Renewable sources of energy with fluctuating output will be supplying an increasing share to the world's power grids. To support balancing needs, flexible and clean gas engine technology is expected to occupy a considerably larger role.
The rapid scale-up of many emerging power markets, at the same time as an introduction of higher levels of solar, hydro and wind renewables, can lead to a mismatch between local power needs and the capacity of the network to meet those needs. Simultaneously there has been a rapid expansion in the availability and extraction of natural gas, although many areas lack gas distribution network infrastructure.
Whether you are powering a single factory or an entire community, you need power you can trust. A quick recovery is also needed when local power consumption has unexpectedly overtaken supply and created high peak demands that threaten the stability of the national or regional grid.
Rolls-Royce Power Systems (RRPS) can provide an effective and efficient means to erect power stations based on reciprocating gas engines in more remote areas rich in gas, while producing significant levels of electrical power to support the national electricity need. In addition, the rapid start-up, quick shutdown and fast ramp rates allow for the quick response needed to meet the variable generation of non-hydro renewables in microgrids, while the use of multiple units enables high levels of plant turn down and availability throughout the year. The benefits become even clearer when seen within the framework of a modular power system where the use of pre-defined customizable modules allows specific site needs to be accommodated, and to keep down the overall plant lead time from order to commercial operation date.
Fig. 1 shows the region wise gas deficit i.e. gas production minus gas demand. In 2014 China’s gas deficit was -58 billion cubic meter (bcm) and India’s gas deficit was -17 bcm making for a total gas deficit of -75 bcm around the region however the rest of Asia (excluding China & India) has an excess of gas production of 51 bcm. So the total gas deficit for non-OECD Asia in 2014 was 24 bcm. Similarly in 2040, China’s gas deficit is predicted to be -264 bcm and India’s gas deficit would be -100 bcm. The rest of Asia would also register a gas deficit of -103 bcm making the total gas deficit for non-OECD Asia 467 bcm until 2040.
The demand is driven by significant growth in all gas consuming sectors in China and India and the emergence of gas as a major fuel in the rest of the region. However, this is against an annual growth rate in gas production of two thirds the growth rate of demand. The result of these changing patterns of production and demand is that the regional deficit will grow to around 32% of the demand by 2040, leaving the region as a significant net importer of gas. (IEA, 2016)
The regional share of gas demand taken by power generation is expected to remain stable at around 37%. However, the gas share taken directly by industry will increase from 21% to almost 30%. This increase in share from industry, coupled with overall increased demand for gas and the large future regional deficit, presents a major challenge for economic development. It is a clear goal stated by many governments to reduce the carbon intensity of their expanding economic activity and to increase the geographical diversity of that economic activity. The addition of grid scale variable renewable energy (RE) to the network supports the first goal. Unfortunately the location of suitable sites for variable RE and the desirable sites for industrial expansion often do not coincide. If the electricity networks can be improved, it is practical to place the needed balancing power stations close by the new centres of electrical demand. In these cases the required gas pipelines can serve both the industrial and power generation need.
Here there are now two major and parallel infrastructure development programs to support clean economic development. The addition of RE as a commitment to control CO2 emissions requires electrical infrastructure development.
The regional gas deficit and increased demand requires LNG (liquefied natural gas) importation terminals to be constructed and a gas distribution infrastructure to meet the needs of new industrial areas. Gas based power can operate at the convenient nexus between both of these developments, balancing the inherent instability of variable RE through the new electrical networks forming so called microgrids and drawing upon the new gas infrastructure being built for industrial growth.
In a recent public tender the benefits of the medium speed gas engine solution became clear when flexible 2-hour pulse cycles and 8-hour peaking cycle performances were required alongside the more regular 24-hour and 72-hour 100% running. The pulse cycles can be considered a form of SRL and MRL.
Referring to table “comparison between heat rate for different operating cycles”: Due to the start stop cycles for the CCGT steam system both the pulse and peaking cycle must be run in simple cycle. As a result the overall plant efficiency suffers. It is only when the plant runs for extended periods that the steam system can be brought on line and that the efficiency improves to better than the gas engine plant. The comparative combined cycle heat rate for 72 hours for the medium speed plant would be 7,263 kJ/kWh, almost matching the efficiency of the CCGT plant.
Benefits of gas engine based power stations
With more gas becoming available in the Asia/ China/India region, either piped or transported as LNG and regasified, it is set to increase as a share of energy consumption in the region from around 8% today to 13% by 2040 with a compound growth rate of 3.7%, well ahead of the overall Power Generation energy consumption growth rate of 2.5%. (IEA, 2016)
Here are some of the main advantages of gas engine based power stations:
Based on current government policies there is expected to be a rapid and sustained growth in overall power generation capacity within Asia/China/India region over the next quarter century. variable renewable energy (RE) such as wind and solar will provide an increasingly larger share of the capacity.
The addition at scale of variable RE can exacerbate network stability problems due to the inherent mismatch between the capacity that they provide and the demand on the network. The progress made to stabilise regional networks and to reduce frequency excursions can be threatened unless suitable balancing capacity is added to the network to handle variable RE-driven instability.
The characteristics of balancing capacity are well defined in developed economy grid codes and it can be expected that similar requirements will emerge in regional grid codes as they are developed. To handle the required power flows that variable RE imposes there is also a significant upgrade required to the transmission & distribution networks. The upgrades are well known but must be carefully planned as part of an expansion and robustification program.
Gas is well suited as fuel to support balancing needs. However, over the next years the region will become a major importer of gas as consumption grows at a faster pace than production. To achieve the joint goals of increasing geographical diversity of economic activity, and a reduction in the carbon intensity of the economy, significant gas infrastructure will be required to be built alongside enhanced electrical network infrastructure to dispatch variable RE to industrial centres. The decentralized power generation approach is in favour of gasbased balancing power stations to be located at new industrial zones, while balancing the effects of variable RE. In combination with e.g. batteries for energy storage, high efficient microgrids are formed. As a further advantage, such microgrids can be established much faster to ensure reliable energy supply to these areas instead investing in long lasting and expensive transmission & distribution network projects.
For gas-based balancing, pure gas engines offer a path to delivering quickly new capacity in remote areas. The modular design and construction of gas engine power plants allows for better matching of financing and revenues while being able to deliver the needed grid support services. The start stop and loading performance as well as the high level of part load efficiency even in open cycle enable this type of plant to match the needs of the region.
mtu Onsite Energy is a brand of Rolls-Royce Power Systems. It provides diesel and gas-based power system solutions: from mission-critical to standby power to continuous power, heating and cooling. mtu Onsite Energy power systems are based on diesel engines with up to 3,250 kilowatts (kWe) power output and gas engines up to 2,530 kW.