Largely driven by the growing use of intermittent energy sources like wind and solar, 2014 will mark the first year in which hydropower is not the United States’ primary source of renewable electricity1. As a result of this shift, the need for clean, grid-scale energy storage solutions effectively balancing intermittent renewables and better accommodating continuously changing electricity demands is increasing dramatically. We believe compressed air energy storage (CAES), which offers renewable grid penetration and operating flexibility (e.g., rapid start-up, high turn-down ratios, short transition times, high ramping rates, black-start capable) is fast becoming the solution of choice for bulk storage energy.
Our involvement with CAES dates back to 1991 at the Power South Plant in McIntosh, Alabama – the first CAES facility commissioned in North America (and the second in the world). Still meeting electrical production demands today, the facility’s. Our involvement with CAES dates back to 1991 at the Power South Plant in McIntosh, Alabama 140-foot machinery train was derived almost exclusively from D-R product lines.
Positioning ourselves as the world leader in CAES technology, we drew from our experience with Power South and combined it with an unrivaled degree of expertise in the field of rotating equipment applications to further enhance our CAES product offering. The result: SMARTCAES® solutions – a “one-stop” power island that includes all rotating equipment applications and ancillary services that are required to meet highly specific grid-scale requirements.
Although the first commercial-scale CAES facility was commissioned in Germany in 1978, grid-scale use of the technology in following years was rather limited. CAES was simply not seen as an economical source of power generation until recently. As intermittent renewables like solar and wind have increased within the electrical market, maintaining electrical grid stability is increasingly difficult. As a result, the use of CAES as an energy storage solution is increasingly viewed as an economic and viable solution.
CAES – What it is and How it Works
CAES uses expander turbine generation to provide electricity when renewable energy is not available. When renewables are available but not in demand, the system receives that renewable energy and an aboveground compressor system compresses air into underground caverns such as solution-mined salt caverns, hard-rock caverns, aquifers, and/or depleted natural gas fields. This process is known as “underground formation charging.” When power is needed, the compressed air is withdrawn from storage and used to drive expander turbines that generate electricity.
SMARTCAES systems give utilities the means to operate their base load plants more efficiently and provide a cost-effective solution for balancing grids, thus enabling renewable technologies such as solar cells and wind turbines to be matched with daily and weekly demand requirements for electricity.
Wind farms typically generate more electricity at night when grid demand is low. CAES gives utility operators the ability to “store” this electricity for use during times when it is most valuable. Similar to pumped hydro plants where dams release water through hydro-turbines during periods of high demand, a CAES system can “release” stored energy during peak hours.
Why CAES Has Become So Attractive
Renewable Grid Penetration
SMARTCAES solutions can provide added stability to electrical grids during periods of high demand. By mitigating the risk and unpredictability of variable energy sources, CAES improves grid reliability and enables the development of renewable projects. Many grids are now replacing each MW of power capacity from fossil fuels with one generated from renewables. Some notable grid providers who have already begun the process of doing this include PJM, ERCOT, California ISO, and SONI.
Some CAES developers model systems as standalone plants; other developers see potential in co-developing CAES plants alongside renewable assets, such as wind and/or solar farms. This later model allows the developer to increase the capacity factor of their renewable assets by storing the energy using the CAES plant. It also allows the developer to engage in long-term power purchase agreements (PPA) at a set MW rating. When the renewable’s power generation is greater than the PPA, the operator uses the excess power to compress air into the cavern. Then, when the renewable generator cannot meet the PPA requirements, the operator discharges air from the cavern generating the needed power through use of expander turbines.
The primary goal of the Power South plant in Alabama was rather simple: create an energy arbitrage by compressing air at night when demands are low and electricity costs are cheap; then expand the air to generate power during periods of high demand when electricity costs are high. In recent years, however, the need for grid stability has become increasingly dire, thus, the ancillary services offered by CAES plants have become more attractive.
Many ancillary services are already being procured by utilities to comply with National Electric Reliability Corporation (NERC) standards and improve Control Performance Standard scores (NERC CPS1); with new regulatory measures on the horizon, their importance will only continue to grow.
One ancillary service that the CAES systems provide is synchronous inertia response. Since the system consists of very heavy rotating equipment, the inertia provides a valuable service that allows it to act as dampers or absorbers when grid events occur.
The generation train also provides primary frequency response as well. If the frequency of the grid deviates outside specified grid frequency limits, the generation train will respond by adjusting its output power proportionately to stabilize the frequency. With a fast acting governor valve on the generation train, the air and fuel can be regulated to meet the dispatch request if such a condition occurs.
Emphasis on Green Technologies
CAES offers a sustainable and cost-effective way to help coal-burning plants comply with new fossil fuel emissions requirements, providing environmental advantages over other energy storage solutions. When used with renewables, it yields the lowest carbon footprint for the incremental, “firm kW-hr.” Combustors in CAES systems also use one-third the fuel of conventional gas turbines, leading to lower emissions.
Increased Efficiency and Lower Operating Costs
CAES facilities help extend the useful life of base load units by minimizing their need to load follow, which incurs life-reducing thermal cycling. Using the energy stored during off-peak hours to meet peak electricity demands is also less expensive than using traditional gas turbine peaking units or purchasing power from other sources.
Flexible Cycling Options
As a renewable enabler, SMARTCAES solutions provide tremendous grid flexibility and storage to enhance variable energy because of the availability of compression duty when not in power generation mode. The system can be configured for daily, weekly or extended cycles, allowing for more effective “grid balancing” and the use of inexpensive power for air storage (charging).
Quick Response and Black Start Capability SMARTCAES generations can be brought to full load in less than 10 minutes, which eliminates the need for intermediate-load plants and provides a cost-effective way to meet spinning reserve requirements.
SMARTCAES plants can also be designed to incorporate black start capability. With the help of a minimal number of diesel generators, CAES plants can be brought online completely isolated from the grid. Critical in blackouts, where the grid has no power for plant start-up, a synchronized CAES plant can provide the power necessary to bring other generating assets online, restoring power to customers quickly.
SMARTCAES plants provide a modern solution for increased grid penetration from intermittent renewables and have drastically transformed the dynamics of the worldwide energy market. The variable and inherent unpredictability of wind and solar has made the development of highly flexible energy storage solutions critical to reducing global emissions and eliminating our dependence on fossil fuels. While in the past the implementation of grid-scale compressed air energy storage (CAES) has been rather limited, it has proved to be an efficient and reliable means of generating power to meet peak energy demands, balancing intermittent renewables and enhancing grid stability.
The number of CAES facilities planned is increasing, and with as many as 40 additional CAES projects being proposed in the next decade, its role in the power generation market throughout the future will only continue to grow.