RENEWABLE ENERGY & ELECTRIFICATION
MUNICIPAL MICROGRIDS PROMOTE
clean energy and autonomy Renewable energy installations at St. Cloud wastewater treatment facility, Minnesota, USA
T
he latest update to the South African government’s Integrated Resource Plan (IRP) places increased emphasis on the greater integration of renewable energy generation. In addition, the IRP gives municipalities permission to consider alternative ways to generate electricity through decentralised alternatives that take pressure off the national grid. It’s no secret that Eskom’s ageing power stations and a growing maintenance backlog have made load-shedding a regular feature for the foreseeable future. Aside from the economic fallout, scheduled and unscheduled power cuts have a devastating impact on municipal ser vice deliver y, especially in terms of water purification and wastewater management. The shortfall in electrical infrastructure investment also fails to close the gap on regional community electrification projects. Within this context, clean-energy-powered microgrids help to bridge the divide while lowering our dependence on fossil fuels. These microgrids can typically range in output from as low as 10 kW to over 100 MW. They are diverse in nature and size, depending on the load, location and resources. However, with few exceptions, their power source is derived from renewable energy. Options include solar photovoltaic (PV) systems, wind turbines, hydropower and biomass, or some hybrid of these that incorporates diesel or gas generation as a backup when the sun sets, or the wind drops.
20
IMIESA May 2022
Before rushing in, though, municipalities need to do their homework to ensure the microgrid systems selected meet the requirements and deliver according to expectations.
For South African municipalities, microgrids present a strong business case in terms of power security and sustained supply, especially for critical infrastructure during downtime on the national grid. By Shireen Sayed
Battery storage Energy storage, which includes batter y storage, plays a critical function in terms of making microgrid energy supply predictable and readily available on demand. Furthermore, it improves microgrid stability by acting as a buffer against renewable intermittency and mitigates load uncertainties. Therefore, choosing the best fit-forpurpose batter y storage system (BSS) is crucial since this represents one of the highest-cost items within the overall microgrid setup (between 20% to 30% of the overall capital cost over its lifespan). In today’s market, batter y options include redox flow, lead-acid, Li-ion, nickel-cadmium, and nickel metal hydride. Due to their simplicity, Li-ion and leadacid batteries are popular for the rural microgrid market. Either way, BSS optimisation and application requires a comprehensive understanding of how batteries behave under various operating conditions. These include exposure to temperature variations, as well as charging-discharging. Typically, a microgrid comprises several batter y storage units, with each unit having a var ying degree of output capacity depending on factors such as initial
Shireen Sayed, managing director, Aspire Project Management
state of charge (SOC), efficiency, ageing (i.e. number of cycles), and temperature conditions. Ideally, the BSS should function as a well-synchronised system.
Battery management system To be able to manage any differences between the various batteries, and to ensure stability, a battery management system (BMS) is required to monitor and control vital functions of the BSS in real time. The BMS relays information such as temperatures, voltages, currents, maintenance scheduling, batter y per formance optimisation, failure prediction and/or prevention, as well as batter y data collection/analysis. The function of battery optimisation must be considered as part of the overall microgrid design right from the onset to achieve maximum results from the storage system, as well as from the overall ability of
