Purchasing a battery bank to store the power for your off-grid home or business is a significant investment and what we consider the most important part of the alternative energy system. Not all batteries are created equal and the advantages and disadvantages of each chemistry option should be carefully considered. One of the biggest considerations is the "life" of the battery. The "life" of the battery is often stated in "cycles", meaning the process of charging the battery completely and then discharging it of all of its usable power. The term "Days of Autonomy" is used to describe the number of days a charged battery can provide usable power before it requires recharging. Normally, due to budget constraints, a single day is what most people will purchase, but it is not uncommon to size a battery bank to last two or more days.
The battery bank most likely will be the most expensive component of your alternative system but when you consider the extremely long lives of the batteries we sell, the economics and practicality just make sense. Not only are these batteries some of the lowest-cost batteries when you consider their lives, you also will save the time and hassle of replacing traditional batteries multiple times during the same time period.
Typically a battery cannot be increased in size once it is placed in service because the life of the additional cells will be compromised by the remaining life of the existing cells. That means it is important consider the long-term requirements of your storage needs and size accordingly from the beginning. If you do need to increase the size of a battery bank in the future, there are some options. The most common is to add a second battery bank. Usually this means a battery of the same voltage, amp hour and chemistry, though some charges do allow for mixtures of battery types and sizes. This method can be quite costly and usually requires the expansion of the solar array to ensure proper charging levels. Another option for increasing the battery bank size is made possible through the use of Iron Edison Nickel Iron batteries. Because of their long life and very robust chemistry, one could start with a 12V or 24V system and within a few years add additional cells to create a 24V or 48V system. The size of the array may need to be increased and the chargers would have to be able to handle the range of voltages and amp hours that would be present in the beginning system and the upgraded system, but this is a way of expanding an existing power storage system without adding an entirely new battery bank.
We chose the batteries we sell because of their long life which has been time-tested. Both the Iron Edison and Solar One HuP® batteries are great choices, but one may be a better choice than the other given the circumstances of the project or based on owner preferences. Upfront cost, expected life, ongoing maintenance and compatibility with charge controllers should all be considered.
Iron Edison Nickel Iron Batteries - The Iron Edison nickel iron battery was created by Thomas Edison himself and there are many examples of batteries built over 100 years ago still in operation today. The battery has a stated life of 30+ years even with recharging it everyday. Unlike a lead acid battery that will no longer store enough usable power after its life, the nickel iron battery still will have about 75% or better of its capacity after that time period. Using nickel iron (NiFe) with an alkaline electrolyte instead of lead acid, the NiFe battery works best when deeply discharged. In fact, the stated depth of discharge (DOD) is 80% versus 20% for the lead acid battery. That means a battery that is one-fifth the amp hour size of a traditional battery. Using a translucent case and a tiered battery rack so the sides of all cells can be seen, keeping the battery filled with distilled water is a simple task. Unlike a lead acid battery, the NiFe battery neither needs to be equalized once a month (a manual, deliberate overcharge) nor does the specific gravity need to be taken from each cell. These two features make maintenance much easier than a lead acid battery.
As good as the NiFe battery sounds, it is not the best choice for certain installations. Because it needs to be maintained and likes to be discharged deeply and regularly, it should not be used for unoccupied locations such as remote cell tower sites (unless maintained regularly), vacation properties that are not frequently used or if the system is tied to the grid and using the battery solely for emergency backup. If the battery does not have enough usage and is kept charged all of the time either through alternative sources or the grid, then the life of the battery can be compromised and the lead acid battery would be a better choice.
Iron Edison Lithium Iron Phosphate Batteries - The other battery that Iron Edison carries is their Lithium Iron Phosphate (LiFe) battery. Being sealed and maintenance-free, this is truly an install-it-and-forget-it battery. Unlike a Lithium ION battery, the Lithium IRON is a stable chemistry that is not prone to overheating and exploding. And unlike other lithium technologies like the Tesla battery, the LiFe battery is compatible with all existing off-grid systems. (The Tesla battery is a water-cooled, 350V high voltage battery compatible only with Tesla products. The Iron Edison LiFe battery is a standard voltage battery compatible with 12v, 24V and 48V systems.) The LiFe battery is rated for 14 years at a 50% depth of discharge. These are much lighter batteries than traditional battery chemistries and come with their own case, overcurrent protection, battery disconnect and BMS (battery management system).
The LiFe has a higher cost per amp hour than the other chemistries, but offers a long life without any maintenance. It also is a good choice if you want a battery that will act as a backup while normally being topped off most of the time by the grid or alternative power. In fact, the less it is used, then longer its life will be. That translates into a much longer life than 15 years if used in this application.
