Technical Report

NREL/TP-6A2-45161

February 2009

Evaluating a Proposed 

20% National Renewable 

Portfolio Standard

Jeffrey Logan, Patrick Sullivan, 

Walter Short, Lori Bird, Ted L. James,

and Monisha R. Shah
National Renewable Energy Laboratory

1617 Cole Boulevard, Golden, Colorado 80401-3393

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NREL is a national laboratory of the U.S. Department of Energy

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Operated by the Alliance for Sustainable Energy, LLC

Contract No. DE-AC36-08-GO28308

Technical Report

NREL/TP-6A2-45161

February 2009

Evaluating a Proposed 

20% National Renewable 

Portfolio Standard

Jeffrey Logan, Patrick Sullivan, 

Walter Short, Lori Bird, Ted L. James,

and Monisha R. Shah

Prepared under Task No. SAO7.9C50
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i

Acknowledgments

This work was funded by the U.S. Department of Energy’s (DOE) Office of Energy 

Efficiency and Renewable Energy (EERE). The authors would like to thank Doug Arent, 

David Hurlbut, and Dan Bilello of the National Renewable Energy Laboratory (NREL)

for their guidance and helpful input. We would also like to thank Ryan Wiser and Galen 

Barbose of the Lawrence Berkeley National Laboratory for providing helpful feedback. 

The authors also offer their thanks to Michelle Kubik in the NREL Technical 

Communications Office for providing editorial support.
ii

Executive Summary

This paper provides a preliminary analysis of the impacts of a proposed 20% national 

renewable portfolio standard (RPS) by 2021, which has been advanced in the U.S. 

Congress by Senator Jeff Bingaman of New Mexico. The paper was prepared before the 

American Recovery and Reinvestment Act was signed into law by President Barack 

Obama on February 17, 2009, and thus does not consider important changes in renewable 

energy (RE) policy that need to be addressed in follow-on analysis.

A renewable portfolio standard is a mandate requiring certain electricity retailers to 

provide a minimum specified share of their total electricity sales from qualifying 

renewable power generation. The draft legislation analyzed here exempts small electricity 

providers—those selling less than 4 billion kilowatt hours (kWh) per year—and allows 

up to 25% of the RPS total to be met through qualifying energy efficiency (EE) projects. 

Existing hydropower and municipal solid-waste generation resources do not qualify 

under the proposed RPS, but are deducted from retail electricity providers’ retail sales to 

calculate their renewable energy compliance obligations. The RPS would allow affected 

electricity providers to use any combination of the following to achieve the target: 1) 

generate their own renewable energy, 2) purchase renewable energy certificates (RECs), 

or 3) pay an “alternative compliance payment” of 3 cents per kilowatt hour (an effective 

safety-valve on the price of RECs). Distributed generators, such as rooftop photovoltaic 

systems, would earn triple credits for every kilowatt hour produced. The proposed RPS 

ramps up in a series of steps from 4% in 2011 to 20% in 2021 and continues at that level

through 2039, before “sunsetting” (i.e., returning to zero). The legislation aims to prevent 

preemption of, or interference with, existing state RPS mandates that meet or exceed the 

federal requirement.

We used NREL’s Regional Energy Deployment System (ReEDS) model to evaluate the 

impacts of the RPS requirements on the energy sector and considered design issues 

associated with renewable energy certificate (REC) trading markets. 

Preliminary findings include:

• After removing the small-utility exemptions and assuming that the maximum 25% 

energy efficiency allowance is fully used, the 20% RPS has an effective renewable 

requirement equal to 12% of total U.S. retail sales in 2021. The assumption that the 

energy efficiency component of the target would be fully used before adding new 

renewable energy supply, due to its cost-effective nature, will be further evaluated in 

follow-on work.

• The base case scenario estimates that qualifying renewable generators will provide 

about 9% of the national load in 2021, much of that due to existing state RPS 

mandates. Thus, the proposed national legislation would require about 3% more 

generation from qualifying renewables beyond the state RPS mandates by 2021. In 

this sense, the proposed legislation does not represent a significant stretch beyond 

existing state policy in aggregate, although ramp-up additions in years that transition 

from one RPS level to another can present challenges.

• Based on the assumptions used in this analysis, wind power capacity expands to 

approximately 129 gigawatts (GW) in 2030 in the RPS scenario, up from about 117 
iii

GW in the base case. Concentrating solar power (CSP) capacity remains virtually 

unchanged at 32 GW that year, while distributed photovoltaics increase from about 4 

GW in the base case to more than 7 GW in the RPS case.

• The federal RPS results in a modest 200 million metric ton (MMT) annual reduction 

in carbon dioxide (CO2) emissions in 2030, compared to the base case. This is 

primarily because significant renewable energy additions are projected to occur even

in the base case scenario.

• Western states, endowed with wind and solar resources, exceed their RPS 

requirements based on renewable energy deliveries, while states in the Southeast 

generally rely on purchasing RECs. 

• Consumer electricity prices are estimated to increase approximately 1% in 2030,

compared to the base case.

Implementers must also address complex REC market design issues to encourage 

investment in renewable generation, capture the economic benefits of credit trading 

across states and regions, and prevent double-counting or other unintended use of credits.
iv

Table of Contents

Acknowledgments................................................................................................................ i

Executive Summary............................................................................................................ ii

Table of Contents............................................................................................................... iv

List of Figures.................................................................................................................... iv

List of Tables ..................................................................................................................... iv

1. Background..................................................................................................................... 1

2. Methodology and Assumptions...................................................................................... 3

3. Impacts............................................................................................................................ 6

4. Policy Design and REC Market Issues......................................................................... 13

5. Comparison with EIA 15% RPS Evaluation ................................................................ 16

6. Potential Follow-on Work............................................................................................. 17

Appendix A – ReEDS Model Description........................................................................ 18

Appendix B – Attributes of Modeling Renewable Electricity: ReEDS vs. NEMS.......... 26

List of Figures

Figure 1. Levelized cost of electricity inputs used in ReEDS ............................................ 4

Figure 2. Contributions to meeting total load in the RPS case ........................................... 6

Figure 3. Contributions to power generation capacity in the RPS case.............................. 7

Figure 4. Differences in generation between the RPS and base cases................................ 8

Figure 5. Annual and cumulative changes in CO2 emissions between the base and RPS 

cases.................................................................................................................................... 9

Figure 6. Cumulative and annual installations of wind power ......................................... 10

Figure 7. Selected state-level contributions to the RPS.................................................... 11

Figure 8. Contributions to the national-level RPS............................................................ 11

Figure 9. Preliminary assessment of RPS on average national electricity prices............. 12

List of Tables

Table 1. Capacity Differences (in GW) in 2030 between the Base and RPS Scenarios..... 7
1

1. Background

A renewable portfolio standard (RPS) is a mandate requiring certain electricity retailers 

to provide a minimum specified share of their total electricity sales from qualifying 

renewable power generation.

