Gas Turbine Air Injection Coupled with Compressed Air Energy Storage Makes Wind Power More Economic

Transcription

1 Gas Turbine Air Injection Coupled with Compressed Air Energy Storage Makes Wind Power More Economic Introduction By Rodney R. Gay, ESPC Mike Nakhamkin, ESPC This paper describes the integration of the new compressed air energy storage (CAES- CT) concept (based on the power augmentation of a combustion turbine (CT) or combined cycle (CC) power plants by injection of stored, compressed air into a gas turbine) and renewable energy resources, particularly wind power, so as to maximize the economic benefit of renewable resources/wind energy while increasing the capacity and flexibility of the power generation system. The first compressed air energy storage (CAES) power plant in the USA is Alabama Electric Cooperative s 110 MW McIntosh plant has been commercialized in 1991 and successfully operating since. Still expectations that this technology will take off had not materialized for a two primary reasons: 1. relatively low NG/fuel oil costs at the level of $2/million Btu, minimizing economic advantages of the CAES technology s low fuel-related heat rate (approximately 4000 Btu/kWh vs. approximately 10,000 Btu/kWh for CTs)) and resulting in a relatively low price difference between peak and off-peak energy, and 2. relatively high the CAES plant specific costs of approximately $ /kW. These economics didn t provide strong support for the use of the CAES technology for load management of the base-load power plants The current situation is drastically changed. Increased fuel costs (to $5-6/million Btu) and the current emphasis on the renewable energy sources made a strong emphasis on the CAES technology that is the only practical and proven technology that can store the hundreds of megawatt-hours of the renewable/wind energy and distribute it in a controlled fashion as needed. Wind power suffers from the fact that its output fluctuates so greatly and in an unpredictable manner such that its power cannot be considered to be available when the system needs it. Some economic means of storing the output of wind turbines, and then utilizing that stored energy to generate electricity must be found before wind power can become a significant fraction of a grid s generating capacity. The presented in the paper the CAES plant concept with the injection of the stored air into existing gas turbines and augmenting their power, denoted as CAES-CT, offers an economic alternative to custom-built CAES turboexpander. The advantage of air injection for gas turbine power augmentation is that existing gas turbines can be utilized with little or no modification to the engine itself. These gas turbines retain the flexibility to operate with or without the injection of compressed air. Thus, the stored energy from

2 wind power can be utilized when it is most economic without losing the generating capacity of the gas turbine or combined-cycle plant when it is not economic to inject stored compressed air. The paper will explore the economic and operating benefits of the CAES-CT concept and obvious benefits for integration with the wind energy- the lower cost of conversions of the wind energy into controllable source of peak energy the better. Description of the CAES-CT Concept The major feature of the CAES-CT concept is that it replaces the customized reheat turboexpander train with an existing combustion turbine or combined cycle plant (CAES -CC), with corresponding significant cost reductions relative to a totally new conventional CAES plant. For the overwhelming majority of electric power customers (in the USA and abroad) power demands reach their peak during summer, when high ambient temperatures reduce the power output of combustion turbines and combined cycle plants to the minimum. The power capability of a gas turbine is increased when compressed and optionally heated air is injected into the engine at a location upstream of the combustor. The expander of an existing gas turbine is sized to accommodate the compressor air flow expected on a cold day (32 F or 0 C). The prime reason that gas turbine power falls off on warmer days is that the compressor air mass flow rate decreases due to the lower density of air. If compressed air from an external source is injected into the gas turbine, the expander power can potentially be increased up to its design capacity on a cold day. The gas turbine output on hot days can be increased by 25% to 30%. A similar situation exists at high elevations. For example, a GE Frame 7FA CT nominally rated at approximately 174 MW at ISO conditions (59 F with 60% relative humidity), will produce maximum power of approximately 191 MW, when the ambient temperature is 0 F, but will produce only approximately 150 MW at 95 F. The significant power loss by a CT during high ambient temperature periods (when the price for replacement electricity is at its highest) requires a power generation company to install additional capacity to meet summer peak demands. Power losses for a CC power plant during high ambient temperature operations are similar to those for a combustion turbine. Therefore CT/CC plants operate for the most of the time with significantly lower capacities than the maximum power generation, which occurs at low ambient temperatures. Existing capacity reserves of CT/CC plants could be utilized for producing additional peak capacities via injection of the stored compressed air, that was generated by a renewable energy sources, like wind energy. This approach allows development of the CAES plants by adding only the air compression and storage facilities to existing CT and CC plants. Highly customized and expensive turboexpander trains are not necessary. This method was invented by Dr. Michael Nakhamkin of ESPC, as described in U.S. Patent #5,934,063 (Reference 1) and in References 2, 3 and 4. Figures 1 and 2 (with and without humidification respectively) illustrate schematic diagrams of the CAES-CT concept (with operating parameters), where the power of the GE 7FA-combustion turbine, operating at 95 F ambient temperature, is augmented using

