Thoughts about Using Lead ACID Car Batteries in Solar Installation

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Lead acid car batteries can be used for more than just starting your car and can in-fact be used within a solar installation to store your electricity. Depending on what you want to do they may be more affordable than there lithium counter parts. In-fact lead acid car batteries may be a great way to get started with your solar project. It was the only way for me to get started in my own solar DIY projects.

The lead acid batteries can be used in series or in parallel to get additional power storage. In my solar installation I actually re-used an old car battery from WALMART that is now over 5 years old. I decided to purchase the exact same battery and place them in parallel to be able to store more amps. For my first solar system I currently have two lead acid car batteries wired in parallel.

It would be nice to upgrade my systems to lithium batteries as there is an array of advantages to them. There are a host of lithium batteries on the market marketed at DIY solar. Unfortunately it is off the table due to costs. In my opinion the biggest advantage to a lead acid battery is the low cost.

Benefits of Utilizing LEAD ACID Batteries

• Cost. I paid $70.00 USD at WALMART for my 595 CCA (Cold Cranking Amps) batteries. The 595 is among the minimum sized car batteries that you can purchase form WALMART. Likewise, WALMART appears to have the best pricing for lead acid car batteries.
  
  
• Availability. Car batteries are available in conventional brick and mortar retail stores such as WALMART and AutoZone. There are often refurbished car batteries available at various local businesses. A lithium battery may not be available locally and may only be available online or at specialized stores.
• Work in Lower Temperatures. Lead ACID batteries typically will work in lower temperatures as per a car can start in cold temperatures - sometimes even lower than 32 degrees Fahrenheit.
• Easy to Interface With. Most charge controllers on the market are compatible with lead acid batteries, right out of the box, by default. Additionally, the top posts are pretty standard and you can readily find terminals for the posts.

Cautions When Using Lead Acid

• Lower Tolerances. It is generally only safe to drain the battery to 50% level. That is right around just north of 12V. Generally it is bad news to go any lower than 12V. A lithium battery is safe to drain down to 30%.
• Less Charge to Dead Cycles. A lithium battery can handle draining to 0% many more times than that of a lead acid. It is never a good idea to completely drain a lead acid car battery. If it happens it isn't necessarily a death story but you should definitely set the charge controller to shutoff all discharge after 12V.

Plausible Uses W/ Car Battery in Play

Pretty much everything, it is just important to make sure your battery doesn't go completely dead or under 50% charge state to many times. Typically things like lighting, light-weight electronics such as cameras, routers, or access points.

Thoughts about why My Batteries are in Parallel

As pictured, my solar system's batteries are wired in parallel. I decided to wire them in parallel as opposed to series for a couple of reasons. A series configuration would make my system more versatile as opposed to a 12 volt system. Longer application wire runs would be possible with a higher voltage.

Wiring the batteries in parallel increase the system's amp hours (aH). The solar panels, under full sunlight produce about 18-19V DC. While 18-19V is higher than 12 volts of a typical car battery, it is important to remember that a lead acid battery can handle up to 15 volts before it gets fried.

The MPPT charge controller drops the voltage down while it regulates the voltage that goes into the battery. As it drops from 19 volts down to 14 volts, some electricity is lost.

Despite the lost electricity, in my view it was still better to configure the batteries in parallel to increase the systems amp hours. Only around 4-5 volts are lost through the regulator's voltage dropping phase. As of updating this post my batteries have been charged daily by my solar panels for 3 years. The batteries have held up great.