How Many Watts of Solar for a 400 Ah Battery Bank?

If you are already using a battery charger for your 400 Ah battery bank, you may want to add an additional charging source – solar for your battery bank.

How many watts of solar do you need? What about the rest of the solar system components that you should have in addition to the solar panels to keep the system charged?

In this post, you’ll get guidance on how many watts of solar you can use for a 400 Ah battery bank plus some guidelines to apply when sizing solar for a battery bank.

Lastly, this post shares some indicative capacities for a charge controller and inverter to use with the solar system

How Many Watts of Solar to Use?

This depends on your appliances’ daily energy use. You should size the solar system to supply more energy than your daily energy consumption to keep the batteries charged with no need for a generator.

The number of watts of solar to use also depends on the battery type – AGM or LiFePO4 battery.

How many watts of solar for a 12V, 400Ah AGM battery bank?

You should use at least 800 watts of solar for the battery bank. This assumes you’re discharging the battery bank to 50% of its capacity, ie.t 50% x 400Ah x 12V, 2400Wh of energy.

Portable Solar Panel
Portable Solar Panel

With a location that receives an average of 4 hours of sunshine per day, it works out as 2,400Wh/ 4 hours, 600 watts of solar.

You should oversize to account for cloudy,overcast days and losses hence the recommendation of 800 watts of solar. If the daily energy draw is lower than 2,400Wh, you can get by with less solar panel capacity.

How Many Solar Panels for 12 V, 400 Ah AGM Battery Bank?

You can use 2 x 400 watt, 4 x 200 watt, or 8 x 100 watt solar panels. These are just a few of the several configurations of solar panels you can use.

The number of panels depends on the watts of the solar panel used as a basic building unit in your solar panel array.

How Much Space the Solar Panels (sq. ft) Take Up?

For 800 watts of panels, plan on at least 60 sq. ft of available space to mount them. This assumes each 200 watt panel takes up about 12-14 sq. ft.

How Many Watts of Solar for a 12 V, 400 Ah LiFePo4 Battery Bank?

A LiFePO4 battery bank has more available capacity compared to an AGM battery bank. If you plan to draw up to 80% of the available capacity then plan on installing at least 1200 -1500 watts of solar if the combined appliances will draw up to 80% of the available capacity.

Calculation

Assuming 80% of the battery back is used up, then you’d need atleast 80% x 400Ah x 12V, 3840Wh of energy from the solar panel to replenish the battery capacity.

With a location that receives an average of 4 hours of sunshine per day, it works out as 3840Wh/ 4 hours, 960 watts of solar.

You should plan on installing about 1200 -1500 watts of solar to ensure that the battery bank is fully charged even during cloudy overcast days.

How Many Solar Panels for a 12 V, 400 Ah LiFePO4 Battery Bank?

You can use 3 x 400 watt, 6 x 200 w, or 12 x 100-watt solar panels. These are just a few of the several configurations of solar panels you can use.

The number of panels depends on the watts of the solar panel used as a basic building unit in your solar panel array.

How Much Space the Solar Panels (sq. ft) require?

For 1200 watts of panels, plan on at least 80-90 sq. ft of available space to mount them. This assumes each 200-watt panel takes up about 12-14 sq. ft.

What Size of Charge Controller and Inverter to Use?

You can use a 60A charge controller and a 1,500-watt inverter or greater for your 800 -1200 watt solar system.

Note: These are just some of the several sizes you can use.

How Long it Takes to Charge the Battery?

The solar panel sizes (watts) above are designed to recharge 50% of the 400Ah AGM battery and 80% of the LiFePO4 400Ah battery in about 4 hours. The actual time to charge depends on how deeply discharged the batteries are.

Closing Thoughts

How may watts of solar you need for a battery bank largely depends on the energy draw of the connected appliances and how many hours of sunshine your location receives each day.

For a 400Ah AGM battery bank, plan on 800 watts of solar. With a LiFePO4, plan on investing at least 1,200 watts of solar.

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