1 At the beginning of 2009, 28 states had an RPS and an 

additional five states had goals for renewable energy deployment.2

• The program includes incremental steps to reach a 20% RPS by 2021, with a 

“sunset” after 2039. The proposal mandates the following minimum RPS levels 

over time: 4% by 2011, 8% by 2013, 12% by 2016, and 16% by 2019. 

Firms that generate 

power from qualifying renewable facilities receive renewable energy certificates (RECs) 

that can be applied to their annual requirements or sold to others. 

The 20% federal RPS bill analyzed in this report has the following provisions:

• Utilities generating less than 4 million megawatt hours (MWh) per year and those 

in Hawaii are exempt. Existing hydroelectric power (including pumped hydro) 

and municipal solid waste (MSW) do not earn federal compliance credits. The 

amount of qualifying renewable generation required per year is calculated by 

applying the percentage targets to total retail electricity sales minus existing 

hydropower, MSW generation, and electricity sales by exempt utilities.

• New renewables, existing renewables, and energy efficiency savings can be used 

to meet the federal requirement. New renewable energy is defined as electricity 

generated from solar, wind, geothermal, ocean, biomass, landfill gas, and 

incremental hydropower facilities placed in service on or after January 1, 2006. 

Existing renewable energy generated from facilities installed prior to January 1, 

2006, can be used to meet the standard; however, the RECs provided to existing 

generators must be assigned directly to the entity purchasing the power and 

cannot be traded.

• Energy efficiency improvements may be used to meet up to 25% of the RPS 

requirement in each calendar year, but only by petition from a state governor. 

Eligible energy savings include reductions in end-use electricity at consumer 

facilities (compared to a base year) as well as reductions in distribution system

losses by a retail electricity distributor. New combined heat and power (CHP, also 

known as cogeneration) efficiency gains are also eligible (with savings based on 

comparison of the combined system to separate thermal and electrical 

requirements). The bill calls for measurement and verification standards to be 

enacted by 2010. 

 1 For more background on existing state RPS policies in the United States, see R. Wiser and G. Barbose, 

“Renewable Portfolio Standards in the United States: A Status Report with Data Through 2007,” Lawrence 

Berkeley National Laboratory, April 2008; and D. Hurlbut, “State Clean Energy Practices: Renewable 

Portfolio Standards,” National Renewable Energy Laboratory, July 2008.

2 A map summarizing state RPS mandates and targets is available on the DSIRE Web site at 

http://www.dsireusa.org.
2

• A system of federal RECs would operate as a separate commodity from state 

RECs. Federal credits can be banked for up to three years from the date issued. 

Distributed generation (less than 1 megawatt – MW) receives triple credits, and 

installations on American Indian lands receive double credits; however, no 

facility can exceed triple credits. Compliance with state RPS obligations through 

RECs or other mechanisms will, in certain circumstances, also count toward a 

utility’s federal RPS. The “secretary”3 may delegate administration of the REC 

tracking system to a third party. 

• Alternative compliance payments can be made at a rate of 3 cents per kilowatt 

hour (adjusted for inflation) in lieu of RECs. Utilities failing to meet RPS 

requirements by purchasing RECs or using alternative compliance payments are 

penalized by multiplying the number of kilowatt hours (kWh) sold in violation by 

two times the value of the alternative compliance payment rate. For circumstances 

not under a utility’s reasonable control, penalties or requirements may be waived 

for up to five years. Federal penalties may be reduced by the amount of state 

penalties if the state requirement is greater than the federal RPS. Implementers 

would put revenues from noncompliance into a fund for states to promote 

renewable energy production. 

 3 The draft legislation does not specify which agency “secretary” is authorized in this statement.
3

2. Methodology and Assumptions

The Regional Energy Deployment System (ReEDS) model, the capacity expansion and 

dispatch tool used for this analysis, was created to compare national policy scenarios; it 

also has built-in capabilities for implementing a renewable portfolio standard (RPS)

policy. To appropriately model the proposed RPS scenario in ReEDS, however, the 

modelers needed to make simplifying assumptions. First, the target RPS—which reaches 

20% from 2021 to 2039—was prorated to 16%-17% because small utilities, which 

provide more than 20% of national load, are exempt from the requirement. The fraction 

of load met by large utilities is expected to increase slightly between 2020 and 2040 to 

above 80%. 

Second, all balancing areas were assumed to use their full efficiency allotment, 25% of 

the RPS, because efficiency measures are usually more cost-effective than adding 

renewable power supply.

4

• Technology cost and performance parameters and projections are from Black and

Veatch as estimated for the 20% Wind Energy by 2030

That further reduced the effective RPS to about 12% of total 

U.S. retail sales, from 2021 to 2039. The effective 12% RPS is the minimum amount of 

renewable power that would be required; in reality, not all states would use the entire 

25% efficiency carve-out or allow their excess RECs to count toward the federal 

obligation. 

Technologies that may contribute to the RPS include wind, concentrated solar power 

(CSP), geothermal, biopower, and distributed photovoltaics (PV)—hydropower and 

municipal solid waste are not counted. As in the proposed legislation, distributed 

renewable energy systems are permitted to claim triple credits toward the RPS; i.e., 1 

kWh from a rooftop PV system counts as 3 kWh for RPS accounting purposes. PV is the 

only distributed technology considered in this analysis.

The model applies the RPS to the nation as a whole, and allows states, regions, or 

individual utilities to purchase renewable energy certificates to meet local shortfalls. In 

the case that the whole country falls short of the RPS, an alternative compliance payment 

of 3 cents per kilowatt hour is assessed.

There are other assumptions made in ReEDS that are not specific to this analysis but can 

be significant drivers in the model and are therefore worth mentioning. These include:

5

 4 This simplification was assumed primarily because ReEDS does not explicitly represent efficiency 

savings. Follow-on analysis should evaluate cases where efficiency measures might not meet the entire 

25% RPS allowance. 

5 U.S. Department of Energy, 20% Wind Energy by 2030: Increasing Wind Energy’s Contribution to U.S. 

Electricity Supply, July 2008.

study (see Figure 1).
4

Figure 1. Levelized cost of electricity inputs used in ReEDS

• Fuel cost projections are from the Energy Information Administration (EIA) 

Annual Energy Outlook (AEO) 2008 high gas price case. The price of natural gas, 

in particular, can have a large impact on both investment and dispatch decisions in 

the model.

• Wind receives a production tax credit (PTC) of 2.1 cents per kilowatt hour

through 2009. With the signing of the American Recovery and Reinvestment Act 

on February 17, 2009, the PTC was extended through 2012. Follow-on analysis 

will evaluate the impacts of this extension and other incentives for renewable 

energy.

• CSP receives an investment tax credit (ITC) of 30% through 2016, after which it 

drops to 10%.

• Nuclear capital costs have been multiplied by 1.5 times from the Black and 

Veatch projections (i.e., from $3,000/kW to $4,500/kW) to represent recently 

publicized cost-estimate increases and the current social political climate of 

uncertainty toward the technology. 

