Evaluating Solar Energy Sites

Tip for Project Success

Know the difference between a screening and a feasibility study.

  • A screening is a high-level analysis, usually conducted when the system is owned by a third party.
  • A feasibility study is a more in-depth, usually conducted when the agency owns the system.

Evaluating the solar energy site is the third step in planning for a federal site solar project.

This section outlines the detailed information needed to evaluate specific sites for solar energy installations. These findings may be available from an agency-wide solar screening if your agency has one, or they may need to be compiled by the solar project team. If no solar screening for the site is available, the team can start with a self-guided solar screening using the attached checklist.

  1. A project solar screening, which is a high-level, preliminary analysis used to determine a site's likely viability, and
  2. A project solar feasibility study, which is a more rigorous engineering and economic analysis to define specific system design considerations for use in requests for proposals and/or scope of work development.

For projects that propose to use alternative financing, a project solar screening is sufficient to proceed. For agency funded projects, a solar feasibility study is recommended. The points that both types of solar evaluations should cover are defined in the sections that follow.

If the team finds that the site screening doesn't cover all the issues relevant to the project and site, a more complete feasibility study should be obtained. To determine what resources might be available based on the specifics of a project, call FEMP (202-586-5772) or hire a private contractor to perform the study. Be sure to address all the relevant points listed below based on the individual site. If the screening or feasibility study covers all of the relevant issues but the quality of the report is questionable, a first-order check can be performed using the solar screening evaluation checklist located in Appendix B of the printed publication.

Project Solar Screening

Photo of five rows of solar modules that are in the shade structure of a roof. The modules are encased in cement.

Alfred A. Arraj U.S. Courthouse in Denver, Colorado, has a photovoltaic system installed in the shade structure. It is the first federal courthouse to get PV glazing.
Courtesy of Atlantis Energy Systems, Inc.

A project solar screening should provide structural or mechanical considerations and economic considerations.

Structural or mechanical considerations include:

  • Roof condition, manufacturer's warranty, and age of roof (if considering a rooftop system)
  • Shading analysis (identification of obstructions that might shade the array location)
  • Available square footage for a solar system
  • Preliminary estimate of the system's size
  • Structural issues and—if the system is to be mounted on a building—height considerations
  • Historic building issues (if the system will be on a building that could be a historic property or is located in a historic district).

Economic considerations include:

  • Cost of energy (electricity and fuels) at a site, plus any details of rate schedules that could favor or penalize solar
  • Economic analysis of project (e.g., simple payback, internal rate of return [IRR], net present value [NPV], life cycle cost [LCC], projected savings)
  • Estimated annual energy production
  • Hot water or space heating demand
  • Incentives (federal, state, local, utility, RECs) and their time sensitivities.

Project Solar Feasibility Study

A project solar feasibility study should encompass the following in addition to the project solar screening components above.

Structural or mechanical considerations include:

  • Capacity of the local industry to supply and maintain such systems
  • Utility interconnection issues (if planning an electric project, it's important to know whether the utility has special hardware or contractual requirements)
  • Electrical room or mechanical room issues (e.g., space for equipment, alternate location, capacity limits, access between system and equipment room).

Economic considerations include:

  • Recommended system size
  • Site load requirements (these should be checked against system sizing)
  • Analysis of 15-minute load data for peak demand
  • Estimated monthly peak production
  • Annual operations and maintenance (tasks, annual costs)
  • Magnitude and timing of the electric and heating loads at a site
  • Size, condition, and efficiency of existing heating systems.

After evaluation the site, the next step in the planning process is to consider requirements and recommendations. Also see the full list of steps in the planning process.