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Federal Energy Management Program Maps

The Federal Energy Management Program (FEMP) has worked with the Geographic Information System (GIS) staff at the NREL to create federal energy management program maps showing the market potential for various solar technologies throughout the country.

About the Maps

Through the use of GIS, NREL examined the viability of two solar technologies in the United States, with and without potential savings from available renewable energy incentives. The renewable energy incentives are taken from the Database of State Incentives for Renewables and Efficiency (DSIRE) and represent the March 2010 version of the database. To assess the impact of the incentives, a specific system size is chosen to represent typical federal installations. Only incentives available to government/nonprofit entities are included. Maps on other renewable energy technologies will be added as they become available.

These maps show where the technologies are cost-effective today and where they will be cost-effective as the utility rates for electricity change. For example, the maps for solar water heating show areas where cost-effective solar systems could be installed now — the areas with a calculated savings-to-investment ratio of 1 or higher. At commercial electric rates of $0.15/kWh or more, however, solar water heating systems would be cost-effective for nearly any federal facility in the United States.

Map of Current savings to investment ratio, without incentives (SIR)

Photovoltaic Maps

The following maps depict six scenarios for photovoltaic systems:

For details on the calculations used for the analyses of photovoltaic systems, see the About the Analysis section.

Solar Water Heating Maps

Map of Current savings to investment ratio, without incentives (SIR)

The following maps depict six scenarios for solar water heating systems using electricity, and six scenarios for solar water heating systems using natural gas:

Electricity

Natural Gas

For details on the calculations used for the analyses of solar water heating systems, see the About the Analysis section.

Map of Current payback period, without incentives

Solar Space Heating Maps

The following maps depict six scenarios for solar space heating systems using electricity, and six scenarios for solar water heating systems using natural gas:

Electricity

Natural Gas

For details on the calculations used for the analyses of solar water heating systems, see the About the Analysis section.

About the Analysis

NREL used ArcInfo® and ArcView® GIS software to conduct the analyses. The base data used in this analysis were annual average energy delivered from a tilt = latitude collector using default PVWatts calculation parameters; and energy cost, using 2006 commercial electricity rates calculated from PowerDat, a database produced by Platts. Three analyses were produced for each technology, with and without potential impacts from incentives:

  1. Current savings to investment ratio (SIR);
  2. Current payback period;
  3. Electricity rate needed to produce a SIR = 1.

We estimated cost-effectiveness "per square foot of solar collector" or "per watt of PV capacity" rather than using a facility's building energy load. This assumes that the solar system's output will never exceed the load; or if it does, that solar electricity will be sold back to the utility at its purchase price.

Photovoltaics (PV)

We calculated and mapped system costs and efficiencies using the following assumptions and equations. For the calculations including incentives, a system size of 100 kW was used.

I: Annual average energy delivered for tilt=latitude = kWh/yr for 1 kW AC system
CS: PV system cost = $7,250/kW
CE: Energy cost = $/kWh
PW: Present worth = 23.15 yrs
OM: Operations & maintenance = $0.006/kWh
  1. Current SIR given current conditions SIR = [I ×(CE - OM) × PW] ÷ CS
  2. Current payback period given current conditions Payback = CS ÷ [I × (CE - OM)]
  3. Energy cost (electricity rate) required to result in a SIR > 1 nationwide CE = [CS ÷ (I × PW)] + OM

Solar Hot Water (SHW)

We calculated and mapped system costs and efficiencies using the following assumptions and equations. For the calculations including incentives, a system size of 500 sq. ft. was used.

I: Annual average solar radiation on tilt = latitude collector
where kWh/m2/day = hrs/day, for hours when array is providing peak output,
e.g. 5.3 kWh/m2/day = 5.3 hrs/day
E: System efficiency = 40%
CE: Energy cost = $/kWh or $/therm
PW: Present worth = 23.15 yrs
CS: SHW System Costs = $150 per sq. ft.
OM: Operations & maintenance = 0.005% of initial cost
  1. Current SIR given current conditions SIR(electricity) = ( I × E × 365 days/yr × 10.76 m2/ft2 × 29.307 kWh/therm × CE × PW ) ÷ [CS × (1 + OM)]
  2. Current payback period given current conditions Payback(electricity) = [CS × (1+OM)] ÷ (I × E × 365 days/yr × 10.76 m2/ft2 × 29.307 kWh/therm × CE × E)
  3. Energy cost (electricity rate) required to result in a SIR > 1 nationwide CE = [CS × (1+OM)] ÷ (I × E × 365 days/yr × 10.76 m2/ft2 × 29.307 kWh/therm × PW )
  4. Current SIR given current conditions SIR(natural gas) = ( I × E × 365 days/yr × 10.76 m2/ft2 × CE × PW ) ÷ [CS × (1 + OM)]
  5. Current payback period given current conditions Payback(natural gas) = [CS × (1+OM)] ÷ (I × E × 365 days/yr × 10.76 m2/ft2 × CE × E)
  6. Energy cost (natural gas rate) required to result in a SIR > 1 nationwide CE = [CS × (1+OM)] ÷ (I × E × 365 days/yr × 10.76 m2/ft2 × PW )

Solar Space Heating (SSH)

We calculated and mapped system costs and efficiencies using the following assumptions and equations. For the calculations including incentives, a system size of 1000 sq. ft. was used.

ED: Energy Delivered = kWh/m2/yr
CE: Energy cost = $/kWh or $/therm
PW: Present worth = 23.15 yrs
CS: SSH System Costs = $27.40 per sq. ft.
  1. Current SIR given current conditions SIR (electricity) = (ED × CE × PW) ÷ CS
  2. Current payback period given current conditions Payback (electricity) = CS ÷ (ED × CE)
  3. Energy cost (electricity rate) required to result in a SIR > 1 nationwide CE = CS ÷ (ED × PW )
  4. Current SIR given current conditions SIR (natural gas) = [(ED ÷ 29.307 kWh/therm) × CE × PW] ÷ CS
  5. Current payback period given current conditions Payback (natural gas) = CS ÷ [(ED ÷ 29.307 kWh/therm) × CE]
  6. Energy cost (natural gas rate) required to result in a SIR > 1 nationwide CE = CS ÷ [(ED ÷ 29.307 kWh/therm) × PW]

For more information on FEMP, access the Federal Energy Management Project Assistance website.

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