Fifty Shades of Flex

Fifty Shades of Flex

In this article, we highlight the need for flexibility on the grid and discuss some of the flexible technologies available today and in the future.

A New Power Equation

Wind and solar energy (“RE”) are now the cheapest energy sources available to power grids and as a result are being introduced at a rapid rate onto power grids all over the world. However, given the non-dispatchable nature of these technologies, this technological disruption is now forcing system operators (and energy traders) to rethink their approach as to how to maintain a stable and reliable power system. The traditional, and predictable, concepts of baseload; mid-merit; and peaking are now being challenged as we see more and more uncertainty being introduced necessitating the need for more flexibility to accommodate this uncertainty. In essence, we are seeing the following change in the ‘Energy Security equation’: 

Peaking + Mid-Merit + Baseload = Energy Security

Renewable Energy + Flexibility = Energy Security

Herein lies our challenge as today, there is no single dominant flexible technology option that we can use in the formulae but rather, a plethora of both mature and maturing technologies will likely be required to meet the evolving flexibility requirements experienced by power systems worldwide.

The Nature of Nature

“One can’t predict the wind but can adjust the sails” – Indian Proverb

The only certainty we have when it comes to renewable energy is that the sun will rise again tomorrow as it did yesterday and the day before that. That, unfortunately, is where the certainty ends, and the uncertainty begins, as our power systems will constantly be exposed to variability caused by wind and cloud induced RE intermittency.
We can observe this in the South African power system whereby consistent daily generation profiles get distorted and serrated caused by the intermittent wind and cloud cover patterns as in the image at the end.

A typical renewable dispatch curve as experienced by the South African Grid (Eskom data portal – Feb 2025)

Various weather phenomena will impose a different type of system challenge in terms of scale and duration. Such examples may include:

• cirrus cloud pattern moving across solar panels in the Karoo resulting in solar spikes within seconds of each other;
• daily weather pattern changes bringing with it constant hourly and daily supply variations;
• An extended cold front that brings overcast conditions across South Africa resulting in days and even weeks of low solar production profiles;
• Seasonal variations resulting in monthly changes; and
• Long term weather changes such as El Nino which bring about annual variations.

In addition to the direct effects of RE intermittency, there will also be indirect consequences on the legacy generators which will increasing become less reliable as they are pushed beyond their original design expectations to meet the growing variability needs of the system. Examples such as the use of coal plants, designed to operate primarily in a baseload fashion, are pushed to undergo constant ramping which places excessive thermal stresses on the equipment and subjecting them to more frequent failures. And in the rare cases, extreme weather events could result in direct destruction of the power system infrastructure.
The result of all these factors is that we have a power system that requires flexible technologies across the flexibility spectrum as depicted in the image below.

A figurative illustration of how certain weather related events can cause variability of varying duration as plotted along the flexibility spectrum.

Choosing the Right Tool for the Job

There is no single silver bullet answer to addressing all the flexibility needs of the power system. If a stable and secure supply of power is a pre-requisite for sustained economic activity and growth, then it is vital that we recognize that multiple Flexible technologies will be required.
The title of this is article is ’Fifty Shades of Flex’ and we have no doubt that there are more than fifty technology solutions that can bring flexibility into the power system. And whilst we recognize that each technology has a role to play, as FlexED, our view is that the combination of batteries (or “Battery Energy Storage Systems” aka: BESS); flexible gas; and hydro/pump-storage provides a compelling, and proven, mix of grid scale Flexible Technologies spanning across the flexibility spectrum.