There has been a lot of buzz in the solar industry about batteries. They are necessary for most off grid solar applications and becoming an add-on trend for grid-tied systems. You can read our article “Should You Add Batteries to Your Solar” to find out if installing batteries is a good idea for you. If you do decide you want them, the next step is to choose which batteries are right for you.
One of the factors involved in this decision is what other equipment you will be using. From a technical standpoint, the inverter you will use will determine the required battery voltage. For example, the Outback Radian inverters typically need a 48 volt battery bank which means you are likely going to buy batteries that are 2, 6 or 12 volt and wire them in series to get a 48 volt battery bank. On the other hand, SolarEdge inverters require a 300 volt battery so you will typically use something like the LG Chem batteries that output that higher voltage.
From an install perspective, there are advantages to the higher voltage batteries. The higher voltage means lower amperage so the wires from the batteries to the inverter can be smaller and can be run much longer distances. Typically, with a 48 volt battery bank, your wires are going to be 2/0 AWG or 4/0 AWG and less than 10 feet. With the 300 volt batteries, it would be 10 AWG or 8 AWG and a 50 distance is no problem.
Battery ventilation requirements are also something to consider as this varies with the different battery chemistries. The least expensive batteries are flooded lead acid chemistry. They vent hydrogen gas and must be installed in a well ventilated area away from sparks or flames and separated from living spaces. Other battery chemistries, like sealed lead acid and lithium, do not vent any nasty gases and are much more flexible on where they can be installed.
The physical space needed for batteries is also a consideration. If you have room for a lot of batteries on the floor or large battery cabinets or shelving, you can get the batteries that are shaped like boxes and spread them out on the floor, install them on sturdy shelves or put them in cabinets that are designed for batteries. They make almost all battery chemistries in this box shaped style. If you don’t have a lot of space, you should consider the lithium batteries like the LG Chem that are a slim box that hangs neatly on the wall. This will be the more expensive option and you won’t get as much storage capacity as you could if install large cabinets, but if all you want is a little back up power for short utility outages or a boost for your solar savings on your time of use electric bill, the wall hanging batteries will do the job.
You should also think about how good you are at maintenance. Flooded lead acid batteries need to have distilled water added regularly. If you are they type of person who can’t be bothered to take your car for an oil change and you never buy new filters for your HVAC system, don’t buy flooded lead acid batteries. Not adding water every month can cost you thousands of dollars in new batteries because if they run dry, they will never work right again.
When comparing battery prices it is important to know that different chemistries are generally not apples-to-apples comparisons. First, make sure you break down capacity to watt-hours instead of just looking at amp-hours. Amp-hours x volts = watt-hours. So, 100 amp-hours at 6 volts is 600 watt-hours but 100 amp-hours at 12 volts is 1200 watt-hours which is double the capacity.
Next, be sure to consider depth of discharge. A typical lead acid battery can only be discharged to 50% while a typical lithium battery can go down to 10%. That means if they have the same total capacity, the lithium battery will have almost twice as much usable capacity.
Finally, cycle life tells you how long a battery will last. Taking a battery from full to empty and then re-charging it is one cycle. A battery with a 6,000 cycle life will last twice as long than a battery with a 3,000 cycle life.
There are other things to look at like batteries specifically designed to perform better under certain circumstances. An example would be the Outback EnergyCell Non-Carbon batteries which are enhanced sealed lead acid batteries with improved charging efficiency and more cycle life in applications when they are regularly at a partial state of charge. This means they last longer in off-grid and self-consumption applications compared to other batteries.
The bottom line is not all batteries are created equal. When in doubt, contact the experts at GoGreenSolar.com who will walk you through the process of choosing the best batteries for you.