Design, modelling and optimisation of an isolated small hydropower plant using pumped storage hydropower and control techniques.

Abstract

Pumped Storage Hydropower (PSH) has proved to be a reliable power generation technology, especially in cases of emergency peak power demand. It is best utilised in areas where the availability of water is a challenge because it allows water retention and reuse using the pump back mechanism instead of the water being discharged to continue its course. A pumped storage hydropower system consists of two reservoirs, one higher in elevation than the other lower, the turbine house (power station) and pumping plant between the two reservoirs. During off-peak periods, excess electricity which is cheap pumps water from the lower to the upper reservoir because power demand is low. The stored energy is released to run back into the lower reservoir through the turbines to generate electricity in peak demand period, converting the stored potential energy into electricity at a higher economic value. South Africa is among the highest emitters of carbon dioxide in the world, with more than 75% of primary energy requirement from fossil fuels. Specifically South Africa is ranked 12th in the world in terms of top emitters of carbon dioxide, exposing its citizens to risks associated with this emission [1]. Therefore there is an urgent need to protect lives by technically reducing release of the poisonous gases through reducing fossil fuel dependency. Renewable Energy (RE), which is abundant and sustainable, can be quickly implemented, offer many work opportunities and have a much lower impact on the environment. With over 8 000 potential small Hydropower sites identified in Eastern Cape and KwaZulu Natal (KZN) Provinces, generation can improve. The system proposed is the design, optimisation and integration of a control system to a standalone micro hydropower hybrid. The conventional hydropower plant, which is a primary electricity source, allocates power to pump from the lower reservoir to the upper at off-peak periods when consumption and price of electricity is low at regulated flow. Various calculations were derived to compute the primary design parameters (flow, head and system efficiencies) with the other inputs. Matlab Simulink was engaged to describe the interaction between these variables and to vary parameters for optimum output, especially in reducing pumping mode power input for maximum pumped storage hydropower plant generation. Different categories of small hydropower plant sizes can be determined and analysed using this model which will give suitable results. Though the value of generation output from the PSH is small compared to input pump power it is able to compensate for peak load demand. The control system is introduced using Flowcode software to automate every technical process to ensure optimum system performance. The automation considers, time of the day, the volume of the upper reservoir and the available pumping power to efficiently manage the hydropower plant model. With the introduction of this generation technique, the results have shown that generation of more electricity at peak time when the price of selling the electricity is very high can be easily accomplished. The control effectively minimises electricity losses, breakdown of equipment, and ensures availability of resource at the exact time of demand. With this design, existing hydro plants may be upgraded for optimum generation without posing any negative effect on the environment in the way that coal fired plants do. Other renewable energy sources may be exploited in pumping activities to reduce the effect of pumping to the upper reservoir on the conventional hydropower plant.