative uses, ground water requirements for irrigation and its availability, affordability, and propensity of the users to invest in renewable energy devices, etc. SPV pumps are estimated to have the maximum utilization potential in India, followed by windmill pumps.     

Comparative study of artificial intelligence techniques for sizing of a hydrogen-based stand-alone photovoltaic/wind hybrid system

As non-polluting reliable energy sources, stand-alone photovoltaic/wind/fuel cell (PV/wind/FC) hybrid systems are being studied from various aspects in recent years. In such systems, optimum sizing is the main issue for having a cost-effective system. This paper evaluates the performance of different artificial intelligence (AI) techniques for optimum sizing of a PV/wind/FC hybrid system to continuously satisfy the load demand with the minimal total annual cost. For this aim, the sizing problem is formulated and four well-known heuristic algorithms, namely, particle swarm optimization (PSO), tabu search (TS), simulated annealing (SA), and harmony search (HS), are applied to the system and the results are compared in terms of the total annual cost. It can be seen that not only average results produced by PSO are more promising than those of the other algorithms but also PSO has the most robustness. As another investigation, the sizing is also performed for a PV/wind/battery hybrid system and the results are compared with those of the PV/wind/FC system.     

Financial evaluation of renewable energy technologies for irrigation water pumping in India

An attempt to develop a simple framework for financial evaluation of renewable energy technologies (RETs) such as photovoltaic (PV) pump, windmill pump, biogas and producer gas-driven dual fuel engine pumps for irrigation water pumping has been made. The unit cost of water and unit cost of useful energy delivered by the RETs have been estimated. The monetary benefits that accrued to the end-user have been quantified in terms of the amount of diesel or electricity saved. Financial figures of merit for the investments made in the RETs have been estimated. The effect of fuel price escalation on these measures of financial performance has also been evaluated along with the estimation of the break-even prices of fuels likely to be substituted by RETs. Results of some exemplifying calculations are presented and briefly discussed.