3 compressed air stored in an underground compressed air storage system. The major components of the CAES-CT plant are as follows: A commercial combustion turbine with the provision to inject the externally supplied compressed air at any point upstream of the combustor. Engineering and mechanical aspects of the air injection for CAES-CT plants are similar to steam injection for power augmentation, which is a standard CT s power augmentation option provided by a number of OEMs; An auxiliary compressor system consisting of commercially available off-theshelf standard compressor modules and sized for the incremental airflow (and not for a full airflow) to be stored and later injected into a CT/CC plant; Compressed air storage, which could be underground storage in salt, hard rock or aquifer geological formations or above ground storage in various types of pressure vessels; Balance-of-plant equipment and systems including interconnecting piping, valves, controls and an optional recuperator. CAES-CT Dry Air Injection Concept Power Augmentation of Gas Turbine GE7FA COMBUSTION TURBINE C T G COMPRESSOR TRAIN Power = 23 MW FILTER Ambient Air 95 F, 895 Lb/sec Fuel 22 Lb/sec 800 F M C HRU Ambient Air 95 F, 116 Lb/sec 300 psia STACK ESTIMATED PERFORMANCE AT 95 F: CT CT-DAI NET POWER, MW INCREMENTAL POWER,MW 0 40 NET HEAT RATE, Btu/kWh 9, Compressed Air underground Storage Figure 1. CAES-CT concept

4 CAES-CT Concept with Humidification Equivalent to 3.5% SI COMPRESSOR TRAIN Power = 12.3 MW GE7FA COMBUSTION TURBINE M C C Fuel T G Ambient Air 95 F, 58 Lb/sec Ambient Air 95 F, 896 Lb/sec 5.5% H2O (M) Moist Air (36% H2O) 373 F, 88 Lb/sec HRU Compressed Air Storage AIR SATURATOR STACK ESTIMATED PERFORMANCE AT 95 F: (M ax. Power) CT CT-HAI NET POWER, MW INCREMENTAL POWER,MW 0 40 NET HEAT RATE, Btu/kWh (LHV) 9, Make-up Water Figure 2. CAES-CT Concept with Humidification Figures 1 and 2 illustrate that the additional compressed air flows (of 116 lbs/sec and 58 lbs/sec, with further humidification, respectively) from the compressed air storage being injected upstream of the combustors will increase the combustion turbine power output from 150 MW to 190 MW. The performance characteristics presented in Figures 1 and 2 should be considered as estimates only because the maximum amount of injected air, at any given ambient temperature, could be restricted by a number of design or operational limitations, like the electric generator and electrical system restrictions, etc. The additional compressor train will be driven during off-peak hours by the energy generated by wind power plants. It should be noted that the auxiliary compressor capacity and operating hours and the underground storage size should be optimized based on the wind energy production pattern. The additional CAES plant incremental capacity of 40 MW achieved by only one CT demonstrates that practically any required CAES plant capacity could be achieved by combining capacity reserves of various number of existing CT/CC plants. This means that the CAES-CT concept could provide load management for a variety of the wind power plants capacities and power generation patterns. In addition to the power increase, the fuel-related heat rate of this additional capacity is significantly reduced to typical CAES plant levels of approximately 4000 Btu/kWh for the CAES-CT plant with dry air injection (Figure 1) and of 6200 Btu/kWh with humidification (Figure 2). In spite of a higher heat rate for the case with humidification, it is important to remember that for the same additional power the humidification concept reduces the underground storage by a factor of approximately two (as compared to the dry air injection concept) with corresponding cost and schedule savings.

