From Maps to Megawatts – A GIS-based renewable energy opportunity analysis for Arizona

Renewable energy. NextEra Energy Resources has built a 5-megawatt solar energy plant, the largest in North America, using concentrating photovoltaic systems on 39 acres in an industrial park near Hatch, New Mexico. According to the company, the plant helps avoid 6,000 tons of carbon dioxide and the consumption of 66 million cubic feet of natural gas annually that would have been used to produce approximately 11,000 megawatt-hours of electricity. Photo by Mark Apel.

Renewable energy. NextEra Energy Resources has built a 5-megawatt solar energy plant, the largest in North America, using concentrating photovoltaic systems on 39 acres in an industrial park near Hatch, New Mexico. According to the company, the plant helps avoid 6,000 tons of carbon dioxide and the consumption of 66 million cubic feet of natural gas annually that would have been used to produce approximately 11,000 megawatt-hours of electricity. Photo by Mark Apel.

by Mark Apel and Melanie Colavito, Bisbee, Arizona

To relieve the dependence on fossil-fuel based energy and reduce greenhouse gases, renewable resources like wind and solar are becoming an increasingly important component of our nation’s energy portfolio.

AltEnergyMag reported that “investments in renewable energy increased from $39.24 billion in 2001 to $336.78 billion in 2009 at a compound annual growth rate of 30.8 percent during the period 2001-09” (Peri 2011). In the West, most investment in renewables is occurring in wind and solar projects, from large wind farms in Wyoming to solar arrays in New Mexico.

In Arizona, all regulated utilities are mandated by the Arizona Corporation Commission to have a minimum of 15 percent renewable energy sources in their portfolio of energy supplies by the year 2025. This mandate has spawned a variety of renewable energy projects throughout the state, including what will be the world’s largest concentrating solar project in Gila Bend, Arizona, which will generate 280 megawatts with enough power to supply 70,000 homes under a 30-year power supply contract with Arizona Public Service, as well as the world’s largest photovoltaic solar project near Yuma at 290 megawatts to be completed this year (State of Arizona 2013 and NREL, 2014).

Projects like these are an economic boon to small communities in the form of construction jobs and local growth. The future of renewable energy project siting in the West’s seemingly vast landscapes is promising. But the initial costs associated with site analysis can prevent small, rural jurisdictions that have suitable land but small budgets from leveraging potential market advantages.

In 2011, the University of Arizona’s Cooperative Extension was asked by a developer to look at the potential for solar development on a large property that he owned and had master-planned in southern Arizona. Since then, the modeling effort was modified, refined and expanded to include an analysis of the solar potential for every one of the state’s 15 counties. The project was completed in 2013.

The Renewable Energy Opportunity Analysis (REOA) is a Geographic Information Systems (GIS)-based land use suitability tool that provides Arizona’s communities with a first-look at high opportunity areas for solar energy development. More specifically, the high-resolution results are assisting Arizona’s decision makers, planners, and economic development interests in their quest for sustainable, renewable energy sources by identifying the lands most ideally suited for utility-scale solar installations.

Capability versus Suitability

The models were developed using land-based criteria for siting utility-scale solar facilities. While many factors go into siting solar facilities, REOA assesses fundamental physical and economic opportunities and constraints on any given piece of land, using GIS data obtained from the state and counties. The models were created using ESRI’s ArcGIS ModelBuilder.TM
The first step of the REOA process was to consider the insolation factor - the amount of solar radiation reaching a given area. The insolation factor is high for virtually all of Arizona. United States Solar Resource maps for photovoltaic (PV) and concentrated solar projects (CSP) produced by the National Renewable Energy Lab ( show Arizona and the southwest U.S. to have the highest insolation rates in the entire country - on average, greater than 6 kWh per meter2 per day. The model only considered areas that have a minimum of 7 kWh per meter2 per day as the best.

The second step was to filter out those lands that would not have any chance of being developed for utility-scale solar facilities due to steep slopes, large washes/rivers, land jurisdiction, or protected status. Topography was taken into account by analyzing the slope of the land, which for most solar installations can be no greater than a 4 percent grade. Lands that are steeper than this, while physically possible to site a solar array, are not likely economically feasible or accessible.

The presence of major washes was taken into consideration by creating a 600-foot-buffer around all major wash centerlines and 1,000 feet from major rivers and lakes. The analysis did not preclude the presence of 100-year floodplains nor minor washes, since construction is feasible in these areas depending on a site’s flood elevations.

Land jurisdictions that were designated as National Forest, National Park Service, wildlife refuges, conservation areas, and other protected areas precluded from solar development were also filtered out. Altogether, these physical factors were applied as a “mask” to eliminate areas, as a primary filter, where solar energy development would not be feasible.
Both incorporated and unincorporated areas were considered feasible in this analysis. This analysis didn’t distinguish between developed versus undeveloped lands because of the feasibility of facilities being located on small parcels within developed areas.

Figure 1: South region capable areas. Provided by Mark Apel.

Once these factors were determined and filtered out, those lands remaining were deemed ‘capable’ and would be analyzed further for ‘suitability.’ Figure 1 shows all of the capable lands in southern Arizona.

