The bulk of solar panels on the market are either 100 watts or 200 watts, and while the more significant wattage is usually preferable, as we’ll see, this isn’t always the case.
A 100-watt solar panel is half as powerful as a 200-watt solar panel. Therefore it will take double as long to charge a battery with 100W as 200W. Placing two 100W panels in parallel will make the system charge faster than a 200W panel, but it will take up more space and more weight.
The differences between a 100W or 200W solar panels
- The physical size
- The charging output
- Weight of the panel
After reading this article, you will be able to figure out every type of scenario you may face effectively.
Are 2 X 100W Panels The Same As A 200W Panel?
Yes, they have the same output capacity but with a slight difference.
The two 100W panels will provide 200W of electricity at peak capacity, so you’d think they’d be the same; nevertheless, there are some differences to consider. Calculations will be used to demonstrate these differences.
If you place the 2 x 100W panels in parallel, you will get 200W of output but with a lower voltage and higher current. To understand this better, we will use the following equation to calculate the amps: Watt ÷ Volt = Amps.
For example, you can calculate the current if you have a Renogy 100 Watt 12 V Monocrystalline Solar Panel with an optimum operating voltage of 20.4V. Calculation: 100W ÷ 20.4V = 4.9A. The optimum rating of their 100W panel on their website is 4.91A.
If you placed the 2 x 100 W panels in parallel to produce a 200W array, the volts would be the same at 20.4V, but the amps will be 2x 4.91 = 9.82A. (You can also place them in series, multiplying the voltage, whereas the amps will stay the same)
Their website shows an optimum operating current for their Renogy 200 Watt 12 V Monocrystalline Solar Panel is 8.85A and 22.6V.
So we conclude that 2 x 100W panels will have a lower voltage (20.4V vs. 22.6V) but higher current 9.82A vs. 8.85A) than a 200W panel. This slight difference does not seem much, but it makes a difference in your system’s total resistance and efficiency.
The dimensions of the panels also come into consideration since a 200W solar panel occupies only 11.90Ft² and weighs 26.46lb, whereas 2 x 100W panels will need 6.01Ft² x 2 = 12.02 Ft² and weighs 14.5lb x 2 = 29lb.
Again, this slight difference does not seem much, but those few inches and pounds may be problematic on an RV or other installation.
How Long Does A 200W Solar Panel Take To Charge A Battery?
The time it will take to charge a battery depends on the battery chemistry, discharge level, the charge cycle degradation, and temperature.
To address this issue, we will compute the recharge time by simply taking into account the battery’s charge and ignoring any draw or other loads from the system and cycle and charging efficiency.
Assumptions about the charging scenario:
- The battery is a 12V, 125AH
- The battery is at 70% capacity
- 200W solar panel
- We will use a charge controller for optimal charging
With a 125AH battery at 70% capacity, we still have 87.5Ah left. Therefore we require 12.5Ah of charge to replenish the 30%. So how long would a Renogy 200 Watt 12 V Monocrystalline Solar Panel with 22.6V optimum charging capacity take to charge the 125AH?
We will use the following equation W = V x A to calculate the charging current.
- 200W ÷ 22.6V = 8.85A
- Now take the 30% required and divide that with the charging current.
- 12.5 ÷ 8.85 = 1.41 (time in decimal)
To convert a decimal to time, you need to take the decimal portion of the number and multiply that by 60 (minutes in an hour)
- 0.41 x 60 = 24.6 hours. Now calculate the seconds in the same manner.
- 0.6 x 60sec = 36sec
Therefore it will take the 200W panel 1hour, 24 minutes, and 36 seconds to charge the battery to 100% capacity assuming optimal charging conditions.
Will The 100W Solar Panel Charge The Battery Quickly?
The Renogy 100 Watt 12 V Monocrystalline Solar Panel will take 2 hours and 33 minutes to charge the remaining 30% of the battery, so don’t expect it to happen quickly.
Using the information in the previous sections, we can calculate the time it would take to charge the battery fully.
- 100w ÷ 20.4V = 4.9A
- 12.5(30%) ÷ 4.9A = 2.55 (time in decimal)
- 0.55 x 60 = 33 (Convert to hours and minutes)
- Therefore 2 hours and 33 minutes
Will The 2x100W Solar Panels Charge Quicker than the 200W?
Yes, it will take the 2 x 100W solar panels in parallel 1hour, 16 minutes, and 12 sec to fully charge the remaining 30% of the battery, which is 8 min quicker.
So now you can see the slight difference we talked about earlier between the 2x 100W and 200W panels is 8 minutes when you calculate the difference.
How Many Batteries Can a 100-Watt Solar Panel Charge?
Depending on the battery capacity, chemistry, and some other factors, one or two.
There is no quick answer to this question since you need to consider many factors such as battery chemistry, discharge cycle, etc. Below, we will go into a more elaborate explanation.
There are a few issues to consider when answering this question.
- What is seasonal ambient temperature: temperature effect battery charging quite a bit.
- Type of battery chemistry: Lead-acid, Lithium-Ion, or Lithium Iron Phosphate
- The battery’s discharge cycle: batteries degrade over time, making their charging efficiency slower.
- The charging controller: pulse width modulation (PWM) and maximum power point tracking (MPPT) are the most common.
- Resistance in the system: every battery, cable, and piece of equipment has a resistance it adds to the solar system
- Drain on the system: do you draw power from the solar system while charging the batteries?
Lead-acid batteries should not discharge below 50%. Because the amount of charge current that lead-acid batteries can withstand is restricted, mainly because they can overheat if charged too rapidly.
Furthermore, when you near full capacity, the charge rate slows dramatically.
100 Watt Solar Panel Charging a Lead-Acid Battery
Lead-acid batteries, for example, are only 80-85% efficient, depending on the brand and cycling condition. That implies that if you have 100 watts of solar power streaming into the batteries, you’ll only have 80-85 watts accessible after the charging and discharging process.
Lithium batteries have an elevated efficiency of over 95%. So you’d have around 95 watts of electricity available in the same scenario. Your batteries will charge faster if they are more efficient.
We will use the Renogy 100 Watt 12 V Monocrystalline Solar Panel again to answer the question. We already know from the previous calculations that this panel will charge at 4.9A per hour.
Therefore, we will assume no efficiency loss, no system resistance, no additional drain, and no cycling degradation on the batteries.
Still, assuming 3 to 9 hours of sunlight per day, your solar array will generate anything from;
- 100W x 3hours = 300W on a gloomy day to roughly
- 100W x 9hours = 900W on a beautiful summer day
With this in mind, we can estimate 14.7Ah (3hours x 4.9A ) to 44.1AH (9hours x 4.9A) of charge per day.
As a result, charging one 60Ah lithium battery from 10% (general rule of max discharge) will take 11hours or two days. On the other hand, a 60AH lead-acid battery discharged to 50% will take 6 hours.
In reality, the lead-acid will take much longer because of inefficiency.