5 For gas turbines equipped with inlet guide vanes (IGV), the incremental power produced by the stored compressed air could be significantly increased by closing the IGV s (and reducing the gas turbine compressor flow) and increasing the injected compressed air flow from the storage. As demonstrated by Figure 3 the CAES-CT incremental power based on the stored air could be theoretically increased from 40MW to over 120 MW (a number to be further confirmed based on detail knowledge of potential limitations, currently not identified). This accordingly increases wind energy capacities that could be managed by a single CT/CC plant. Figure 4 shows distribution of the CT s total power between the so-called the CT power, the power that could be provided either by the CT or by CAES-CT s the stored air and the power exclusively provided by the CAES-CT. Table 1 describes performance characteristics of the CAES-CT with IGV s when it operates at various modes The major features of CAES-CT/CAES-CC concepts are similar and can be summarized as follows: The CAES-CT concepts utilize the existing reserve capacities of combustion turbine (CT) and Combined Cycle (CC) plants, as explained below. These concepts do not require development of highly customized specifically engineered (for various powers and geologies) CAES turbomachinery trains with reheat and recuperation, with associated complications and costs. The use of existing CT power plants avoids costs associated with new projects development like site permits, licenses, etc. These CAES-CT concepts could be easily applied to meet a variety of the CAES plant power and storage requirements by achieving required storage capacities through combining CTs of various capacities with various numbers of units. The CAES plants based on the conventional concept with a customized turbomachinery trains have no such flexibility. The existing CTs as a rule present a state-of-the-art proven technology with the highest performance characteristics and the lowest possible NOx emissions. The stored compressed air could be easily humidified before injection into CT/CC plants (with associated efficiency improvements and storage cost reductions) without the aforementioned complications associated with HAT and CHAT concepts. The CAES-CT plant has three modes of operation: Conventional combustion turbine operation, where the CT is disconnected from the compressed air storage. CAES mode of operation, where during peak periods, compressed air flow from the storage is injected upstream of the combustors to complement the CT s compressor discharge air flow. The compressed air from the storage could be optionally preheated in the recuperator and humidified. The storage is charged with the compressed air by the auxiliary motor-driven compressor during off-peak hours utilizing renewable resources, nuclear or coal generated power.

6 Power augmentation mode of operation, when a CT/CC plant power is augmented during peak hours by injected airflows supplied by the auxiliary compressor operating simultaneously with a CT/CC plant. These features primarily described in application to CAES-CT plants are similarly applied to CC plants with the difference that the CT is replaced by a CC. The CAES-CC plant operations are similar to the CAES-CT plant; the only difference is that in the CAES-CC plant, the increased power of the CT will be complemented by additional power produced by the steam turbine of the bottoming cycle due to the added CT exhaust flow. The effects of the dry and humidified air injections on a CT performance and operations (including the compressor surge, maximum torque, combustors operations, disk space temperatures, etc.) had been analyzed and test validated on the GE 7FA combustion turbine (Reference 5). CAES-CT Dry Air Injection Concept Maximum Air Injection, IGV s Closed GE7FA COMBUSTION TURBINE C T G FILTER Fuel 18 Lb/sec Ambient Air 95 F, 522 Lb/sec 900 F M C Injected Air 95 F, 350 Lb/sec 300 psia HRU STACK ESTIMATED PERFORMANCE AT 95 F: CT (IGV Closed) CT-DAI NET POWER, MW INCREMENTAL POWER,MW NET HEAT RATE, Btu/kWh Compressed Air underground Storage Figure 3. CAES-CT Concept with closed IGVs.

