Transformation of Demand-Response Aggregator Operations in Future US Electricity Markets: A Review of Technologies and Open Research Areas with Game Theory  
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attention away from conventional fuels. Specifically, the Environmental Protection Agency (EPA) proposed the Clean Power Plan (CPP) policy in 2014, which suggests reducing carbon dioxide (CO\({}_{2}\)) by 32% in the years 2005-2030 and reducing coal plants' CO\({}_{2}\) emissions, increasing renewable integration, and investing in energy-saving programs [3]. Although multiple measures have been taken to reduce CO\({}_{2}\) emissions and achieve the CPP policy goals, the climate change crisis continues to persist due to an increase in energy generation emissions in the 2020s in order to cover the increasing global energy demand. Therefore, the CPP policy goals were revised to the more aggressive 2030 generation decarbonization and 2050 net-zero economy goals. Specifically, the International Energy Agency (IEA) set four pillars for action in the 2020s [4], which, if implemented, will be sufficient to keep the global temperature increase under 1.7 \({}^{\circ}\)C by 2100, i.e., aligning with the net-zero emissions scenario. These pillars concern [5] deforestation reduction by 2030 and land use decarbonization; the reduction in non-CO\({}_{2}\) emissions; the use of carbon capture, utilization, and storage (CCUS); and the decarbonization of electricity generation by 2030. IEA has summarized the importance of revising existing market instruments, mechanisms, and regulations to achieve the 2030 and 2050 goals [6], knowing that, by 2050, the global electricity demand is expected to more than double compared to 2020. These revisions include the following:  
1. Deploying significantly more renewable resources and completing the demand coverage with low-carbon resources, such as nuclear and hydrogen, is important [7]. Battery storage and DR are not considered as additional generation capacity but rather important enablers if sufficiently incentivized due to the introduced flexibility [8]. 2. Incentivizing clean technology market players with effective investment frameworks, carbon pricing, and other decarbonization instruments. 3. Improving market price signals to better represent the time and geographical value of the energy. 4. Ensuring that hedging with long-term contracts does not harm the short-term market dispatch. 5. Offering decarbonization financial instruments that help reduce the long recoupment periods of wind and solar to attract new private investment. 6. Incorporating distributed energy resources via aggregators to increase flexibility and resilience in systems with high-penetration renewable resources and defer system upgrade costs. Digitization via metering devices is necessary to increase visibility and ensure fair compensation with adequate customer privacy. 7. Facilitating battery storage investments with taxation and network tariffs that appropriately recognize its role as a flexibility provider, ensuring that it is not charged twice as a consumer and as a generator, and compensating for its fast response and flexibility services. 8. Rewarding capacities that can respond in periods of high system stress to reduce price volatility. 9. Protecting retail customers against market risks, natural gas price peaks, and extreme weather phenomena. 10. Planning system expansion to support low-carbon resources (including DR). As a result of the CPP, 2030, and 2050 policies, the US energy mix has changed significantly in the last decade, with oil and coal resources progressively being replaced by renewable and natural gas-based generation (less polluting than oil and coal; backs up intermittent renewable sources) [9; 10]. However, over-investment in renewable resources has introduced manufacturing pollution (renewable devices), natural-gas-related pollution from backing up renewable sources [9; 11; 12; 10], and operational issues.