• Load growth rates are from the EIA Annual Energy Outlook 2008, and seasonal 

and diurnal load curves are from Platts, an energy information service. 

• There is no price, cap, or tax of any kind on CO2 or other greenhouse gases; sulfur 

dioxide (SO2) is subject to the Clean Air Interstate Rule caps.
5

• All existing state-level RPS targets with enforceable penalties are met in the 

baseline case. Most state RPS programs run through 2020 or 2025 before 

expiring.6

• The analysis explicitly accounts for the cost of new transmission for all power

generation options by determining when new transmission lines are needed and 

evaluating factors in the cost of building them.

• Other assumptions are outlined in Appendix A (ReEDS documentation) and in 

the 20% Wind Energy by 2030 study.

Although the above inputs and assumptions have been vetted for reasonableness, some 

aspects of the future most likely will differ from the projections made in the model.

 6 See the DSIRE database for information on specific state RPS mandates (http://www.dsireusa.org).
6

3. Impacts

We ran two scenarios, with and without the proposed RPS. The scenarios will be referred 

to here as the “base case” and the “RPS case.” In the RPS case, the bulk of the renewable 

generation share (after accounting for exempt utilities and allowing efficiency savings) is 

met by wind power. CSP is the second-largest contributor, with biopower, geothermal, 

and distributed PV being minor players (see Figures 2 and 3.)

The dotted line in Figure 2 shows the penetration rate over time of qualifying renewable 

energy sources. If read from the top down, it shows that approximately 12% of total 

eligible load is met through qualifying renewable sources in 2022. To meet reserve 

requirements, natural gas-fired capacity increases substantially over time, but actual 

generation from gas declines. New coal plants continue to come online after 2030 due 

largely to the decommissioning of nuclear power plants. Again, the results assume that 

there are no requirements to mitigate carbon dioxide.

Figure 2. Contributions to meeting total load in the RPS case

 

0.0

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Cofired Biomass

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Storage

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Gas-CC-CCS

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Coal-new

Cofired Coal

Coal-Old Scrubbed

Coal-Old Unscrubbed

RPS (down from top)
7

Figure 3. Contributions to power generation capacity in the RPS case

Notably, the capacity differences between the base case and RPS case are small, as 

shown in Table 1. The base case, with state renewable standards implemented as 

currently legislated, builds nearly as much wind as (and slightly more CSP than) the RPS 

case. Coal capacity decreases, while natural gas capacity increases in the RPS case vs. the 

base case. 

Table 1. Capacity Differences (in GW) in 2030 between the Base and RPS Scenarios

Base Case RPS Case Difference

Gas 363 398 36

Coal 415 379 -36

Nuclear 102 102 0

Hydropower 76 76 0

Wind 117 129 11.5

CSP 32.7 32.2 -0.5

Distributed PV 3.7 7.2 3.5

Geothermal 2.9 3.6 0.7

Biopower 2.0 2.1 0.1

The similarity of the two scenarios reflects the fact that the federal RPS is largely met 

through assumptions about efficiency and existing state RPS programs. As mentioned 

earlier, the RPS nominally peaks at 20% from 2021 to 2039, but exempt utilities reduce it 

to 16%-17%. If the efficiency allowance is fully used, 12% of load is met by renewable 

power. The base case provides 10.6% of its load from renewable sources in 2030, not a 

large difference from the 12% in the RPS case.

Assumed efficiency savings account for the bulk of the generation differences; although, 

around 2022, wind and CSP replace gas to a noticeable degree. After peaking in 2022—

the first year of the full RPS—the difference in renewable generation between the RPS 
8

case and base case shrinks steadily as shown in Figure 4. (The graph shows generation in 

the RPS case minus generation in the base case in a given year—reductions in generation 

from a particular source appear below the x-axis, and increases in generation are above 

the x-axis.) The RPS case continues to build renewables: The gap closes because the base 

case is building slightly more renewables in later years than in the RPS case. In the 

figure, the dashed line represents the difference in load between the two cases, primarily 

due to the assumption on the efficiency allowance. Most years see a reduction in coalfired generation between the two cases, and an increase in wind and co-fired biomass 

generation.

Figure 4. Differences in generation between the RPS and base cases

There are noticeable, though not large, incremental carbon reductions in the RPS case—

they are mostly due to the load reduction from efficiency savings. Figure 5 indicates that 

CO2 emissions in the 2030 RPS case decline by approximately 220 million metric tons 

(MMT) compared to that in the base case. Much of the reduction is due to the assumed 

efficiency measures because renewables do not replace large quantities of fossil fuel 

generation. Cumulative CO2 emissions of the RPS case decline by about 2,500 MMT by 

2030.

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20062010201420182022

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Cofired Biomass

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Distributed PV

CSP

Wind-Offshore

Wind-Onshore

Nuclear

Coal-CCS

Coal-IGCC

Coal-New

Cofired Coal

Coal-Old, Scrubbed

Coal-Old, Unscrubbed

Gas-CT

Gas-CC-CCS

Gas-CC

Hydro

Load Difference
9

Figure 5. Annual and cumulative changes in CO2 emissions between the 

base and RPS cases

Cumulative Carbon Savings

0

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Annual Carbon Emissions

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RPS

Base
10

Wind capacity expansion is similar between the two cases (Figure 6), with the notable 

exception of an increase in wind built in the 2018-2022 period in the RPS case. This 

increase in capacity meets the increase in the RPS in 2021.

7 The base case catches up 

somewhat in the following two periods and parallels the RPS case from then on. The 

smoother expansion plan simulated in the base case would be healthier for the wind 

industry than the spike in the RPS case.

Figure 6. Cumulative and annual installations of wind power

 7 ReEDS runs two-year periods, so the 2021 standard is first seen in 2022.

Cumulative Installed Wind Capacity

0

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11

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20062012201820242030203620422048

REC

Distributed PV (3x)

Biopower

Geothermal

CSP

Wind

Efficiency

The western half of the country, endowed as it is with wind and solar resources, provides 

more than its share of renewable energy toward the RPS target. In California, for 

example, renewable power options generate more than half of the state’s total electricity 

(Figure 7). Some states in the Southeast, on the other hand, are projected to buy RECs to 

make up for regional shortfalls.8

0

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Biopower

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Wind

Efficiency

NJ

NC AL

CA AZ

In all charts, vertical axis measures fraction of total load met.

The country as a whole, however, always meets the RPS 

target, never opting for the 3 cents per kilowatt hour alternative compliance payment.

Details of the contributions to the RPS at the national level are shown in Figure 8.

Figure 7. Selected state-level contributions to the RPS

Figure 8. Contributions to the national-level RPS

 8 This finding differs from past EIA modeling of federal RPS legislation, which project relatively large 

amounts of biopower in the Southeast. See Section 5 for more on this topic.
12

Because differences between the two scenarios are small, we do not anticipate an RPS of 

this sort to have major impacts on supply, transmission, or prices. Calculated electricity 

price differences between the scenarios are small, with prices in the RPS case being 

slightly more expensive, as shown in Figure 9. In 2030, for example, electricity prices 

are about 1% higher than in the base case. In later years, the estimated increase grows to 

about 2%.

