How Long Does it Take to Fully Charge a Solar Power Bank?


Written by qualified solar engineer Aniket. Last updated:

Depending on the solar panel’s size and its rechargeable battery, the time to fully charge a solar power bank using only solar panels can range between 20 to 50 hours. The larger the solar panel and the smaller the battery, the faster the charging and vice-versa.

Solar power banks are not designed to entirely rely on solar power and come with a charging port for regular wall charging. The best way of using a solar power bank is to charge it to maximum capacity at home using a wall outlet. Top it up using direct sunlight for some added backup power, while being outside. This adds some extra ‘juice’ to it, ensuring your phone stays charged longer it would with a traditional power bank.

How to Find Out Charging Time

Before you buy one, it is good to know how long it takes for solar power banks to be fully charged using solar. The same applies to the time it takes to charge your electronic devices from the charger. These can be excellent comparison criteria, along with quality and durability.

In most cases, a manufacturer does not mention the charging time required using only solar, since a solar battery charger is not designed to charge solely using direct sunlight as its only power source.

Reading a Product Spec-Sheet

Although we cannot find the hours until the solar powered battery is fully charged, there is some other useful information on the product specification sheet. Some of this information can be used to calculate the time required for charging using only solar, since these chargers’ basic working principle is like a regular solar system.

The following is an image of a specification sheet for one of the solar power banks available in the market. It has some vital information, such as battery life, type, voltage, weight, etc. But the most important, and the ones we are looking for are underlined in red – the battery capacity and the solar panel rating.

image showing specification sheet of a solar power bank

Think of this as a water tank and a water hose. Once you know the tank capacity and the discharge rate of water through the hose, you can easily calculate the time required to fill the tank completely.

This solar battery charger, at 20,000 mAh, can be charged with a wall unit (AC) in about 8 hours. When its battery is fully charged, it should have enough backup power to charge a typical mobile phone at least 4 times, which means 8 hours is a brief time for it to be fully charged using an AC power source.

But we are more interested in the time required using only solar charging. For this, we will need to do some simple calculations.


We’ll find out how much time will be needed to charge the battery, if we ever decide to or are forced to charge a solar power bank using only solar power. In our example, the power bank capacity is 20,000 mAh, or 20 Ah. The solar panel has a power rating of 5 V, 5 W. Let us convert the Ah to Wh, since it is a more convenient unit for solar calculations.

Since watt is a product of amperes and volts, watt-hour is a product of ampere-hours and volts. Thus,

Wh = Ah × V = 20 × 5 = 100 Wh

We have a 5 W solar panel, which needs to churn out 100 Wh, the time required will hence be:

Hours = watt-hours ÷ watts = 100 ÷ 5 = 20 hours

Thus, we have found out that the solar battery charger in question can be fully charged with direct sunlight in about 20 hours, which means it takes longer to charge using solar – more than twice what it would need with a wall unit and micro USB port. But is still impressive, since the calculation means that in 4-5 hours it will be charged enough to charge a phone fully, which is not bad at all.

However, this solar battery charger has 4 foldable solar panels layers, meaning the panel has a significantly large solar collector. Some power banks that do not have foldable layers of solar panels can have solar panel capacity around 1.5-2 W. Using this in our calculation means we will easily need 50 or more hours to charge when using only direct sunlight. This re-iterates the point we have previously discussed – the length of time required for the solar panel to charge the power bank is more when the solar panel is smaller.

Other factors affect the performance, such as exposure to the sun, scratches on the solar panel surface, etc.

Should You Buy A Portable Solar Power Bank?

woman charging mobile phone with portable solar power battery bank while lying on the beach

Solar power banks are excellent for charging your electronic devices when you are away from electrical infrastructure. Some of the top solar power banks even come with led lights to make your adventures in the dark easier. Some solar battery chargers also have the feature to speed up the charging process using an auxiliary solar system with 10- or 20-watt panels.

Though solar power technology has not yet evolved to the extent of allowing us to charge solar power banks using only solar comfortably, it can still be used to charge the battery. This can be between 20-30% in emergency situations, making solar power banks an essential emergency power gadget.

When choosing which charger to buy, look for solar panels’ size and rating on it, the battery capacity, and other features such as led lights, waterproof rating, and durable casing.

Whether it is a regular solar system or solar powered portable phone chargers, solar has come a long way, and going solar today is always an excellent choice.

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