7 GE7FA Flexibility to Operate At Various Levels of CAES Injection 200 MW Normal GT Power CAES Power Either CAES or Normal GT Power Generator Limit Baseload GT Power GT Power: IGV s Closed 0 Ambient Temp (F) 100 Figure 4. Power Composition for the CAES-CT Concept with closed IGVs. Gas Turbine Can Operate With or Without Power From Injected Air Ambient Temp Generator Capacity (MW) Baseload Normal GT Power (MW) MW with Fully Closed IGV s (MW) Max Power from Injected Air (MW) Max Air Injection (lb/sec) GT Heat Rate with Max Air Injection (Btu/kWhr) Cold (0 F) Hot (95 F) Table 1 Modes of Operation of the CAES-CT with IGVs

8 LARGE SCALE UNDERGROUND STORAGE FACILITIES During optimization and engineering of the 110 MW CAES plant for Alabama Electric Cooperative, and prior to this in the course of a number of feasibility studies, ESPC, jointly with a number of contractors, developed empirical equations for engineering and cost estimates for underground storage reservoirs in various geological formations ( hard rock, salts, aquifers). These equations had been integrated in a software for integration and optimization of CAES plants. As an example, for AEC project with underground the storage in the salt dome and specific CAES plant power generation requirements, the optimized storage (solution-mined at 1500 ft depth and the volume of 22 m. cu.ft.) had the storage specific cost of approximately $3/kWh of the CAES plant continuously produced energy or approximately $75/kW. EPRI (Electric Power Research Institute) conducted very extensive geological studies to identify locations in the U.S. with geological characteristics acceptable for development of underground storage facilities for the CAES power plants and produced a data base for estimated construction and operating costs for various geological formations. The published report and produced maps confirmed that more than 80% of the U.S. territory has salt, hard rock and aquifer formations acceptable for creation of underground storage facilities in a cost-effective manner. It should be noted that at any given moment more than $30 billion worth of strategic materials are stored in underground formations. The CAES-CT provides a huge reduction of the storage volume and costs per MWh of the peak power generated due to the following reasons: The lower specific air consumption per kwh produced the smaller volume required. The CAES-CT s has lower specific air consumption per kwh produced due to higher Turbine Inlet temperature (TIT) of contemporary CTs vs. the temperatures of the CAES Turboexpander. The storage volume is inversely proportioned to a maximum minus minimum pressure differences in the storage. CAES-CT has higher pressure change in the storage, because, for the same the maximum storage pressure, the withdrawal pressure for the CAES-CT concept is significantly lower than that for the CAES reheat turboexpander. Table 2 provides comparative analysis of the storage volume requirements for the conventional CAES plant concept and for the two alternative operations (without and with IGVs) of the CAES-CT plant based on GE 7241 FA CT. It is built based on the assumption that we will have geological conditions similar to those of the AEC s CAES plant (1500 ft. depth, with maximum allowable pressure of 1100 psia and minimum allowable pressures of 800 psia and 450 psia for conventional and CAES-CT concepts, respectively. Table 2 shows that the CAES-CT concept with closed IGV generates 123 MW power vs. 100 MW for the conventional AEC s CAES plant concept and requires 9.3 millions ft 3 storage vs. 22 millions for the AEC CAES project. The CAES-CT with the humidification of the injected stored air further reduces the storage size by the factor of two.

9 Power (MW) Flow (lbs/sec) Volume millions of ft 3. for 26 hrs of storage Volume, millions of ft 3 for 8 hrs of storage Volume, millions of ft 3 for 8 hrs of storage with Humidification (ft 3 /MWh) Alabama CAES plant (8,460) CAES-CT based on Power Augmentation CAES-CT based on Power Augmentation w. closed IGV (3,750) (3,750) Table 2- Comparative Analysis of the Storage Volume Requirements for the Conventional CAES and CAES-CT Concepts SUB-SURFACE MAN-MADE AIR STORAGE FACILITIES This concept is patented by the US Patent # 5,845,479 Method for Providing Emergency Reserve Power Using Storage Techniques for Electrical Systems Applications and presented in a number of publications. The development of man-made above-ground storage facility had been driven by two considerations: To allow the CAES-CT concept to be used without considerations of local geology limitations; The fact that underground storage makes economic sense only when the compressed air is stored in quantities that support hundreds of megawatt-hours of the storage. This is not the case for MW CAES plants with three (3) to five (5) hours of the storage that are typical for the storage and management of small wind farms or other dispersed renewable energy sources. ESPC conducted extensive exploratory engineering to develop a cost-effective subsurface compressed air storage approach. Various industrial pressure vessels, buried highpressure piping and other alternatives were analyzed for the storage applications. They were engineered, laid-out, cost estimated and subjected to variety of potential applications. As a result, the above ground compressed storage in the buried highpressure piping was selected, based on the capital cost and other considerations.