Figure 9. Preliminary assessment of RPS on average national electricity prices

 

80

85

90

95

200620102014201820222026203020342038204220462050

$/MWh

Base

RPS
13

4. Policy Design and REC Market Issues

The proposed legislation raises some questions regarding trading of renewable energy 

certificates (RECs) as well as the overall design of the REC trading market. In cases 

where potential ambiguity exists, or conflict appears between existing state and federal 

RPS requirements, options are presented that could help address uncertainties.

A. Dual RECs System: The draft legislation creates a dual RECs system, with 

federal RECs separate from state RPS RECs. While this method may be required based 

on other elements of the draft legislation, it may also create tracking problems and 

confusion over appropriate claims, because there could be two RECs (federal and state) 

issued for a single megawatt hour of renewable generation. Because states generally 

specify that RECs contain renewable energy attributes and establish a basis for claiming 

renewable energy, the federal REC cannot also contain these attributes. The legislation 

does not clearly define a REC—the federal REC should be defined in a way to avoid 

confusion. Alternatively, legislators may want to consider employing a single RECs 

system; however, that would require other necessary changes to the draft bill. 

B. State RPS Interaction: The bill could present difficulties for states to set RPS 

standards that are more stringent than the federal standard. For example, utilities in states 

with higher RPS targets (e.g., 25%) than the federal 20% target may be allowed to sell 

“excess” RECs to utilities in other states for federal compliance. Without further clarity,

if this is allowed, state targets would not necessarily be more stringent than the federal 

RPS. Language could be included to ensure that utilities are not able to trade federal 

RECs that are used to meet a higher state RPS standard; or, alternatively, the language 

would more-clearly give states the authority to decide how to treat this issue.

Similarly, small utilities that are exempt from the federal RPS—but may be subject to 

state RPS policies—could also sell RECs they use for state compliance to entities in other 

states for federal compliance. Again, this would mean that state standards are not 

additional to the federal standard.

The legislation calls for state penalties to be applied to the federal penalty in cases where 

a utility is in noncompliance of both a state and federal RPS. Further clarity of 

implementation authority and rights would alleviate ambiguities and potential 

implementation challenges. 

C. REC Issuance to Utilities Subject to State RPS: Under the draft 

legislation, federal RECs will be issued to electric utilities to match compliance with state 

renewable portfolio standards pursuant to subsection (610h4Ai). Upon an initial review 

of the legislation, this language seems to imply that federal RECs could be provided to 

both the generator and the electric utility for the same megawatt hour of renewable 

generation, creating the possibility of double-counting. Managing this situation 

consistently with other provisions of the draft—and to ensure no double-counting—

would require the federal REC tracking system to associate generator-awarded federal 

RECs with their corresponding state RECs, and to ensure that the generator-awarded 

federal RECs automatically transfer with the state REC to the entity that uses the state 
14

REC for state RPS compliance. If this is indeed the intent (i.e., to ensure that the federal 

REC is conveyed with the state REC for the purpose of state RPS programs), then the 

language should be clarified. The current language is unclear, and absent clarification, 

regulatory implementation may be a challenge. 

D. Double-Counting: The double-counting language in the bill addresses only 

double-counting of the same megawatt hours for federal compliance. Counting state 

compliance toward federal compliance is contemplated generally. The potential gaming 

between federal RPS compliance and voluntary sales by means of state RECs also is not 

addressed. The draft, which would permit assigning state RECs and federal RECs to the 

same generation, allows a utility to apply federal RECs to its federal compliance, and 

then use the state RECs associated with the same megawatt hour for voluntary sales. This 

is potentially harmful to consumers who expect voluntary REC purchases to represent use 

of renewable power beyond what would have occurred without the voluntary purchase. 

The definition of double-counting would be clearer if it were to exclude RECs used for 

federal RPS compliance from being sold to voluntary purchasers of renewables. This 

could be accomplished if the law were to state explicitly that such gaming constitutes a 

deceptive trade practice and may be prosecuted as such by the Department of Justice and 

the Federal Trade Commission.

E. REC Tracking: The bill calls for a new, separate federal REC-tracking system. It 

does not use the existing regional REC-tracking systems, although there is authority in 

the bill to do so. Given the significant effort in developing these systems, a pragmatic 

approach to the development of a federal system would use these systems to the extent 

feasible. The regional systems have established protocols for obtaining and verifying 

meter data for verification purposes, and that effort should not be duplicated. 

F. Treatment of Existing Renewable Generation: The provision in the 

legislation that establishes nontradable RECs for existing generation may be difficult to 

implement. For example, generators that came online prior to 2006 may have already 

traded RECs (and potentially any future federal RECs) in transactions conducted for state 

RPS compliance. It also may be unclear what “nontradable” actually means regarding 

implementation. Exempting REC trading from existing renewable generation requires 

additional renewable generation to be built (that is eligible for tradable RECs). This 

provision may slightly drive up pricing and requires further detail in the REC tracking 

systems. Consideration of a provision to make all RECs tradable, with no distinctions 

between existing and new, may be worth evaluating. 

G. Treatment of Distributed Generation: The bill defines distributed generation 

as no larger than 1 MW. Given the trend toward larger distributed PV systems in recent 

years, a definition greater than 1 MW could be considered. Several states offer net 

metering for systems larger than 1 MW.

H. Treatment of EE Credits: The legislation does not clearly define an energy 

efficiency (EE) credit. Also, there is no date established for qualifying energy efficiency 

measures. If the goal is to incentivize new efficiency investments, the legislation should 
15

specify a date after which efficiency investments would be eligible to receive federal 

credits. 

In many states, entities other than electric utilities administer energy efficiency incentive 

programs. In some cases, the administrator is a state agency; in others, it is a nonprofit 

organization. The legislation does not clearly indicate whether EE credits could be 

generated by these incentive programs and, if so, to whom they would be issued. 

Evaluating the option for allocating energy efficiency credits in these instances to the 

state or nonprofit incentive program administrator would clarify the impact of this 

provision. The bill currently would only allow a state agency to receive the EE credits if 

that agency directly installed the EE system. 

The bill states that EE credits will be issued for “qualified electricity savings achieved by 

an electric utility” and “qualified electricity savings achieved by other entities.” It is 

unclear what is meant by “achieved”: Does it refer to the source of the funding or the 

administrator of the efficiency program? (In some states, efficiency programs are funded 

through a surcharge on utility bills, but the programs themselves are administered by 

other entities.) Some clarification on this issue would be helpful.

I. Standards for EE Measurement and Verification: The bill calls for the 

Department of Energy to issue measurement and verification (M&V) standards by 

January 2010. This timeline may be too aggressive, given the complexity of developing 

such standards.

