Tim Wrinch
Water Powered Generator
Tauranga Boys' College
Year 13 Product Technology, full year project
Teacher: Steve Ronowicz
Tim selected renewable energy as the context for his Year 13 project. Working with a client building a house to be self sufficient in energy consumption and therefore not connected to the mains power grid, Tim set out to construct and test a prototype of a device to generate electricity from free-flowing water. As well as being able to efficiently convert the kinetic energy of the water into electrical energy, the device would have to be durable, waterproof, easily handled and cause minimum disruption to the marine environment it was working in.
Tim started by researching the functionality of a range of existing products in terms of materials used, design of turbine blades, waterproofing capability, ease of handling and operation, and level of protection from the hazards of the marine environment. Access to high quality technical feedback would be critical as his development progressed, so he planned for ongoing e-mail, phone and face-to-face contact with a number of mentors with related experience and technical expertise.
Tim's initial research established that the design of the blades was key to the operation of the unit. "Once you have the blades worked out you can work out the amount of power they produce and match that to the generator that would suit best," he said. The blade structure he settled on was designed to be used in zero head situations with an approximately 0.2 cubic metres per second (cumecs) water flow rate. It was to be a propeller-type blade set with six to eight flat blades set at an angle between 60 and 80°.
After finding that a fibreglass casing was too expensive and difficult to construct, Tim decided to use a section of rigid pre-formed plastic piping instead. The inside diameter was slightly smaller than the 500mm specified, but this was not only fit for purpose but helped to keep the weight of the device within acceptable limits.
Tim machined the central hub from solid 5086 aluminium, on to which he welded the blades and an outside ring made from 5086 sheet aluminium.
The main shaft of the generator ran in a set of two bearings, set in an aluminium casing in the front plate of the central casing, providing a secure point that the main shaft and the blades could spin on with little friction or vibrations.
Tim decided to use a stepper motor to convert the rotational kinetic energy of the main shaft into electrical energy. However, given the low RPM of the blades, he concedes that the device would have worked better if an alternator had been used instead.
A water-tight wire seal was fixed into the middle of the rear plate with the wire trailing out the back end of the generator. This allowed the energy conversion of the generator to be conveniently measured and tested on-shore and ensured there was no risk of the wire getting tangled in the blades.
Two important operational aspects had to be considered – the weight of the generator and how easy it would be to grip and carry. "The weight factor was addressed by my choice of materials with a large part of the prototype being made from plastic and aluminium," said Tim. "The handling was made easier because the outer casing was longer than the actual generating unit which meant that you could safely put your hands on the inside of the edges of the outer casing to lift it in and out of the water."
The prototype also had to be able to be securely positioned in the water. "I bolted four mild steel brackets to the outside of the outer casing, two at the front and two at the back," said Tim. "The two at the front each had a steel loop to attach the ropes from the river bank to stop it from being swept downstream as well as a loop each to connect to the floatation tanks holding it off the river bed. The two at the back had a single loop each to connect to the floatation tanks above."
"I produced a very simple prototype for testing the technology. My plan is to keep it simple like this through the next stages of prototype testing. Once I have developed the technology sufficiently I can vary the design of the unit to suit the output requirements and the environment it will be operating in."
Feedback from his client and mentors showed the effectiveness of his design: "It is impressive that you were able to get a set of blades to run so smoothly inside the outer casing with such a small gap between the blades and the casing," said one. "This is a big advantage because it means that there is little energy loss due to friction."
"The flat support plates between the central casing and the outer casing do a very good job of straightening out the water coming out of the blades, so that if you were to put a second set of blades on the back end the water would be hitting them straight on."
The results from the prototype testing showed Tim that the device could turn the kinetic energy from the moving body of water into electrical energy. However, the data obtained confirmed that his final design will have to operate much more efficiently to be practical. Improvements suggested included putting a gearbox between the blades and the alternator and using an alternator more suited to working at low RPM. Investigating the effects of changing the pitch of the blades will also be a focus in future development work.
Teacher comment
When I looked at what Tim has achieved, rewards far greater than his NCEA achievements shone through. Here is a young man who has developed a passion for renewable energy sources, who sees that our society has to make changes and is prepared to take risks to give it a go himself.
School assessment is only a small measure of what has been attained – what Tim can now take forward into our society in terms of capability linked to sustainable values is huge. Our young men can do remarkable things when given the opportunity through technology education.
The technical requirements in Tim's generator are very high. It would be fair to say that it has been the scaffold of skills developed over his years in the engineering workshop that have enabled him to attempt such an advanced project. Tim already knew how to MIG-TIG weld and machine to fine tolerances before entering the Year 13 class.
As a department, we have tried to keep pace with technology in industry. Recent purchases have included aluminium and steel MIG welders, plasma cutters, standard and pulse TIG welders and also industry standard milling machines with digital readouts to increase machining accuracy. This investment is now paying off with the fitness of purpose of products produced improving markedly.
The biggest thing that Tim and others in my Year 13 class have taught me is that, at this level, the teacher's role changes somewhat. You become more of a facilitator and critical support person than the traditional manager of a classroom. These learners can mostly mange themselves, what they need is to be challenged and supported to take risks. Also the teacher has to be able to "let it go", allow learners to follow their own course and especially bring in outside expertise – people who have the higher knowledge that learners need at this level that may well be beyond that of the teacher.
