	Introduction

A clean energy standard (CES) has been proposed as a tool to provide a more sustainable domestic energy supply, reduce greenhouse gas emissions, and secure the United States as a leader in clean energy technology. Some assert that a CES could contribute to economic growth. Opponents of a CES contend that a CES could raise electricity prices, introduce grid reliability concerns, require significant investment in additional transmission lines, and depend on adopting some technologies not yet established for widespread commercial-scale use. A CES could require certain electricity providers to obtain a portion of their electricity from qualifying clean energy sources. On March 1, 2012, Senator Bingaman introduced the Clean Energy Standard Act of 2012 ( S. 2146 ), which would require large utilities to sell a percentage of their electricity from clean energy sources—at least 24% in 2015 and gradually increasing over time to 84% by 2035. RES legislative discussions date back to at least the 105 th Congress. A CES expands qualifying energy sources to include other "clean" energy sources (e.g., nuclear, natural gas, clean coal) along with renewable energy sources (e.g., wind, solar). Renewable sources constituted roughly 12% of total electric power net generation in 2011 (including conventional hydroelectric). Analysis from the Energy Information Administration (EIA) that does not include the addition of a federal RES or CES suggests that electricity generation from renewable sources (including conventional hydroelectric) will grow from 10% in 2010 to 16% in 2035. EIA analysis indicates that most of the growth in renewable electricity generation in the power sector, excluding hydroelectricity, from 2010 to 2035 will consist of generation from wind and biomass facilities. Each energy source has advantages and disadvantages, and each brings different natural resource, economic, and technical challenges. In evaluating individual energy sources for possible inclusion, Congress might consider the following criteria: geographic location of the energy source, energy source supply levels, job creation associated with the energy source, implementation time frame, EPA regulations (existing and forthcoming), environmental issues (air quality, water quality, water quantity, wildlife), greenhouse gas emissions, baseload versus non-baseload, energy balance, energy content, land use change, scalability, and cost. Issues Applicable to All Clean Energy Resources

A number of cross-cutting issues are associated with large-scale electricity production for many or all of the clean energy sources:
Technology. Electricity Transmission. In some cases, the energy source is located a considerable distance from where the electricity is needed. Variability. Material cost and supply. The following policy questions might arise when considering biomass as a qualifying CES energy source:
Will agricultural producers continue to receive support from the federal government to grow certain crops if a CES is established? Clean Coal36

There has been considerable discussion about including clean coal (coal-fired power plants equipped with carbon capture and sequestration) as a qualifying energy source for a CES. In order to reduce the cost of solar electricity, research and development initiatives may be necessary. Should legislation account for other sources and technologies that are not yet developed? How much clean electricity can be generated in the time frame specified from each qualifying energy source? Should a carbon accounting factor be assigned to each qualifying energy source? Will a time come when some resources (e.g., wind, solar) used to generate clean electricity cease to be considered a "free" resource? Should energy efficiency be included in a CES, and if so, how should it be included? How would a CES interact with state renewable electricity requirements? Who would assume the costs of new transmission capacity?
A clean energy standard (CES) has been identified as one possible legislative option to encourage a more diverse domestic electricity portfolio. A CES could require certain electricity providers to obtain a portion of their electricity from qualifying clean energy sources. A CES is broader than a renewable energy standard (RES), including "clean" energy sources along with renewable sources. The RES has been a topic of legislative attention since at least the 105th Congress. A CES gained legislative attention with the introduction of the Clean Energy Standard Act of 2012 (S. 2146). The bill would require large utilities to sell a percentage of their electricity from clean energy sources—at least 24% in 2015 and gradually increasing over time to 84% by 2035. Some assert that a CES could lead to economic growth, reduce greenhouse gas emissions, and secure U.S. leadership in clean energy technology. Others argue that it could raise electricity prices, necessitate additional financial investment in grid infrastructure, and—in some cases—depend on energy technologies that are not yet established for widespread commercial-scale use.
Without a CES, some clean energy sources—mostly the renewables—may face barriers to penetrating and gaining traction in the electricity market. Renewable sources (including conventional hydroelectric) constituted roughly 12% of total electric power net generation in 2011. Analysis from the Energy Information Administration (EIA) suggests that without a CES or RES, electricity generation for renewable sources (including conventional hydroelectric) will grow from 10% in 2010 to 16% in 2035. EIA analysis indicates that most of the growth in renewable electricity generation, excluding hydroelectricity, in the power sector from 2010 to 2035 will consist of generation from wind and biomass facilities.
Policy, economic, and technical considerations arise when evaluating CES options. A primary question in the CES legislative discussion is which energy sources would be eligible to participate. Congress could take into account the following clean energy source selection criteria: geographic location of the energy source, energy source supply levels, job creation associated with the energy source, the implementation time frame, environmental regulations (existing and forthcoming), and cost. Each potential qualifying energy source has advantages and disadvantages, and has different natural resource, economic, and technical challenges. For instance, the cost to build, operate, and maintain clean energy power plants varies widely, from $63 (natural gas advanced combined-cycle) to $312 (solar thermal) per megawatt-hour. Moreover, some of the sources proposed have encountered public opposition (e.g., nuclear energy). Many proposed sources (e.g., solar) have received government support in the form of research and development assistance or favorable tax treatment. In some cases, the technology that might allow certain sources to qualify for a CES is not yet at commercial scale (e.g., coal-fired plants equipped with carbon capture and sequestration). Cross-cutting issues including electricity transmission, variability, and material cost and supply are associated with large-scale electricity production for many of the commonly discussed clean energy sources.
Many questions will need to be answered if a CES is established. How much clean electricity can be generated from each qualifying energy source, given the proposed CES time frame? Should a carbon accounting parameter be assigned to each source? Will a time come when some resources (e.g., wind, solar) used to generate clean electricity cease to be considered a "free" resource? Should energy efficiency be included in a CES, and if so, how should it be included? How would a CES interact with state renewable electricity requirements? Who would assume the costs of new transmission capacity?