Municipal microgrids promote clean energy and autonomy

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

The 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 service delivery, 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.

Before rushing in, though, municipalities need to do their homework to ensure the microgrid systems selected meet the requirements and deliver according to expectations.

Battery storage

Energy storage, which includes battery 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 battery 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, battery 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 battery storage units, with each unit having a varying degree of output capacity depending on factors such as initial state of charge (SOC), efficiency, ageing (i.e. number of cycles), and temperature conditions. Ideally, the BSS should function as a well-synchronised system.

A microgrid installation for a small town

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, battery performance optimisation, failure prediction and/or prevention, as well as battery 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 the microgrid to respond adequately to the energy demand.

For microgrid applications, there are some quick wins in terms of achieving optimisation of the BSS. These include:

- on-the-ground optimising, incorporating the correct positioning of batteries, adequate ventilation or insulation of the battery storage facility

- fully trained resources to carry out repairs and maintenance

- the quality and technology of the energy storage systems must be carefully selected and designed.

According to the International Renewable Energy Agency (IRENA), studies show that battery storage worldwide is predicted to grow from approximately 2 GW in 2017 to around 175 GW in 2030, and that costs will continue to fall as technology improves. Technology gains include longer life, increased numbers of cycles, and improved overall storage performance.

Benefits for municipalities

In addition to a degree of autonomy, towns and cities have a greenfield opportunity to map out their current and future microgrid footprint in line with their energy requirements.

Any additional power that is not used can be pushed into the transmission grid and offset as savings to the municipality.

Revenue streams can also be guaranteed by installing prepaid smart metering to ensure payback on the initial investment and longerterm profit generation. In addition, investor confidence is restored when there’s an assurance of sustained power to support current and future industrial and commercial expansion within the municipal zone.

Case studies from Africa and the world

As statistics from IRENA and allied bodies show, the traction for microgrids and renewable energy in general is rapidly gaining ground in both the developed and developing world.

On the African continent, a prime example is Tanzania. According to various literature, just under 40% of the population of Tanzania had access to electricity in 2017. With a concerted effort from the Tanzanian government, this deficit is steadily narrowing. Today, Tanzania is recognised as a regional leader in microgrid deployment, with over 100 microgrid systems serving businesses and local communities.

These microgrids are either governmentowned or owned by private developers selling electricity back into the national grid through power-purchase agreements or sold directly to end consumers. While Tanzania has been successful in the deployment of microgrids, there have been challenges, one of which has been funding.