Turbine Considerations

For the turbine design we have a variety of options to choose from. We have highlighted a few key points in determining the best option: operation on different geographical feature (Installation, head and flow rate), cost and availability, maintenance, efficiency & power production

Of all the products available in market such as cross flow turbine, Francis and Kaplan turbine, we have opted to use a Pelton wheel turbine design because it fulfils the requirements in the above. First the system must be able to fully utilise the geographical features that have been selected to produce electricity. The amount of power potential that we can achieve from the generator is dependent on both the flow rate of water (water pressure) and the head through which the water can be made to fall. Flow rate is the quantity of water flowing past a point in a given time (litres per second). Head is the vertical height in meters from the turbine to the point where the water enters the intake pipe.

Pelton turbine is a form of impulse turbine. It operates using the rotational kinetic energy due to flow of high velocity fluid to spin the permanent magnets in generator to produce electricity. Our area of case study, Upper Guinea has mountainous range with fast-flowing streams. Following from this, we can use pressured water fed from the streams to drive the Pelton wheel turbine. The turbine also benefits from its small compact size as it can be easily installed anywhere although it requires high head of >15m, easily achievable considering the location. Combination of high head and flow rate increases the amount of power produced. Likewise, we can step up the speed using the belt and pulley transmission to generate more power. But this option might not viable since it will incur more cost and increase complexity of the original design.

The turbine is very economic because it can produce high amount of power (based on efficiency) relative to fixed setup cost as compared to other turbines. With efficiency up to 90%, the system can generate up to 1kW/s of power with 0.3-diameter Pelton wheel operating at 500rpm. This type of turbine can be easily obtained because it’s high availability in the market. Depending on the size of the population, we can easily scale the size of the turbine/generator to generate more electricity.

Maintenance is not a main issue for turbine as it is fairly robust. It is also easy to construct because the different components can be built separately and assembled at the site. The system do need water filter to prevent nozzle blockage. Occasional filter cleaning and maintenance check is necessary to prolong the life of turbine. Other than that, we can also place a valve on the pipe connecting the tank and water inlet when it is not in use or for maintenance purposes.

Last but not least, our design implements an AC synchronous electricity generation. From the discussion on the previous page, it requires load and water speed to not vary during operation. Pelton wheel turbine eliminates this necessity as it can maintain the power output with low flow rate (e.g. seasonal drought). Hence it is more efficient in the long run.