This map shows the locations of IDOT offices and maintenance yards. Rooftop solar on the office and maintenance buildings may be feasible at these sites. Click the dots for more detailed information about each site.
The Site Solar Index is rated as blue for all sites as these buildings are not typically shaded by trees.
● Blue (promising): Suitable for solar
Solar system details are determined by the loads (how much electricity is consumed on site). The system is sized to meet the estimated electrical load on site, and the system cost is estimated for a solar array of this size. A solar system can be sized smaller but not larger than what is needed by the electrical load on site. Actual sizing depends on the amount of suitable, available space on a roof or the ground. System area indicates the estimated amount of roof space or ground area required (in square feet) for a solar system.
● Further considerations. Once a site is selected for further study, it is important to “ground truth” it to verify suitability and refine the sizing estimate. Here are a few factors to consider:
● Roof conditions, including age, quality, direction, slope, size. A south-facing roof slope or flat roof are desirable, east or west-facing are less desirable, and a north-facing roof slope is undesirable. An old roof or a roof in poor condition is unsuitable.
● Trees and shading potential. If there are trees or other tall objects on site that could cast a shadow on a solar system location at any point in the year, this could affect feasibility.
● Utility delivery provider. We have listed the area utility provider(s) based on the site location, but it is important to verify which is serving the site. Properties served by Rural Electric Cooperatives and Municipal Utilities have different rules for solar that may affect system sizing and connection.
● Actual site electricity use. On site solar systems are sized according to actual site electricity use and site conditions. 10 kW of solar system capacity could generate approximately 13,000 kWh/year and requires about 10,000-20,000 square feet of space.
● Future site changes. Site improvements and capital projects may change electricity use or impact solar system performance. Solar sizing and site location decisions should account for known or likely future site changes.

This map shows the locations of IDOT rest areas and welcome centers. Solar at these sites may be developed either on the roofs of the buildings or on the adjacent land. The colors of the dots indicate that the site has promising suitability (blue), fair suitability (gray), or poor suitability (red). Click the dots for more detailed information about each site.
The Site Solar Index is based on tree coverage and shading for rooftop solar systems.
● Blue (promising): Minimal tree coverage
● Grey (fair): Nominal tree coverage
● Red (poor): Heavy tree coverage
The solar suitability score addresses the suitability of the larger (20+ acres) site for a ground-mounted solar array. The score is based on several criteria and is applicable to large scale arrays. Click on (Link) to view the reference suitability map for rest areas and open lands.
● Solar system details are determined by the loads (how much electricity is consumed on site). The system is sized to meet the estimated electrical load on site, and the system cost is estimated for a solar array of this size. A solar system can be sized smaller but not larger than what is needed by the electrical load on site. Actual sizing depends on the amount of suitable, available space on a roof or the ground. System area indicates the estimated amount of roof space or ground area required (in square feet) for a solar system.
● Further considerations. Once a site is selected for further study, it is important to “ground truth” it to verify suitability and refine the sizing estimate. Here are a few factors to consider:
● Roof conditions, including age, quality, direction, slope, size. A south-facing roof slope or flat roof are desirable, east or west-facing are less desirable, and a north-facing roof slope is undesirable. An old roof or a roof in poor condition is unsuitable.
● Trees and shading potential. If there are trees or other tall objects on site that could cast a shadow on a solar system location at any point in the year, this could affect feasibility.
● Utility delivery provider. We have listed the area utility provider(s) based on the site location, but it is important to verify which is serving the site. Properties served by Rural Electric Cooperatives and Municipal Utilities have different rules for solar that may affect system sizing and connection.
● Actual site electricity use. On site solar systems are sized according to actual site electricity use and site conditions. 10 kW of solar system capacity could generate approximately 13,000 kWh/year and requires about 10,000-20,000 square feet of space.
● Future site changes. Site improvements and capital projects may change electricity use or impact solar system performance. Solar sizing and site location decisions should account for known or likely future site changes.

