Jordan's IPP3 tri-fuel power plant. Source: Wärtsilä

Today, South Africa needs flexible capacity that can be implemented quickly, cost-effectively, and that will support a just energy transition for the future energy system, writes Wayne Glossop, business development manager at Wärtsilä South Africa.

As we await the much anticipated ‘Risk Mitigation Power Purchase Programme’ RFP, to be issued by the Department of Mineral Resources and Energy (DMRE) “latest early August” (quoted from DMRE Budget Speech), it is useful that we take the time to assess and articulate what we understand the main power system challenges to be and how best to address those challenges through this programme.

Read more:
A business case for distributed dispatchable generating units

The IRP2019 confirms the need for “incremental capacity (modular) and flexible technology, to complement the existing installed inflexible [coal] capacity” (quote from IRP2019). And with reference to the DMRE RFI, such flexibility may be characterised by the ability of new generation capacity to undertake system “gap filling” in a cost-effective manner (i.e. cheaper than diesel OCGT’s which are the current gap fillers). But what is ‘system flexibility’ and what are the best technologies to provide such flexibility?

Why flexibility is the future for South Africa

Flexibility will have a different meaning within different power systems but within the South African power system, we believe that a flexible generator is one that can address three growing issues (on a fast track basis):

  1. Act as a back-up to an ailing coal fleet;
  2. Balance the intermittency arising from a growing renewable base and;
  3. Meet the growing peak demand energy requirements.

In order to address these challenges, which is currently met by diesel OCGT capacity, flexible capacity – which is “flexible over time to be ramped up and down as circumstances change” and can “come online within a short period of time i.e. short ramp up and ramp down rates” (quoted from RMPP RFI Dec 19’) – should be considered.

Gas power is widely regarded as being a preferred provider of flexible energy (as reflected in the IRP2019) and within the gas power technology options available, Internal Combustion Engines (ICE) technology comes out tops as the most effective provider of flexibility. But why is this?

Modular ICE power plants offer the system operator (SO) a limitless number of fast starts and stops at no operational costs. With sub 5-minute starting times (from idle to full load), ICE power plants, of any scale, are the perfect operating reserves provider without the SO having concerns about incurring start-up fuel or additional maintenance expenses.

ICE power plants are also the most efficient open-cycle technology available. This efficiency is maintained across the entire output range of the power plant due to the modularity of the technology.

With these characteristics, the SO will have the freedom to optimise the entire power system by cost-effectively backing up failing coal units and reducing their balancing responsibilities; reducing the excessive usage of expensive diesel OCGT’s thereby saving billions on the energy tariff and; enabling the introduction of more cost-effective and sustainable renewable energy sources which will lower the cost of energy for South Africa.

Flexibility also extends beyond a short-term power system fluctuation to longer terms such as annual and seasonal dispatch variations. The last 10 years in South Africa have proven how difficult it is to predict the supply/demand balance accurately, so a plant that can operate across a wide range of annual load factors in a cost-effective manner will bring further benefits to the power system. ICE power plants are extremely competitive across a very wide range of capacity factors thus ensuring a role for these plants in an uncertain future.

But flexibility is not limited to only dispatch related aspects, it also applies to fuel option flexibility. Again, ICE emerges victorious due to their ability to run off a wide range of liquid and gaseous fuels including diesel; LPG; HFO; LNG (natural gas) and in the future, carbon-free gasses such as hydrogen. Such fuel flexibility affords projects to consider fuel transition strategies and also provides a fuel price hedge to ensure the lowest tariff based on the cheapest fuel at the time is achieved.