Gas technology makes case for flexibility as South Africa mulls power road map

The 180 MW Sasolburg gas-engine plant The 180 MW Sasolburg gas-engine plant

Leading gas-engine technology provider Wärtsilä has started making the case for greater flexibility within South Africa’s evolving electricity supply industry, as well as within the gas-to-power subsector itself, as the country seeks comment on its future electricity road map.

The Finnish group, which has completed a detailed modelling exercise of the domestic power system, goes so far as to argue that flexibility should be prioritised over project-level cost optimisation, as flexible gas solutions improve system reliability and enable greater levels of renewable energy to be introduced to the grid.

Besides manufacturing gas engines in Finland and Italy, the company has capabilities across the full gas-to-power supply chain, from project development and financing to operations and maintenance. It has a global installed base of 60 000 MW, 7 000 MW of which is in Africa, including a 180 MW gas-engine facility in Sasolburg, which has been replicated by Sasol in Mozambique.

Wärtsilä South Africa business development manager Wayne Glossop says he is encouraged by the inclusion of higher levels of gas in the draft Integrated Resource Plan (IRP) base case, which outlines the introduction of 35 292 MW of open-cycle and combined-cycle gas turbine capacity by 2050. The trajectory is suggestive, he tells Engineering News Online, of policymakers grasping the need for greater flexibility as the penetration of variable renewable-energy grows.

Glossop is also pleased that the small and large gas engines have been included in the list of technologies canvassed in the document, which is currently undergoing public consultation. However, he strongly disputes the Electric Power Research Institute-derived cost figures, which he will be countering during the IRP public consultation process.

Wärtsilä also believes that there is an imbalance between flexible and baseload gas in the draft IRP, with 21 960 MW allocated to combined-cycle gas turbines and only 13 332 MW for load-following gas, which has been lumped under the heading of open-cycle gas turbines.

Wärtsilä South Africa business development manager Wayne Glossop
Wärtsilä South Africa business development manager Wayne Glossop

Using power system modelling software to re-create the domestic power system, the company found that gas serves two key functions: displacing expensive diesel generation; and optimising inflexible coal generation.

“These system requirements are best met with ultra-flexible gas capacity, which is able to efficiently provide system energy and operating reserves,” Glossop asserts.

The outcome reveals a “re-optimised gas-technology mix” containing a combination of engines and turbines, with the majority of flexibility being provided by the engines, which are manufactured by Wärtsilä. The group’s medium-speed internal combustion engine, dubbed CC/OC-ICE for either combined-cycle or open-cycle configurations of internal combustion engines, is analogous to a large car engine. In other words, the engine can be switched on and off without causing long-term damage, enabling flexible load following, with the start-up from idle to full load taking only five minutes.

However, Glossop insists that the system benefits can be proven and that these benefits will increasingly come to the fore as the penetration of renewables expands and as the reliability of South Africa’s aging coal fleet declines. “The system is already experiencing swings of up to 500 MW every ten minutes and the effect will be magnified as the renewables penetration grows beyond 10%.”

For this reason, Wärtsilä is also lobbying for greater flexibility in the way South Africa deploys its proposed 3 000 MW-plus liquefied natural gas (LNG)-to-power programme.

The company has modelled both flexible and inflexible gas supply agreements for the LNG programme, using a 100% take-or-pay agreement priced at $10/GJ for the inflexible scenario and a fully flexible scenario priced at $15/GJ. “The results show that even with a significant premium for flexibility built into the gas supply agreement, the overall power system operating cost is lower for the flexible option,” Glossop states.

Source: Mining Weekly