Water Use in Concentrating Solar Power...

NREL is a national laboratory of the U.S. Department of Energy Office of Energy Efficiency and Renewable Energy operated by the Alliance for Sustainable Energy, LLC

Craig Turchi and Chuck Kutscher

[email protected]@nrel.gov

National Renewable Energy LaboratoryGolden, Colorado, USA

Water Use inConcentrating Solar Power (CSP)

National Renewable Energy Laboratory Innovation for Our Energy Future

Outline

• Solar Resource Potential• CSP Technology Overview

- Parabolic Troughs- Power Towers- Dish / Engine Systems- Comparison with Photovoltaics (PV)

• Announced Projects• Water Consumption

- Wet vs. dry cooling

Solar Resource Screening


All Solar Resources

Locations best forDevelopment

1. Start with direct normal irradiance (DNI) estimates derived from satellite data.

2. Exclude locations with less than minimum DNI threshold.

3. Exclude culturally and environmentally sensitive lands, urban areas, lakes and rivers.

4. Exclude land with greater than 1% to 3% average land slope.

5. Exclude areas of less than 1 km2

6. Locate near load centers and transmission corridors

Site filtering example - USA


Solar > 6.75 kWh/m2/day

Land Exclusions

Slope & Area Exclusions

CSP Resource Potential - USA

02000400060008000

1000012000140001600018000

Land (thousand

km2)

Capacity (GW)

Energy (TWh)

USA Total CSP Potential


Assumptions :

• Solar Resource ≥ 6.75kWh/m2/day• Land use 5 acre/MW• Land slope < 1%• Capacity factor 27%• Water, urban areas, and environmentally sensitive lands excluded


CSP Technologies and Market Sectors

CSP w/ Storage (Dispatchable)– Parabolic Trough– Power Tower– Linear Fresnel

CSP w/o Storage (Non-Dispatchable)– Dish/Engine

Parabolic Trough


www.centuryinventions.com


Parabolic Trough Power Plant w/ 2-Tank Indirect Molten Salt Thermal Storage

Trough Field

Salt Storage Tanks

390°C


354 MW Luz Solar Electric Generating SystemsNine “SEGS” Plants built 1984-1991 (California, USA)

64 MW Acciona Nevada Solar OneNevada, USA

50 MW Andasol 1 with 7-hr StorageAndalucía, Spain


Power Tower (Central Receiver)

Different design approaches:

• Direct Steam Generation – Abengoa PS10 (Spain)– Abengoa PS20 (Spain)– BrightSource (USA/Israel)– eSolar (USA)

• Molten Salt – Solar Two (USA demo)– SolarReserve (USA)

• Air Receiver• Jülich (Germany)


Cold SaltHot Salt

Conventional steam turbine & generator

Steam Generator

288°C565°C

Condenser

Molten Salt Power Towers

Ability to store hot salt allows molten salt Towers to run at high capacity factors.

Heliostat Field

Power Tower Pilot Plants

6 MW thermal BrightSourceNegev Desert, Israel

5 MWe eSolarCalifornia, USA


• Modular (3-25kW)

• High solar-to-electric efficiency

• Capacity factors limited to <25% due to lack of storage capability

Dish/Stirling: Pre-commercial, pilot-scale deployments

Concentrating PV: Commercial and pre-commercial pilot-scale deployments

Dish Systems

Tessera 25kW Dish/Stirling1.5 MW demo in Phoenix under construction

Technology Comparison

Trough Power Tower

Dish / Engine

PV

Utility scale (>50 MW) x x x x

Distributed (<10MW) x x

Energy Storage (dispatchable)

x x

Water use for cleaning x x x x

Water use for cooling preferred preferred

Technical maturity medium low low low to high

Cost(nominal, with 30% ITC)

16-19¢/kWh

? ? 14-25¢/kWh*


* Utility scale only, rooftop PV higher.


Outline





Solar Plants and announced Projects

Plant or State Capacity (MW) Technologies

SEGS I thru IX 354 Trough

Nevada Solar One 64 Trough

Kimberlina pilot 5 Linear Fresnel (Ausra)

Sierra pilot 5 Power Tower (eSolar)

Utility-scale PV 32 Three sites in CO and NV

Utility-scale PV 3500 Sites in CA, NM, NV, TX, CO, others

California 6390 Trough, Tower, Fresnel, Dish/Stirling

Nevada 484 Trough

Arizona 1147 Trough, Dish/Stirling

New Mexico 92 Tower

Texas 27 Dish/Stirling

Florida 75 Trough/NGCC

Total ~ 12,000


See http://seia.org/csp/


Outline





Water Use per Land Area

0

0.5

1

1.5

2

2.5

3

3.5

CSP (wet-cooled)

CSP (dry-cooled)

Alfalfa Cotton Fruit Trees Golf Courses

Acr

e-ft

/ ac

re p

er y

ear


Sources:CSP: Reducing Water Consumption of CSP Electricity Generation, Report to Congress 2009.Crops: Blaney, Monthly Consumptive use of Water by Irrigated Crops & Natural Vegetation, 1957.Golf : Watson et al., The Economic Contributions of Colorado’s Golf Industry: Environmental Aspects.

