|By Chirag Rathi, Frost & Sullivan Senior Consultant|
Renewable energy has emerged as a substantial source in the global energy mix, accounting for about a fifth of worldwide electricity production. Today, renewable energy technologies are becoming increasingly cost-competitive and useful in advanced and emerging economies alike.
Along with renewable energy, another highly influential development has occurred in the world of energy over the last decade. A very high success rate in the exploitation of the seemingly impermeable shale gas resource in the U.S. has opened up a new frontier for unconventional natural gas resources in the world. Cheap and abundant natural gas has brought about a challenging issue: whether natural gas will be a threat or co-exist with the renewable energy.
Golden Age of Natural Gas
Natural gas on the other hand is rising swiftly in the order of primary fuels. This unbridled growth in natural gas is largely attributed to shale gas. As it turns out, shale gas is only one aspect of larger unconventional natural gas production. Coal bed methane (CBM) and tight gas can potentially provide an additional 7000 trillion cubic feet (TCF) of natural gas, taking the overall natural gas supply to 250 years. Other, unconventional hydrocarbons such as methane hydrates are yet to be even explored. It is estimated that global natural gas consumption will increase by more than 50 percent and will account for a quarter of the global energy consumption in the next two decades.
Is Natural Gas a Boon or Bane for Renewables ?
Natural gas emits the lowest carbon dioxide of any fossil fuel: about 40 percent less than coal and 20 percent less than oil per unit of energy used. Renewable power emits zero emissions, but intermittency of power generation owing to vagaries of wind and sun are huge challenges. Despite several advancements, the industry still lacks a cost-effective power storage solution. Natural gas has the ability to supplement renewable power generation almost instantaneously to ensure uninterrupted power in the event of falling wind or solar supply. By acting as peaking or balancing units, gas-fired power plants can act as a bridge for the decarbonisation of energy from the high carbon sources such as coal and oil to non-carbon sources such as solar and wind energy.
Gas Turbine Technology
Gas turbines are almost an ideal technology to compensate for renewable power variability. They have quick start-up time that enables frequent starts/stops to support the variable generation. However, conventional frame-type gas turbines operate optimally only at full-power, steady conditions where they are at their best fuel and emissions efficiencies. Operating at part load results in significant inefficiencies (particularly with NOx emissions) and, not to mention, higher operational costs.
In recent years, aeroderivative gas turbines have proven to be a perfect answer for some of these challenges. Aeroderivatives in general have a faster start-up time compared to frame-type turbines, which means they can follow loads up and down at any point in between synchronization and full load, allowing for better load management. With the addition of dry low emission combustors and other innovations in combustor design, aeroderivatives perform better in emissions efficiency at part load. With optimal performance tuning of selective catalytic reduction and non-selective catalytic reduction turbines that are heavily cycled, the NOx emissions have been controllable. Turbine manufacturers such as General Electric have expanded their aeroderivative fleet of models to specifically suit the requirements of the renewable industry. In recent years, the General Electric LM6000 turbines have been successfully deployed as back-up or peaking units to support wind farm sites.
Use of gas turbines as back-up power comes with added cost considerations. First, the cost of emission permits to produce gas-fired power must be considered. Secondly, gas turbines used as peaking or back-up units have to be cycled continuously over their power range. Continuous cycling causes maintenance budget escalations. Wind, solar and other renewable energy sources are largely supported by some form of tax credits or feed-in tariff support programs, and many of these programs don’t take into account the added cost of using natural gas as a back-up. As renewable support policies around the world evolve in light of the availability of natural gas, some policy changes are likely to occur. Renewable power technology and unconventional natural gas production are likely to grow simultaneously in the years to come, with the coexistence of both shaped by the economic incentives and renewable policies of major power-producing countries.