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Research Papers

Power Gain and Daily Improvement Factor in Stand-Alone Photovoltaic Systems With Maximum Power Point Tracking Charge Regulators. Case of Study: South of Spain

[+] Author and Article Information
F. J. Muñoz

Grupo IDEA
e-mail: fjmunoz@ujaen.es

M. Fuentes

Grupo IDEA

J. D. Aguilar

Grupo IDEA
Departamento de Ingeniería
Electrónica y Automática,
Universidad de Jaén,
Campus las Lagunillas,
Jaén 23071, Spain

Contributed by the Solar Energy Division of ASME for publication in the JOURNAL OF SOLAR ENERGY ENGINEERING. Manuscript received March 1, 2013; final manuscript received July 5, 2013; published online August 19, 2013. Assoc. Editor: Santiago Silvestre.

J. Sol. Energy Eng 135(4), 041011 (Aug 19, 2013) (9 pages) Paper No: SOL-13-1073; doi: 10.1115/1.4025205 History: Received March 01, 2013; Revised July 05, 2013

The performance reliability of a stand-alone photovoltaic system (SAPV) depends on the long-term performance of the batteries. In this way, a charge controller becomes an essential device which not only prevents the batteries from suffering deep discharges and overvoltages but also monitors the battery state of charge (SOC) in order to maximize charging efficiency and energy availability. At present, pulse width modulated (PWM) charge regulators dominate the market for this type of component in SAPV systems. However, in recent years, to improve energy management, more manufacturers have developed controllers with strategies for maximum power point tracking (MPPT). PWM charge controllers do not always make optimum use of the available power given by the maximum power point and this gives a loss of power. These power losses depend on battery voltage, irradiance and temperature. However, they can be avoided by using a MPPT charge controller which operates the array at its maximum power point under a range of operating conditions, as well as regulating battery charging. The advantage, in terms of energy gain, provided by this type of charge regulator depends on weather conditions. This paper will study the power gain provided by this type of charge controller, depending on the module temperature and the battery voltage. The paper will, additionally, provide a study of the gain in energy yield, also shown as improvement factor, F, for SAPV systems installed in Jaén (South of Spain). This study may illustrate the behavior of these two types of charge controllers in warm weathers, like Mediterranean climates. Furthermore, it will analyze the suitability of MPPT charge controllers and their benefits in this type of climate. It will be shown that MPPT charge regulator global efficiency constitutes a key issue in making a choice between MPPT and PWM charge regulators. The results given here may be not only of interest for SAPV systems with no access to the electricity grid but also for battery back-up PV grid-connected PV (GCPV) systems.

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References

Figures

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Fig. 1

I–V and P–V characteristic for a monocrystalline PV module I-106 (GI = 600 W/m2 and Tm = 50 °C). The shaded area corresponds to the upper and lower thresholds determined by a charge regulator when operating with a 12 V battery in a SAPV system.

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Fig. 2

I–V and P–V curves for different irradiances and module temperatures

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Fig. 3

Diagram of the outdoor measurement system (IVCT) developed in the Solar Energy Laboratory of the High Technical School building at University of Jaén

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Fig. 4

Parameters to be considered in MPPT (a) and PWM (b) charge regulators in order to get the power gain

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Fig. 5

Power and intensity gain in a MPPT charge controller as a function of module temperature and irradiance

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Fig. 6

Power and intensity gain in a MPPT charge controller as a function of module temperature and battery voltage

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Fig. 7

Monthly average daily improvement factor for different mean daily battery voltages. For PWM charge controllers, it has been taken into account efficiencies of 96% and 98%. For MPPT charge controller, the efficiencies considered are 90%, 95%, and 97% as an appropriate minimum acceptable threshold to MPPT controller efficiency is 90% although the state of the art allows efficiencies above 95% when working around the nominal power. The MPPT efficiency algorithms considered in any case is 98%.

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Fig. 8

Monthly average daily improvement factor for different mean daily battery voltages. For PWM charge controllers, it has been taken into account efficiencies of 96% and 98%. For MPPT charge controller the efficiencies considered are 90%, 95%, and 97% as an appropriate minimum acceptable threshold to MPPT controller efficiency is 90% although the state of the art allows efficiencies above 95% when working around the nominal power. The MPPT efficiency algorithms considered in any case is 98%.

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