# How many solar panels does it take to charge a 150 AH battery?

If you’ve been planning to install an off-grid solar energy solution, it is an obvious thing one can ask: How many watts of solar panels do I need to charge a 150 AH battery? Or how much time it takes to 600 watts of the solar panels to charge a 150 AH battery full?

In this article, we’ll explain the basic calculation of the solar panels’ capacity or wattage requirements to charge a battery bank.

First, let us calculate the battery watts. Inverter batteries come in 12 Volts capacity, let’s say you have a 150 AH battery bank then multiply the battery’s AH with its Volts to calculate the total battery wattages.

150 AH * 12 Volts = 1800 Watts

Battery AH * Battery Volts = Battery Watts

Second, in how many hours you want the battery bank to charge full using just solar panels. Let’s assume to charge a 150 AH battery full in just 4 hours. So divide the watts of battery by charging hours.

1800 Watts / 4 Hours = 450 Watts

Battery Watts / Charging Hours = Watts Required

So, we would require more than 450 watts of solar panels to charge a 150 AH battery around 4 hours under a clear and sunny sky.

But no inverter will charge the battery with such a high current.

A 150 AH battery rated with C10 will be charged with 15 (+1 or 2) Amps of current. Thus, for the battery’s long life you should not charge it more than that. Even an inverter won’t do that even if you supply more than the required current, rather the inverter moves those additional energies to direct output for day load.

Let’s adjust the formula little bit:

A 180 Watts of solar panel will generate around 8-9 Amps and 2 Panels in parallel will generate more than 15 Amps, which will be enough to charge an inverter battery. So assume we have a 2 * 180-watt panel.

1800 Watts / 360 Watts = 5 Hours (theoratical)

Battery Watts / Watts Required = Charging Hours

You just need 200+ Watts of solar panels to charge a 150 AH 12 V battery in 5+ sunny hours. This may take more than one and a half days to charge completely. So, in the end, just add 30% additional solar watts if you stick to a minimum, as there are some current losses in electricity conversion.

Smart Note: Better use MPPT (Maximum Power Point Tracking) solar charge controller over PWM (Pulse-Width Modulation) to extract the most from solar panels. Power losses are negligible in MPPT and over 97% efficient, whereas, PWM loses around 20 to 30% of its energy.

When we are talking about a clear and sunny sky, things are not bright always. Weather conditions like clouds, rains, and winter season also affect solar energy generation, we need to take such conditions into account as well.

If you’re relying completely on solar power, then add more watts of the solar capacity. This way you can rely on solar power in the day time and use the battery bank power at night time.

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### Published by AtulHost

Creator of AtulHost. An ardent Linux user. Loves to do research on modern enterprise solutions and technological trends like automation, artificial intelligence, cloud and edge computing, computer hardware and networking, data science, and the internet of things. He holds a business management degree, hence he shares crucial business insights like finance, investments, and marketing.

### Comments and feedback

1. Satheesh says:

Can I charge 2*12 Volts 150 AH battery (two batteries same time use) with 12 Volts and 540 Watts solar panel?

• Hello Satheesh, you can charge 2 batteries at the same time while they are connected in parallel. Whenever we connect 2 batteries in parallel we achieve double ampere and same voltage. About charging with solar, yes it will be affected. Since the battery AH has increased to 300 AH (150 AH * 2) the charging time will be double, so the backup will be double.

If you haven’t bought anything, I’ll recommend 24 volts setup, it will give you higher output.

2. Arpit says:

Hi, In how much time 320 watt solar panel can charge 150 Ah battery? Can you please suggest something as my battery is charging and discharging very quickly as per the inverter’s indicators and backup is very poor now 😔.

• Hi Arpit, to charge a 150 Ah battery using 320 watt solar panel, it will take more than 6 hours. But only when you get clear sunlight and using MPPT charge controller. PWM based charge controller will take 10-20% more time. Also keep in mind that you cannot use 100% capacity of a lead-acid battery, it is meant to used up to 60-65%. For better backup, either increase the capacity of a battery bank or switch to a lithium-ion based battery.