Representative Technology

Concentrating solar power (CSP) technology is assumed to be molten-salt power towers. Thermal energy storage (TES) is accomplished by storing hot molten-salt in a two-tank system, which includes a hot-salt tank and a cold-salt tank. Stored hot salt can be dispatched to the power block as needed, regardless of solar conditions. In the ATB, CSP plants with 10 hours of TES are illustrated.

The first large molten-salt power tower plant (Crescent Dunes 110 MWe with 10 hours of storage) was commissioned in 2015 with a reported installed CAPEX of $8.96/WAC (Danko 2015; Taylor 2016 ).

Resource Potential

Solar resource is prevalent throughout the United States, but the Southwest is particularly suited to CSP plants. The direct normal irradiance (DNI) resource across the Southwest is some of the best in the world and ranges from 2,000 to 2,800 kWh/m2/year. The solar resource for the Southwest was found in Ballaben, Poliafico, and Hashem (2015). The raw resource technical potential of seven western states (Arizona, California, Colorado, Nevada, New Mexico, Utah, and Texas) exceeds 11,000 GW (almost tenfold current total U.S. electricity generation capacity), assuming an annual average resource > 6.0 kWh/m2/day and after accounting for exclusions such as land slope (>1%), urban areas, water features, and parks, preserves, and wilderness areas (Mehos, Kabel, and Smithers 2009).

Renewable energy technical potential, as defined by Lopez et al. (2012), represents the achievable energy generation of a particular technology given system performance, topographic limitations, and environmental and land-use constraints. The primary benefit of assessing technical potential is that it establishes an upper-boundary estimate of development potential. It is important to understand that there are multiple types of potential - resource, technical, economic, and market (Lopez et al. 2012; NREL, "Renewable Energy Technical Potential").

The Solar Programmatic Environmental Impact Statement identified 17 solar energy zones for priority development of utility-scale solar facilities in six western states. These zones total 285,000 acres and are estimated to accommodate up to 24 GW of solar potential. The program also allows development, subject to a more rigorous review, on an additional 19 million acres of public land. Development is prohibited on approximately 79 million acres.

According to NREL's Concentrating Solar Power Projects website, 15 of the 17 currently operational CSP plants in the United States use parabolic trough technology. And, two power tower facilities - Ivanpah (392 MW) and Crescent Dunes (110 MW), are operational. One small 5-MW linear Fresnel plant is non-operational in California (NREL's Concentrating Solar Power Projects). This 5-MW solar-enhanced oil recovery site was a development site.

Base Year and Future Year Projections Overview

For the ATB, three representative sites were chosen based on resource class to demonstrate the range of cost and performance across the United States:

• CAPEX are determined using manufacturing cost models and are benchmarked with industry data. The CSP performance and cost are based on the molten-salt power tower technology with dry-cooling to reduce water consumption.
• O&M cost is benchmarked by industry input.
• Capacity factor varies with inclusion of thermal energy storage and solar irradiance. The listed projects assume power towers with 10 hours of thermal energy storage.
  • Fair Resource (e.g., Abilene Regional Airport, Texas 5.59 kWh/m2/day based on the site TMY3 file)
  • Good Resource (e.g., Las Vegas, Nevada 7.1 kWh/m2/day based on the site TMY3 file)
  • Excellent Resource (e.g., Daggett, California 7.46 kWh/m2/day based on the site TMY3 file)
• Representative CSP plant size is net 100 megawatts electrical (MWe).

The Base Year estimates are made for 2015 (via an updated index of the ATB 2016) and for 2018, which has utilized a recent assessment of the industry and has expected project completion in 2018.

Future year projections are informed by published literature and technology pathway assessments to inform CAPEX and O&M cost reductions. Three different projections were developed for scenario modeling as bounding levels:

• High cost: no change in CAPEX, O&M, or capacity factor from 2018 to 2050; consistent across all renewable energy technologies in the ATB
• Mid cost: CAPEX reduced by 25% by 2030 and based on median of literature projections of future CAPEX to 2050; O&M technology pathway analysis.
• Low cost: technology pathway analysis demonstrating feasibility of achieving SunShot targets by 2030 through reductions to CAPEX and O&M.