Charge Controllers

The solar charge regulator (also named solar charge controller) main task is to charge the battery and to protect it from deep discharging. Due to overcharging electrolyte boiling could occur causing damage to the battery or even its destruction. Deep discharging could also damage the battery. Charge regulator electronics is most sensitive and crucial to assuring stable photovoltaic system operation. Charge regulator malfunctioning result in high maintenance cost including battery replacement. An important parameter to consider is charge regulator efficiency percentage. For small photovoltaic systems charge regulators from 5 A to 30 A are available. Some of them could be used in both 12 V and 24 V DC systems. Special charge controllers are available for mobile (vehicles and marine applications) and hybrid applications.

CHARGE REGULATORS BASICS

There are many different types of charge regulators 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. MPPT charge regulators are more expensive and suit large systems better, where the investment in an expensive MPPT regulator returns quickly. 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, usually 12.4 V for 12 V batteries, charge regulator switches the load to the battery, at lower voltage, typically 11.5 V, regulator switches the load off. On the market you can find charge regulators which allow manual settings of these thresholds, or you could merely adjust the battery type to 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. If excessive ambient temperature swings of more than 5°C are expected, temperature compensated charge regulator electronics should be used.

Paralell (left) and serial (right) charge controller

Charge regulators produced by Morningstar Corp.
(courtesy: Morningstar Corp.)

TECHNICAL DATA

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.

Maximum battery current	Ibat max	A
Rated load current	Iload	A
Rated solar current	Iinp	A
Maximum open cirquit (input) voltage	Voc max	V
Nominal input voltage	Vinp	V

TABLE 1: Electrical parameters of charge controllers

Charge regulators produced by Steca
(courtesy: Steca)

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. 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.

CHARGE CONTROLLERS MANUFACTURERS

Steca - as a leading supplier of products for the solar electronics industry, Steca sets the international standard for the regulation and control of solar energy systems.
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Morningstar - Morningstar Corporation is a world-leading supplier of photovoltaic (PV) controllers and inverters using advanced technology. Morningstar's mission is to enhance the global market position as the market and technological leader in PV electronics.
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ETA Engineering - Manufacturing and worldwide distribution of a patented line of solar charge controllers and battery capacity meters. ETA has manufactured and sold charge controls and meters since 1992.

Blue Sky Energy - Blue Sky Energy, Inc. is a quality driven, customer oriented company. Whether the system is a remote telecomm site, security camera, portable solar power system for the military, an RV or boat, their products are selected because of their proven reliability, consistent quality and affordable prices.

Helios Technology - established in 1981, Helios Technology is the oldest european manufacturer of solar cells, and modules. Helios product portfolio include also charge controllers and accessories.
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Mastervolt - Mastervolt develops, manufactures and distributes high-quality electrotechnical systems for independent energy supply.
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victron energy - products portfolio include sinewave inverters, sinewave inverters/chargers, battery chargers, DC/DC converters, transfer switches, battery monitors and more.
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Xantrex - Xantrex Technology USA, a subsidiary of Schneider Electric, produces advanced power electronic products and systems for the mobile power markets. The company’s products convert and control raw electrical power from any central, distributed, renewable, or backup power source into high-quality power required by electronic equipment and the electricity grid.

Digital Solar - charge controller for hybrid systems.

EP solar - Beijing Epsolar Technology Co. provide products including solar charge controller, off-grid inverter, grid inverter, LED driver and special power units etc., as well as design and supply of relevant solar systems.
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Panelectron - Panelektro's portfolio streches out from power supplies through hobby electronics to garden lighting equipment.
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MSTE SOLAR - MSTE SOLAR bietet durchdachte Lösungen für die vielfältigen Einsatzbereiche in der solaren Stromerzeugung.
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ADDITIONAL INFORMATION

Web sites

	Electropaedia, Battery Chargers and Charging Methods.
	Maxim: Harnessing Solar Power with Smart Power-Conversion Techniques.

Reports & Manuals

	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

	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, IEE Proc.-Electr. Power Appl., Vol. 151, No. 2, March 2004.
	Koutroulis, E., Kalaitzakis, K., Voulgaris, C.: Development of a Microcontroller-Based, Photovoltaic Maximum Power Point Tracking Control System, IEEE Transactions on Power Electronics, Vol. 16, No. 1, January 2001.
	Dankoff, W.: What is a charge controller? Home Power, September 1999.