Car Batteries & Solar Panels

Those new to the solar world have the same question when they see the price of batteries. “Can I use car batteries for my solar system?”

Let me save you a lot of headaches and money with one word, no. Although, they can be used for some small infrequently used solar systems.

Here are some of the things we’ll be covering in this article

  • Types of batteries
  • How Batteries work
  • Car Batteries with solar
  • The best battery for your solar system

This guide will save you time and money – make sure you get the right battery for your solar panel setup.

Car Battery Checking the voltage
Car Battery Checking the voltage

All Batteries Are Not Made the Same?

Before we can discuss why a car battery is not suited for solar applications, it is necessary to know a little about how a battery works.

There is a lot of chemistry involved in battery operation. This is a highly simplified explanation of how a battery provides electricity.

How Batteries Work

Lead Acid Batteries rely on an exchange of ions between sulfuric acid and lead plates to produce current. Acid strength and lead plate configuration determine the power produced by the battery.

How Are Batteries Rated?

Batteries are rated two ways;

A Car Battery is designed to produce a high current for a short time period. Several thin layers of lead are used to create a large surface area for ion exchange to occur.

Such a configuration creates the high Cold Cranking Amps rating advertised on car batteries.

The Cold Cranking Amps (CCA) defines the number of amps the battery can provide for 30 seconds while maintaining at least 7.2 volts.

The range for this value is usually between CCA 300 to CCA 600. While most car batteries do not specify an Amp Hour rating, the average range is 60 – 70 amps at 20 hours.

Deep Cycle Batteries are designed to produce a lower current for a long period of time. They use fewer, thicker lead sheets to create a smaller, more stable, longer-lasting surface area. This configuration provides the higher Amp Hour rating required in deep cycle batteries.

The Amp Hour ([email protected]) rating of Deep Cycle batteries ranges from 100 to 400 amps @ 20 hours. This means that the battery will provide the specified number of amps for 20 hours.

Why Batteries Fail

All batteries experience normal wear. A car battery used in a solar application suffers faster normal wear since the plates are not designed to provide prolonged current. There are two basic wear factors.

Normal Wear

  • Sludge
  • Positive Grid Corrosion

The lead plates shed small flakes during charge/discharge cycles. As lead is shed from positive plates, the material will eventually wear away causing an open connection.

At the same time, the lead being shed falls to the bottom of the battery case as a brown sludge.

If material builds up enough it can bridge several plates causing an internal short. Both of these conditions will result in a dead battery.

Battery Care and Maintenance

The life of Flooded Lead Acid batteries is dependent on regular care and maintenance. There are three basic maintenance factors.

  • Water Level
  • Proper Charging
  • Deep Discharge

All batteries can suffer from these factors. Deep discharge is the greatest enemy of even a well-maintained car battery.

Prolonged load on a car battery can not only cause accelerated wear but can also cause plate damage. Plates can overheat and warp. This will cause an instant failure of the battery.

What Battery Do You Need For Solar Panels?

Since you are reading this article you have probably been looking at batteries.

You have noticed that there are a wide variety of batteries on the market. Many of these are special-use batteries and can be easily eliminated from your search.

Are Car batteries Good For Solar Panels

Car batteries are not suited for solar applications, I must confess that they do have a small range of use.

Car batteries are perfectly suited for light-duty solar applications.

I use a car battery for a solar garage door opener system. The car battery is suited for such an application because it draws a fairly high current for a short period a few times a day.

PROS

  • Inexpensive
  • Saves space
  • Availability
  • Usually 12 volts

CONS

  • Low Amp Hour rating
  • Short lifespan (2-3 years)
  • Light duty only
  • Potential for damage
  • Limited uses

Top rated car battery from Amazon;

ACDelco Gold 48AGM 36 Month Warranty AGM BCI Group 48 Battery

Click the image to see more details on Amazon.

Multi Purpose batteries

Another style of lead-acid battery is the Multi-Purpose battery. As you might suspect, they are a sort of hybrid battery.

They are the same size and voltage as a car battery but are designed to produce current for a longer period without damage.

The CCA ratings tend to be lower than a typical car battery. The Ah rating of these batteries generally remains in the 60 – 70 Ah @ 20-hour rate.

Such a battery may be a better option for a light-duty solar system.

PROS

  • Inexpensive
  • Saves space
  • Usually 12 volts
  • Better lifespan (3-5 years)

CONS

  • Low Amp Hour rating
  • Light duty only
  • Limited uses
  • Can be hard to find

Deep Cycle Batteries

For a real solar power application, Deep Cycle batteries are the best option.

Designed to withstand repeated deep discharge, recharge, and prolonged current draw, these batteries are your best bet when designing a solar system.

Variety

There is a wide variety of configurations available in the Deep Cycle market: 12 volts, 6 volts, small, large. They all have a purpose.

If space is an issue, 12-volt batteries with 100 Ah @ 20 hr ratings are commonly available. Higher Ah units are available but with more capacity the size increases.

PROS

  • 12 volt
  • Easy to handle
  • Easy to store
  • Reasonable Ah rating
  • Good Lifespan (5-7 yrs)

CONS

  • Limited Ah hour ratings
  • Higher Ah requires larger size

The L16 Lead Acid battery is a standard in off-grid solar applications. These units have ratings of up to 400Amps @ 20 hrs.

They are 6-volt batteries, so usually need to be used in pairs to create 12 volts. They are big and heavy but have life spans of up to 10 years. For an off-grid home, these are a good place to start.

PROS

  • High Amp Hr rating.
  • Long life span
  • Industry Standard

CONS

  • Big and heavy
  • Can be pricey

Here’s a power 200Ah deep cycle battery – Renogy on Amazon;

Renogy Deep Cycle AGM Battery 12 Volt 200Ah for RV, Solar, Marine, and Off-grid Applications

Click the image to see more details on Amazon.

How To Choose The Right Battery For Your Solar Panel

When setting up a solar system, whether it be in an RV or an Off-Grid Home, the batteries are the most expensive part of the project.

They can also be the Achilles Heel if not chosen wisely. If there is not enough Amp Hour capacity, they will not get you through the night.

Low capacity will also shorten the lifespan of the batteries due to the high depth of discharge.

Inexpensive car batteries may ease the pain today, but they will cost you tomorrow. Improper battery construction and chemistry will reduce the effectiveness of your system and shorten the life of the battery.

Your best course of action is to do some research before you shop.

There are many good websites with information and calculators to help you determine how much battery capacity you need. If research is not your strong suit, find a reputable solar supply or battery shop.

They will work with you to evaluate your needs and find the best battery for your situation. I can promise, that battery will not be a car battery.

Sources:

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