Creating Baseload Wind Power Systems Using Advanced 

Compressed Air Energy Storage Concepts 

BACKGROUND/OVERVIEW 

Greatly expanded use of wind energy has been proposed to reduce dependence 

on fossil and nuclear fuels for electricity generation. The large-scale deployment 

of wind energy is ultimately limited by its intermittent output and the remote 

location of high-value wind resources, particularly in the United States. Wind 

energy systems that combine wind turbine generation with energy storage and 

long-distance transmission may overcome these obstacles and provide a source 

THE BASElOAD WIND CONCEPT 

The basic components of a baseload wind system, 

illustrated in Figure 1, include a large amount of wind 

generation, a large-scale energy storage system, and 

long-distance transmission. 

Compressed air energy storage (CAES) is a hybrid 

generation/storage technology well-suited for use in 

the baseload wind concept. CAES systems, illustrated 

in Figure 2, are based on conventional gas turbine 

technology and use the elastic potential energy of 

Figure 1. Simplified Shematic of a Wind/CAES Power Plant 

compressed air. Energy is stored by compressing air 

in an airtight underground storage cavern.To extract 

the stored energy, compressed air is drawn from the 

storage vessel, heated, and then expanded through a 

high-pressure turbine that captures some of the energy 

in the compressed air.The air is then mixed with fuel 

and combusted, with the exhaust expanded through a 

low-pressure gas turbine.The turbines are connected 

to an electrical generator. 

As part of a baseload wind system, CAES would be used 

to enable a nearly constant output by smoothing the 

The baseload wind power plant can achieve 

varying levels of performance in terms of expected 

capacity factor. Actual performance is dependent 

on optimizing the system component size and the 

highly variable output from wind turbine generation. 

Figure 3 illustrates how the combination of 2,000 

MW of wind and 900 MW of CAES could be combined 

to produce a nearly constant 900 MW output.When 

operating at a high capacity factor (>75%), about 

60-80% of the wind energy (averaged over a year) is 

placed directly onto the grid, while the remainder is 

stored (to be retrieved when the wind energy output 

falls below average) or “spilled” (due to limits of the 

storage cavern and transmission capacity). 

ContaCts 

Paul Denholm 

paul_denholm@nrel.gov 

national Renewable Energy Laboratory 

(nREL) 

1617 Cole Blvd. 

Golden, CO 80401-3393 

tradeoff between high annual capacity factor and 

utilization of wind energy. Figure 4 illustrates the 

energy flow through a baseload wind plant for a 

variety of possible scenarios. 

The use of “conventional” CAES requires around 

4,600 kJ of natural gas for each unit of energy 

stored by the CAES system. However, most 

wind energy does not need to be stored, so 

the effective “heat rate” of the entire baseload 

wind power plant is substantially less. Figure 5 

illustrates that a baseload wind plant operating 

at a high capacity factor will require around 

1,000 kJ of fuel for each kWh placed onto the 

grid. Several cases are illustrated, using data 

from existing wind farms, and also simulations 

of advanced wind farms in higher quality wind 

resource regions. Use of natural gas fuel in the 

CAES system also leads to greenhouse emissions 

of about 40 to 80 g/kWh. 

of power that is functionally equivalent to a conventional baseload electric 

power plant. A “baseload wind” system can produce a stable, reliable output that 

can replace a conventional fossil or nuclear baseload plant, instead of merely 

supplementing its output. This type of system could provide a large fraction 

of a region’s electricity demand, far beyond the 10-20% often suggested as an 

economic upper limit for conventional wind generation deployed without storage. 

Figure 2. Basic Components of a Compressed Air Energy 

Storage System 

Figure 3. Sample Baseload Wind Generator Output (Target 

Output = 900 MW) 

TECHNICAl AND ENVIRONMENTAl PERFORMANCE 

Figure 4: Energy Flow through a Baseload Wind Power Plant Figure 5: Baseload Wind Plant Fuel Requirements 

ADVANCED WIND/CAES CONCEPTS 

In addition to greenhouse gas emissions, the use of natural gas in 

CAES systems results in additional fuel price risk. Replacing natural 

gas with synfuel derived from local, more stable fuel sources is a 

possible alternative. One possible fuel source is gasified biomass, which 

eliminates the use of fossil fuels, virtually eliminating net CO2

 emissions 

from the system. In addition, by deriving energy completely from 

farm sources, this type of system may reduce some opposition to long 

distance transmission lines in rural areas, which may be an obstacle to 

large-scale wind deployment. Coal-derived syngas is another alternative 

in areas with existing coal mining infrastructure and where local 

economies are dependent in part on coal-extraction industries. 

While the current penetration of wind energy is far too low to 

require energy storage, projected growth in the installed base of 

wind generation motivates thinking about scenarios of extremely 

large use of wind energy. Development of the “baseload” wind 

concept will require a greater understanding of the local geologic 

compatibility of air storage, and additional work will be required 

to examine the feasibility of advanced wind/CAES concepts 

described here. 

Power (MW) 

System Heat Rate (KJ/kWh) 

The information contained in this poster is 

subject to a government license. 

CU Energy Initiative/NREL Symposium 

University of Colorado, Boulder 

October 3, 2006 

NREL/PO-640-40674