10 The conceptual arrangement of the sub-surface compressed air storage system is presented below. The above ground storage optimization resulted in the significantly higher storage pressure (to reduce the volume) and in the overall CAES-CT plant parameters and operations that are different from those for the underground storage. Optimized above ground storage systems could be competitive with large underground storage facilities on the $/kw basis when storage capacities are limited to three (3)-five (5) hours. The estimated costs for the pipe storage for the CAES-CT with the humidification is approximately $30/kWh versus. $3/kWh for the AEC s project with the underground storage in the salt dome. For a 40 MW CAES-CT with three hours storage, the pipe storage cost is approximately ($30/kWh*40,000 kw* 3hrs) $3.6 million, which is a capital cost equal to $90/kW of electric capacity. The estimated costs for the pipe storage for the CAES-CT with the dry air injection are approximately $70-$80/kWh. Figure 5: The Sub-Surface Storage Conceptual Arrangement. ENGINEERING AND CAPITAL COSTS The conceptual engineering and cost estimates for the CAES-CT concept based on GE Frame 7FA has been performed, with the underground compressed air storage in the salt dome (with geological characteristics similar to the AEC s CAES project) sized for continuous eight (8) hours operation with the incremental (CAES) power of approximately 40 MW. The overall plant has been optimized based on the lowest

11 specific incremental capital costs (incremental costs divided by incremental power) as a primary criterion with strong consideration of cost of electricity generation. This included, concurrent optimization of parameters, performance and economics of the compressed air storage in a salt dome, the compressor train and other equipment involved including the compressed air charging costs. The resulting storage requirement is approximately 1.2 million cubic feet (see Table 2) with estimated costs of $2-$3 million. These data are based on prorating of actual parameters and costs of the underground storage in the salt dome for 110 MW CAES plant. The compressor train has been sized for two hours of compression for each hour of peak power generation at 95 F. That is, the compressor is sized for 30 lbs/sec which is approximately half of the supplementary flow from the cavern of 58 lbs/sec (see Figure 2). Estimated total incremental cost for equipment and systems required (for the conversion of the Frame 7FA combustion turbine into the 40 MW CAES-CT plant with aforementioned operating requirements) is less than $5.0 million dollars, which is less than $125/kW. For the CAES-CT with the above-ground storage the storage sized for six hours, based on the estimated above specific costs of $70/kWh, the specific storage costs are $420/kW and the estimated specific costs for the 40 MW CAES-CT plant with six hours above ground storage is under $550/kW. These specific costs compare favorably with the approximately $ /kW specific cost for a turnkey installation of a large capacity CAES plant with the underground storage in the salt dome (the lowest cost geological formation). The total operating cost of the CAES-CT plant should include the fuel cost consumed during the CAES-CT plant operation (peak periods) and off-peak energy cost for recharging the compressed air storage system with the compressed air. The fuel and offpeak energy related costs of electricity (COE) (without O&M costs) produced are calculated as: The operational cost of electricity from CAES-CT is equal to the incremental heat rate of the additional power produced when the compressed air is injected into the gas turbine multiplied by the cost of the fuel plus the ratio of the electric power consumption of the compressor used to compress the stored air to the electric power produced by that stored air when it is injected into the gas turbine multiplied by the cost of the electric power used to drive the compressor. where, C = H C + R Electric Rate Fuel Power C AuxPower C Electric is the operational cost of the electric power (not including maintenance and capital costs) produced from stored air energy (($/kwh). H Rate is the incremental heat rate of the electric produced by the stored air when injected into a gas turbine (Btu/kWh), equal to the change in fuel consumption