9

 9 The Department of Energy supported the International Performance Measurement and Verification 

Protocol (IPMVP) in the 1990s. The M&V standards developed are voluntary. Details are available at 

J. State EE Credit Interaction: The bill is silent on the issue of whether energy 

efficiency used to meet a state standard can also be used to meet the federal requirement. 

It appears that utilities that meet their state EE requirements could sell federal credits for 

the same efficiency to utilities in other states. 

http://www.evo-world.org/. 
16

5. Comparison with EIA 15% RPS Evaluation

In June 2007, the Energy Information Administration (EIA) released an analysis of the 

impacts of a 15% RPS using the National Energy Modeling System (NEMS).10 NEMS 

and the Regional Energy Deployment System (ReEDS) model have some fundamental 

differences (see Appendix B) and differing baseline assumptions, which explains why 

they arrive at different estimates.11

 10 Available at 

 

Although this analysis uses a 20% RPS instead of the 15% in the EIA analysis, the 

effective targets are similar because energy efficiency credits can account for up to 25% 

of the RPS in this analysis. Many of the other legislative requirements are also similar: 

Existing hydropower cannot be used to meet the target, small electricity providers are 

exempt, and distributed PV systems earn triple credits. 

Biomass generation is the largest contributor to the EIA’s analysis of the 15% RPS, with 

wind and solar contributing as well. A detailed analysis would be required to fully 

explain these differences with the ReEDS results. However, the basic difference is that 

NEMS uses a more expensive supply curve to capture transmission, siting, and intangible

costs associated with wind; while ReEDS directly assesses these costs in line with 

industry practice. This results in the lower cost for wind as the NEMS supply curve 

would suggest. Consequently, ReEDS results emphasize wind, while the NEMS model 

meets the RPS with other renewable resources—namely, biomass. By 2030, solar 

installations produce about 8% of qualifying renewable generation in the EIA analysis 

due to the triple-crediting; this is more than the ReEDS simulation estimates. 

Relative to the reference case, retail electricity prices increase by about 2% in the EIA 

scenario in 2030, while the ReEDS analysis estimates a 1.3% increase. This is due to 

lower overall costs of the required renewable generation in ReEDS compared to EIA. 

Annual carbon dioxide emissions decline by 222 million metric tons (MMT) in the EIA 

15% RPS scenario, compared to approximately 220 MMT in the ReEDS analysis. 

http://www.eia.doe.gov/oiaf/servicerpt/prps/index.html. 11 Documentation on NEMS is available at http://www.eia.doe.gov/oiaf/aeo/overview/index.html.
17

6. Potential Follow-on Work

As noted previously, this analysis is preliminary and should not be considered 

comprehensive or final. Potential follow-on work could include:

• Conducting sensitivity analysis on the draft 20% RPS legislation. Key 

sensitivities that could be run on the draft legislative bill include different energy 

efficiency allowance penetrations, gas price trajectories, nuclear power plant costs, 

RE technology improvements over time, and policy assumptions on PTC extensions 

and/or carbon caps/taxes. Additionally, it might be useful to explore the extent to 

which excess federal RECs, accrued as a result of state RPS compliance, are retired 

rather than sold. As noted previously, a substantial change to national tax credits for 

renewable energy occurred just after this analysis was completed and follow-on work 

should consider this new legislation.

• Comparing past and ongoing work. Several other organizations, including the 

Union of Concerned Scientists, Lawrence Berkeley National Laboratory, and the 

Energy Information Administration have published findings from similar RPS 

analyses. Follow-on work could include more comprehensive comparisons of these 

findings with those from other organizations. 

• Analyzing other proposed RPS legislation. This work would look at proposals such 

as the 25% target by 2025 introduced by Rep. Edward Markey of Massachusetts.
18

Appendix A – ReEDS Model Description

The Regional Energy Deployment System (ReEDS) model is a multiregional, multitimeperiod, geographic information system (GIS), and linear programming model of capacity 

expansion in the electric sector of the United States. The model, developed by NREL’s 

Strategic Energy Analysis Center (SEAC), is designed to conduct analysis of the critical 

energy issues in today’s electric sector with detailed treatment of the full potential of 

renewable electric technologies.

The principal issues addressed include access to and cost of transmission, access to and 

quality of renewable resources, the variability of wind and solar power, and the influence 

of variability on the reliability of the grid. ReEDS addresses these issues through a highly 

discretized regional structure, explicit accounting for the variability in wind and solar 

output over time, and consideration of ancillary services requirements and costs.

Qualitative Model Description

ReEDS minimizes system-wide costs of meeting electric loads, reserve requirements, and 

emission constraints by building and operating new generators and transmission in 23 

two-year periods from 2006 to 2050. The primary outputs of ReEDS are the amount of 

capacity and generation of each type of prime mover—coal, natural gas, nuclear, wind, 

etc.—in each year of each two-year period. 

Time in ReEDS is also subdivided within each two-year time period; each year is divided

into four seasons, and each season into four diurnal time-slices. There is also one superpeak time-slice. These 16 annual time-slices (spring has only three time-slices) allow 

ReEDS to capture the intricacies of meeting electric loads that vary throughout the day 

and year both with conventional and renewable generators.

While ReEDS includes all major generator types, it has been designed primarily to

address the market issues of greatest significance to carbon-constrained scenarios—

carbon taxes or caps. As a result, renewable and carbon-free energy technologies are a 

focus.

Diffuse resources, such as wind and solar power, come with concerns that conventional 

dispatchable power plants do not have—particularly regarding transmission and 

variability. The ReEDS model examines these issues primarily by using a much higher 

level of geographic disaggregation than other models: 356 different regions in the 

continental United States. These 356 resource supply regions are then grouped into four 

levels of larger regional groupings—balancing authorities, regional transmission 

operators (RTO), North American Electric Reliability Council (NERC) regions, and 

national interconnect regions.

Much of the data inputs to ReEDS are tied to these regions and derived from a detailed 

GIS model/database of the wind and solar resource, transmission grid, and existing plant 

data. The geographic disaggregation of renewable resources allows ReEDS to calculate 

transmission distances, as well as the benefits of dispersed wind farms or CSP plants 
19

supplying power to a demand region. Both the wind and solar supply curves are divided 

into five resource classes, based on the quality of the resource—strength and 

dependability of wind or solar insolation—that are further described in ReEDS reference 

documentation.

Regarding resource variability and grid reliability, ReEDS also allows electric storage to 

be built—either co-located with wind farms or sited at load centers—and used for load 

shifting, resource firming, and ancillary services. Three varieties of storage are supported: 

pumped hydropower, batteries, and compressed air energy storage.

Along with wind and solar power, ReEDS has supply curves for biomass and geothermal

resource and allows biopower and geothermal plants to be built in each balancing 

authority. The geothermal supply curve is in megawatts (MW) of recoverable capacity 

while the biomass supply curve is in MMBtu (one million British Thermal Units) of 

annual feedstock production. Other carbon-reducing options are considered as well. 

