When you want to charge a 12v battery with a 100-watt solar panel, there are several things that can affect how long it takes.
In this article, we will consider all factors that affect charging time and come up with an estimate on how long it would take to charge a 12v battery from 0% capacity to 100% capacity.
The first and most important thing to know is that solar panels typically produce a lot more power at higher voltages.
To put it in perspective, a 100w solar panel (which we will be discussing in this article) actually produces an average of about 160w at 17v.
To see the exact wattage output for a given voltage, look up your solar panel on one of the many solar panel calculators found online.
Factors that affect charging time of 12v Battery with A 100-Watt Solar Panel
There are many different factors that can affect how long it takes to charge a battery with a solar panel, but we will discuss the five main ones.
1. Intensity of the sun
The intensity of the sun will affect how fast your battery charges. With almost no cloud cover, solar panels can generate significantly more power than when covered in thick clouds.
According to the solar intensity table, on a sunny day (about one hour after sunrise) you will be able to get about 1320w from a 100-watt solar panel.
This means that it will take about two hours to charge a 12v battery from 0% to 100% on a sunny day.
2. Maximum power point voltage
The maximum power point voltage is the voltage at which your solar panel will operate at its maximum PowerPoint.
With this voltage usually being about 0.5v-1v higher than the panel’s voltage rating, it is important to know this number if you want to calculate your panel’s wattage rating.
The maximum power point voltage is different for every solar panel, so you will need to find yours. For example, 100-watt Renogy solar panel has a maximum power point of 17v.
If you look for this number on your panel, it should be printed somewhere on the panel’s circuit board.
3. Wattage Rating of The Solar Panel
As we mentioned in an earlier paragraph, the wattage rating of a solar panel is very important.
This number tells you how much power your panel can produce at a given voltage, which will come in handy when we calculate how long it takes to charge a battery.
4. Battery Capacity
The capacity of your battery will affect how long it takes to charge your battery. Usually, you want to choose a battery with half the capacity of what you’re trying to charge, and this is especially important when charging at low voltages.
For example, if you use a 100-watt solar panel to charge a 12v 100ah battery, it will take twice as long to charge. This is because your panel can only produce half the power at this low voltage.
5. Charger Efficiency
The last thing that affects your charging time is how efficient your charger is. Different chargers have different efficiencies, so it is important to research your charger before buying.
For example, our 100w Renogy solar panel has an efficiency of about 18.5%, so when charging with this panel, you should expect it to take about 20% longer than normal (if your charger is 100% efficient).
How Long It Takes to Charge A 12v Battery
Now that we have discussed all of the factors affecting charging time, it’s time to put it all together. But first, there are a few assumptions we have to make.
In this calculation, we assume that the solar panel is always getting direct exposure from the sun, and we assume that the battery is at 0%.
With this in mind, we will now calculate how long it takes to charge a 12v battery with a 100-watt solar panel.
First, we need to find how much wattage our panel can produce at 12v. Dividing the 100-watt rating by 12v, we get 8.3 watts.
Next, we need to find the maximum power point voltage of our panel. Dividing 17 by 8.3, we get 1.8v (maximum power point voltage).
We can now calculate how long it takes to charge a 12v battery with a 100-watt solar panel. To do so, we need to know the capacity of our battery and how efficient our charger is.
Since we need the charger efficiency in percent, we will divide 100 by our charger’s efficiency. For example, if we have a 20% efficient charger, we would divide 100/20 = 5. If we used a 100-watt solar panel with this charger, it would take our battery 5 hours to reach a full charge.
As you can see, there are many variables that will affect your solar charging time. Charging time also changes based on how many hours of direct sunlight your solar panel receives per day, so it is important to do research before you buy a solar panel.
Now that you know how long it takes to charge a 12v battery with a 100-watt solar panel, we can use this information to calculate how long it takes to charge any size battery with any solar panel.
Here is the equation we will use: (Power of your solar panel in watts) x (how many hours your solar panel is getting direct sun) / (your battery’s capacity in amp-hours) = how many hours it takes to charge your battery
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I am Baker Hughes and I live in the USA. I am an electrical engineer and work with 12 Volt products. I want to explore this section more because it is an area of interest for me that has been developed over time. I have 10 Years of experience with 12 Volt products, specifically wiring, installation, guide, reviews, and troubleshooting.