Charge Controllers features & System Sizing

The solar charge controller's (also named solar charge regulator) main task is to charge the battery and to protect it from deep discharging. Overcharging and deep discharging can damage the battery. Charge controller electronics is most sensitive and crucial to assuring stable photovoltaic system operation. Charge controller malfunction result in high maintenance cost in worst case premature battery replacement is necessary. An important parameter to consider is charge regulator efficiency percentage. For solar home systems charge controllers up to few Amp of current are available. Some of them could be used in both 12 V and 24 V DC systems.

Paralell (left) and serial (right) charge controller

There are many different types of charge controllers available on the market, the simplest switch on/off regulators, PWM charge regulators which charge the battery with constant voltage or constant current (they are the most often used regulators in PV systems) to the most complex MPPT (Maximum Power Point Tracking) charge regulators. In most cases, including inexpensive charge regulators for small systems, regulator set includes all necessary electronics for battery protection, such as protection against deep discharging and against overcharging. Charge regulator functioning is characterised by two different voltage thresholds, battery and module voltage, upon which the battery is charged. At higher voltage charge controller switches the load to the battery, at lower voltage, typically controller switches the load off. Tresholds depend on battery type used. In some cases battery type can be selected manually (e.g. lead (Pb) acid or gel type) and the regulator will adjust the two voltage thresholds automatically according to the battery type without losing the performance. Newest battery types like Li-Ion batteries require also electronics for cell balancing not only for battery charging.

General electrical and mechanical properties

The most important charge regulator parameters include include a maximum battery current, maximum open cirquit (input) voltage and rated solar/load current. Mechanical parameters include ambient operating temperature (usualy from -40°C to +45°C), terminal size (mm² or AWG), weight and dimensions. Some charge regulators also allow positive terminal grounding what should be specified in technical data.

TABLE 1: Electrical parameters of charge controllers

Battery Types and Charging

The energy produced during the day, which wasn’t consumed by loads, is saved in batteries. Saved energy can be used at night or during the days with bad weather conditions. Batteries in photovoltaic systems are often charged/discharged; therefore, they must meet stronger requirements than ordinary car batteries. Car batteries are not suitable for PV systems use! There are many solar battery types available in the market. Most often used classic Pb acid batteries are produced especially for PV systems, where deep discharge is required. In recent years Li-Ion batteries are also common battery type used in PV systems. Other battery types, such as NiCd or NiMH are rarely used, unless in portable devices. Hermetical batteries often consist of electrolyte in gel form. Such batteries do not require maintenance. Typical solar system batteries lifetime spans from 3 to 5 years, depending heavily on charging/discharging cycles, temperature and other parameters. The more often the battery is charged/discharged the shorter the lifetime. Lifetime depends on charge/discharge cycle rates numbers. The deeper the battery is discharged the shorter the lifetime. The most important battery parameter is battery capacity, which is measured in Ah. Battery capacity depends on discharging current; the higher the discharging current the lower the capacity, and vice versa. Batteries can be charged in many different ways, for example with constant current, with constant voltage etc., which depends on the battery type used. The charging characteristics are recommended and prescribed by different standards. The solar batteries prices are higher than the prices of classic car batteries, yet their advantages are longer lifetime and lower discharging rates. Consequently, the maintenance costs of the photovoltaic system are lower.

Books and Reports

	Köthe Hans. (1996). Stromversorgung mit Solarzellen. Franzis Verlag.
	Lasnier, France, Ang, Tony, G. (1990). Photovoltaic Engineering Handbook. IOP Publishing.
	Dunlop, J.P.: Batteries and Charge Control in Stand-Alone Photovoltaic Systems Fundamentals and Application; Florida Solar Energy Center, prepared for Sandia National Laboratories, Photovoltaic Systems Applications Dept, January 1997.
	Handbook of Secondary Storage Batteries and Charge Regulators in Photovoltaic Systems; Final Report, prepared by Exide Technologies, orginally Printed August 1981.
	Usher, E.P., Ross, M.D.: Recommended practices for charge controllers; CANMET, Energy Diversification Research Laboratory, Renewable Energy and Hybrid Group, IEA IEA PVPS T3-05:1998.
	Andersson, B. et al.: Lead-Acid Battery Guide for Stand-Alone Photovoltaic Systems; IEA Task III, Report IEA-PVPS 3-06:1999.

Papers & Articles - Charge Controllers

	Müer, M. et al. 2013, Performance of MPPT Charge Controllers - A State of the Art Analyses 28th EUPVSEC, 30 September - 4 October, Paris, France.
	Grzesiak, W. et al. 2009, Selected Problems in Designing of a Charge Controller for 6V PV Installations, 24th EUPVSEC, 21-25 September 2009, Hamburg, Germany.
	Echbarthi, I. et al. 2008, New Test Procedure to Evaluate Battery & Charge Controller Used in Stand-Alone Photovoltaic (PV) Systems, 23rd EUPVSEC, 1-5 September 2008, Valencia, Spain.
	Lorenzo, E., Navarte, L., 2000, On the usefulness of stand-alone PV sizing methods. Progress in Photovoltaics: Research and Applications, Volume 8, Issue 4, pages 391-409, July/August 2000.
	Balouktsis, A. et al.: Sizing Stand-Alone Photovoltaic Systems; International Journal of Photoenergy, Volume 2006, Article ID 73650, Pages 1–8.
	Koutroulis, E., Kalaitzakis, K.: Novel battery charging regulation system for photovoltaic applications, IEEE Proc.-Electr. Power Appl., Vol. 151, No. 2, March 2004.
	Koutroulis, E. et al. Development of a Microcontroller-Based, Photovoltaic Maximum Power Point Tracking Control System, IEEE Transactions on Power Electronics, Vol. 16, No. 1, January 2001.

Papers & Articles - Batteries

	Diaz, P., Egido, M. A., 2003, Experimental analysis of battery charge regulation in photovoltaic systems. Progress in Photovoltaics: Research and Applications, Volume 11, pages 481-493.
	Guasch, D., Silvestre, S., 2003, Dynamic battery model for photovoltaic applications. Progress in Photovoltaics: Research and Applications, Volume 11, Issue 3, pages 193-206, May 2003.
	Bopp, G. et al., 1998, Energy storage in photovoltaic stand-alone energy supply systems. Progress in Photovoltaics: Research and Applications, Volume 6, Issue 4, pages 271-291, July/August 1998.
	Casacca, M. et al., 1994, Optimum battery configuration for maximum utilization of photovoltaics. Progress in Photovoltaics: Research and Applications, Volume 2, Issue 1, pages 65-72, January 1994.
	Copetti, J. B. et al., 1993, A general battery model for PV system simulation. Progress in Photovoltaics: Research and Applications, Volume 1, Issue 4, pages 283-292, October 1993