How gas engine power plants can close the gap in the uk

As stated by the UK Government, “gas will continue to play an important role in keeping the lights on, acting as a bridge to a clean power system and complementing the growth of renewables” [4].

Compared to lignite or hard coal, gas combustion has lower CO2 emissions and can become CO2-free by burning green hydrogen instead of methane. Gas power plants are also more flexible than coal technologies in terms of start intervals and load changes.

Two types of gas technologies are generally to be considered: Turbines (namely Combined Cycle Gas Turbines (CCGT) & Open-Cycle Gas Turbines (OCGT)) and Reciprocating Internal Combustion Engines (ICEs, namely Medium Speed Reciprocating Engines & High-speed Reciprocating Engines).

Turbine power plants are the technologies of choice for large power generation facilities. High runtime at full load and only a few starts per year result in low Total Cost of Ownership (TCO) and Levelized Cost of Energy (LCOE).

With more intermittent renewable energy production to be balanced, the need for large conventional facilities decreases, and the importance of flexible production profiles increases. Medium-load gas power plants, initially designed to run for 4,000 hours+ at full load, without ramping up and down frequently, run less than 2,000 hours per year with start-up counts in their hundreds. So, they have already adjusted their output in line with the availability of renewables.

Figure 3: Energy Generation from Wind and Solar, January & August 2020. [5]

As an example, an 800 MW CCGT was initially running at full load for more than 4,700 hours per year. In recent years, the generation profile changed to a more variable one, running roughly 1,700 full load hours and starting up more than 100 times per year.

A simplified 15-year TCO calculation comparing a CCGT power plant and an ICE¹ power plant² shows that in Conventional Load Profile operation, the CCGT is the cheaper solution (cf. Table 1 and Figure 4).
However, applying the more Variable Load Profile, which considers a greater share of intermittent RES in the energy system, the ICE solution becomes cheaper (cf. Figure 4). Assuming that annual runtime might decrease even further to 300-1,000 hours per year, the gap becomes wider (Maximum RES-enabling).

Turbine power plants are optimized for full-load operation to exhibit high electrical efficiencies. However, since turbine power plants often consist of one or two large
turbines, a plant’s efficiency drops significantly for partial load operations/load increments. In the case of engine power plants composed of many small engine modules, partial load operation strategies can differ. To run on load increments, an engine power plant will shut down/not utilize a certain number of superfluous engines. At the same time, the rest will continue to run at maximum load, i.e. maximum efficiency. In conclusion, engine power plants are more suited for frequent partial load operations and demonstrate superior flexibility.

Furthermore, ICEs can respond faster to load changes and do not have significant costs related to start-up, while a CCGT has a minimum up- and downtime, and needs more time to ramp up entailing higher costs. In a world in which conventional power plants primarily provide resilience and security of energy supply, and complement intermittent power generation by PV and wind, fast response times and utmost efficiency, along with versatility, are crucial success factors and enablers of the energy transition.

Figure 4: TCO Comparison CCGT vs. ICE³ in conventional load profile (past), variable load profile (present) and maximum RES-enabling (future).

The energy transition has come to stay. Hence, flexible solutions with short start-up times and a high degree of modularity, capable of ramping up many times per week, month and year, and providing the greatest efficiency across a wide output range (and at low cost), are becoming a strategic imperative. They are the enablers of a greener energy future and can generate green power themselves by switching to carbon-free combustion gases. The ICE can therefore be regarded as a future-proof technology which is already mature today.

Due to its modularity, an ICE system can run as many engines as needed at full load while keeping the remaining engines shut down, thus achieving greater efficiency than one large turbine running at partial load. High efficiency reduces the need for primary energy, thus reducing cost and greenhouse gas emissions. At the same time, small increments do not limit the handling of large loads, as major customers already operate backup capacity at the higher
end without difficulty (e.g. data centers with 100 MW+ capacity run hundreds of backup ICEs).

One might argue that small-scale turbines are also available and offer the same benefits as ICEs. However, ICEs are available on an industrial scale, making their commissioning faster. And short lead time solutions are crucial for an uncompromised energy transition.

Furthermore, containerized solutions can turn a power plant into a mobile asset. Their capacity can be integrated into the grid where needed to alleviate grid constraints. Later, when it is no longer needed, the power plant can be moved, e.g. when long-term carbon-neutral storage systems become more mature. Moving existing assets instead of decommissioning and building new power plants reduces the investment cost in new capacities and in grid infrastructure. It also reduces the risk of a stranded investment.

Looking at the challenges the energy transition now faces and will be facing in the short-, mid- and long-term, ICEs provide a viable option which is becoming more and more worth considering to meet the challenges of the energy transition. ICE technology can provide clean, cost-effective solutions quickly by adopting a modular approach, as containerized gas systems are prefabricated on an industrial scale. Lastly, due to the relatively small unit size (optimized for road transportation) of an ICE module in contrast to a large heavy-duty turbine, redundancy can be achieved with minimal additional investment by simply adding individual units to boost plant capacity (cf. Table
2)

Table 2: Summary – Qualitative comparison between turbine and ICE power plants along a multitude of different criteria. Key criteria for future power plants are highlighted in blue.

This paper focuses on electricity generation from conventional natural gas. Future publications will shed light on combined heat and power generation and the hydrogen readiness of engines and turbines, respectively.