UA Identifies Solar Sites with Greatest Potential

Factors used to determine a site's solar energy suitability range from its physical aspects, such as the slope of the land and soil quality, to economic factors, such as proximity to existing roads, railroads and transmission lines.
April 5, 2013
The UA is using computer models to identify prime locations in Arizona for solar energy production.
The UA is using computer models to identify prime locations in Arizona for solar energy production.

Rural areas in Arizona have two prime assets for solar farming abundant sunshine and large expanses of undeveloped land. Yet county planners and solar investors need fundamental details about a site to determine its real-world potential for utility-scale solar energy production.

The University of Arizona is analyzing comprehensive databases and producing detailed maps that show which sites meet essential criteria and have the best potential for generating solar energy on a large scale.

"Initial feasibility studies often are cost-prohibitive for underfunded communities with large expanses of undeveloped land," said Mark B. Apel, the UA Cooperative Extension agent for Cochise County the first county to be mapped in this statewide project. UA Cooperative Extension is part of the College of Agriculture and Life Sciences.

"Using computer modeling, we can eliminate land that we know would never work and see where the areas of highest potential are," he said. "Once the more promising sites are identified, rural communities can get solar developers to look more carefully."

Parameters Identify Promising Sites

Critical factors range from physical aspects such as the slope of the land, the direction it faces (south exposures get more sun), soil quality and amount of shade to economic factors such as proximity to existing roads, railroads and transmission lines.

"Our database computer system allows us to map data geospatially so data is portrayed visually on a map," Apel said. Layers of existing county, state and federal data are combined to create GIS shapefiles with color-coded polygons indicating high, medium or low suitability for siting utility-scale solar facilities. Planners and communities can then incorporate their own local data, selecting criteria such as ownership, floodplains, washes, wildlife habitat and corridors, recreation areas, archaeological sites, farmland and residential developments.

Apel spearheaded the analysis of the entire 6,200-square-mile jurisdiction of Cochise County in the southeast corner of Arizona. The results show significant opportunity for solar development around Sierra Vista. The Willcox area also has many areas of high suitability, partly because of the higher density of roads for site access, compared to a smaller community like Cochise.

"This is the first step in helping the county and any renewable energy developer to understand where the greatest potential is for solar energy power plants within the county's jurisdiction. This is a first cut not a final assessment of the real-world suitability of a given area of land," Apel said.

UA Plans Geospatial Database for Every County

"Our ultimate goal is to use this GIS computer model to develop a geodatabase for every county in Arizona all 15 of them," Apel said. (GIS stands for geographic information system.)

Apel has worked on this project with Iris Patten, assistant professor in the UA School of Landscape Architecture and Planning, and Melanie Myers-Colavito, a doctoral candidate in geography: "We hope to have the whole state done by the end of the spring 2013 semester."

Funding is provided by a grant from the U.S. Deptartment of Commerce's Economic Development Administration. The project is administered by the UA Regional Center for Sustainable Economic Development.  

The solar analysis reports can assist counties and communities as they plan for solar energy development and infrastructure and as they process applications for land use.

"They help determine right up front if what's being proposed is valid and feasible," Apel said. For example, if a developer is considering acreage that faces north, with loose sandy soil and a slope of greater than two percent, county planners would know that it is not a suitable site for large-scale solar energy generation.

"Just like real estate, in land planning, everything is location, location, location," Apel said.

Proximity to existing transmission lines and substations is critical, he said: "The costs of putting in new lines can be really exorbitant."

Cochise County Research Leads to Statewide Model

The Cochise County Planning and Zoning Commission cited the UA solar analysis as a factor when it approved a 1.2 megawatt solar photovoltaic project to be developed by Sulphur Springs Valley Electric Cooperative in San Simon, near the New Mexico border. (A rule of thumb is that 10 acres will generate 1 megawatt of solar energy, enough to power more than 600 homes.)  

A 5 megawatt photovoltaic project typically would cover 50 acres and generate power for 3,000 to 4,000 homes, Apel said. In the report, he noted that neighboring New Mexico is developing solar-generating facilities of this size all over the state to meet solar energy requirements more stringent than those in Arizona. The Arizona Corporation Commission has mandated that utilities obtain at least 15 percent of their power from renewable sources by 2025.

"Cochise County surpassed 125,000 people as of the 2010 census which means it is now required by state statute to include an energy element in its comprehensive plan," Apel noted. That's an important reason why officials wanted this renewable energy opportunity analysis. The U.S. Department of Energy provided crucial data for this project.

"They have wonderful maps that show the areas of greatest solar isolation the amount of solar energy that shines onto the Earth's surface," he said. But those maps were grainy low-resolution images. Another vital resource was the Arizona State Land Department, which spent years developing detailed geodatabases, then provided that information to individual counties.

After incorporating all the data into the GIS computer model developed at the University, "our results reflect the suitability for solar development down to a 1,100-square-foot area of land," Apel said.

Apel was with the Cochise County Planning Department for a decade before joining UA Cooperative Extension in 2007. Cochise County requested this analysis, funded by the federal grant, which led to developing the model that will now be used to access all counties in Arizona.

"We've found this incredibly useful," said Mike Turisk, Cochise County planning manager during an interview in January. "We had a solar project just last month. It was located in an area that according to the analysis was very suitable for utility-scale solar development from a number of perspectives. The grade of the site was less than two percent. It was a wide open area, very rural, away from major residential developments."

Addded Turisk: "The planning and zoning commission indicated this suitability analysis is very beneficial in making a determination about whether a proposed solar project is sited in an optimal area."