SimpliPhi PHI Smart-Tech Lithium Ferro Phosphate Batteries - Our newest offering is the SimpliPhi PHI Smart-Tech Lithium Ferro Phosphate maintenance-free battery with a stated 5,000 cycle life at 100% depth of discharge and a 10,000+ cycle life at 80% depth of discharge. That's over 27 years of daily cycling of maintenance free power storage! At 98% efficiency and no memory effect, this battery just makes sense. The SimpliPhi PHI Smart-Tech batteries are unique because instead of wiring multiple cells to increase the voltage to 12V, 24V or 48V, you connect these 24V or 48V batteries in parallel to increase amp hours. This makes adding additional storage capacity easy as explained below. These batteries were designed to work flawlessly with existing equipment at 24V or 48V as a drop-in replacement for lead acid or other battery chemistries and have a much greater power curve over a wider range of temperatures. And like the Iron Edison Lithium Iron Phosphate batteries, since these batteries are up to 2/3 lighter than certain other technologies, the freight charges also are lower.
Solar One HuP Lead Acid Batteries - The Solar One HuP lead acid battery has a much thicker lead plate than other batteries allowing it to come with a 10 year warranty and an expected life up to 20 years with proper maintenance. While still best utilized at a 20% depth of discharge, frequent discharges up to 50% and an occasional discharge of 80% will not affect it. If a regular lead acid battery were discharged 80%, it would never come back to life.
"Can a battery bank be expanded?" - We often get this question from people who want to start with a modest system and expand it as their budgets allow. Before the answer, a little about how batteries are wired.
Most battery banks are made of up individual cells that are wired together in series to achieve the desired voltage. For example, a 48V Nickel Iron battery would have 40 1.2V cells wired in series (positive to negative, positive to negative, etc.) to achieve 48V while a Solar One HuP lead acid battery would have 24 2V cells wired in series to reach the same voltage. Wiring in series increases voltage, so 40 1.2V 500Ah cells wired in series would create a bank that still is 500Ah but at 48V. This is just like putting a couple of 1.5V AA batteries in a flashlight to achieve 3V.
Some battery banks are wired in parallel where all of the cells' positive terminals are wired together and all of the negative terminals are wired together. This approach increases amp hours but keeps the voltage the same. For example, if two 1.2V 500Ah cells were wired in this manner, the result would be a 1.2V 1,000Ah battery. Very few battery banks are wired this way, but a hybrid approach of wiring multiple series-based banks in parallel is not unusual.
If your battery bank consists of individual cells wired in series to achieve the required voltage, you have a couple of options for expanding your storage capacity. Inverters usually allow for a single battery bank, but if you have multiple inverters in your system, then you typically can have one battery bank for each inverter. Therefore, in a multiple inverter installation with a series battery bank, you can simply add a second series-wired bank connected to the second inverter. However, all of the banks should be the same amp hour size and the same chemistry. If you have just one inverter, the most common approach for increasing the capacity of your system is to add a second bank of equal size and chemistry and wire it in parallel to the first bank thus treating the two banks as one. This expansion approach can be multiplied several times based on the limitations of your inverter.
The main problem with expanding your battery bank by wiring multiple series-wired banks in parallel to be treated as a single bank is that the life of the newer battery bank is compromised by the older life of the original bank. Another problem with this approach is the cost. Since you essentially are adding another equal-sized bank, the cost is double of that of a single bank. But if this is the plan and you budget accordingly, then this really is not a problem. Because of their robustness, if you plan to use this approach to start with one size of battery bank and increase it later, using the Iron Edison Nickel Iron battery is the best choice as long as it is within one to two years.
With the introduction of batteries like the SimpliPhi PHI batteries, you have another option for expanding the capacity of a battery bank. These are not cells wired together to make a single battery but are standalone 24V or 48V batteries. Rather than wiring these batteries in series to increase voltage, you wire them in parallel to increase amp hour capacity. While wiring in parallel is a little more complicated than wiring in series, expanding this type of battery bank is easier and does not have the same problems as the series-based banks. For example, instead of adding an entire bank of the same size, chemistry and cost to increase the size of the bank, a single battery in parallel can be wired to the existing bank to incrementally increase the bank's capacity. That means the expansion cost can be spread out over time rather than all at once and you can increase the capacity by exactly how much you want rather than one large chunk. Additionally, parallel wiring does not compromise the life of the new battery that was added to an existing bank.
It needs to be noted that anytime a battery bank is expanded, you need to account for the added power that will be required to charge the expanded bank. That could mean more solar panels, another inverter/charger or another power generation source. If you have any questions regarding expanding an existing battery and what updated charging requirements the resulting bank will need, please contact us.
A Personal Note - After finding the Solar One HuP battery and using it for our personal system, I became a dealer. At the time it was the only one of the four batteries we sell that was available and if I were to do it again, I would have to weigh the pros and cons of each battery to determine which one is best for my power system. For some systems it still is the best choice--even above the nickel iron or lithium iron batteries--which is why each system needs to be designed according to the specific needs of the customer.
Remember, the battery is the heart of any backup or off-grid system and choosing the right battery type and size is the most important part of its design.
For help with sizing nickel iron, lithium iron or lead acid batteries or for complete system design, contact us today at 208-946-5550.