There are two main focuses for wave-power; off-shore waves, where the rolling action is exploited by floating buoys or the proven Pelamis system, and on-shore systems, where waves are used to push volumes of air through turbines, like the Limpet system, currently running off the Island of Islay.
This project is a proof-of-concept for a micro-scale system, based on the general concepts of the Limpet, that could developed into a useful source of power for remote beach communities, or exploited commercially to charge tourists' gadgets at the beach.
There are three motivations behind this project:
1. Disaster relief / Power-poverty relief.
A device like this (made of light materials) could be delivered as a flat-pack to areas that are deprived of power (through natural disaster or material poverty), and close to the sea. Although not enough to cook with, it could be used to charge batteries for radios, lighting or cell-phones (there are a surprising number of areas with good cell-phone coverage, and yet no available mains electricity). The parts for a unit like this are cheaper and lighter than a solar- or wind-based unit, and wave power is usually more reliable than either wind or solar. It could even be sent as just the turbine unit, with diagrams on how to make the shell from indigenous materials or debris, maybe with a selection of design tweaks that could be chosen from depending on the local beach conditions.
2. Commercial applications.
I can imagine beach-side stalls, the ones that sell sun-tan lotion and trinkets to tourists, could also provide a service charging up tourist iPads, Kindles and phones. Again, because of the simplicity and low cost of the component parts, it would be easier to fund for an independent start-up in a poverty-stricken area.
For some reason, discussion of renewable resources in the media begins with solar, ends with wind, and mentions nothing else. Unfortunately, the same is also true in education.
I can tell my students about wave power systems, and show them pictures of experimental or commercial installations, but the only hands-on kits available are all solar or wind-power based. Having a project like this available encourages younger students to think outside the box, gives them a chance to get hands-on with a real system, and also provides a starter for older students to work on their own projects (this design is far from perfect, and I am really keen to see where other people can take this idea - see the final step).
Step 1: The General Concept.
Islay, where the Limpet system is installed, typically has high-amplitude waves, breaking against a steep cliff/shoreline.
Most people who go near the sea, though, go to flatter beaches with more horizontal motion to the water. That is what I will be working with.
Step 2: The Shell Concept
No need for aerodynamic niceties in a proof-of-concept, so this is made from panels of plywood. The tower containing the turbines was to be built as a single unit, but for the sake of portability, the shell was to be held together with zip-ties, and air-gaps sealed with duct tape.
The original concept sketches, paper model and a more detailed plan drawn up in InkScape (but saved as PDFs) are attached.
Step 3: The Actual Shell
I realised quickly during the build that I had made a fundamental error - the sloping rise in height of the "mouth" will compensate for the horizontal narrowing, which will stop the compression effect I am after.
As a basic, prototype-level fix, I just made the roof of the shell horizontal. This also meant I could simplify the plan and the panels, so the whole thing became a stack of flat panels, with the turbines to be fitted flat against the back wall of the tower section.
I drew up the "final" plan directly onto a sheet of cheap half-inch plywood, using a big T-square and an actual yard-stick.
The main square cuts were done on Noah's table-saw, which is actually bigger than my shed, and the angled cuts were done by hand with a jigsaw.
I drilled holes along the edges of panels that butt together for zip-ties to be fed through later, countersunk on the assumption that this will put less stress on the zip-ties, helping them last longer.
A thick coat of water-based* sealant, and we're ready to install the turbines.
*Yes, I know, but I don't need this particular unit to last a long time, just long enough to prove my idea has legs.
Step 4: The Turbine
There are designs that will take air-flow from more than one direction, but I am using what is to hand (I'm working to the hypothesis that, if a rough design works roughly, future refinements can be funded on the basis that the concept has been proven.
Two PC fans are fixed over holes in the housing. Each is connected to a 1K resistor. Checking the voltage across the resistor will allow me to calculate the power output of the fans.
To make sure that air flows in one direction through each fan, a simple valve consisting of a sheet of polythene bag lays across the outlet side of the fans. On top of that, it turns out that these particular fans spin merrily when air blows through them one way, and barely twitch when air blows through the other way.
Unfortunately, the frame of the fan did not match up with the best direction to blow the air, so I had to add ducting around the fans to give a flat end for the valve to close off. The ducting was simply a short section of soda bottle, which happened to match in diameter.
Why two fans, and not one sucking in and out? It's a matter of efficiency - if I use the same fan for the air to blow back and forth through, a significant part of the available energy will be wasted in stopping the fan turning one way before it speeds up in the other direction.
Step 5: Results.
- The venting fan spun madly when waves entered the device (success).
- The inlet fan did not spin when waves entered the device (success on the valve).
- The inlet fan did not seem to move at all (failure - the retreating wave did not create any suction).
- Sea-water and sand spewed out of the turbines (design failure - rectify by using a taller tower).
- The generator floated too easily as waves entered - I needed to sit and stand on the shell to hold it down (design failure - easily rectified in future by the use of sand-anchors).
Overall, I count the test a success - all the aspects that failed can be fixed with relatively small amounts of work.
Step 6: Next Steps
Well, maybe not that extreme, but any step in the right direction is a useful step in the right direction.
As I said in the introduction, I am keen to see where other people take this project. So, I want to see other people turning it into a functioning, useful device. If you do any work with this idea as a starting point, publish it online (either here on Instructables, or on any other website), and send me a link, I will include that link in this step, and also reward you with a "pro" code from my personal, resources. The better the project, the more pro I will send you.