This map shows the locations of IDOT open lands. A larger ground-mounted solar array may be developed on these open lands. The colors of the dots indicate that the site has promising suitability (blue), fair suitability (gray), or poor suitability (red).
Site Solar Index is based on the amount of land available. Solar feasibility on open lands is impacted by their ability to utilize economies of scale. Open lands do not have onsite loads and are only cost effective if they are large enough to utilize economies of scale.
● Blue (promising): 20+ acres
● Gray (fair): 5-19 acres
● Red (poor): 0-5 acres
The solar suitability score addresses the suitability of the larger site for a ground-mounted solar array. The score is based on the following criteria: Competing land uses, land slope, direction of slope, elevation, solar radiation, distance to transmission lines, proximity to dense population, tree coverage, and road density. Click on (Link) to see the reference suitability maps for rest areas and open lands.
● System size and cost is determined by how large of a system the land parcel will allow.
● Further considerations. Once a site is selected for further study, it is important to “ground truth” a site to verify suitability. Here are a few factors to consider:
● Infrastructure. A large ground-mounted solar array must connect to the electric grid. Check on whether there are any electrical distribution or transmission lines preferably within 1.5 miles of the site.
● Utility delivery provider. We have listed the area utility provider(s) based on the site location, but it is important to verify which is serving the site. These types of solar systems are eligible to apply for grid interconnection with Ameren Illinois, ComEd, and MidAmerican. Grid interconnection is often less economically feasible in the territories of Rural Electric Cooperatives and Municipal Utilities.
● Land. Does the parcel have significant slope or tree coverage? The suitability scoring includes slope and tree coverage, but sometimes the scoring algorithm doesn’t account for localized site conditions.

This map shows the locations of IDOT interchanges. A ground-mounted solar array may be developed on these sites. Feasibility is best when the solar system can be connected to a lighting system or other significant electrical load located on site. The colors of the dots indicate that the site has promising suitability (blue), fair suitability (gray), or poor suitability (red). Click the dots for more detailed information about each site.
The Site Solar Index is based on whether the interchange has a controlled intersection (stop/yield) or not. Sites without a controlled intersection are rated as poor as installation and maintenance could inhibit the free flow of traffic through the interchange, and approval by FHWA is generally less likely.
● Blue (promising): Controlled intersection
● Red (poor): No controlled intersection
Solar system details are determined by the loads (how much electricity is consumed on site). The system is sized to meet the estimated electrical load on site, and the system cost is estimated for a solar array of this size. A solar system can be sized smaller but not larger than what is needed by the electrical load on site. Actual sizing depends on the amount of suitable, available space on the ground. System area indicates the estimated amount of space required (in square feet) for a solar system.
● Further considerations. Once a site is selected for further study, it is important to “ground truth” a site to verify suitability and refine the sizing estimate. Here are a few factors to consider:
● Land cover. Steep slopes and significant tree coverage can impact feasibility. Ditches and areas with standing water are unsuitable.
● Electrical connection. To support a lighting system or other electrical load the solar system must be near to the electric meter, panelboard, or controller for the load so that it can be connected.
● Utility delivery provider. We have listed the area utility provider(s) based on the site location, but it is important to verify which is serving the site. Properties served by Rural Electric Cooperatives and Municipal Utilities have different rules for solar that may affect system sizing and connection.
● Actual site electricity use. On site solar systems are sized according to actual site electricity use and site conditions. 10 kW of solar system capacity could generate approximately 13,000 kWh/year and requires about 20,000 square feet of space.
● Future site changes. Site improvements and capital projects may change electricity use or impact solar system performance. Solar sizing and site location decisions should account for known or likely future site changes.

This map shows the locations of IDOT facilities and lands. This includes offices and maintenance yards, rest areas and welcome centers, open lands, and IDOT interchanges. Feasibility is best when the solar system can either be connected to a lighting system or other significant electrical load located on site or of a large enough scale to take advantage of economies of scale. Each category of locations may be found in its own map for easier viewing. The colors of the dots indicate that the site has promising suitability (blue), fair suitability (gray), or poor suitability (red). Click the dots for more detailed information about each site. Refer to the individual maps for more detailed descriptors.

These maps were produced using a variety of metrics to determine a rating system useful for large scale arrays that are larger than 20 acres. The background color displays the ratings of individual dots that are 30x30m each. The points show the average rating of the IDOT parcels with provided boundary data. More saturated point colors indicate higher suitability ratings. Ratings are not absolute and there may be localized field conditions that may make a site better or worse than the rating may indicate.
● Further considerations. Once a site is selected for further study, it is important to “ground truth” a site to verify suitability and refine the sizing estimate. Here are a few factors to consider:
● Land cover. Steep slopes and significant tree coverage can impact feasibility. Ditches and areas with standing water are unsuitable.
● Electrical connection. To support a large array, proximity to grid would be beneficial so that the array can be connected.
● Utility delivery provider. Each utility provider has different rules for solar that may affect system sizing and connection complexity and cost.