Global Photovoltaic Business Magazine

hilrE MAY, 2011

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IMPACT OF JAPAN’S CRISIS ON PV MARKET THE IMPACT OF THE RECENT EARTHQUAKE S AND ONGOING NUCLEAR CRISIS IN JAPAN ON THE GLOBAL SOLAR MARKET SHOULD BE ANALYZED . FROM DIVERSE DIMENSIONS.

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OLIC&LEGISLATION PI1LŁ islative Changes in the Czech Republic CELL &MUIE Smart Pa .liels�What Are They and Why Do We Need Them?

GLOBAL MARKET REPORT The German PV Market in Transition�Preparing for Grid Parity PV in the Developing World �A ’Cell Phone’ Model for Microrids Driving New PV Adoption LG, Samsung, Hyundai in Solar Efficiency Battle COMPONENT & MATERIAL Energy Yield and Solar Trackers

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Battery Selection & Maintenance Critical for Longevity of Renewable Energy Systems

76 May, 2011 INTERV

Rapid growth in renewable energy markets worldwide has : stimulated an increased focus on deep-cycle battery

technology. The battery bank is a key component in a � Renewable Energy (RE) system whether it is grid-tied with A battery backup or working completely off-grid. Battery

MiddletonDean storage is critical to consistent power availability. Since the battery bank can represent a large cost of an RE system, careful attention to selection and maintenance of batteries is critical to ensuring maximum return on an RE system investment. BY DEAN MIDDLETON

Battery 101 As energy storage devices, regular main-

tenance of batteries is critical to ensuring an RE system performs at maximum levels. Batteries store, in chemical form, the Direct Current (DC) electrical energy produced by renewable sources, such as solar, wind and hydro power. Because renewable energy charging sources are often intermittent in their nature, batteries provide energy stor -age to deliver a relatively constant supply of power to electrical loads regardless of the time of day or weather conditions.

In off-grid Photovoltaic (PV) systems, battery storage provides a way to power common household appliances and light-ing when the sun goes down, while in a grid-tie PV system with battery backup the batteries provide uninterrupted power in case of utility power failure. Batteries used in any renewable energy system designed for cycling applications, whether off-grid or grid-tied, should be engineered for ’deep cycle’ use�meaning the battery’s con-struction is optimized for the deep dis-charge and recharge cycles characteristic of RE systems.

Battery Types�Selection Is Key Deep-cycle batteries typically used in

RE systems fall into two primary groups: Flooded (FLA) and sealed-Valve regulated (VRLA) such as AGM and gel. Flooded batteries provide the best cycling perfor-mance at high Depth Of Discharge (DOD) of all deep-cycle battery technologies and are the most ideal option where lowest life-cycle cost is a key system design objective. However, to achieve their maximum po-tential life, FLA batteries require regular care and maintenance.

For some applications FLA battery tech-nology is not a viable option because maintenance cannot be guaranteed. Appli-cations that require maintenance-free bat-tery technology, AGM or gel battery tech-nology may be the best options. ACM bat-teries have a higher discharge current ca-pacity and are often used as a backup

power supply for a grid-tied system. Gel batteries provide better cycling perfor-mance in off-grid applications and are less sensitive to the high operating tempera-tures often found in hot climates. However, the upfront cost of both AGM and gel bat-teries can be more than FLA batteries and they do not provide the longevity of a FLA battery.

Maintenance�A Fundamental, Yet Critical Process

As flooded batteries charge, hydrogen gas is produced and vented in the process. This ’off gassing’ of hydrogen reduces the electrolyte level in the flooded battery, so periodic ’watering’ of the batteries with distilled water is required to ensure maxi-mum life. Distilled water should only be added to batteries that are fully charged in float mode, where the charge current and voltage are reduced to maintain a full bat-tery. This provides just enough charging to compensate for self-discharge.

While there may be some variation from manufacturer to manufacturer, electrolyte levels should never be allowed to go so low as to expose the battery plates to air. Trojan, for instance, recommends watering their flooded batteries so that the final level of the electrolyte is 1/8" below the vent well. While it is often recommended to water batteries on a monthly basis, the fre-quency will really depend upon how the batteries are used and the operating tem-peratures of the battery bank. With that in mind, new installations should be moni-tored more closely, perhaps weekly, until a sense for the watering frequency require-ment is determined. Also, as flooded bat-teries age, their gassing rate will increase, requiring more water on a regular basis. Always wear protective clothing, gloves and goggles when working with batteries. The electrolyte in a flooded battery is a so-lution of acid and water so take extra pre-caution to avoid contact with skin and clothing.

No matter how frequently a battery bank

is watered, it is important that it be done according to a regular schedule, as well as doing a routine check of terminal connec-tions. A poor electrical connection any-where in a system, whether caused by a loose connection or corrosion, can lead to poor performance. To tighten battery con-nections, the use of tools with insulated handles is recommended since they can be easily short circuited by connecting the positive to negative terminal.

VRLA batteries are referred to as main-tenance-free due to the minimal amount of maintenance required. Since VRLA batter-ies are sealed, adding distilled water is not required as is necessary in FLA batteries. With VRLA batteries, it is important that the terminals are tightened and cleaned as needed on a regular basis, otherwise the battery bank will not operate at full capaci-ty. In addition, monitoring the battery’s overall health and inspecting the battery management system is a vital step to en-sure optimal operation of a VRLA battery bank.

The Importance of Equalization Equalization is another important aspect

in maintaining the longevity of flooded batteries in RE systems. The process for equalizing FLA batteries involves periodi-cally overcharging the batteries at a higher voltage for a set period of time in order maintain a consistent charge among indi-vidual cells and maintain overall battery capacity at the highest possible levels. It also reduces the effects of electrolyte strati-fication, sulfation and cell inconsistencies that develop over time which diminishes overall system efficiency. As with water-ing, batteries should be fully charged to float mode prior to equalizing. For bat-teries that are deeply discharged on a daily basis, it may be necessary to equal-ize every few weeks otherwise equaliza-tion may be needed on a monthly basis. The equalization process produces more hydrogen gas than normal charg-ing, so steps should be taken to provide

INTERV May, 2011 77

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