12 divided by the change in power generation when air is injected into the gas turbine. C Fuel is the cost of fuel ($/Btu) to power the gas turbine where the compressed air is used. R Power is the ratio of the auxiliary power consumed by the compressor while storing the compressed air to the electric power produced when the air is injected into a gas turbine. C AuxPower is the cost of the electricity used to drive the compressor ($/kwh). Table 3 shows significant reductions in capital recovery component of cost of electricity (COE) for the CAES-CT concept (with the estimated specific capital costs of $125/kW) vs. the standard concept (with estimated capital costs of $600/kW) - both with the underground storage in the salt dome. Assuming that other components of the COE associated with fuel, O&M costs, and T&D charges are approximately the same for the CAES-CT and conventional CAES plant, Table 3 presents practical difference between total costs of electricity. The Table 3 shows that at 1000 hours of annual dispatch, the CAES-CT concept has by approximately 6 /kwh lower components of the COE associated with the capital cost recovery. That amount is critical to differentiate between an economically attractive and unattractive integration of the wind power project with the storage technology. Hours of Annual Dispatch Capital Recovery Cost of Electricity Component (12% ROI) Conventional CAES Plant at $600/kW, CAES-CT Plant at $125/kW /kwh 3.0 /kwh /kwh 1.5 /kwh /kwh 1.0 /kwh Table 3. Capital Recovery Components of the Cost of Electricity. Special Considerations for CAES-CT concept General CAES-CT concept generates an incremental power by augmenting capacity of the existing CT plant that is already properly sited, permitted, manpowered, T&D connected,

13 with all auxiliary systems and electrical/transmission equipment in place, with fuel supply contracts, etc. It should be anticipated that only some incremental permits and upgrades will be required. The Conventional CAES plant is practically a new power plant that needs all required licenses, permits, T&D connections, etc. These CAES-CT concepts could be easily applied to meet a variety of the total CAES plant power and storage requirements by achieving required storage capacities through combining CTs of various capacities with various numbers of units. The CAES plants based on the conventional concept with a customized turbomachinery trains have no such flexibility. CAES-CT Plant Engineering, Construction, Commercialization For the case when CTs are available there are no costs associated with the purchase of a CT and its installation and commercialization. The engineering and construction is limited to the storage facility and installation of the auxiliary compressor and its integration with the CT. The schedule for the CAES project will be dictated primarily by the storage facility development while the AI technology implementation schedule is between 6 and 8 months. If there is no CT available for the CAES-CT application, the purchased CT could be of an old generation that could potentially be acquired at very low costs. As it was stated above, the CAES-CT power is generated with the heat-rate of approximately 4000 Btu/kWh and that heat rate is a week function of the TIT (turbine inlet or firing temperature), i.e. it will be slightly higher at lower than the state-of-the art TIT. This CT will be standard equipment, skid- mounted with well established and simplified installation techniques. The conventional concept turbomachinery developed by Dresser Rand for the AEC s 110 MW CAES has been successfully operating since Still, as experience showed, it has a number of specific features that require relatively complicated installation and tuning up: The reheat expander train with HP and LP expanders/combustors (vs. one for a CT); The custom made HP combustors are unprecedented except for the Alabama CAES project. They operate at a higher pressure with associated operational and emission complications. The HP combustors have inherently higher emissions due to the fact that NOx emissions are proportional to pressures in the power of 0.5. The installation and operational controls of the multi-component conventional turbo expander is relatively complicated due to the facts that: It requires installation of the HP and LP expanders/combustors with special tuning up as it relates to the frequency, torque, thrust bearings and most important sequential combustor operations

