The number of solar panels to charge our batteries should always be calculated correctly to avoid undercharging of our solar batteries.
In my previous post, I wrote about how we can connect our solar panels to get our batteries charging through sunlight. But I came to understand that many are finding it difficult to calculate how many solar panels to charge our battery within a period. We have so many wattages (watts) of solar panels and different amp-Hour (AH) ratings of solar batteries. When choosing the batteries and the panels to charge them, we should be careful with our calculations to make sure our batteries charge well during the day.
In this article, I will explain in detail how many solar panels we need to charge particular batteries. So is expected that after going through this blog post, you should be able to tell how many watts of panels are to charge particular batteries within some hours. So stay focused as I lick the secrets behind the calculations.
how do solar panels charge our solar system batteries?
The solar panels charge batteries just like our motor battery charger which is used to recharge our car batteries. But little difference exists in the solar panel because all the energy it generates to charge the batteries are coming from the sunlight.
our solar panels charge our system batteries by generating energy from the sun and injecting them into our battery cells to energize the weak cells. In the aspects of the solar panels, we will be focusing our attention on the power of the panels. Because that is what will help our calculations to be correct.
In charging batteries using solar panels, there are some factors we must put into consideration. These factors contribute a lot to the time to charge a particular battery. These factors are as follows;
- The amount of charge the panels are receiving from the sunlight at a particular time.
- The depth of discharge of the battery. (DOD). The discharge rate of a battery depends on the type of the battery. Lithium and AGM are the most common use solar batteries. They are deep cycle batteries having DOD of 50%, which makes them discharge slowly unlike car batteries.
How to calculate watts of solar panel to charge solar batteries.
After you might have installed the batteries and the inverter, the next thing is to do this calculation to keep the battery charged all the time. From this calculation, you will be able to determine the number of panels to use for the installation.
To start this simple calculation, we will find out the followings from our solar system.
- The volt of the batteries, or the inverter.
- Watts per hour (watts-hour) of the batteries. You can get this by multiplying the amp-hour of the battery by its voltage.
- The percentage of depth of discharge of the batteries.
Depth of battery discharge of our solar batteries.
the DOD of a battery is the percentage of energy a battery can deliver before recharging again. It is measured in percentage. Different type of solar batteries has their DOD. Some are 50% 70% or even 90% depending on the type of materials used to manufacture the batteries. When determining the solar panels to charge our batteries, we should always consider this factor as it helps in our calculation.
Let’s, for instance, a 200Ah battery with a DOD of 50%. What it means is that the battery only discharges 100AH while it retains the other 100AH. So in charging this type of battery, we only charge for the discharged 100AH. Is always ideal not to drain our battery charges to 0% before recharging them again so as not to strain the battery cells and cause damage to them.
some solar batteries like lithium and AGM are the most commonly used batteries for solar systems. They have a DOD of 50% and discharge slowly compare to other car batteries.
how many 300watts of solar panel can charge a 200AH battery.
The 300watts solar panel can charge the 200AH battery but the issue is how long will it take to charge it fully. Because it will be of no use if the panels spend like 48hour before charging full our battery.
So to tell how long it will take the panel to charge the 200AH battery, we need to convert the battery from AH amp- hour to Watts- hour. To do this we are to multiply the Amp-hour (AH) by the voltage of the battery.
that is 200AH × 12V = 2,400watts per hour.
so is clear that the 200AH battery needs a solar panel that can produce 2,400W power to charge them for an hour.
so depending on the rating of the panels to be used, will determine how we can configure them to achieve a 2,400W 12V panels. But when we have a 300W 12V solar panel it can as well fit in to charge the 200AH. So far that the panel rating in W must be greater than the battery rating in Watts-Hour.
So to know how long it will take before 300W of panel charge 200AH full. i.e the time for the panel to charge the battery. To calculate for how long it will charge the battery, we divide the battery rating in Watts- hour by the watts of the solar panel.
Time to change the panel = 2,400WH/300W = 8hours
From our calculation above, it will take 300W of panel 8 hours of steady sunlight to charge the 200AH battery. That is when the sunlight reaching the panel is at its peak. When we increase the panel watts, then the time to charge the battery is then reduced. To make our estimates and calculation correct, then we put the Dept of battery discharge into consideration.
Determining the watts of solar panels to charge solar batteries.
Let for instance, am having a 220AH, battery with DOD of 50%. How do I choose the correct watts of panels to be able to charge the battery within 24hours.
To solve our problems, we need to convert the AH of the battery to WH. Which is 220AH × 12V = 2640WH.
Then the battery rating in WH multiply by the DOD. which is 2640WH × 0.5 = 1320WH. So this system battery is meant to power a 1340watts of load for only an hour. To keep the battery safe, we don’t suppose to drain the battery below 50% which is its DOD.
so in choosing the Watts of solar panels to charge this battery, I will consider how many watts will be able to charge 1340WH within some hours of sunlight reflection.
let’s say I want the battery to charge fully within 8hours. Then it will be 1340WH/watts of the panel. = 8hours of sunlight. So cross dividing and arranging the equation, we then have 167.5 watts. So the battery needs 167.5watts to be able to charge the battery for 8 hours. But because the sun intensity changes and weather effect too. 167.5W panel will not give you exactly 167.5W. So we then choose higher watts of like 200watts panels.
For us to build a good solar panel installation, we need to understand how we can calculate the watts of solar panels to charge our batteries within a specific time. This alone helps us to build a system that will not fail easily. Hope you find the contents useful. Use the comments section for questions relating to the topic.