The capable areas were then modeled using physical and economic factors as weighted criteria for determining high, medium or low suitability for solar development. Suitability was determined based on:

  • Aspect of land (north facing, south facing, etc.)
  • Proximity to transmission lines and sub-stations
  • Proximity to roads and railroads

Each of these criteria was assigned a weight based on its relative importance to the others. These weights were determined, based on expert input and consensus. For this analysis, there were two main goals – one to determine the potential for small scale solar projects of 5 megawatts or less and one for large-scale solar projects greater than 5 megawatts.

Topography was more critically assessed using digital elevation models to look at the potential impact of shading from adjacent steep-sloped areas and what is ideal for capturing the sun’s energy. This was accomplished by giving lands that were flat or with southwest, south, and southeast facing slopes a higher weight than other aspects.

Distance to large transmission lines (115-230 kV) becomes an important factor for large scale solar projects, especially where capacity in an existing line and regulatory approvals for new lines from the Arizona Corporation Commission may be an issue. Proximity to existing sub-stations is an important economic factor for proposed solar facilities. Proximity to roads is an important factor to consider for transporting equipment and materials to build and maintain a solar facility. Accessibility to railroads is more important for large scale projects since transporting equipment from a railroad siding to a construction site can be very costly, depending on the distance.

The resolution (level of detail) of this analysis is a cell size of 10 meters by 10 meters or approximately 1,100 square feet. A conventional solar photovoltaic project requires about 10 acres per megawatt, so this modeling is aptly suited to understanding not only the spatial opportunities for projects, but also the amount of potential energy output based on available and consolidated acreage.

Results - How The Models Can Be Used

Figure 2: Provided by Mark Apel. Click on image to open in larger size.

While it’s no surprise that Arizona is ideally suited for solar energy development, the results of REOA spatially depict high, moderate, and low opportunities throughout the state. The analysis reveals nearly 12 million acres that may be considered as high potential for solar development. The results are posted as regional maps on Arizona’s Changing Rural Landscapes website, hosted by Cooperative Extension and the University of Arizona:

It’s important to keep in mind that the results of REOA are based on fundamental siting criteria, as discussed earlier, but other criteria can be used by a planning jurisdiction or developers to further assess the potential of a particular parcel of land. Overlays like wildlife corridors/habitat, city, county or state designated scenic corridors, open space, archaeological and cultural sites, clusters of address points, recharge areas and any other locally relevant constraints may be applied as transparent layers on top of the suitability outputs to further preclude certain acreages and target more appropriate locations.

The results of this work are being used to help communities throughout Arizona target solar energy as a source of local economic development. In addition to the maps that are available online, the GIS shapefiles of the results have been made available to planners throughout the state through Cooperative Extension. Cochise County, located in southeastern Arizona, is one jurisdiction in particular that has incorporated the results into their own GIS and have used the information to support their decision-making for several large solar photovoltaic projects that required approval by the county. As cities and counties deal with solar energy development proposals in their communities, this analysis can help planners see, in very short order, whether or not applicants have done the appropriate due diligence in selecting their proposed sites.

Moreover, these results can also assist community economic development interests in targeting appropriate locations for solar energy development as a first step to recruiting solar companies into their community. Prospective solar developers will save considerable amounts of time and money by focusing on those geographic areas with moderate to high potential.

In Arizona, counties with populations greater than 125,000 are required by state statute to amend their comprehensive plans with an Energy Element and those with a population less than 125,000 may do so voluntarily. The state planning statutes pertaining to counties stipulate planning for energy use that encourages and provides incentives for the efficient use of energy and identifies policies and practices for the greater use of renewable energy. The statutes pertaining to cities’ general plans stipulate that they include consideration of air quality and access to incident solar energy for all categories of land uses. Any county, city or town as a baseline resource may adopt these maps for new plan policies related to renewable energy development.

Cooperative Extension and the University of Arizona have been promoting the REOA results and their availability to planners and community organizations through presentations to GIS user groups, regional planning organizations, county planning commissioners, and at conferences. As cities and counties throughout Arizona seek to become more resilient and less reliant on non-renewable energy, they now have one more tool to help them in that quest.

Mark Apel works for the University of Arizona Cooperative Extension as an agent in community resource development. He is the chair of the Western Planner Editorial Board and is on the Western Planning Resources Board. Melanie Colavito is a Ph.D. candidate in the School of Geography and Development at the University of Arizona with a minor in Remote Sensing and Spatial Analysis. She also holds professional graduate certificates in Geographic Information Systems and College Teaching.


  1. Peri, S. 2011. Global Investments in Renewable Energy are Expected to Reach $653.35 Billion by 2015. AltEnergyMag. August 3, 2011
  2. National Renewable Energy Lab, 2014. Concentrating Solar Projects. Retrieved from 
  3. State of Arizona, Office of the Governor. 2013. Governor Jan Brewer: Arizona now the Nation’s 2nd-Largest Solar Market [Press Release]. Retrieved from

Published in the December 2014/January 2015

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