What solar panel size do I require to charge a 12V battery?

By Lee Stauss Updated on October 07, 2021

If you have plans to run a completely off-grid solar system, or you prefer to use solar energy to meet your energy needs while you are away camping or in your RV, having a knowledge of the type and size of solar panels required to charge your battery is very vital.

In reality, inasmuch as you’re using 12V solar panels, the truth is that you can use any style and size of the panels to charge your 12V battery. However, this is not relatively simple as just connecting your panels directly to the battery.

In this article, we will explain what size solar panels you require to charge your battery, what type of equipment is needed to ensure everything runs smoothly, and how long it will take your battery to charge using solar power.

Batteries and your solar installation

To meet all your energy needs, a solar-powered system having battery storage is an excellent option for those who live in RVs, vans, or cabins. After you have chosen your solar panel kit, you’ll need to purchase a battery to store the energy generated by your panels. But, how can you ensure that your battery is fully charged and can provide the energy you require? Follow this article.

Deep-cycle batteries

Although they might appear similar to the batteries in your car, however, they’re quite different. Unlike car batteries that are designed to only offer energy in short bursts, deep cycle batteries provide prolonged energy over a longer period. These batteries can be discharged up to 80 percent, however, manufacturers recommend that you do not discharge less than 45 percent. Continually going lesser than that limit can reduce the battery’s life span.

How are batteries charged using solar panels?

The energy generated by solar panels is stored in solar batteries. The larger the capacity of your battery, the more solar energy it will store. For your solar installation, you’ll require solar panels, a charge controller, an inverter, and batteries.

Using batteries as part of a home solar system allows you to store excess electricity generated by your panels instead of sending the excess energy back to the grid. However, if the batteries are charged to capacity, and your panels continue to produce energy, electricity will be sent to the grid in your area.

A charge controller prevents overcharging. It monitors the amount of energy stored in your batteries. Charge controllers will automatically shut down the system when the batteries are depleted.

An inverter converts the DC energy from the solar panels to AC. Make sure that your batteries are connected to an inverter before putting on your appliances.

What are Amp Hours?

Amp-Hour rating is the amount of current that is provided by the battery for a certain period. All deep-cycle batteries have a unique amp-hour rating. For Instance, if you have a 150Ah battery, it can supply 10 continuous amps for 15 hours or 15 amps for over 10 hours.

How many Amps do 100-Watt panels produce?

You calculate Current (Amps) by dividing the power (Watts) by the voltage (Volts). A solar panel rated as 100W, 12V has an instantaneous voltage rating. If all conditions are fulfilled when tested, the output voltage is usually around 18 Volts. Since Watt = Volts X Amps, Amperage equals Watts divided by Volts. This implies that 100 Watts divided by 18 Volts will equal 5.5 amps. Thus, your solar panel will produce 5.5 Amps per Hour.

How many panels will it take to charge a 200AH battery?

As a result of depletion limitations, only 80 percent of a 200AH battery is usable. This means you only have about 160 Amp-Hour worth of energy to use. If you typically consume 80 Amps daily, this means that you can last up to two days on that battery.

Based on the previous calculation, a 100-Watt solar panel produces around 30AH daily (for an average sunny day). To fully recharge your battery, you will require three solar panels of 100 watts, or a 300-watt panel.

How long does it take to charge a battery?

The time required to charge a battery is dependent on the weather conditions, as well as the state and type of the battery. A panel can typically charge a completely drained battery between five to eight hours.

The total charging time will differ based on the condition of the battery. A solar panel can fully charge the cells of a completely drained battery within five to eight hours. The sun’s position in the sky can affect a panel’s charging speed. When sunlight is directly shining on a panel during the middle of summer the charging speed will be higher. However, on cloudy days, charging cycles are slower.

What are the best conditions for charging a battery?

There are specific requirements for every battery such as operating temperature, storage temperature, and operating charge temperature. Most batteries have an average operating temperature of 77°F or more or minus 5.4°F. Most batteries operate between 50°F and 85°F. The internal chemistry of the batteries slows down, charge acceptance and capacity drop, and resistance increases. The decrease in capacity is only temporary.

Does the type of battery matter?

Yes! Batteries can have a significant impact on the operation of your solar installation. There are three main kinds of deep cycle batteries utilized in solar systems. They include sealed lead acid, lithium iron phosphate, and flooded lead-acid batteries. Each battery comes with a distinct price, capacity, voltage, and life expectancy.

Lithium vs flooded lead-acid batteries: which ones charge faster?

Lithium iron phosphate batteries are better than flooded and sealed lead-acid batteries. They also charge faster. This is because they can handle a higher amperage. Therefore, they recharge much quicker than flooded lead-acid batteries. The charge current that lead-acid batteries can handle is limited. This is mainly because they can overheat if charged too fast. Also, as you approach full capacity, the charging rate will become significantly slower.

How can I determine the size of my battery bank? Why is this important?

It is vital to correctly size the deep-cycle battery bank. The amount of battery storage needed is dependent on your energy usage. Energy usage is calculated in kilowatt-hours. For instance, 500 Watts/Hour for 8 hours per day would equal 4kWh per day. For a typical four-person household, a battery capacity between 4 and 8 kWh is sufficient. However, your energy requirements may differ from this based on what you’re powering in your home.