Best Batteries to use with Solar
When diving into building a photo-voltaic system, things can get confusing quickly! Trying to determine which battery is best for the system you plan to build can be daunting, so hopefully I can help you in narrowing down your options to save you some of the headache. Since there are many different types of batteries, I’ll try to break them down one by one.
Lead-Acid batteries are the most common and come in three different versions: SLI, Marine and Deep Cycle.
- SLI or Automotive batteries:
Automotive starting, lighting, and ignition batteries (SLI) have a short or “shallow” depth of discharge, as they are designed to produce a high amount of current in a very short time. These batteries are not recommended for use in a photo-voltaic system, as they would quickly be ruined by the deep cycles required for extended use. Short and sweet answer to this: Regular or Car type batteries should not be used at all because they cannot be discharged very much without internal damage.
- Marine batteries:
RV or Marine type deep cycle batteries are basically for boats & campers and are suitable for only very small systems. They can be used, but do not really have the capacity for continuous service with many charge/discharge cycles for many years. These are best suited for trolling motors and live well pumps that are used a few times out of the year but don’t normally see an everyday charge/discharge cycle.
- Deep Cycle batteries:
Deep cycle batteries are designed with thicker lead plates, which have less overall surface area than their thinner SLI counterpart. Because of the reduced availability of surface area for chemical reactions, deep cycle batteries produce less current than an SLI type battery, yet they produce that current for longer periods of time. Deep cycle batteries can be discharged up to 80 percent Depth of Discharge without damage depending on the model. In order to increase battery life, manufacturers recommend discharging deep-cycle batteries only down to 50 percent in order to increase battery life. The Deep Cycle Lead-Acid batteries can be broken down even further by the way they are constructed: Flooded, Gel, and AGM.
These are the lead acid batteries that have caps to add water. Many manufacturers make these types for Solar Energy use. They are reasonably priced and work well for many years. All flooded batteries release gas when charged and should not be used indoors. If installed in an enclosure, a venting system should be used to vent out the gases which can be explosive.
Not to be confused with maintenance free batteries, sealed gel batteries have no vents and will not release gas during the charging process like flooded batteries do. Venting is therefore not required and they can be used indoors. This is a big advantage because it allows the batteries to maintain a more constant temperature and perform better.
- Absorbed Glass Mat (AGM):
Absorbed Glass Mat batteries are in my opinion the best deep cycle battery for Solar Power use. A woven glass mat is used between the plates to hold the electrolyte. They are leak/spill proof, do not out gas when charging, and have superior performance. They have all the advantages of the sealed gel types and are higher quality, maintain voltage better, self discharge slower, and last longer. They are more expensive, but you usually get what you pay for. You will find this type of battery used in airplanes, hospitals, and remote telephone/cell tower installations.
Lithium ion batteries:
The majority of new home energy storage technologies, such as the Tesla Powerwall, use some form of lithium ion chemical composition. Lithium ion batteries are lighter and more compact than lead acid batteries. They also have a higher Depth of Discharge and longer lifespan when compared to lead acid batteries. They are the most dense and able to hold the most charge for their size and weight. However, lithium ion batteries are more expensive than their lead acid counterparts. Lithium ion batteries are the best option for solar, hence they are used by Tesla’s Powerwall. Since they have a longer lifespan than the lead acid batteries, they are a better investment long term.
Nickel cadmium or NiCd batteries have been around since the early 1900s. Though they may not have the energy density (the power) of other technologies, they provide long life and reliability without complex management systems. Nickel cadmium is relatively inexpensive compared with other technologies.
NiCd batteries are vented to allow gases to dissipate. They traditionally require some watering, but new designs allow the gases to recombine to form water which makes the battery nearly maintenance free. This, along with the ability to tolerate extreme temperatures, makes these batteries ideal for off-grid applications in harsh environments. They have been used for storage in megawatt-sized projects.
NiCd batteries are rugged batteries with a high cycle life. Some companies promise a service life of up to 20 years. Cadmium is a hazardous material. In fact Europe limits the applications NiCd batteries can be used in. Toxic materials must be removed before the battery is disposed of. NiCd batteries can be recycled, however. The cadmium can be extracted and reused in new batteries. The nickel can be recovered and used to make stainless steel.
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