How Many Watt Solar Panel to Charge Deep Cycle Battery

Written by John Ho on October 11, 2020
How Many Watt Solar Panel to Charge Deep Cycle Battery

Switching to an off-grid lifestyle can be a little tricky for many people. Especially for people who have never been exposed to solar panels' technicalities before and have no idea about how many watt solar panels charge a deep cycle battery.

A similar case occurred with me back when I was installing solar panels for my home's water pump. Due to my lack of experience and knowledge of solar panels, I installed a low wattage solar panel, and what happens if you install a weak solar panel is that the battery takes up a lot of time to charge fully. My water pump could not function properly due to this problem.

Eventually, I replaced the weak solar panel with the one which was actually compatible with the battery after doing some in-depth research.

If you are also a first timer in the 'go green' trend, then you can take full assistance from this article and easily determine what solar panel is best for your needs.

Know Your Power Appliances

The first thing you should do before figuring out the size of the solar panel you want to install is learning the power outputs of all the power appliances you are planning to hook up to the solar panel.

You can find the power output information on the labels of the electrical appliances. Usually, the information is given in the unit of watts.

After checking the wattage of the appliances, multiply the respective wattage of an appliance with the respective time that it is used.

For instance, if an appliance is of 40 watts and it is used for 5 hours.

40 watts × 5hr = 200WH


Watt×time used


If the power output on the label of your power appliance is given in Ampere. Then, you can easily convert into watts by this formula,

Watt = Amp × Volt

The voltage is always given whenever the output is shown in Ampere.

How To Select The Size Of The Dry Cell Battery

The size of the battery is pivotal when opting for a solar panel because it is not the solar panel that powers the hooked electrical appliances.

In fact, a solar panel only charges the battery.

It is the battery that powers the appliances.

Always go for the battery that will be able to store enough power for you to run your appliances smoothly.

To calculate the size of the battery for pairing with a solar panel, use this method.

Convert the Ah (amp hours) of the battery into Wh ( watt-hours) by multiplying Ah by voltage.

In simple words,

If the Ah of the battery is 60 and the battery voltage is 6 V.

WH = Ah × V

360 = 60 × 6

Now, if your total power consumption in a day would be around 400 watts, then you should get a 60 Ah battery with a battery voltage of 12 V in order for you to run your appliances smoothly.

Always get a battery that can fulfill your needs at around 50 % charge.

If you are still confused about calculating the total amount of wattage of your electrical appliances, follow this detailed explanation.

For say, the microwave that you will be hooking with solar energy is of 40 W, and you will be using the microwave for a total of 5 hours in a day, then the total power consumption of your microwave would be,

40W × 5hr =  200WH

In the same way, if the iron is of 20 W and is used for a total of 7 hours per day, then the total power consumption of your iron would be,

20W × 7hr = 140WH

The total consumption of these appliances in a day would be,

200 + 140 = 340 watts

In the same way, you can also easily calculate the total/day power consumption of your electrical appliances and decide the battery's size best for your needs by yourself.

How To Select The Best Wattage Solar Panel For Your Battery

After selecting the battery size that would be best for you, it is now time to choose the most suitable solar panel size for that particular battery.

Keep in mind that a solar panel is only capable of generating electricity during the day time. It is important to calculate the amount of energy it can calculate over a certain period.

To calculate the amount of energy the solar panel will generate in a day, you will need the power generation rating of the solar panel, which is given in watts and can be found on the solar panel label.

If your solar panel rating is 70 W, then multiply it with the number of hours it will be exposed to the sunlight in a day.

For instance, if it will be exposed to sunlight for 7 hours a day.

The power generated over some time = 70 × 7 = 490WH

This calculation shows that 490W will be the amount of energy that the solar panel will give to the battery in a day.

The calculated energy is just an estimate as many other factors like weather and more often cause the calculated number to fluctuate.

Now, if you want to calculate which solar panel will be best for charging your required battery, follow the method given below.

If your battery's capacity is 90Ah with a battery voltage of 12V and the rating of the solar panel is 20W.

First, convert the rating of solar panel from watts to Ah by this formula,

Ah = watts/V

In our case,

Ah = 20/12

Ah = 1.6

Remember that the voltage in a solar panel is not always 12 V. You can find the voltage on the label or any paperwork given with the solar panel.

After converting the solar panel rating into amps per hour, divide the capacity of the battery by the converted rating of the solar panel.

In our case,

= 90/1.6

Charging time = 56.25 hours

Now add 10% of the charging time, which is 56.25 into 56.25.

Average charging time = 56.25 + 5.62 = 61.8 (approximately)

Using this method, you can determine the solar panel that will be best for charging your battery.


Now, I am going to answer some questions that get asked frequently. So, if you have any questions, you can find the answers here.

In case your concern is not addressed here. You can add it in the comments, and I will surely try to respond there.


I hope you find the answer for your question "How many watt solar panel to charge deep cycle battery".

As the technologies used to harvest renewable energy are progressing and becoming more efficient with each passing year.

More and more people have started to switch their home electrical grid systems to renewable energy.

And one of the finest forms of renewable energy is solar energy. Solar panels are required to extract this form of energy.

You have to keep certain things in mind when selecting a solar panel to make sure that it will work best for your needs.

For you to select the best solar panel and battery to power your appliances, I have shown all the calculations and methods through which you can figure out the best equipment for yourself that will prove to be beneficial for you in the long run.

Article written by John Ho
Our goal is to provide you with comprehensive and thorough solar-energy product guides, which will leave you confident that you have made the right purchase decision for your home.

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