14 It requires special consideration to transient operations (due to the fact the compressor train is disengaged) and the over speeding problem due to a sudden loss of the power. Emissions CAES-CT is based on utilization of standard CTs with well-developed state-of the art combustors with the lowest possible NOx emissions. The older generation of CTs probably haves diffusion type combustors with elevated emissions and that with relatively low efficiency are two prime reasons that they are not dispatchable. As was mentioned above, the CAES-CT concept will increase these older generation CTs efficiency plus NOx emissions will be significantly reduced for the following reasons: Injection of the cold stored air in the flame zone will reduce the firing temperature with associated reduction of the thermal NOx (lesser but similar effect to steam/water injection) As was demonstrated by humid air combustor tests sponsored by EPRI if humidified air is injected, NOx emissions could be reduced by as much as 80%. The HP and LP combustors of the conventional turbomachinery are unique and require special considerations: the HP combustors inherently produce higher emissions (proportional to the operating pressure in 0.5 powers) and LP combustors (though have pressure similar to that of CTs) operate with a vitiated air. The experience of the AEC project demonstrated significantly higher emissions (as compared to CTs), i.e. these combustors require massive NOx reduction measures. The CAES-CT could be a completely green project, i.e. the project without any additional fuel burning by using two potential approaches: The stored air that presents a fraction of the total CT airflow could be added without increasing the CT fuel flow. That will result in the reduced the TIT, but while it is critical for CT efficiency, it is less important for the CAES-CT plant due to the fact that the CAES related share of the power (generated with approximately 4,000 Btu/kWh heat rate) is introduced without simultaneous the auxiliary compressor power deduction and more than compensate for the reduction of the TIT. The renewable energy sources (like solar, woodchips burning, etc.) could be used for the preheating of the external flow of the stored air prior to injection, i.e. the additional power will be introduced without fuel burning. Underground Storage. The CAES-CT concept reduces the size of the required air storage (see Table 2). This is important because it reduces costs, construction schedule and widens opportunities including locations of a restricted geology. For situations where the sub-surface storage systems with their higher specific storage costs makes sense, the CAES-CT concept provides critical advantages: - Significant cost reductions due to smaller required volumes

15 - Due to the fact that CAES-CT will provide a total storage capacity via multiple projects, this provides additional opportunity to build small storages supporting a single CAES-CT project. Schedule The CAES-CT project delivery schedule is significantly reduced from approximately three (3) years for the conventional CAES concept (based on the experience of the 110 MW AEC project) to practically the time needed for the storage development that could be less than two (2) years. The CAES-CT project development schedule is expected to be reduced due to the fact the existing CT/CC plant is sited, permitted, eclectically connected to the grid, etc. Integration of the CAES-CT with the Wind (or Any Other Renewable Sources) As it was mentioned above, the wind energy requires storage to provide an opportunity of being stored during off-peak hours and being dispatched when it is needed and when price of electricity is high. The CAES-CT concept provides the most cost effective alternative for integration with the wind energy: - It has the lowest specific costs of approximately less than $200/kW if the existing CT is available; - It has the best economics, i.e. reduces by approximately 0.06 $/kwh (as compared to convectional CAES plant, see Table 3) incremental costs of electricity for the conversion of the wind energy in the peak energy - It can meet variety of wind energy power requirements by combining a variety of CAES-CT plants - It has the shortest schedule for the implementation, that could be less than two (2) years; - It reduces volume and costs of the underground storage and significantly widens opportunities for the wind energy storage in locations with limited underground geological formations - For the sub-surface man-made storage it provides a significant advantage of reduced volumes and costs. - Project development schedule is reduced by years because CAES-CT utilizes a licensed, sited, electrically connected CT. References 1. US Patent # 5,934,063 Method of Operating a Combustion Turbine Power Plant at Full Power having Compressed Air Storage 2. New Compressed Air Energy Storage Concept Improves the Profitability of Existing Simple Cycle, Combined Cycle, Wind and Landfill Gas Power Plants, ASME Turbo Expo 2004, Vienna, Austria

16 3. Dr. M. Nakhamkin, R. Wolk Compressed Air Inflates gas Turbine Output, Power Engineering, March Dr. Michael Nakhamkin, Sep van der Linden, Ron Hall, Dale Bradshaw and Ron Wolk - Small Capacity CAES Plants with Manmade Subsurface Storage (SSCAES) is Effective Distributed Generation Plant and Effective Tool For Improvement of Economics for Wind, Other Renewable Plants, Landfills. PowerGen Air Injection Power Augmentation is validated by Peaker tests, Gas Turbine, World, March-April, 2002.