Nuclear power is an option, as is carbon capture and sequestration (CCS) on some coal

and natural gas plants. For now, CCS is treated simply, with only an additional capital 

cost for the extra equipment and an efficiency penalty to account for the parasitic loads of 

the separation process. In the future, it is intended that ReEDS will have geographically 

varying costs for CCS as well as piping and sequestering constraints on the CO2.

The major conventional electricity-generating technologies considered in ReEDS include:

hydropower, both simple and combined-cycle natural gas, several varieties of coal,

oil/gas steam, and nuclear. These technologies are characterized in ReEDS by their:

• equipment lifetime (years)

• capital cost ($/MW)

• fixed and variable operating costs ($/MWh)

• fuel costs ($/MMbtu)

• heat rate (MMbtu/MWh)

• escalation in operating costs and heat rates with plant aging (%/year)

• construction period (years)

• financing costs (nominal interest rate, loan period, debt fraction, debt-service

coverage ratio)

• tax credits (investment or production)

• minimum turndown ratio (%)

• quick-start capability and cost (%, $/MW)

• operating-reserve capability

• planned and unplanned outage rates (%).

Renewable and storage technologies are governed by similar parameters, accounting for 

fundamental differences, of course. For instance, heat rate is replaced with round-trip

efficiency for storage technologies, and the dispatchability parameters—fuel cost, heat 

rate, turndown ratio, quick-start, and operating reserve capability—are not used for nondispatchable wind and solar.
20

The model considers distinguishing characteristics of each conventional generating 

technology. For example, there are several types of coal-fired power plants within

ReEDS, including gasification, biomass co-firing, and CCS options. Any of these plants 

can burn either high-sulfur or, for a cost premium, low-sulfur coal. Generation by coal 

plants is restricted to be base and intermediate load with cost penalties (representing 

ramping/spinning costs) if power production during peak-load periods exceeds 

production in shoulder-peak hours.

New coal plants are assumed to be able to provide more spinning reserve capability than 

older units. Combined-cycle natural gas plants are considered to be able to provide some 

operating/spinning reserve and quick-start capability, while simple-cycle gas plants can 

be cheaply and easily used for reserves and quick-starts. Nuclear power is considered to 

be base load. Hydroelectricity is not allowed to increase in capacity, due to resource and 

environmental limitations. Hydropower is also energy-constrained, due to water resource 

limitations, but is assumed to be able to provide both quick-start capability and 

operating/spinning reserve.

Retirements of conventional generation can be modeled either through exogenous 

specification of planned retirements (currently used for nuclear, hydro, and oil/gas steam 

plants), economic retirements, or as a fraction of remaining capacity each period. All 

retiring wind turbines are assumed to be refurbished or replaced immediately—because 

the site is already developed with transmission access. Similarly, any storage at the wind 

site is assumed to be replaced immediately upon retirement while grid-sited storage 

retires automatically when its assumed lifetime has elapsed but is not automatically 

replaced.

ReEDS tracks emissions from both generators and storage technologies of carbon, sulfur

dioxide, nitrogen oxides, and mercury. Caps can be imposed at the national level on any 

of these emissions. There is also the option of applying a carbon tax instead of a cap; the 

tax level and ramping pattern can be exogenously defined.

ReEDS is a national electric capacity expansion model, not a general equilibrium model. 

To define each time period of the optimization, the model requires that the scenario be 

exogenously specified in terms of fuel costs and electric loads for each NERC region 

over the 44-year time horizon of ReEDS. To allow for the evaluation of scenarios that 

might depart significantly from the scenario used to develop the input fuel prices and 

electricity demands, there are price elasticities of demand and demand elasticities of fuel 

prices integrated into the model. For demand, the exogenously defined demand escalation 

is adjusted up or down based on the price of electricity; while for coal and natural gas, the 

price is adjusted based on how the calculated fuel use compares to the use assumed in the 

inputs.

Qualitative Details on Transmission

ReEDS considers the availability of capacity on existing transmission lines, the cost of 

accessing and using those lines, and the cost of building new transmission lines for new 

generation (e.g., dedicated to new wind or CSP farms) when existing lines are not 
21

available. To determine how much wind or CSP can access existing transmission lines 

and the cost of building a line from the wind site to the grid, we use a GIS database to 

develop a four-step supply curve for each class of wind/solar in each supply region, 

which presents the amount of capacity that can access the grid at each of four different 

costs. (The supply curve is formed of discrete steps, with each step represented by a 

different variable within the linear program.)

The costs increase with increasing distance from the resource to an existing transmission

line that has adequate remaining capacity available to accommodate the generation. 

Although the lines are usually carrying generation from other sources, at any given 

instant, they may or may not have the capacity to transmit additional power from new 

wind or CSP generators. It is practically impossible at the national level to assess the 

capacity available at any given time on each line in the country. Thus, ReEDS requires 

that the user input the fraction of the capacity of each line that will be available for wind 

or CSP; the default fraction is set at 10% for all lines.

This transmission availability constraint severely limits the amount of wind or CSP that 

can be transmitted on existing lines, well below that found in previous studies12

 12 See, for example, B. Parsons and Y. Wan, U.S. Wind Reserves Accessible to Transmission Lines. IEEE 

Power Engineering Review. Vol. 15(9), September 1995; pp. 5-6; NREL Report No. 21239.

that 

required only that the wind resource be within 20 miles of an existing transmission line.

In addition to the cost of building a line from the wind/CSP site to the grid, ReEDS also

allows the user to input a cost for the use of the grid. That cost can be based on the 

distance the power is transmitted or on the number of power control areas that the 

electricity must pass through (called a “pancake rate”). ReEDS also verifies that the 

existing transmission lines crossing the border of a supply/demand region have enough 

capacity to carry the wind and CSP generation into and out of the region. In addition, all 

generation (from both renewable and conventional generators) is constrained from 

flowing between any two balancing authorities in each time-slice by the capacity of lines 

that connect the two balancing authorities. ReEDS does not account for loop-flows,

contingencies, etc. that could further restrict transmission on existing lines.

While new transmission lines dedicated to renewables are not constrained by the 

remaining transmission capacity available, they do have additional cost. For lines built to 

serve remote sites, the entire cost of constructing and maintaining a new line is attributed 

to the wind or CSP capacity at that site. This means that the lines are used only when the 

wind is blowing (or sun is shining), and their costs must be amortized over that 

intermittent power. The costs of new transmission lines can vary significantly based on 

terrain, congestion, labor costs, etc. Currently, ReEDS assumes a single cost for new lines 

expressed in $/MW-mile, which is increased for rough terrain and population congestion. 

In the future, we anticipate modifying ReEDS to vary the new transmission line cost per 

mile with the length of the transmission line and the amount of renewable capacity 

potentially available within the supply region.
22

New transmission lines dedicated to wind or CSP can be built either between 

supply/demand regions as described above or within a region. Dedicated in-region 

transmission lines are assumed to transport the electricity generation directly from the 

wind/CSP site to a load center within the region, bypassing the transmission grid and 

connecting to the distribution system within the load center. As with the construction of 

lines connecting renewables to the grid described above, the GIS is used to develop 

supply curves for each resource class in each supply region for the cost of building these 

intraregional transmission lines directly to load centers.

