Raspberry PI Pico and, even more, the Pico W model are excellent devices for IoT projects. Where the power supply is hard to find, powering the Raspberry PI Pico with a solar cell may give you the ability to make your project flexible enough for deploying it in remote zones
In this tutorial, I will show you how to power a Raspberry PI Pico with Solar Cells. Moreover, I will also include an external battery as a backup power supply for the
moments when light is unavailable.
The Solar Cells
A solar cell, or photovoltaic cell, is an electronic device that converts the energy of light directly into electricity by the photovoltaic effect. Which is a physical and chemical phenomenon (ref. wikipedia.org). I’m not going to describe in detail how solar cells work. The web is full of web pages able to do this job better than me. For the sake of this tutorial, what is important to understand is the measures coming from their datasheet.
All solar cells come with a definition of their capacity to provide energy from the sun. Usually measured in the best case. The producers usually provide at least 2 between the following 3 items:
- the peak Voltage capacity
- the peak Watt capacity
- the peak Ampere capacity
Those measures are linked by the well-known Ohm law: Power [Watt] = Voltage [Volt] x Current [Ampere]. For this reason, knowing 2 of these will always let us get the third one. When choosing the solar cell for our projects, we must pay attention to the cell capacity: different production processes and materials can bring different cell efficiencies. Because I’m going to connect my Raspberry PI Pico with the solar cell by the TP4056 module. Which we’ll see in the following paragraphs, I looked for a solar cell able to provide at least 5V with a decent power output. One that I found interesting comes from the ALLPOWERS and has the following peak values:
- V = 5V
- C = 500mA
- P = 2,5W
There are many solar cells in the market available at affordable costs that you can evaluate. But take always care of these parameters in order to get a decent solar power input. At a fixed voltage input, the higher the current will give you a faster battery recharge.
Usually, the solar cells are sold without the wiring, having only the 2 terminals. (Positive and negative in their back to be soldered with your wires:
Many times these solar panels are sold in multiple packages. When the current provided by a cell is not enough for your project. You can connect more cells in parallel (to get higher current) or in series (to get higher voltage) in order to fit your needs. Or you can use a mixed schema, so getting the benefits from both of the connections. Depending on the number of cells you get. Also consider that, depending on the place where your project resides. You could get more light or less light. the combination of the solar cells will give you enough room to fit your power budget.
The 18650 Battery
When the sun is out, our Raspberry PI Pico and the solar cell will not work. For this reason, I’ve planned this tutorial already including a power backup with a 18650 battery. This kind of battery is not a new format in the market. You can find a lot of these on whatever e-commerce website at very affordable prices. Differently from the AA and the AAA I’ve used in my Powering the Raspberry PI Pico from External Batteries tutorial, this format has a bit higher sizes, but it can assure higher voltage (3,7V) and a longer capacity (usually more than 3000mAh). It is important to understand this value: 3000mAh means that it can provide 3000 mA for 1 hour or 300 mA for 10 hours or 100 mA for 30 hours and so on. This is important as in your projects you will need, sooner or later, to calculate your power drain budget based on the devices attacked to your Raspberry PI Pico. And you will need to make this complaint with the current that you collect from the solar cells and what you can store in your power backup system (this battery, in our case).
Please remember that you will need to get a rechargeable 18650 battery. From the e-commerce stores, you can also get the cases fitted to store the 18650 battery. This is really useful as it allows you to avoid soldering the wires directly on the battery and/or attaching them with tape. Another DIY solution, for people owning a 3D printer, is also getting a 18650 case design from sites like thingiverse and creating it by yourself.