Mechanical design, control and optimization of a hybrid solar microgrid for rural electrification and heat supply in sub-Saharan Africa

This thesis aims at developing, optimizing and controling a hybrid solar microgrid for rural
electrification and heat supply in sub-Saharan Africa. The considered system includes
PV, Parabolic Trough Collectors, Organic Rankine Cycle and LPG generator, as well as
chemical battery storage and thermal energy storage. The work focuses on multiple aspects
of the ongoing development of solar hybrid microgrids for the rural electrification of remote
areas in Lesotho. These aspects range from very specific improvements (the mechanical
design of a high expansion ratio expander) to the more global evaluation of their impact
once included into a complex micro-grid system. Special attention has also been paid to
the links between thermal and electrical demands.
The main contributions of this thesis are:
– The mechanical design of a high expansion ratio scroll expander, involving drawing,
machining and assembly of the parts.
– The detailed model of an organic Rankine cycle with the purpose of evaluating the
improvement brought by the high expansion ratio scroll expander and mapping the
ORC performance.
– A building model developed to predict the thermal loads of a health clinic in rural
communities of Lesotho. The developed lumped-parameter model can be used for
various building typologies and communities. The model is designed to be as generic
and simple as possible, and contrasts with the data-intensive models generally proposed in the literature.
– The gathering of monitoring and weather data relative to a health clinic in Lesotho,
and their use for the calibration of the building model.
– A microgrid model built by interconnecting all of its subcomponent models. A rule-
based control strategy is developed, accounting for interactions between thermal and
electrical loads, and dispatching heat and power flows of each component in order to
cover the demand while minimizing the fuel consumption.
– A particle-swarm optimization model used to optimize the microgrid under different
cost assumptions and control strategies.
The above models prove that the system performs better with the developed high
expansion ratio expander. The maximum output power of the ORC is increased by 33%,
and the fuel consumption of the microgrid is reduced by 25%.
For the studied community of Ha Nkau in Lesotho, the determined optimal system
infrastructure is composed of PV (65 kW) and batteries (259 kWh) only, and the optimum
control strategy achieves a levelized cost of electricity of 0.202 USD/kWh. Fuel consumption is mainly due to the burner, which supplies all the thermal load because no other
heating system is selected by the optimization.