Building a solar stirling engine can be easy and useful in a lot of ways. This engine converts heat into mechanical work by compressing and expanding a fixed amount of a gas. This post will teach you how to make a simple demonstration solar Stirling engine and where you can find out how to build a productive one.
Let’s cover how a stirling engine works. In some ways it is like an automobile engine except that it is an external combustion engine instead of internal combustion. Heat produced outside is used to heat an expansion cylinder while heat sinks are used to cool a compression cylinder. Connecting these two cylinders is a passage which contains the “regenerator” or gas. This can be any gas even air but air, hydrogen, and helium are the most common. Often the “regenerator” or gas is at a higher than atmospheric pressure. This is done with a pump, compressed gas source, or even filling the system when the temperature is lower than when it will be operated.
Basic Stirling engine example.
|The temperature difference between the two cylinders causes pressure oscillations in the gas which drives the pistons. Then the movement of the piston or pistons can be harnessed for useful purposes such as a Stirling engine generator. In the case of a solar Stirling engine a Fresnel lens is used to concentrate light onto the heat cylinder. The different between a Fresnel lens and a traditional convex lens light in a magnifying glass is a much thinner lens resulting in more light passing through instead of reflecting off. There are a lot of adjustments and factors that weigh in when considering how powerful a solar Stirling engine will be such as the size of cylinders and passage, pressurization of the regenerator, amount of heat and cooling in the system, and even external conditions.|
On to building solar Stirling engines. A simple demonstration can be built using little more than aluminum cans, CDs, coat hanger, aluminum wire, and a couple other simple pieces. Complete cost should be under a couple dollars. As with all of these engines it can be a solar Stirling engine simply by concentrating light on the heat cylinder using any lens but a Fresnel lens will work the best. Again this model is for demonstration purposes as a proof of concept and won’t be very useful. Scroll down if you’d like a list of places that will teach you how to build a productive solar Stirling engine.
The most simple design uses a single piston and a straight cylinder which is closed on one side and open on the other side with the piston placed inside. The closed side of the cylinder is heated using solar energy, a candle, burning wood, even your hand. This is the heat cylinder. The other side has a heat sink attached to provide cooling. This is often a simple fin heat sink made out of copper or another heat conducting metal. So, imagine a metal tube with one end closed. On the open end is a fin heat sink. Now you’ll need a piston that fits inside the tube creating a seal. This can be made out of any material like metal or even wood. On the end of the piston that isn’t inside the cylinder a rotation point will need to be created. This can be done using a simple nut a bolt with a slip washer.
Attach this end of the piston to a rod and then at the other end of the rod make another roation point. Connect this to a wheel on a drive shaft and you’ll have a complete Stirling engine. If you then place a magnet on the drive shaft inside some wound copper wire you’ll have an electric generator Stirling engine.
Below is a video of a small air cooled solar Stirling engine using a fresnel lens to focus light for heat. There is also a simple electric generator attached.
If you’ve always been interested in using solar energy in useful ways a solar Stirling engine is a great way to start. Get out there and make your own or if you’re strapped for time you can buy a kit like the one below. Also, as mentioned above there are a lot of variations in components and design that will work differently. I suggest you pick up the Stirling Engine Design Manual below if you’re interest