Sunday, January 25, 2009

Solar Electric Power And Renewable Energy Futures For Colorado

SES Stirling Energy Systems Solar One Power Plant in the Mojave Desert near Barstow, CA will develop 500 megawatts (MW) of electricity generating capacity with an expansion option to 850 MW. The plant will use 20,000 to 34,000 solar Dish/Stirling concentrators like the ones shown here.

A recent report on the renewable energy future of Colorado assesses the state’s potential to meet its own renewable energy standards (RESs) while also producing renewable energy for export to other markets.

The report is entitled, “Connecting Colorado’s Renewable Resources to the Markets -- Report of the Colorado Senate Bill 07-091 Renewable Resource Generation Development Areas Task Force Revised Edition July 2008”

The 64-page document treats wind, solar, hydroelectric, and geothermal power generation, and biomass, ethanol, and biodiesel fuels. The report sets these energies in the context of policy, economics, power transmission, land-use, and related elements. Importantly, the Task Force assesses electricity generation costs for different carbon dioxide (CO2) emissions penalty scenarios.

For wind and solar power, the Task Force identified “Generation Development Areas” or GDAs indicating power generation potential from specific regions of the state.

For wind power, the GDAs lie on the High Plains east of the Rocky Mountain Front and within which the Task Force found a potential for ninety-six (96) gigawatts (GW) of wind power generation. I will treat the implications of wind power development for Colorado and other regions in a future post.

For solar power, the Task Force defined two GDAs in the southern part of the state together having a potential to generate as much as thirteen hundred (1,300) gigawatts (GW) of electricity.

One "Central Solar Power" GDA is the San Luis Valley of south-central Colorado. The other, larger GDA includes a region extending from the eastern base of the Sangre de Cristo Mountains well into the High Plains of southeastern Colorado along the Colorado-New Mexico border.

The Task Force acknowledges the impracticality of the 1,300-GW scale of generation, saying that all the land in the GDAs would need to be covered with solar generation equipment. Further, the 1,300-GW output would be more than one hundred (100) times the current peak energy demand for the state.

The Task Force makes no specific recommendation for the level of solar power generation, but says about two (2) percent of the total land area of the two GDAs would allow production of about twenty-six (26) gigawatts (GW) of electrical generation capacity.

The Task Force then describes three utility-scale solar technologies currently available and operating elsewhere in the USA and the world. These technologies are grouped under the heading of Concentrating Solar Thermal Power (CTSP), frequently referred to in other reports and the media as Concentrating or Concentrated Solar Power (CSP).

The three technologies are Parabolic Trough Systems, Dish/Stirling Systems, and Solar Tower Systems. In each of these systems, large mirrors focus reflected solar radiation onto receivers that transform the intense heat into energy.

Parabolic Trough Systems focus solar radiation onto oil-filled pipes, and the heated oil is used to boil water, creating steam to drive electricity-generating turbines.

Sandia National Laboratories Researcher Rich Diver poses with a Parabolic Trough solar power concentrator, Albuquerque, NM, May 15, 2007. The parabolic mirrors focus sunlight on the oil filled pipe running above his head. The oil then flows though a heat exchanger to generate steam to power a turbine to generate electricity.

As illustrated by SES Stirling Energy Systems, Dish/Stirling Systems use large, mirrored, lens-shaped dishes to focus solar radiation on a Stirling engine mounted at the focal point of the lens. The heated fluid in the Stirling engine expands, creating pressure to drive pistons or turbines for electrical power generation.

The SES Stirling Energy Systems SunCatcher is a 25-kilowatt (kW) Solar Power System consisting of a 38-foot diameter dish structure that supports 82 curved glass mirrors. The system is also called a heliostat because it tracks the movement of the sun throughout the day. The device labeled "Power Conversion Unit (PCU)" is the Stirling engine and its housing.

Solar Tower Systems use a mirror array to concentrate and focus solar heat on a tower containing molten salt. The heated salt is used to produce steam to drive electricity-generating turbines.

Solar Tower System at Sandia National Laboratories National Solar Thermal Test Facility, Albuquerque, NM. In this 2006 view the nine-acre test facility at Sandia consists of a 200-foot-high solar tower, 212 computer-controlled mirrors called heliostats, and a separate five-story control tower. The heliostats focus sunlight on the tower to generate heat that produces steam to drive electricity-generating turbines.

Each of these three industrial-sale systems has different land-use and water-use requirements plus heat storage potential across a broad range of existing and evolving technologies. Despite many references to steam, the Task Force does not assess water use for different industrial-scale solar power systems in the July 2008 revision of its report.

In fact, Parabolic Trough and Solar Tower Systems can either consume significant quantities of water through evaporation as steam, or they can minimize water consumption using closed-loop and other dry-cooling systems. Dish/Stirling Systems operate at high temperatures, and require essentially no water other than what is needed to wash the mirrors from time to time.

The U.S. Department of Energy, Sandia National Laboratories (SNL) in 2006 published comparative water uses for coal, coal IGCC (Integrated Gasification Combined-Cycle), other fossil fuels, biomass, nuclear, geothermal steam, solar trough, solar tower, natural gas, and hydroelectric power. This report for the USA Congress is entitled “Energy Demands on Water Resources,” and the water demand tables are on pages 17 and 38.

I will devote a future post to land- and water-use requirements for specific renewable energy technologies. I will also devote a separate post to rapidly developing opportunities and technologies for storing solar and other forms of renewable energy.

In concluding the section on solar power generation potential for Colorado, the Task Force discusses solar photovoltaic systems (Solar PV), distributed solar photovoltaics (DG), and current and necessary future policy for Colorado regarding solar power development.