You’ve heard of a ‘microgrid’? I Googled it and found that: “A microgrid is a miniaturised version of the larger grid, a configuration of energy resources, distribution wires and buildings, all within a distinct geographic footprint. There is no size limit, but microgrids tend to be scaled to discrete operations, such as a small village, neighbourhood, community, business park, education campus, mine or industrial facility” (quote from Energize magazine).

After reading similar descriptions, I came to the conclusion that a microgrid is like the power supply in a normal commercial building. It has a connection to nonrenewable-energy supplies (like a local Eskom connection and a standby diesel engine) and maybe a photovoltaic (PV) system and an uninterruptible power supply (UPS). In theory, there is a ‘microgrid controller’ which switches between these sources of energy so as to optimise power system reliability and energy costs.

In all the articles, the microgrid controller is the magic box. It makes all things possible. But, for myself, 42 years as a qualified engineer, I don’t get it. If a microgrid is to manage a building and if the building was to have a significant supply from a PV system, then for an average building using say 5 MW at peak demand the PV system, if rated at 1 MW, would occupy an area of 10 000 m2. This will probably be way too large for the building to accommodate. The building will accommodate a 1 MW diesel generator but it would be more costly to run it than using the main supply, since diesel generation is double the cost of energy from the supply from the local authority. The microgrid controller could switch on and off the UPS, but that would be a very poor idea, since the UPS is the emergency backup power supply and you should not run it unless you need to.

So, I think this is all flag waving, smoke and mirrors. But others will disagree. It happens that Robben Island is run as a microgrid. I quote from ESI Africa magazine: “The microgrid consists of three power production elements. The solar PV farm consists of 1 960 monocrystalline modules with a total of 666.4 kW power supply. The battery bank, consisting of 2 420 lithium-ion battery cells, is able to store 837 kWh and output a maximum of 500 kVA. The third power production element is the diesel generators, used when no solar or battery storage is available. Multiple controllers between these power production elements are said to balance the power supply and create a smart microgrid, ensuring a seamless supply of power.”

This whole arrangement cost about R25-million. Since the island previously used diesel generation, there is a saving of 280 000 𝓵 of diesel a year, which will pay back the cost in about 12 years. So, all wonderful or what? I don’t think so. Quite obviously, the diesel generators will have to run at night (the battery won’t carry the load for very long) so it’s all a very sweet concept but, in my view, not the best idea. What should have happened was for the island’s diesel generation to be replaced with a power supply from the mainland, through an underwater cable. It’s perfectly feasible from all points of view and would have cost a lot less. But no harm done.

Where harm is being done is when (as is happening) snake oil salespersons visit large property developers and convince them that they should install a microgrid controller to reduce the energy costs of buildings. Sooner or later, the client becomes convinced that the microgrid is a great idea. It gets installed and the snake oil salesperson gets paid and trots off. After a while, the client has no idea if money is being saved or not, since power accounts regularly differ, based on weather conditions, tenancy occupation and many other factors. But the cause of the microgrid is advanced – when it is, in fact, a nothing. I think the idea is rubbish. But anyway.