	Introduction

The U.S. energy sector is large and complex. The U.S. electric power sector generates approximately 4 million gigawatthours of electricity each year. This report addresses two fundamental questions about U.S. renewable electricity generation potential: (1) How much renewable electricity generation might be possible in the United States? Renewable Electricity Terminology and Units

This section defines terms and units used to describe and quantify renewable energy sources, and electricity generation potential from these sources, and how renewable energy might be compared to other forms of energy. Summary of Current U.S. Renewable Electricity

In 2009 renewable energy resources provided 11% of U.S. electricity net generation. Future Renewable Electricity Generation Potential

The following sections discuss the estimated range of electricity generation potential from wind, solar, geothermal, hydro, ocean-hydrokinetic, and biomass renewable energy sources. Table 2 provides a summary of U.S. renewable electricity generation potential, based on the research and analysis performed for this report, current and projected renewable electricity generation potential, cost of electricity estimates, and a summary of key challenges for each renewable energy source. Research and analysis conducted for this report indicates that renewable energy sources may, theoretically, have the potential to satisfy a large portion of U.S. electric power needs. Third, different system configurations are used to collect data and calculate solar resource estimates. However, estimating the amount of electricity that might be generated from biomass depends on the amount of biomass material available and on the portion of that material that might be used for electricity generation. Since different organizations often use different assumptions, the variation in LCOE estimates is not surprising. To date, there is no standard methodology to produce these estimates. In addition to new transmission requirements, some renewable energy sources may require investments in specialized infrastructure in order to provide a source of renewable electricity. Based on the current status of renewables in the United States, policy makers may consider some key questions about the future of renewable energy: 
Should the United States actively seek greater use of renewable energy to supply electricity, or should the energy and electricity markets be allowed to work without further interference with the existing structure of subsidies and incentives? In 2010, renewable sources of energy provided approximately 11% (7% from hydropower and 4% from other renewables) of total net electricity generation and the EIA AEO 2011 reference case projects that renewable electricity generation will increase to between 14% and 15% by 2035. However, renewable electricity generation will likely encounter serious challenges, issues, and barriers as technologies and projects look to realize large-scale deployment. As Congress evaluates various energy policy objectives, policy makers may move to holistically evaluate the potential intended benefits, such as emissions reduction and job creation, with potential risks and consequences, such as electricity cost/price increases and electricity delivery reliability issues associated with increasing renewable electricity generation.
The United States faces important decisions about future energy supply and use. A key question is how renewable energy resources might be used to meet U.S. energy needs in general, and to meet U.S. electricity needs specifically. Renewable energy sources are typically used for three general types of applications: electricity generation, biofuels/bioproducts, and heating/cooling. Each application uses different technologies to convert renewable energy sources into usable products. The literature on renewable energy resources, conversion technologies for different applications, and economics is massive. This report focuses on electricity generation from renewable energy sources. In 2010, renewable sources of energy were used to produce almost 11% (7% from hydropower and 4% from other renewables) of the 4 million gigawatthours of electricity generated in the United States.
This report provides a summary of U.S. electricity generation potential from wind, solar, geothermal, hydroelectric, ocean-hydrokinetic, and biomass sources of renewable energy. The focus of this report is twofold: (1) provide an assessment of U.S. renewable electricity generation potential and how renewables might satisfy electric power sector demand, and (2) discuss challenges, issues, and barriers that might limit renewable electricity generation deployment.
Data sources from 15 different organizations were reviewed to derive estimates of electricity generation potential. One key finding is that there exists no uniform national assessment of renewable electricity generation potential. No standard methods or set of assumptions are used to estimate renewable electricity generation potential. So even existing assessments for individual energy sources are difficult to compare objectively. In order to compare various estimates on an equivalent basis, CRS engaged experts in each renewable energy resource area to help normalize electricity generation potential estimates into a common metric: gigawatthours per year.
After surveying, researching, and normalizing all of the third-party electricity generation estimates, results indicate that renewable energy sources may, in principle, have the potential to satisfy a large portion of U.S. electricity demand. However, a number of potential barriers to large-scale deployment exist, including cost, power system integration, intermittency and variability, land requirements, transmission access, possible limits to the availability of key materials and resources, certain environmental impacts, specialized infrastructure requirements, and policy issues. Ultimately, the amount of renewable electricity generation in the U.S. may be dependent on the ability to address these deployment barriers. The Energy Information Administration projects that U.S. renewable electricity generation will increase from 11% today to between 14% and 15% in 2035.
As Congress considers policy options associated with increasing renewable electricity generation, policy makers may assess potential benefits such as emissions reduction, job creation, and global competitiveness, along with possible risks and consequences such as electricity cost and price increases, electricity delivery reliability, and environmental impacts associated with large-scale deployment of renewable electricity generation technologies.