Adding large solar photovoltaic (PV) resources into an electric grid influences the flexibility characteristics of its net load profile. The dispatch of the existing generation fleet changes as it adjusts to accommodate the new net load. This study categorizes and defines these flexibility characteristics. It utilizes a unit commitment and dispatch (UC&D) model to simulate large solar generation assets with different geographic locations and orientations. The simulations show the sensitivity of the wholesale energy price, reserve market prices, total dispatch cost, fuel mix, emissions, and water use to changes in net load flexibility requirements. The results show that generating 22,500 GWh of solar energy in a 2011 simulation of the Electric Reliability Council of Texas (ERCOT) reduces total dispatch cost by approximately $900 Million (a 10.3% decrease) while increasing ancillary services costs by approximately $10 Million (a 3% increase). The results also show that PV reduces water consumption and water withdrawals as well as CO 2 , NO x , and SO x emissions. It also reduces peak load by 4% but increases net load volatility by 40-79% and ramping by 11-33%. In addition, west-located, west-oriented solar resources reduce total dispatch cost more than the other simulated solar scenarios. The west-located, west-oriented solar simulation required greater system flexibility, but utilized more low-cost generators and
This research analyzed an integrated energy system that includes a novel configuration of wind and solar coupled with two storage methods to make both wind and solar sources dispatchable during peak demand, thereby enabling their broader use. Named DSWiSS for Dispatchable Solar and Wind Storage System, the proposed system utilizes compressed air energy storage (CAES) that is driven from wind energy and thermal storage supplied by concentrating solar thermal power (CSP) in order to achieve firm power from intermittent, renewable sources. Although DSWiSS mimics the operation of a typical CAES facility, the replacement of energy derived from fossil fuels with energy generated from renewable resources makes this system unique. West Texas is a useful geographical testbed for this system because it has abundant co-located wind and solar resources; it has competitive electricity markets, which give producers an economic incentive to store night-time wind energy in order to be sold during peak price times; and it has a significant number of locations with geological formations suitable for CAES. Through a thermodynamic and a levelized lifetime cost analysis, the power system performance and the cost of energy are estimated for this integrated wind-solar-storage system. We calculate that the combination of these components yields an energy efficiency of 46% for the CAES main power block, and the overall system cost is only slightly more expensive per unit of electricity generated than the current technologies employed today.
The US power sector is a leading contributor of emissions that affect air quality and climate. It also requires a lot of water for cooling thermoelectric power plants. Although these impacts affect ecosystems and human health unevenly in space and time, there has been very little quantification of these environmental trade-offs on decision-relevant scales. This work quantifies hourly water consumption, emissions (i.e., carbon dioxide, nitrogen oxides, and sulfur oxides), and marginal heat rates for 252 electricity generating units (EGUs) in the Electric Reliability Council of Texas (ERCOT) region in 2011 using a unit commitment and dispatch model (UC&D). Annual, seasonal, and daily variations, as well as spatial variability are assessed. When normalized over the grid, hourly average emissions and water consumption intensities (i.e., output per MWh) are found to be highest when electricity demand is the lowest, as baseload EGUs tend to be the most water and emissions intensive. Results suggest that a large fraction of emissions and water consumption are caused by a small number of power plants, mainly baseload coal-fired generators. Replacing 8-10 existing power plants with modern natural gas combined cycle units would result in reductions of 19-29%, 51-55%, 60-62%, and 13-27% in CO2 emissions, NOx emissions, SOx emissions, and water consumption, respectively, across the ERCOT region for two different conversion scenarios.
The intermittency of wind and solar power and the mismatch between when they are available and when demand is high have hindered the expansion of these two primary renewable resources. The goal of this research is to analyze an integrated energy system (named DSWiSS for dispatchable solar wind storage system) that includes a novel configuration of wind and solar together with compressed air energy storage (CAES) that is driven from excess nighttime wind energy and thermal storage energized by concentrated solar power in order to make these sources dispatchable during peak demand. This paper builds off prior published work for the DSWiSS configuration with an analysis of actual historical meteorological data for West Texas solar insolation, generation output data for a wind farm in West Texas, recorded electricity demand data of the Electric Reliability Council of Texas (ERCOT) grid, and historical temperature data for West Texas to assess system performance. In this analysis, a comparison approach was taken by optimizing both the operation of a conventional CAES facility that does not incorporate wind and solar directly and the operation of a CAES facility directly coupled to a wind farm, which will be referred to as CAES-plus-Wind. Dynamic parameters for wind generation, electricity price, and ambient temperature were utilized in the optimization models. Through the use of optimization models and the incorporation of a thermodynamic model of the CAES equipment, we found that in each season the electricity price is a key factor in determining whether the facility stores or generates energy. For the CAES equipment, the summer season yields the highest profits primarily because of the larger spread between highest and lowest daily price for electricity. Even though profits for the CAES equipment in the other seasons are small or negative, it appears that the value of the facility in the summer is greater than the costs in the other three seasons combined. Additionally, we found that the value of directly coupling the CAES facility to a wind farm versus operating the two entities separately yielded no significant increase in profits. Lastly, this analysis did not attempt to quantify the possible increase in wind farm generation output that could result from reduced curtailment with the use of an energy storage system such as is proposed in this paper. This additional source of revenue could be a major contributor to the economic justification for large scale energy storage.
Wind and solar technologies have experienced rapid market growth recently as a result of the growing interest for implementation of renewable energy. However, the intermittency of wind and solar power is a major obstacle to their broader use. The additional risks of unexpected interruptions and mismatch with demand have hindered the expansion of these two primary renewable resources. The goal of this research is to analyze an integrated energy system that includes a novel configuration of wind and solar coupled with two storage methods to make both wind and solar sources dispatchable during peak demand, thereby enabling their broader use. The proposed system utilizes compressed air energy storage (CAES) that is driven from wind energy and thermal storage supplied by concentrated solar thermal power in order to achieve this desired dispatchability. While current CAES facilities use off peak electricity to power their compressors, this system uses power from wind turbines to compress air to high pressure for storage. Also, rather than using natural gas for heating of the compressed air before its expansion through a turbine, which it typical for conventional systems, the system described in this paper replaces the use of natural gas with solar thermal energy and thermal storage. Through a thermodynamic and a levelised lifetime cost analysis we have been able to develop estimates of the power system performance and the cost of energy for this integrated wind-solar-storage system. What we found is that the combination of these components resulted in an efficiency of over 50% for the main power components. We also estimated that the overall system is more expensive per unit of electricity generated than two of the current technologies employed today, namely coal and nuclear, but cheaper than natural gas peaking units. However, this economic analysis, though accurate with regard to the technologies chosen, will not be complete until cost values can be placed on some of the externalities associated with power generation such as fuel cost volatility, national security, and emissions.
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