How to Choose a Solar Panel for Your Electronics Project

Embarking on an electronics project powered by solar energy can be both exciting and challenging. One of the crucial decisions you'll face is determining the right solar panel to meet your project's power needs. In this guide, we'll explore practical steps to make this decision effectively, drawing from real-world experience and calculations. This is follow up tutorial on the following previous blog post on power supply using solar power and battery.

a. How to Make a Solar Power Supply with Battery

b. How to Make a DIY Joule Thief Circuit for Powering Batteries

c. How to Make a DIY LiPo Charger

Understanding the Problem

Imagine you have a project, like a garden temperature sensor, that requires continuous power, even during night time. You need to calculate the energy consumption of your device over a 24-hour period to determine the appropriate solar panel size.

solar panels various size

The Solution: Calculations and Estimates

Let's crunch some numbers. For instance, our garden temperature sensor draws a constant 70mA from a 5V power supply, totaling 350mW. Over 24 hours, this sums up to 30,240 joules (J) of energy consumption. Now, we need a solar panel capable of providing this energy within a day.

PV solar charger circuit

We can use the formula Psolar = E / (H * 24 * 60 * 60) to estimate the required solar panel power, where Psolar is the solar panel power, E is the energy needed (30,240J in our example), and H is the average hours of direct sunlight. Assuming 10 hours of sunlight in the tropics, we find Psolar = 30,240 / (10 * 60 * 60) = 0.84W.

So theoretically, a 1W solar panel should suffice. But what if you anticipate prolonged periods without sunlight, like during a tropical storm? In such cases, you'd need a backup battery. Using the same energy calculation, we determine the required battery capacity (Cbattery) in ampere-hours (Ah). For example, if we need 90,720J of energy storage and have a 5V battery, Cbattery = 90,720 / (5 * 3600) = 5Ah.

Discussion: Real-world Considerations

While these calculations provide a starting point, real-world conditions can significantly impact solar panel performance. For instance, different locations experience varying sunlight hours. A location like Seattle might have only 2 hours of sunlight a day in December, necessitating larger solar panels.

Moreover, efficiency losses in voltage conversion and battery charging must be considered. Using a higher power solar panel than needed can help compensate for these losses.

Additionally, the project's load profile affects energy consumption. Devices may have varying power requirements, transitioning between standby and active modes. Logging multi-meters can aid in understanding actual power usage and optimizing performance.

Practical Tips

To optimize power consumption, consider implementing low-power modes for devices like microcontrollers. Projects such as solar-powered water pumps may not require battery backups, operating only when sunlight is available.


Choosing the right solar panel for your electronics project requires careful consideration of energy needs, sunlight availability, efficiency losses, and load profiles. By making informed calculations and accounting for real-world factors, you can ensure your project receives reliable and sustainable power from solar energy. Remember, experimentation and iteration are key to finding the perfect fit for your needs.

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