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Sometimes working out the number of batteries and the capacity (Ah) can be daunting as the power requirements often vary – for example, if you use the appliances only occasionally vs. using them regularly.
If you’ve settled on or already have 400 watts of solar and need to work out the battery setup then this post is for you.
Here, you’ll find information on how many batteries, their capacity (Ah), charge controllers, and inverter to get you started on the right foot!
How Many Batteries can a 400-watt Solar system Charge?
A 400-watt solar panel system generates an estimated 1,600 watt-hours of electricity a day (assuming 4 hours of sunshine) or about 400 watts per hour.
This is only a guide, it may generate more or less depending on the average hours of sunshine received.
Using AGM Batteries
You can use a 300 Ah, 12V AGM Battery bank (2 x 150Ah or 3 x 100Ah batteries connected in parallel).
If you’re to store this energy in a 12V battery bank, you’ll need 133Ah of storage. AGM batteries have a recommended depth of discharge of 50%.
So you’ll need double the capacity since only 50% should be used or 2 x 133Ah, 266Ah, or about 300Ah of AGM battery storage.
Using LiFePO4 Batteries
You can use a 200Ah LiFeP04 battery (1 x 200Ah or 2 x 100 Ah LiFePO4 batteries connected in parallel) with a 400-watt solar panel system.
Note: This is one of the several battery configurations you can use with 400 watts of solar.
If you’re to store this energy in a 12V battery bank, you’ll need 133Ah of storage. LiFePO4 batteries have a recommended depth of discharge of about 80%.
So you’ll need double the capacity since only at least 170Ah of battery or can be rounded up to the next standard size of 200Ah storage.
Do You Actually Have to Use this Much Storage?
Not really. However, doing so ensures that most of the energy that is generated on a daily basis is stored.
If you only use the solar system occasionally, you could use a smaller battery bank but be mindful that more of the generated electricity will not be stored.
You may also be interested in this post: How many watts of solar to charge a 400 Ah battery bank?
How Long to Charge a Battery bank with 400 watts of Solar?
The estimated time to charge a 200Ah LiFeP04 battery or a 300Ah AGM battery with 400 watts of solar is about 6-8 hours.
This assumes that the batteries have only been discharged to their recommended depth of discharge – 50% for AGM and 80% for LiFeP04.
The actual time to fully charge the batteries mainly depends on the depth of discharge of the batteries and how many hours of sunshine are received each day.
How Long to Charge 100 Ah Battery with 400 watts of Solar?
LiFeP04 battery
The estimated time to charge a 100Ah LiFeP04 battery is about 3-4 hours. This assumes that the batteries have only been discharged to their recommended depth of discharge – 80% for LiFeP04.
AGM battery
The estimated time to charge a 100Ah AGM battery is about 2-3 hours. This assumes that the batteries have only been discharged to their recommended depth of discharge – 50% for AGM.
This really depends on the combined energy draw of your appliances. That said, this is generally a good starter system to consider when the energy draw is limited such as for an off-grid solar system for an RV, boat or cabin provided the total daily energy consumption of the connected appliances is about 1,600 watt-hours.
An example of what appliances you can run off such a system is shown below.
What Appliances a 400-watt solar panel system can run?
Assumed daily energy production of the system 1,600 watt-hours
- A small fridge, 80 watts for 10 hours, about 800 watt-hours
- 10pcs of 10-watt LED lights for 5 hours, about 500 watt-hours
- 40-watt LED TV for 3 hours, about 120 watt-hours
- 15″, 60-watt Laptop for 3 hours, about 180 watt-hours
Total daily energy consumption is 1,600 watt-hours.
Related Questions
What Size of Inverter (watts)?
The inverter size to use depends on the total AC power consumption of the connected appliances.
That being said, you may consider 1,000 watt or larger pure sine wave or modified sine wave inverter especially if you plan to connect more appliances in the future.
What Size of Charge Controller?
Use a 30-40A MPPT charge controller or larger to protect the battery bank from overcharging.
The 400 watts of solar can supply up to an estimated current of 24 amps (4 x 100-watt solar panels connected in parallel).
Fuse protection for a 400-watt System
You’ll need to install fuses to protect the solar system wiring from damage. The fuse rating (amps) will depend on the wire gauges used.
An example of fuse sizes you’re likely to find used for protection against short-circuit and overcurrent faults in a 400-watt solar system are:
- between panels and controller, 30A
- between controller and battery, 30A
- between inverter and battery, 150A
*Note: Fuse sizes above are indicative. The actual fuse rating depends on the wire gauges used. Always contact a qualified solar professional.
Closing Thoughts
To get started with using a 400-watt solar system optimally, you can use 2 x 100Ah LiFePO4, 3 x 100 Ah AGM batteries, and a 30-40 amp MPPT or PWM charge controller.
There are several inverter options available to you depending on the maximum power consumption of connected AC appliances. You can start with a 1,000-watt pure sinewave or modified sinewave inverter or larger.
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