The most common mistake made when sizing battery banks is not having accurate load information. If manufacturer's data is not available for a particular load, steps should be taken to measure actual power use instead of making a guess. Small mistakes can have a big impact, causing the end user to eventually lose power and potentially require a replacement battery bank sooner than expected. Since most battery based renewable energy systems are off-grid and all power will be generated and stored on-site, it's critical that the designer understand the nature of the loads the system is designed to run.
Batteries for Alternative Energy Systems
Dean Middleton & Bryan Godber | Trojan Battery Company
Question: What is the role of batteries in a renewable energy system?
Dean Middleton: Batteries store Direct Current (DC) electrical energy produced by renewable sources such as solar, wind and hydro power in chemical form. Because renewable energy charging sources are often intermittent in their nature, batteries provide energy storage in order to provide a relatively constant supply of power to electrical loads regardless of whether the sun is shining or the wind is blowing.
In an off-grid photovoltaic (PV) system for example, battery storage provides a way to power common household appliances regardless of the time of day or the current weather conditions. In a grid-tie with battery backup PV system batteries provide uninterrupted power in case of utility power failure.
Batteries used in any renewable energy system, whether off-grid or grid-tied, should be designed for “deep cycle” use, meaning that their design and construction is optimized for the deep discharge and recharge cycles characteristic of renewable energy systems. Deep cycle batteries typically used in renewable energy systems fall into two primary groups; flooded lead acid (FLA) and sealed valve regulated lead acid (VRLA).
Question: How do I decide when to use flooded lead acid (FLA) vs. sealed valve regulated lead acid (VRLA) batteries in a renewable energy system?
Dean Middleton: Flooded lead acid (FLA) batteries provide the best cycling performance of all deep cycle battery technologies and are the most ideal option for most renewable energy applications where lowest life-cycle cost is a key system design objective, however to achieve maximum potential cycle life, FLA batteries require regular maintenance. As FLA batteries charge, hydrogen gas is produced and vented in the process. This off gassing of hydrogen reduces the electrolyte level in the FLA battery and so periodic “watering” of the batteries are required to ensure maximum life.
For some applications FLA battery technology is not a viable option because maintenance cannot be guaranteed on a regular basis. For applications that require a maintenance free battery technology, a sealed VRLA battery such as GEL or AGM should be considered.
While a maintenance free battery provides more convenience, that convenience comes with a price. Sealed VRLA batteries are going to be more expensive and will have lower cycle life when compared to FLA batteries. As with FLA batteries, when choosing a sealed VRLA battery it is important to consider only a deep-cycle GEL or AGM technology that is optimized for renewable energy applications.
Question: What is the difference between AGM and Gel battery technology?
Dean Middleton: GEL batteries are constructed with a micro porous separator and utilize an acid electrolyte that has been mixed with silica to form a gel. AGM batteries are constructed with a highly porous fiberglass mat which is sandwiched between the positive and negative plates and saturated with acid electrolyte. Both AGM and GEL batteries are considered ‘recombinant’ which means that sealed pressure relief valves force the recombination of oxygen and hydrogen back into water during recharge so that almost no electrolyte is lost and unlike FLA batteries, they do not require regular watering.
Gel batteries typically provide better cycling performance in off-grid applications compared to AGM batteries and are less sensitive to the high operating temperatures often found in hot climates.
AGM batteries, with their higher discharge current capacity compared with GEL batteries, are often used for backup power supply or grid-tie with battery backup systems in which the batteries are not cycling on a daily basis. And because AGM batteries are most commonly used in standby applications which allow the batteries to maintain a nearly full state of charge majority of the time. Many AGM batteries are not designed for true deep cycle applications. Trojan AGM batteries are unique in that they have been designed for true deep cycling applications, combining the convenience of AGM technology with the cycle life needed for renewable energy applications.
While both AGM and GEL batteries provide solutions for applications that require maintenance free energy storage, both are costlier than FLA batteries and do not provide the longevity in terms of cycle life that FLA batteries offer, often only having 50 percent cycle life or less when compared to FLA batteries.
Question: What types of batteries does Trojan Battery Company manufacture for renewable energy?
Dean Middleton: Trojan Battery Company only manufactures true deep cycle batteries and as such every one of our products can be used in renewable energy applications. Trojan manufactures FLA, GEL and AGM deep cycle batteries for renewable energy including our newest RE Series which is our premium line of FLA batteries optimized for maximum cycle life under the challenging conditions often found in renewable energy applications. We are proud to be one of the only battery manufacturers that offer all three: FLA, GEL and AGM deep cycle technologies. This allows us to offer our renewable energy clients unbiased technical support when choosing the right battery for their system.
Question: What types of renewable energy applications are Trojan batteries used in today?
Bryan Godber: Trojan batteries are used in renewable energy systems in over 100 countries around the world. From remote telecommunications sites in North America, rural medical clinics in Africa to village electrification projects in Central and South America, Trojan batteries are recognized around the globe for providing reliable power under the most challenging of conditions. In fact, in the aftermath of the recent earthquake in Haiti, Trojan Battery Company provided battery donations to relief organizations to provide power for field hospitals, water filtration systems and emergency lighting systems working to provide for basic human needs as part of the recovery effort.
