DIY Solar Panel

thehardwareguy

Overview

The motivation behind this project was to create something that would benefit the real world. I regularly use devices such as a mobile phone & tablet. The batteries in these devices need regular re-charging, this contributes to a significant amount of monthly energy consumption. I took it upon myself to build something that is able to efficiently charge smart devices for free.

Specification

12V (5V USB).
22.5W Output Power.
2A output.
£40 build cost.

Why Solar?

Solar technology is progressing rapidly, with price to performance cheaper than ever. The production cost of solar panels is decreasing by 15% each year. The 15 panels I used cost just £30 in total. In comparison to the price of pre-built solar panels, this is very cheap.

Building The Panel

I built the panel using some spare wood and cut-offs. The gallery below shows the construction process of the panel.

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The Solar Panels

The solar panel I made is simply a parallel arrangement of 15 mini solar panels. In a parallel configuration, the total output voltage remains the same, while the total output current is a sum of each panels output. (i.e. 1.5W x 15 = 22.5W) and (22.5W / 12V = 1.875A).

Panel Specification

115mm x 90mm.
12V output.
1.5W power output.

Power Output Circuit

A small output circuit was designed which utilises a DC-DC buck converter. Images of this circuit are shown below.

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DC-DC Step Down Converter

USB devices typically operate at 5 volts. The output of the solar panel is 12V. To regulate the voltage, a DC-DC step down (buck) converter is used. It is usually cheaper to buy one as opposed to making your own.

Circuit is available here: https://amzn.to/2znjpUp

USB Charging Circuit

This circuit allows for safe charging of USB devices. The 12V solar panel voltage is stepped down to 5V, with a max output current of 2.3A.

Battery Pack

Smart phones and tablets have small battery capacities. Therefore, they will charge quickly. It makes sense to use an energy storage device. This will harvest more of the suns energy per day, and allow for safe, smart charging of USB devices. The total capacity of the battery pack below is 22000mA. When fully charged, this is enough power for 10 consecutive iPhone charges.

Battery pack available here: https://amzn.to/2zmX7Cr

Performance

The panel performs very well in ideal conditions (direct sunlight). When there are clouds in the sky, there is a significant drop in output current. This is as expected. Solar panels are optimized to perform in direct sunlight. It is inevitable that performance will be reduced when clouds are in the sky.

Panel Outputs

Direct sunlight: 2.3A
Light cloud: 500mA - 1.5A
Heavy Cloud: <300mA.