NWNS Battery Back-up Design, Selection and Implementation Service
Battery back-up is smart in regions that can suffer from severe weather, which are off-grid or with an unreliable power grid.
NWNS can help you finding out when you need to add batteries to your system (and when it makes sense to skip them), we can help you selecting the right type of battery and we can help you sizing your battery bank so that you don’t under- or overcharge your batteries.
Eventually it is all about making sure your power back-up does do what it has to do and to preventing you from potentially shortening the batteries life-cycle.
Moreover, if you don’t have enough battery capacity, you will run out of power and end-up using a lot of (expensive) generator fuel. On the other hand, buying too much battery capacity can be a waste of money because there is no need for it. And to fully recharge your battery bank will cost you unnecessary extra power = recurring cash loss.
Every battery type has a different purpose and use case. And there are many many battery options. It is very common for people to make selection and design mistakes and this can affect system performance and the lifespan of the battery. Therefore, allow NWNS to assist you in making the right choices. It will prevent you from disappointments and it will safe you serious money over time. Savings that can be calculated and quantified upfront.
Click here if you are interested in NWNS’s Battery Back-up, Design & Selection Service.
If you are not an expert, professional assistance may be cheaper than “doing it yourself.”
A Little Bit of Technical Background
It is commonly known that batteries come in many shapes and sizes. In the solar industry (which is NWNS’s prime focus), two battery chemistries work well for the purposes. Lead-acid and lithium.
- Lithium (LFP) is the premium option, with a longer lifespan and fewer maintenance requirements. LFP batteries are 95-98% efficient and expanding an “old” LFP bank is typically not much of a problem. Lithium DoD is 80%.Lead-acid costs much less up front, but regular check-ins are required to keep the battery bank working properly.
- Lead acid batteries are 80-85% efficient. Expanding an existing old lead-acid bank or replacing individual batteries can be difficult or even not possible. Lead-acid DoD is 50%.
You’ve got flooded lead-acid and sealed lead-acid batteries also known as VRLA (Valve Regulated Lead Acid). The latter group can be broken down into AGM (Absorbent Glass Mat) and gel batteries.
- For many years, the flooded lead-acid battery has been the standard in the solar industry. Such batteries are meant to be mounted upright so it does not leak. While flooded lead-acid is the most economic battery on the market, it will only reach its potential lifespan (3-5 years) if they are maintained frequently and properly. Moreover they release toxic hydrogen gas when charging.
- The sealed lead-acid batteries are very similar to the flooded version but can be mounted in any orientation without fear of them leaking. You sometimes see these referred to as VRLA (valve regulated lead-acid) batteries, because they have a small valve to allow for the escape of the gasses that occur during charging. Sealed batteries allow for a more relaxed maintenance program.
- Absorbent Glass Mat (AGM) batteries are the most popular VRLA battery because they can work in a wide range of conditions. Downside is that they are more expensive and do not last quite as long as flooded lead-acid. They are a good fit for remote locations where maintenance will not be possible on a regular basis, and places where the batteries could be subject to extremely cold temperatures. Moreover, AGM batteries are resistant to vibration, which makes them a great choice for mobile applications.
- Gel batteries are another VRLA battery very much like an AGM. The main difference between gel and AGM batteries is the charge rates. AGM batteries can handle higher charge and discharge rates than gel batteries. Gel batteries are the most costly of the VRLA batteries, but excellent candidates for projects that need a very slow deep discharge. They also last a bit longer in hotter temperatures, so we might pick them if you are concerned about high ambient temperatures in the space where the batteries are enclosed.
- Lithium Iron Phosphate (LFP) are more expensive, but there are several benefits to justify the higher price tag. Benefits such as longer lifespan (10+ years), no maintenance, more efficient power usage, deeper discharged and no need for ventilation.
Some more important key terms and concepts:
- Capacity [Wh]: The amount of energy that can be stored and supplied as a function of voltage, amp hours and rate of discharge. Capacity=Voltage x Ah
- Amp hours [Ah] is a measurement of how much current batteries output over time.
- Cycle: Every time a battery is discharged and then recharged. Cycle life is the number of cycles over the course of its lifespan. Cycle life is heavily affected by Depth of Discharge (DoD).
- Depth of Discharge [%] is the amount of energy pulled out of a battery during each cycle.
- Efficiency: Batteries are simply not 100% efficient. The best way to explain is via example: Assume your source is 1 kWh of power and your battery’s efficiency is 80%. Then your battery can only store 0.8 kWh.
- Absorption Time: The amount of time the battery is held at bulk voltage. This time period allows the battery to full recharge.
Sizing Battery Banks:
Understanding how to size a battery bank can sometimes be complicated.
The size of a battery bank very much depends on how much power (kWh) you will use or want to use on a daily basis. This is called your power profile. The result of the calculation is a battery bank capable of storing that much power after accounting for efficiency, DoD, ambient temperature and a few other things. A reliable battery bank with a long life span requires a good working battery charger with temperature compensation to prevent the system from chronic undercharging.