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Which Type of Batter to Use in Solar Energy Systems


There is a great deal of focus on the panels and solar cells when it comes to installing a solar system on your home. Technicians will expound on the benefits and efficacy of their solar cells compared to competitors but something that is often overlooked but is just as important is the battery that you will be using.

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									Which Type of Battery to Use for Solar Energy Systems

                                       There is a great deal of focus on the panels and solar cells when it
                                       comes to installing a solar system on your home. Technicians will
                                       expound on the benefits and efficacy of their solar cells compared
                                       to competitors but something that is often overlooked but is just
                                       as important is the battery that you will be using.

                                       Spoiler: In my opinion the battery you should use in your system is
                                       an AGM (Absorbed Glass Matt) battery which is a form of lead-
                                       acid battery. Read on if you are interested in knowing more about
                                       the different options.

                                        Batteries all essentially work the same. For simplicity sake
                                        batteries are made up of a number of sheets of metal that come in
                                        pairs. Each pair of sheets is called a cell and the battery is full of
                                        several cells that are wrapped up in the battery’s plastic container.
                                        In each cell there is a positive cathode sheet and a negative anode
                                        sheet. When the cell is charged electrons or ions will move from
the cathode to the anode where they sit as stored energy. The electrons move through a medium that
separates the two cells that is called an electrolyte. Finally there is a semi-permeable, thin material that
sits between the two metal sheets preventing them from touching and causing a short circuit while
allowing electrons to pass through between the sheets. When the battery is used the stored electrons
move back to the positive cathode expending the stored energy. The real difference between batteries
is the type of materials used and the associated chemical process.

There are three general types of batteries that potential solar energy users can consider. These include
NiCad (Nickel Cadmium), NiFe (Nickel Iron) and Lead Acid Batteries. Your best option is probably a good
Lead Acid battery but let’s talk about the other two options first.

Nickel Cadium
In NiCad batteries the positive cathode material is nickel oxide and the negative anode material is
cadmium. The chemical process between these two materials is very much like the generic model
described above. These batteries do have a number of strong points that include low self-discharge
(they don’t lose power over time), non-freezing, and a few other points. However, they are also very
expensive to purchase and dispose of and have low efficiency, between 65-80 percent. They are also
particular in the equipment that can be used with them in a solar power system. The most important
factor is that they really have no better cycle life than a lead-acid battery. This means they don’t
perform particularly well when charged and discharged daily. They are great for back-up systems as
they don’t lose much energy over a long period of time but not for daily use.
Nickel Iron
NiFe batteries use potassium hydroxide as the
electrolyte substance between cathodes of
nickel plated steel and anodes of iron and
steel wool substrate. Don’t worry about the
chemistry between the two materials what
matters is that they have very long life cycles
and can take thousands of charges. More
bang for your buck you may be thinking but
wait one moment as there are a number of
downsides. These batteries have very low
efficiencies; around 60-65 percent as well as a
very high rate of self-discharge (they lose power even when not being used). The energy flow out of
these batteries is also not very steady resulting in flickering lights or appliances. They will lower the
efficiency of your solar system by as much as 25%. Combine this with their limited availability makes
them a poor choice of battery for your home system.

Lead-Acid Batteries
These batteries have been around for over a century and are still used in numerous applications. This is
because the chemical process and efficiency are actually pretty good. The lead and lead oxide materials
used inside of them for the anode and cathode along with diluted sulfuric acid for an electrolyte are also
plentiful in nature making them cost-effective batteries. For 99 percent of solar energy systems these
batteries are your best choice.

There are three main variations of the lead-acid battery: Wet Cell (flooded), Gel Cell, and Absorbed Glass
Mat (AGM). Rather than going into the chemistry of these three different cells I will simply list their
different benefits. The Wet Cell battery is the most common and is probably the one that you have
underneath the hood of your car. They last for a decent amount of time (normal batteries will last 7-12
years while industrial sized batteries can last twenty years). Wet Cell batteries are plentiful and can be
                                                        bought for low prices; however there is nothing
                                                        very significant about their performance.

                                                       Gel batteries contain a silica additive inside their
                                                       electrolyte which causes it to stiffen hence the gel
                                                       name. The recharge voltage of gel batteries is
                                                       lower than other lead-acid batteries making them
                                                       great options for systems like solar energy which
                                                       does not supply high voltage charge to the battery.
                                                       Unfortunately, these cells are also very sensitive to
                                                       over-charging which will destroy the battery. You
                                                       will need to add a regulator to avoid over-charging
                                                       (regulators lower your efficiency). These batteries
are very deep cycle meaning that they store energy well and can distribute low amounts of energy for
extended periods of time vs power batteries which give a short burst of high voltage (like the kind you
use to start your car). Gel batteries will come with a higher price.

AGM (Absorbed Glass Matt) construction have a high discharge and recharge efficiency. These batteries
give the best life cycle of all the lead-acid batteries if they are not discharged below 50 percent. While
this means lowering your efficiency by adding a regulator to ensure the batteries don’t fall below 50
percent the batteries have such high efficiency that this shouldn’t be a problem. These batteries are
becoming increasingly more popular and have taken over the markets that gel batteries have been used
in. They are more resilient than Gel batteries and cost about the same. Both Gel and AGM batteries
carry a higher price tag than normal lead-acid batteries but their performance makes it worth it in the
long run.

Hopefully, this gave you a better idea of the type of battery you will choose. Selecting between an AGM
and Nickel-Cadium battery is just as important as choosing between Helios 255 watt and Helios 310 watt
panels when constructing your solar energy system.

(For those wondering about Lithium-Ion Batteries I didn’t write about them because they are a very
poor choice of battery for solar energy. They have great qualities but only last 3-4 years which makes
them good for cellphones but a terrible idea for solar energy systems.)

Photo Credit: Living Off Grid, Presidency Maldives, RacingMix

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