Water Usage of Solar Technologies

0

100

200

300

400

500

600

700

800

900

Collector Cleaning

Boiler Makeup Cooling Total

Gal

/ M

Wh

Trough (wet cooled) Trough (dry-cooled) Dish/Stirling PV

Reference:Concentrating Solar Power Commercial Application Study:

Reducing Water Consumption of CSP Electricity Generation, Report to Congress, U.S. DOE, 2009Values representative; specific usage varies by plant.


Steam Rankine Power Cycle

Trough Field

Salt Storage Tanks

23

Thermal cycle efficiency is proportional to 1 –Tlow

Thigh

Wet- and Dry-cooled Condensers

Dry-cooled systems are inherently less efficient

Wet-cooled systems are limited by wet-bulb temperature:Tcondensate = Twet-bulb + (~25°F)

Dry-cooled systems are limited by dry-bulb temp:Tcondensate = Tdry-bulb + (~40°F)


Condensate temperature can be ~35°F higher with a dry-cooled system.

Optimum turbine design depends on anticipated condensing temperature(s)



Reducing Water Consumption of CSP Electricity Generation, Report to Congress, U.S. DOE, 2009

Hybrid Cooling

Hybrid systems have wet- and air-cooled condensers (ACC) installed in parallel. Wet system used to reduce load to ACC on hottest days.

Hybrid Designs look appealing

Hybrid estimated to use 85% less water with only 2% drop in energy output(but capital cost is higher too).


Reducing Water Consumption of CSP Electricity Generation, Report to Congress, U.S. DOE, 2009

Solar plants may optimize to a larger ACC than coal plants

1. Switching to an ACC (dry-cooling) requires a larger solar field and turbine to achieve same MWe output

2. Solar field is expensive relative to the ACC; therefore investing in a bigger ACC may be more effective than building lots more solar field.

3. Big ACC and extra solar field yields more power during off-peak (vs. wet-cooled system). This helps offset lower efficiency.


A large ACC can reduce the cost of dry-cooling

Design parameter Wet-cooled baseline

Dry-cooled with large ACC

Design point net power output 1 1

Design point steam turbine efficiency 1 -5%

Turbine size (gross output) 1 +2%

Solar field size 1 +8%

Design point parasitic loads 1 +17%

Total installed cost 1 +8%

O&M cost 1 -3%

Annual net energy output 1 +3%

Annual Revenue 1 +3% ?

Levelized Cost of Energy (LCOE) 1 +3% to +10%


Dry-cooled plant annual energy output increases because parasitic loads fall quickly at off-design conditions, allowing the larger solar field/turbine to generate more power.

Reference:WorleyParsons, Analysis of Wet and Dry Condensing 125 MW Parabolic Trough Power Plants, Sept. 2009

Cooling Comparison Summary

Type Advantages Disadvantages

Wet Lowest costLow parasitic loadsSmall footprintBest cooling, especially in arid climates

High water consumptionWater treatment and blowdowndisposal requiredPlume can cause problems

Dry (ACC) No water consumptionNo water treatment requiredLower O&M costs

More expensive equipmentHigher parasitic loadsLarger footprintPoorer cooling at high dry-bulb temps (turbine derate)

Hybrid Less water consumptionPotentially less expensive than dry-coolingMaintain good performance during hot weather

Complicated system involvingwet and dry coolingSame disadvantages of wet system, but to lesser degree



Conclusions

• Parabolic Trough and Power Tower technologies prefer to use wet cooling (lower cost, higher efficiency).

• Cooling accounts for over 90% of water consumption at a wet-cooled plant.

• Dish/Engine and PV systems use water only for collector cleaning.

• Dry-cooling can reduce water consumption by 90%, but increases capital cost and decreases plant efficiency, especially on hot days.

• The penalty for switching to dry cooling can be minimized by optimizing the turbine and size of the air-cooled condenser (ACC).

• Hybrid wet/dry systems can reduce water consumption by 50% to 80% while maintaining plant efficiency on hot days.

• Cost impact of switching to dry or hybrid cooling will be site specific, depending on solar technology, water availability, climate, and market economics. Likely to raise LCOE by 3% to 10%

Thank you!

Craig TurchiConcentrating Solar Power [email protected]


Water Use in Concentrating Solar Power...

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