Optimization of a Wind Powered Water Pump

Pedro Arauz is a low-income agricultural community in Nicaragua characterised by high winds and a long dry season. Winds of Change is a Toronto-based foundation that partnered with CGEN, the local NGO Seeds of Learning, and the community to automate the pumping of water from the local well for irrigation by harnessing wind energy to extract groundwater for irrigation. This water, much needed during the dry season, is used for drinking and irrigation for locally grown crops. Over three years, teams of students designed and optimized the windmill.

The first group carried out their work in 2014/2015. The function of the design is to lift water from a depth of 26m below ground using wind power at a rate of 15m3/day. Since the pump must be able to operate in the local physical environment as well as by the local inhabitants, some notable objectives and constraints include low cost, low maintenance and use of local services. Several designs were considered, and the Direct Drive Rope Pump design was chosen to be the final design as it is able to meet all constraints and to best meet the design objectives overall. The Direct Drive Rope Pump consists of a rotor with a 2m radius coupled directly with a pump wheel that has a radius of 15cm. The rotor and pump wheel are concentric connected by the rotor shaft at a height of 10m. At average local operating wind speed of 5m/s, the pump wheel is expected to rotate at a speed of 10.7 rad/s which corresponds to approximately 15.7m3/day of water. The design of the pump wheel and the braking system were notably different from existing design and are therefore subjected to more rigorous testing.

The objective of the next group of students was to optimize the wind pump by increasing robustness while reducing overall cost. This had to be achieved using locally available skills and materials.

The existing design lacked crucial functionalities. The team identified and addressed them by integrating new systems and modifying the original design: (1) a locking system, which allows an operation to engage the brakes from the ground and keep them engaged, ensuring the rotor remains stationary, (2) a a re-positioning system for the rotor to reset the orientation of the windmill from the ground, and (3) a system of pumps that enables pumped water to return to the well when the tank is full. Due to limited material availability, the original lower configuration was not optimal. After the redesign, a reduced tower height resulted in simplified assembly, increased strength, and reduced material cost. Analytical models were used to prove that the reduced height would not impede the performance of the wind pump.

 In 2016, the third group of students set out to refine the design of the  windmill, specifically the control and safety system, to protect components during high force winds and to allow for maintenance activities.

The windmill is to have two methods of braking the rotor: one manual, and one aerodynamic. The primary objectives are that the system must be reliable, easy to fabricate and assemble, and low cost. There were strict constraints on the design as the group was limited by tools, expertise and materials available in Nicaragua, by the constraints of the existing windmill design, and by the interface with the power transmissions system. Design alternatives were evaluated based on their ability to meet the design objectives. Once the basic designs were chosen, moment balance calculations, brake force calculations, prototype construction and testing served as proof of concept for the designs. Two brake systems were finalized: the manual brake, similar to a pair of bolt cutters, can be engaged from the ground and clamps around the rotating shaft, and the Aerodynamic brake was designed based on a force balance between a tail vane and an auxiliary vane, that rotate the pump/rotor assembly out of the wind when speeds reach 8 m/s.

The group travelled to Nicaragua in January 2016 to build the design. This gave them the opportunity to test the windmill design full-scale, and to evaluate and refine the manufacturing process for future windmill construction. The most significant design alterations made include changes to the aerodynamic brake vane sizes, increased weld area on the tower support structure, and rotor, and changes to the design and assembly process of the nacelle. Some design improvements to windmill components such as increased mechanical advantage on the manual brake, and collars for the rotor shaft have not yet been fully addressed and have been recommended for on-going improvements.

A complete, successful windmill design and construction will increase production of the dry plots during the dry season so that they may flourish with plants and livestock, increasing community income. Furthermore, a successful design will be able to be reconstructed by the community to promote sustainable development.

 

Read about the Winds of Change and CGEN collaborative project on the award-winning photojournalism initiative Transformations: Stories of Partnership, Resilience and Positive Change