Research Project Summary Information
Compressed Air Energy Storage Engineering Study (ST10467-1)
The generating capacity of wind energy facilities has grown rapidly in recent years, adding over 8,500 MW of generating capacity in 2008. As wind generation continues to penetrate the grid, the inherent variability in the wind requires additional standby reserves to compensate for low wind energy production during peak load. These standby reserves are traditionally gas turbines, which have a low startup time and operational cost. Still, the recent growth of the wind industry and national targets to reach upwards of 20% grid penetration may require additional options to offset the effects of wind’s variable output and supply a base load generating capacity. Energy storage, particularly Compressed Air Energy Storage (CAES), provides a possible solution to help address this challenge. CAES is a hybrid energy storage and generation concept that has many potential benefits when coupled with a wind energy generation facility. The system could convert off-peak or curtailed wind energy to compressed air for storage in an airtight underground reservoir. The stored air is then used to regenerate electricity when the plant is not curtailed or during peak time periods. To date, there have only been two long-term operational CAES installations, neither of which was designed to supplement a wind generating facility.
The Contractor (New York State Electric & Gas) performed a preliminary study that focused on four primary aspects of CAES and its probable affect on the New York State (NYS) energy market. Contractor researched the current state of the technology including the input air compressor train, the combustion turbine arrangements, and the heat recovery/recuperation devices. Contractor interviewed NY Geologists and reviewed mining maps to examine the existence of suitable underground storage geologies that could provide adequate air storage for such a facility. The availability and characteristics of Class 4 wind resources that would favor siting of a CAES plant were evaluated, to determine cost effectiveness and probable power input to the New York Independent System Operator (NYISO) electrical grid matrix. Lastly, the revenue expected from an owner/operator CAES plant, with the ability to bid into and collect from the NYISO market was evaluated and rated. Detailed economic assessments for any selected site and its hourly variability of wind resource for capturing, storing, and exporting during on-peak time periods was performed. This assessment was then related to the economics that depend upon rated Mega watt hours (MWH) of storage, locational energy pricing, hours of charging/discharging the storage cavern, size of equipment, cost of fuel and all applicable energy and environmental policies, that would affect a CAES plants operation and viability.
CAES technology possesses a unique feature that fits the NY wind profile, which uses off-peak power to charge the air storage cavern typically when wind in NYS is most plentiful, and discharges the compressed air to generate power during on-peak time periods, typically when wind is at a lull. Innovations have been made in the technology that replaces the single line shaft with independent shafts for the compression and expansion cycles of the CAES, respectively. Additionally on the expansion side, a standard CAES plant will use a standard combustion turbine (CT) engine as the only equipment that consumes fuel. On locating a CAES plant in proximity to a wind farm and using a ring-bus electrical grid-tie configuration could optimize the wind conversion to electrical grid power. This optimized siting will also prevent the grid from compensating for the fluctuations typical of wind generation. When wind generators are available, the NYISO has to scale back base load generation plants, which typically lose operation efficiency under part-load conditions. New York has several viable CAES sites, 11 of which were explored during this study. The underground geology containing bedded salt caverns can be solution mined using fresh water, and provide large airtight reservoirs to store the compressed air made from the Class 4 wind resources. The Western half of NY, from Syracuse to the south contains these salt formations.
From the economic modeling that encompassed four geographic zones of NY including loads, actual electrical, and natural gas pricing between 2001 – 2007, the analysis indicates CAES can be profitable in NY, accounting for the environmental and policy concerns associated with the energy storage market. When compared to current base load power sources, a wind/CAES facility may not currently compete in terms of total cost of energy. This study estimates total capital costs for a Conventional CAES plant (no turbo expander or chilling) at 110 MW capacities, to be $727/kW. While this total capital cost is greater than a natural gas plant, a CAES facility will consume significantly less fuel, resulting in a retail price of energy of approximately 25% less for the wind/CAES system. A wind/CAES system will lead to a reduction in natural gas (NG) consumption and CO2 emissions of approximately 64% when compared to the wind/NG system. Several scenarios could increase the need or economic feasibility of a wind/CAES system, including the following; (1) Electricity pricing volatility, (2) Carbon constraints or increased fossil fuel costs, (3) Increased penetration of renewable energy on the grid, leading to more curtailment of conventional fossil generation sources. The engineering study has also provided the intelligence to begin planning for a CAES demonstration project to be initiated within Schuyler County, NY, and has received a funding award from the Department of Energy.
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