Utility-Scale Solar Site Suitability

As Wisconsin has no substantial in-state fossil fuel resources, reliance on a fossil fuel-based energy profile leads to an annual energy spending deficit of $14.4 billion. This profile is rapidly shifting, however. There is increased development of utility-scale (greater than 100 megawatts) photovoltaic production, including several projects under construction and in the queue.

Did you know? Utility-scale solar is considered any facility which has a capacity greater than or equal to 100 Megawatts.

Through an executive order in 2019, Wisconsin Governor Tony Evers pledged that all electricity consumed in Wisconsin be 100 percent carbon-neutral by 2050. Utility companies are beginning to follow suit. Wisconsin-based provider Alliant Energy announced plans in 2020 to eliminate coal from its generation portfolio by 2040 and achieve net-zero CO ₂  emissions by 2050. In doing so, they have simultaneously set about increasing their solar production. They are on track to add over 1,000 megawatts of solar power by the end of 2023 with the creation of 12 solar farms across nine Wisconsin counties. WEC Energy Group, the state’s largest utility, plans to add approximately 800 megawatts of solar.

Did you know? One megawatt of solar capacity requires about 5-7 acres of land.

A  recent study by the Center on Wisconsin Strategy (COWS)  suggests that development of utility-scale photovoltaics (UPV) could supply 31.7% of energy in a proposed 100% in-state energy profile. If all else remains constant, this projection translates to the offset of 20.2% (260.9 Trillion BTU) of the current end-use consumption.

This study implements suitability modeling in GIS to estimate the capacity of Wisconsin’s landscape to meet the COWS projection. Multiple datasets (explained further in the methods below) were combined and weighted to identify areas suitable for UPV development and estimate the implied land conversion of said development.

Areas in the east are on average the most suitable due to the high density of transmission lines – infrastructure critical to for utility-scale solar facilities. The central region follows closely in ranking because of its abundant, flat agricultural land. The least suitable land is found in the Driftless region in the west-southwest due to hilly terrain.

The methodology used to conduct this analysis is based, in part, off the work of Janke, and Zarby and Grandstrand. The flow chart below illustrates the GIS suitability modeling process and explains each of the several input datasets were considered.

As both a test of the suitability map and an example of its real-world applications, a case study was conducted on Portage County in central Wisconsin. Selection criteria relating to parcel ownership and size were employed to locate possible development sites.

In this example, the high-resolution suitability map was used to locate contiguous land areas greater than 500 acres comprised of parcels greater than 100 acres with only a single owner. Given the estimate of 5-7 acres per megawatt of solar capacity, 500 acres characterizes the lower end land requirement.

Using the above criteria, 119,922 acres of land under the ownership of 398 parties were located. Of this selection, 13,867 acres owned by 53 parties were determined to be of high suitability, for a possible 1,000-3,000 MW solar capacity.

Additionally, the proposed site of a 2,584-acre solar project in the county was extracted to assess the accuracy of the suitability model for selecting parcels. Areas in yellow and orange are lands of high suitability.

Areas in black were found to be not suitable for one reason or another, for example preexisting structures, like homes. While only a small fraction of the total proposed solar project, these excluded areas underscore the role of suitability models as often accurate, but not always precise, tools for estimation.

Given a capacity factor of 18% in Wisconsin, a 1 MW solar farm produces 1,576.8 megawatt hours (MWh) annually. Therefore, to meet the COWS projection, necessary development totals 48,494 MW solar capacity converting 242,470 to 339,458 acres of land (5-7 acres per MW), or about 1% of the total land area of the state. Further, this estimate is equivalent to about 6% of the state's agricultural land land planted in soybeans and corn.

In considering several land characteristics as criteria in this study, 896,137 acres were found to be highly suitable for UPV solar development supporting 128,019 to 179,227 MW capacity (263% of that required by the projection).

While suitability analysis proves a valuable tool for modeling, the output results remain estimations. Further in-depth analysis is critical to determine true suitability on more local levels. For example, consideration of areas of cultural and natural significance may prove decisive for a specific site.

 Click here to view the full report and methodology