How Many Watts Solar Panel to Charge a 12V 200Ah Battery

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A 200ah battery is a sizable battery used in stationary applications such as backup power and UPS (uninterruptible power supply) systems. It has enough capacity to operate numerous appliances including Computers, TVs, and even refrigerators.

Adding Solar Panels adds an extra advantage for uninterrupted power from blackouts, brownouts, and downtime caused by natural disasters.

To charge a 200 Ah battery you will need around 40 Amps. This is a lot of power. To get 40 Amps from a Solar Panel you will need around 480 Watts. But you may need to scale up the system up to 600 Watts to charge the battery fully.

We show how to size the solar panel and create a system that can run your appliances with these solar panels.

How to Size Solar Panels to Batteries

The best way to match a solar panel to a battery is to match the watt-hour requirements. A watt-hour is a unit of energy equivalent to one watt of power produced for one hour of time. Batteries capacity is usually indicated in Amp-hours but this can be converted to Watt-hours. Some batteries will actually have the Watt-hours indicated.

To convert Amp-hours to Watt-hours you simply multiply the Amp-hours by the Voltage. In this case, our battery is a 12v battery so:

200 Ah x 12v =  2400 Watt-Hours

2400 Watt-hours is the total power capacity of our battery. So to fully charge the battery from solar panels you will need 2400 Watt-hours from a solar panel.

Does this mean you need a 2400-watt solar panel? No. That will be a stretch. Your Solar Panel or Panels will need to produce 2400 Wh in the course of the day. So depending on the conditions, location, and time this will determine the number of sun-hours you will get.

Assuming you get 5 hours of optimal conditions in a day. Then you will divide the watt-hour requirements by this time. Therefore:

2400 Watt-Hours/ 5 Hours =  480 Watts

A 480-watt solar panel can produce 40 Amps in direct sunlight. In 6 hours this should be provided around 240 ah. This should recharge a 50% discharged 200 ah AGM battery.

However, you will always need to oversize your system. As you can see in our example we have only gone halfway with our 100 ah. You will need to double the solar panel if you want to recharge the battery fully. There are also other reasons as to why you need to compensate.

What Solar Battery Maintainer for 200 Ah Battery

For a maintenance charge, even 1 amp is enough to maintain the battery. An AGM battery bank discharges around 1 – 3% per month.

So a small 10-watt trickle charger is enough to maintain the battery bank for long periods of time. Actually, a trickle charger can be left on all the time as it only charges the battery at the discharge rate.

How to Make Sure Your Solar Panels are Efficient

It is important to ensure that you are getting the best out of your system. You may think you need to add solar panels but you get a few more precious with the following tips

A charge controller is a device that regulates the flow of electricity from a solar panel to a battery. There are two types of charge controllers: MPPT and PWM. An MPPT Controller uses an algorithm to constantly monitor the solar panel’s voltage and current output. It then adjusts the voltage to push up the amps to ensure that the battery is being charged at its maximum possible rate.

A PWM Controller simply switches the solar panel’s output on and off very rapidly. This on/off switching protects the battery from overcharging and overvoltage.

Use a Temperature Sensor

A temperature sensor is attached to the battery to monitor the battery’s temperature. Lead Acid batteries usually heat up when power is being pumped in and a temperature sensor allows the controller to take note of this and adjust the current going to the batteries to avoid overheating.

Overheating can damage the batteries and lead to gas hazards from lead-acid batteries.

Lithium batteries can also not be discharged in low temperatures and you’ll need to disconnect them in case temperatures fall below 5 degrees.

Other Ways to Ensure Solar Panel Efficiency

Angle the Panels

Always make sure the panels are facing direct sunlight and make sure there are no shadows where you have placed the panels. This will ensure that you get the maximum sunlight exposure to your panels.

Make Sure the Panels Are Clean

Always make sure to wipe off any debris or dust on the panels as they can also interfere with efficiency.

Minimize Cables

Long cables and a lot of wiring can cause losses. They may be insignificant but if you add them throughout many cables they can cause significant losses.

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