Question: Can golf cart batteries be used in renewable energy systems?
Dean Middleton: Golf cart batteries that are true deep cycle FLA design and construction are an excellent choice for renewable energy systems. Trojan Battery has a long history of serving both the renewable energy market and the golf cart market with deep cycle FLA batteries designed for high performance and long life. Golf cart applications, often with hilly terrain and requiring constant stop and go activity combined with daily charge-discharge cycles have always demanded reliable power and long life similar to the design requirements for batteries in renewable energy systems.
Trojan Battery has been the primary choice of the world’s top golf cart manufacturers for decades and our popular T-105 deep cycle FLA battery originally designed for golf cart applications has been used in renewable energy applications around the world since the earliest installations of photovoltaic systems for off-grid applications.
Today, the Trojan T-105-RE battery combines Trojan’s most popular golf battery design with a range of new features to produce a FLA battery specifically optimized to deliver unparalleled performance in renewable energy applications
Question: What is the RE Series and how is it different than your other flooded batteries?
Bryan Godber: Trojan’s Renewable Energy (RE) series is a line of advanced FLA deep cycle batteries optimized for renewable energy applications. The RE Series brings together over 85 years of experience in deep cycle battery manufacturing and life cycle testing to offer our renewable energy customers a product line with superior life, durability and charge performance. Batteries used in renewable energy systems tend to operate in partial states of charge for extended periods of time and the RE Series has been designed to provide maximum life under these conditions. The combination of robust grid design, thicker separators and advanced paste formulation contributes to this premium line of batteries. Everything we have learned about how deep cycle batteries function in renewable energy systems has been applied to this new design in order to offer our customers the best long-term investment when considering the total cost of ownership over the life of the battery. Our RE Series L16 batteries are available in 2-volt and 6-volt models and are designed for 10-year life and come with a seven-year worldwide warranty.
Unlike many companies that simply re-label an existing product for solar applications, Trojan’s RE product line was designed in direct response to the needs of our renewable energy clients. The development of the RE line shows our ongoing commitment to the renewable energy industry as we continue to design and manufacture the most reliable deep cycle energy storage products available in the market today.
What factors need to be considered when sizing batteries for a renewable energy system?
Dean Middleton: When sizing renewable energy systems, the single most important factor to consider is the electrical power requirement or load. Proper calculation of the load will not only have a direct impact on the overall system size and cost but will also affect whether the system functions as intended and provides reliable power to the end user.
Autonomy refers to the amount of time that a battery bank needs to power the loads without access to a charging source and is usually calculated in terms of days. Autonomy assumptions will vary depending upon the geographic location as well as the nature of the loads and how critical the supply of power may be. An off-grid PV system in the sunny state of Arizona will experience far fewer days of cloudy weather in the winter compared to an off-grid PV system in the mountains of Washington and so system designers should take this into account when making their calculations.
The nature of the application and how critical access to power is to the end user must also be considered. For example, systems that provide emergency communications are often designed with much greater autonomy given their direct impact on human safety than systems that are intended for recreational purposes like cabins or recreational vehicles. Access to backup power sources, such as utility power or a standby generator, can also influence autonomy calculations.
Understanding the loads and the context of the application are just several of the variables that the system designer needs to take into consideration when sizing a battery bank for a renewable energy system. Relying on the expertise of a local professional with experience in the design and installation of renewable energy systems will be invaluable when considering each of these variables.
Question: What are the most common mistakes made in sizing battery banks for renewable energy applications?
Dean Middleton: Many common, yet seemingly minor, mistakes made when designing renewable energy systems contribute to poor performance and shortened life of the battery bank as a result. Most often, these mistakes result in a battery bank that appears to function well initially but never reaches a full state of charge on a regular basis and ends up suffering long term damage as a result. The net effect on a battery bank of spending long periods of time under conditions of partial state of charge is the potential for shortened life and premature failure of the battery bank.
The most common mistake made when sizing battery banks is not having accurate load information. If manufacturer’s data is not available for a particular load, steps should be taken to measure actual power use instead of making a guess. Small mistakes can have a big impact, causing the end user to eventually lose power and potentially require a replacement battery bank sooner than expected. Since most battery based renewable energy systems are off-grid and all power will be generated and stored on-site, it’s critical that the designer understand the nature of the loads the system is designed to run.
A common oversight is not taking into account the temperature that the batteries will be exposed to since this will impact their capacity and therefore needs to be taken into account as part of the design process. Battery capacities are typically rated by manufacturers at 77°F and name plate rated capacity will decrease at lower temperatures and increase at higher temperatures.
Another misconception is that deep cycle FLA batteries can be fully discharged to 100 percent of its capacity on a regular basis. In fact, deep cycle FLA batteries should never be discharged to 100 percent of their capacity. The depth of discharge (DOD) refers to the percent capacity that will be regularly discharged from the battery and has a direct impact on the overall life of the battery. The shallower the design DOD, the longer the battery will last. Understanding this relationship is critical to getting the longest life possible out of a battery bank. To put it in perspective, a battery designed for 50 percent DOD will last about twice as long as a battery designed for 80 percent DOD, assuming all other factors are equal.
