Renewable Energy Vol. 2, No. 6, pp. 543-549, 1992 096(~1481/92 $5.00+.00 Printed in Great Britain. Pergamon Press Ltd MAXIMUM POWER POINT TRACKING: A COST SAVING NECESSITY IN SOLAR ENERGY SYSTEMS J. H. R. ENSLIN Department of Electrical and Electronic Engineering, University of Stellenbosch, Stellenbosch 7600, South Africa (Received 2 January 1991 ; accepted 30 March 1991) Abstraet--A well engineered renewable remote energy system, utilizing the principal of Maximum Power Point Tracking (MPPT) can improve cost effectiveness, has a higher reliability and can improve the quality of life in remote areas. A high-efficient power electronic converter, for converting the output voltage of a solar panel, or wind generator, to the required DC battery bus voltage has been realized. The converter is controlled to track the maximum power point of the input source under varying input and output parameters. Maximum power point tracking for relative small systems is achieved by maximization of the output current in a battery charging regulator, using an optimized hill-climbing, inexpensive microprocessor based algorithm. Through practical field measurements it is shown that a minimum input source saving of between 15 and 25% on 3 5 kWh/day systems can easily be achieved. A total cost saving of at least 1~ 15% on the capital cost of these systems are achieveable for relative small rating Remote Area Power Supply (RAPS) systems. The advantages at large temperature variations and high power rated systems are much higher. Other advantages include optimal sizing and system monitor and control. INTRODUCTION Energy, together with the other production factors, forms the primary input to the development and pros- perity of any community, and more specifically to Southern Africa. Energy is a prerequisite for human existence at large, while electric energy, at a moderate cost, is necessary for the development of any devel- oping community. Whilst Southern Africa is blessed with an abundance of insulation, more than 3000 hours sunlight per year, the solar energy is however spread over a large area with a peak power density of less than 900 W/m 2 at midday on a horizontal surface. This implies that to use this large resource of renew- able energy in an economic way, a large area and power converters with ultra-high efficiencies, are necessary [1, 2, 3]. Several solar-electric power con- verter topologies have been introduced, which include heat engines, thermal systems, photovoltaic cells, chemical systems, biomass, wind systems, hydro sys- tems and others [1, 7]. For the generation of electricity in remote areas at a moderate price, sizing of the power supply is of the utmost importance. Photovoltaic systems and some other renewable energy systems, are therefore excel- lent choices in remote areas for low to medium power levels, because of the easy scaling of the input power source [1, 7]. The technologies associated with photo- voltaic (PV) power systems have not yet benefitted from the low costs of large quantity production and therefore the price of an energy unit generated from a PV system is an order of magnitude higher than conventional energy supplied to city areas, by means of the grid supply [2, 3]. In Southern Africa the power supply grid is not extended to remote areas and thus PV systems can be compared favourably to conventional energy systems by means of grid extension on capital, development and energy costs [2, 3]. When energy systems are com- pared in developing areas, photovoltaic and some other renewable energy systems can even be more cost effective than extended grid or diesel generator systems if Maximum Power Point Tracking is included in the total energy system [2, 3, 5]. Hybrid energy topologies can also make PV systems more cost effective in remote areas [2, 8]. Renewable energy systems in stand-alone appli- cations have, however, a disadvantage in the sense that practical systems have an extremely low total efficiency. This is the result of the cascaded product of several efficiencies, as the energy is converted for example from the sun, through the PV array, the regulators, the battery, cabling and through an inverter to supply the AC load [4]. This paper will address the advantages of using dedicated MPPT systems in a single regulating con- verter or even in a compound converter using a single converter system to perform several tasks including battery charging, regulating and inversion [3, 4]. 543