New transmission lines are also built in ReEDS to transmit power from one balancing 

authority to another. These lines can be accessed by either conventional or renewable 

generators. ReEDS builds these lines when it is cost-effective and when there is a need 

for more transmission capacity between the balancing authorities in one or more of the 16 

time-slices in each year; or when it is needed to ensure capacity reserve margins are met 

in the different balancing authorities, NERC regions, or interconnection regions.

Transmission losses are modeled in ReEDS as a linear function of the distance the power

is transmitted. These losses apply to the transmission of both renewable and conventional

generation, and are currently specified using the fraction of power lost per MW-mile.

Qualitative Details on Wind Variability

Wind power—because the resource is variable and unpredictable and neither the resource 

nor the resulting electricity can readily be stored—is complicated to model. ReEDS, in an 

attempt to capture the peculiarities of wind power, has a detailed stochastic treatment of 

wind power that is unique among power sources. Solar power, were it not assumed in 

ReEDS to have six hours of thermal storage, would have similar issues; as it is, for now, 

only wind has such involved variability calculations. The variability of the wind resource 

can impact the electric grid in several ways. One useful way to examine these impacts is 

to categorize them by time, ranging from multiyear planning issues to small 

instantaneous fluctuations in output.

At the longest time interval, a utility’s capacity expansion plans may call for the 

construction of more nameplate generation capacity. To meet this need, the planners can 

plan to build conventional dispatchable capacity or wind. The variability of wind 

precludes the planners from considering a MW of nameplate wind capacity to be the 

same as a MW of nameplate dispatchable capacity: Wind capacity availability cannot be 

counted on when peak demand for electricity occurs; and, actually, conventional capacity 

also cannot be considered 100% reliable.

The difference is in the degree of reliability; conventional generators experience forced 

outages on the order of 2%-20% of the time, while wind energy is available at varying 

levels that average about 30%-45% of the time depending on the quality of the wind site. 

For planning purposes, this lack of reliability is handled in the same way—a statistical 

treatment that calculates how much more load can be added to the system for each MW 

of additional nameplate wind capacity, or effective load carrying capability (ELCC).
23

Effective load carrying capability is less for wind than for conventional capacity; first,

because the wind availability is less than that of conventional generators. And second, 

because at any given instant, the generation from a new wind farm can be heavily 

correlated with the output from the existing wind farms—if the wind isn’t blowing at one 

wind site, there is a reasonable chance it is also not blowing at another nearby site. On the 

other hand, there is essentially no correlation between the outputs of any two 

conventional generation plants.

Fortunately, there are ways to partly mitigate both the low availability of the wind 

resource and its correlation between sites. In the past 20 years, there has been 

considerable improvement in wind capacity factor (the ratio of actual output over a 

period of time to its output if it had operated at full capacity over that same interval) of 

new wind installations. This is attributable to both better site exploration/characterization 

and to improvements in the wind turbines themselves (largely higher towers).

The correlation in wind output between sites also can be reduced. Increasing the distance

between sites and the terrain aspects that separate them reduces the chances that two sites

will experience the same winds at the same time. With its multiple regions, ReEDS is 

able to approximate the distance between sites and, therefore, the correlation between 

their outputs. ReEDS uses the correlation between sites to estimate the variation in wind 

output from the total set of wind farms supplying power to a particular region.

Between each two-year-period optimization and for each demand region, ReEDS updates 

its estimate of the marginal ELCC associated with adding wind of each resource class in 

each wind supply region to meet demand within an RTO. This marginal ELCC is a strong 

function of the wind capacity factor and the distance from the existing wind systems to 

the new wind site for which the ELCC is being calculated. It is also a weak function of 

the demand region’s load-duration curve as well as the size and forced outage rates of the 

conventional capacity. This marginal ELCC is assumed to be the capacity value of each 

MW of that wind class added in the next period in that wind supply region to serve the 

RTO’s demand. Everything else being equal, when expanding wind capacity, ReEDS will 

select the next site in a region that is as far from the existing sites as possible to ensure 

the lowest correlation and the highest ELCC for the next wind site. (More practically, 

everything else is never “equal,” and ReEDS considers the tradeoffs between ELCC and 

wind site quality, transmission availability/cost, and local siting costs.)

Generally, for the first wind site supplying a demand region, these capacity values 

(ELCC) are almost equal to the capacity factor. However, as the wind penetrates to 

higher levels, the ELCC can decline to almost zero in an individual wind supply region.

The next time frame of major interest is the day-ahead time frame. Utilities generally 

make decisions on which generating units to commit to generation a day ahead of time. 

To comply with these unit-commitment procedures, independent power plant owners 

may be expected to provide a bid for firm capacity a day ahead. Obviously, this can be 

problematic for operators of wind farms. For example, if the wind operator bids to 

provide firm capacity, and the wind does not blow as forecast, the operator may have to 

make up the difference by purchasing power on the real-time market. If that power costs 
24

more per kilowatt hour than he is being paid for his day-ahead bid, he will lose money on 

those kilowatt hours he is forced to purchase.

Not all of today’s electric-grid systems operate day-ahead and real-time markets, as 

described in the preceding paragraph. California, for example, allows a monthly 

balancing of bid and actual generation for wind that is much more tolerant of the 

inaccuracies in forecasting wind a day ahead of time. No matter the market structure, 

however, the imbalances must be offset with adequate operating reserves. Therefore, to 

capture the essence of the unit-commitment issue, ReEDS estimates the impact of wind 

variability on the need for operating reserves (includes quick-start and spinning reserves) 

that can rapidly respond to changes in wind output. The operating reserves are assumed 

to be a linear function of the variance in the sum of generation (both wind and 

conventional) minus load. Because the variability of wind is statistically independent of 

the load variability and forced outages, the total variance with wind can be calculated as 

the sum of the variance associated with the normal (i.e., no wind) operating reserve and 

the total (all the wind supply regions) variance in the wind output over the reconciliation 

period. Before each two-year optimization, ReEDS calculates the marginal operating 

reserve additions required by the next unit of wind (added in a particular wind supply 

region from a particular wind class) as the difference between the operating reserve

required by the total system with that new wind and the operating reserve required by the 

total system, if there were no new wind installations in that wind supply region. This 

value is then used throughout the next two-year linear program optimization as the 

marginal operating reserve requirement induced by the next MW of wind addition in that 

region of that wind resource class.

At the shortest time interval, regulation reserves must compensate for instantaneous 

changes in wind output. Regulation reserves are normally provided by automatic

generation control of conventional generators whose output can be automatically adjusted 

to compensate for small changes in voltage on the grid. Fortunately, these instantaneous 

changes in wind output do not all occur at the same time, even from wind turbines within 

the same wind farm.

