How to Build Solar-Powered Robots
Why worry about batteries when we orbit around the ultimate energy source? The sun radiates vast amounts of energy, and we can use this to power our robots—and other stuff—all through the cool science of solar cells (Figure 4.1), which convert light into electricity.
FIGURE 4.1 Solar cells can be a great way to power your robot.
Your initial thought might be, “Simply add solar panels for free energy!” Not so fast. As I alluded to in Chapter 3, “Rolling Robots,” it’s not that simple. Even if you have a panel big enough to power your rig the way you like it, there’s no guarantee the sun is out. Furthermore, even if the sun is out, the earth’s orbit makes it appear to move across the sky, meaning the voltage generated will fluctuate.
All that being said, there’s a lot to like about solar-powered robots. You can store them away for a couple years and they’ll still work. You don’t have to buy new batteries periodically. Finally, you can do some intriguing things with robotics, like create autonomous crawlers that creep around your yard like a friendly robo-insect. However, even if you do use batteries in your robot, you can have a solar panel as well, to continuously charge the batteries. The best of both worlds!
In this chapter, you’ll learn about how to use these panels in your projects. Then you’ll bone up on breadboarding, which is a cool way of temporarily constructing circuits. Finally, you’ll build two sweet projects. The first is a solar-powered battery charger, and the second is a simple robot that is entirely powered by sunlight .
How Do Solar Panels Work?
Solar cells are layers of semiconductive materials (shown in Figure 4.2) that create an electrical current when exposed to light. The earliest recorded observation of the photovoltaic effect took place in 1839 when Alexandre-Edmond Becquerel’s experiments with silver chloride produced voltage and current when exposed to light. By 1959, all satellites launched into space bore solar panels, and a little more than 50 years after that, we’re using them to power robots.
FIGURE 4.2 Silicon wafers consist of two layers of semi-conductive material.
You often hear different terms associated with solar technology. A solar cell is a piece of photovoltaic material, usually crystalline silicon. Solar cells are often connected into groups on a support structure, and these are called panels. A group of panels is an array.
Solar cells are rated for direct current (DC) output under certain test conditions—a sunny June day in San Francisco, for instance. Measurement is in watts as well as photovoltaic efficiency. Finally, because the output is DC, you’d need an inverter to run household appliances off of it.
There are two kinds of solar cells. The most common are the crystalline silicon wafers I’ve been describing, which are covered in glass or plastic to protect the fragile cells.
The other kind of solar cell is flexible plastic. Called thin film solar cells, or TFSC, these consist of photovoltaic material deposited on a substrate. Originally used for solar-powered watches, flexible-film solar cells are more expensive than crystalline silicon and have a lower efficiency. However, they’re useful for situations where the panel needs to flex, or the weight of the panel becomes a consideration.