Technology - The Basics of Power Banks and Solar Panels

How do power banks work? What is important to know when selecting a product? We will help you to choose the right product.

Basically, power banks consist of a housing with an integrated battery and associated electronics for charging and discharging. You can also see the power bank as a mobile charging device which enables you to have a mobile power supply.

A lithium-ion or lithium polymer technology is used nowadays as a battery. Their advantage is that the energy density is relatively high and therefore the weight and volume of the power bank can be kept as small as possible.

The more capacity/energy that the battery provides, the larger the power bank has to be, however.

The electronics in the power bank ensures safety and switches of the charge and discharge current in case these get too high or the voltage of the battery runs into unauthorised areas.

Furthermore, the electronics controls the different input and output voltages and monitors the state of charge.

The capacity of the power banks available on the market is indicated in mAh by all manufacturers. This reflects the capacity of the battery installed internally. Since it is a lithium=ion or lithium polymer battery, the average voltage of 3.7V applies to this capacity figure. In order to reach an output voltage of 5V or more, the voltage must be regulated to the maximum which is why at 5V (or higher)  correspondingly lower capacity is then available. You have to additionally take into account a loss of approx. 10% depending on the electronic components used.

The best calculation can be determined on the basis of the watt hours per day. A power bank with a capacity of 10000mAh has an energy content of 37Wh. If you use these for charging via the 5V output, you can charge a capacity of 7400mAh. If you take some power loss into consideration, such a power bank reaches a charge of ca. 6700mAh.

This often leads to misunderstandings among customers when calculating how often you can then charge your device with a certain capacity, since the energy cannot be transferred without potential transformers and without any loss. Here, you have to factor in different voltages and power dissipation. This applies, as has already been said, to all commercially available power banks with which these are once again comparable. 

The power bank is charged via a (micro) USB port or via a special higher voltage input. In the latter case, an appropriate adaptor is provided. 

It is important to note when charging the power bank and other devices with lithium-ions/polymer batteries that the current is reduced at the end of the charge in order to keep the battery voltage stabile. As a result, approximately 80% of the charge will be loaded quickly, while much more time is needed for the remaining 20%.

The discharging is done via standard USB ports or specially supplied adaptors. These power banks are often called (rechargeable) USB batteries due to the possibility to charge them via USB ports.

The solar panels offered convert the sunlight into electrical energy which can then be made available via a 5V USB output.  Outputs of between 2 and 8 watts are available depending on the size and technology of the solar panels. 

This energy can of course also be stored in our power banks in which case the solar panel serves as a charging device for our USB batteries.