Experienced renewable energy system designers and installers serve a critical role to help you avoid these and many other common design mistakes so I cannot over emphasize the need for working closely with a local professional. While it might seem like a more costly approach than doing it yourself, buying a battery bank twice because of poor design or incorrect installation is far more expensive. Relying on the experience of local professional means you can learn and benefit from their experience while helping to build a strong renewable energy industry in the process.
Question: Which battery technology is the most cost-effective Flooded (FLA) or sealed Valve Regulated Lead Acid (VRLA)?
Dean Middleton: FLA batteries have a lower initial cost when compared to VRLA batteries however it is important to take into account the total life-cycle cost of each battery technology when considering your options. It makes little sense to select a FLA battery because of its lower up-front cost if you know the system will be installed at a very remote site with no potential for maintenance. In this circumstance, the life-cycle cost of a VRLA battery might actually be less than the life-cycle cost of a FLA battery that suffered premature failure as a result of not being maintained properly.
When designing any renewable energy system, always consult with an experienced professional that can help you weigh your options in order to make an informed decision that meets your design objectives.
Question: How long will batteries in a renewable energy system last?
Dean Middleton: This is a difficult question to answer since no two renewable energy systems are alike given the wide range of potential loads, environmental conditions and sizing methodologies that might impact the system design approach. Battery life depends on a number of factors, many of which are difficult to predict or control. A properly designed system, installed by a well trained renewable energy professional has the potential for longest battery life if maintained according to manufacturer’s recommendations.
We have seen batteries in poorly designed systems that did not last a year while in some cases batteries that were initially designed for a five-year life are still going strong after eight years in service due to proper care and maintenance. Our premium line of RE Series L16 batteries are designed for 10-year life assuming 50 percent DOD, however all deep cycle batteries must be properly installed and maintained to ensure maximum potential life.
With the largest R & D facility in the United States dedicated to performance testing of deep cycle batteries, Trojan Battery continually monitors product performance under true life-cycle conditions. This dedication to continual product improvement allows us to set the standard for quality and longevity in deep cycle batteries.
Question: What new products or technologies can we look forward to from Trojan in the future?
Bryan Godber: Trojan is consistently working to improve battery technologies and introduce innovative products specifically engineered to meet our customer’s needs in the renewable energy industry.
Our latest innovation, the HydroLink™ single point watering system, offers customers a convenient, cost-effective way to maintain FLA batteries and ensure battery maximum life. HydroLink gives customers a way to easily protect their battery investment and keep their overall cost of ownership down throughout the life of the battery.
To facilitate the need for larger battery bank configurations, Trojan Battery Company will be expanding its line of both 2-volt FLA and VRLA battery models. The introduction of larger 2-volt products will allow system designers more flexibility in designing larger capacity systems while minimizing parallel connections.
Question: Has Trojan Battery Company been involved in renewable energy since the founding of the company?
Bryan Godber: When Trojan Battery Company was founded in 1925 the renewable energy industry as we know it today did not yet exist. By the time Trojan began supplying batteries into the earliest off-grid PV applications of the late 1970’s and early 1980’s, in the early years of the emerging photovoltaic industry, the company already had over 50 years of experience manufacturing deep cycle batteries.
Today Trojan is one of the oldest manufacturers to serve the photovoltaic industry and is recognized around the world for setting the industry standard in quality for deep cycle batteries used in renewable energy applications.
Question: How is Trojan Battery Company positioned to serve the needs of renewable energy customers?
Bryan Godber: With over 85 years of experience in the deep cycle battery business and four ISO 2001:2009 quality management certified plants within North America, Trojan Battery Company supports it’s renewable energy clients through a worldwide network of master distributors in over 50 countries.
As the renewable energy market continues to grow, Trojan Battery Company is committed to making this market a strategic growth objective and will continue to invest in the right mix of people, products and services needed to maintain our leadership role in the industry. As the only deep cycle battery manufacturer in the United States with a fully dedicated team of renewable energy professionals, we are focused on truly understanding the needs of our customers in order to continually improve the performance of our products and provide the best long- term investment to our clients.
Bryan Godber, vice president of renewable energy for Trojan Battery Company is the fourth generation member of Trojan’s family ownership responsible for driving the strategic development, manufacturing, partner alliance and global expansion of Trojan’s renewable energy division.
Dean Middleton, director of renewable energy sales, Americas for Trojan Battery has more than 18 years of experience in global sales and export of photovoltaic systems and manages Trojan’s key sales initiatives for renewable energy markets throughout North, Central and South America.
Trojan Battery Company is the world’s leading manufacturer of deep cycle batteries, offering a complete portfolio of technologically-advanced Flooded, Gel and AGM batteries that provide maximum long-lasting performance to meet the requirements of today’s advancing renewable energy systems. Trojan Battery Company, founded in 1925, is ISO 9001:2008 certified with operations in California and Georgia.
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