This lack of correlation over time and the ease with which conventional generators can 

respond allows us to reasonably ignore this second order cost. ReEDS assumes that any 

wind generation delivered to a specific demand region in a specific time-slice that 

exceeds the total electric load in that region/time-slice will be lost. In addition, as 

mentioned above, ReEDS also statistically accounts for surplus wind lost within a timeslice due to variations in load and wind within the time-slice. ReEDS has three 

endogenous options for mitigating the impact of variability. The first is to add 

conventional generators that can provide spinning reserve (e.g., gas combined-cycle) and 

quick-start capabilities (combustion turbines). The second, and usually least costly, is to

allow the dispersion of new wind installations reducing the correlation of the outputs 

from the different wind sites. The third, and usually most costly, is to allow for storage of 

electricity at the wind site. If it is cost-effective, ReEDS will build storage capacity at an 

onshore wind site that can be used during peak electric demand periods to generate 

electricity when the wind is not blowing to its full capacity. Storage options available in 
25

ReEDS are pumped hydro, compressed air, and batteries. ReEDS endogenously selects 

the capacity of the turbines at a site, the transmission capacity to the site, and the capacity 

of the storage. It assumes that all output from wind turbines is used either to provide 

power directly to the grid or to charge storage. ReEDS also assumes that power can be 

delivered to a wind site from the grid (with industrial power-purchase retail markups) to 

charge storage even when the onshore wind turbines are not generating power.

This allows the power capacity (and, therefore, the capital cost) of the storage facility to 

be reduced without compromising its ability to provide adequate energy. The energy 

stored at a wind site can be discharged in any time-slice. ReEDS also allows the 

electricity storage technology to be placed at the load centers rather than at wind sites. 

General storage at the load centers would have greater capacity value than that located at 

an onshore wind site because it would not be constrained by the availability of

transmission capacity from the wind site. On the other hand, as mentioned above, storage 

at an onshore wind site allows for the downsizing of transmission-line capacity.

To keep the number of variables in the linear program of ReEDS to a minimum, storage 

at offshore wind sites is not simulated. Such systems are assumed to be less likely, due to 

the relatively higher costs of offshore wind and storage.
26

Appendix B – Attributes of Modeling Renewable Electricity: ReEDS vs. NEMS

[Most important differences are in bold.]

Attribute Details ReEDS: Electric-Sector 

ONLY (Capacity Expansion 

Model)

NEMS: ALL Energy Sectors 

(Energy-Economic Model – EMM)

Costs dominated 

by capital costs

Finance, depreciation, 

materials costs, 

learning/decreasing costs

ReEDS base case capital 

costs are intended to represent 

“mainstream” industry 

expectations (largely from 

Black and Veatch)

EIA staff draws on various sources 

of expert opinion to select capital 

cost assumptions

Operating costs 

are fixed and 

small

Risks, variability Does not address risk Does not address risk

Modular plant size Reduces over/under 

capacity problems and 

transmission requirements

Assumes all plants (including 

conventionals) can be built in a 

modular fashion

Assumes all plants (including 

conventionals) can be built in a 

modular fashion

Environmental 

impacts are 

generally minimal

Air emissions, life-cycle 

analysis of materials 

Includes air emissions Includes air emissions

Resource sites 

vary in quality

Resource level, time of 

availability, access to 

infrastructure, terrain

Models resource site-quality 

issues at relatively fine 

geographic resolution (more 

than 350 regions); models use 

of existing grid and new 

transmission construction 

necessary to obtain resource

Applies long-term multipliers, 

based in part on geospatial analysis 

of access to infrastructure and in 

part on expert judgment. 

Geographic resolution at NEMS 

region level (13). Due to coarse 

geographic resolution, it is not 

possible to model transmission
27

Conversion to 

usable energy 

must occur near 

the resource site

Transmission, siting High spatial resolution enables 

relatively detailed modeling of 

transmission and siting (see 

above)

Transmission cost is represented by 

a regional adder to the cost of every 

KWh, e.g., wind transmission cost is 

same as gas-fired power 

transmission cost

Resource 

variability

Backup requirements, 

ancillary service 

requirements, 

curtailments, forecasting, 

diversity

Represents variability and 

diversity through stochastic 

treatment of capacity value, 

operating reserve 

requirements, and 

curtailments.

Represents variability in resource 

and has some decrease in capacity 

value as a function of amount of 

wind installed, but not as a function 

of diversity

Distributed 

capability - solar, 

biomass, wind

Competition at the retail 

level, interaction with 

owner’s loads

Represents distributed PV on 

buildings at the 350+ regional 

resource variation level

Represents load at the 13 region 

levels of the EMM and distributed 

PV.

Immature industry Comfort/experience of 

investors, uncertainty in 

future cost and 

performance, 

supply/demand 

imbalances

Includes learning.

Includes growth penalties 

(rapid growth causes price 

increases)

Includes learning.

Includes growth penalties. 
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Evaluating a Proposed 20% National Renewable Portfolio Standard 

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J. Logan, P. Sullivan, W. Short, L. Bird, T.L. James, and M.R. Shah 

5d. PROJECT NUMBER

NREL/TP-6A2-45161

5e. TASK NUMBER

SAO7.9C50

5f. WORK UNIT NUMBER

7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES)

National Renewable Energy Laboratory

1617 Cole Blvd.

Golden, CO 80401-3393

8. PERFORMING ORGANIZATION

REPORT NUMBER

NREL/TP-6A2-45161

9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES) 10. SPONSOR/MONITOR'S ACRONYM(S)

NREL

11. SPONSORING/MONITORING

AGENCY REPORT NUMBER

12. DISTRIBUTION AVAILABILITY STATEMENT

National Technical Information Service

U.S. Department of Commerce

5285 Port Royal Road

Springfield, VA 22161

13. SUPPLEMENTARY NOTES

14. ABSTRACT (Maximum 200 Words)

This paper provides a preliminary analysis of the impacts of a proposed 20% national renewable portfolio standard 

(RPS) by 2021, which has been advanced in the U.S. Congress by Senator Jeff Bingaman of New Mexico, The paper 

was prepared before the America Recovery and Reinvestment Act was signed into law by President Barack Obama on 

February 17, 2009, and thus does not consider important changes in renewable energy (RE) policy that need to be 

addressed in follow-on analysis. We use NREL’s Regional Energy Deployment System (ReEDS) model to evaluate the 

impacts of the RPS requirements on the energy sector and consider design issues associated with renewable energy 

certificate (REC) trading markets.

15. SUBJECT TERMS

NREL; renewable portfolio standard; RPS; Regional Energy Deployment System model; ReEDS; renewable energy 

certificates; RECs; generation capacity; National Energy Modeling System; NEMS; federal 20% RPS by 2021

16. SECURITY CLASSIFICATION OF: 17. LIMITATION 

OF ABSTRACT

UL

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OF PAGES

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Unclassified

b. ABSTRACT

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Standard Form 298 (Rev. 8/98)

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