Managing PV Installations with a Gantt Chart
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A project schedule is an important tool for managing a solar installation. A schedule allows the project manager to schedule deliveries, crews and subcontractors; to track progress and costs on a project; and to anticipate and prevent delays. It is much more than a mere list of activities with start dates on a calendar.
The most common format for a project schedule in the construction industry is the Gantt chart, or bar chart, named for its creator, mechanical engineer and management consultant Henry Gantt. This schedule in graphical form helps project managers and crews visualize timelines and interconnectedness for a project’s scopes and corresponding tasks. You can create it manually or with a computer program, but in either case you do so based on project-specific information.
Before creating a Gantt chart, you must develop the supporting information in the form of a work breakdown structure (WBS) and a network diagram. In this article, I use the terms schedule and Gantt chart interchangeably. I review the steps to develop a Gantt chart and describe how to use it effectively to manage PV installations.
Developing a Gantt Chart
Ultimately, a Gantt chart is only as good as the information you use to develop it. A WBS organizes and defines the scope of the project using a hierarchical structure, similar to an outline or an information tree with multiple levels. The network diagram identifies the relationships among the activities.
Step one: Establish a WBS. The top level of the WBS is the project, which represents the entire scope of work and all deliverables. The project consists of smaller, distinct scopes of work called work packages. The project manager often divides work packages according to responsibility, with the entire package assigned to an individual, department or subcontractor. Each package contains the activities—and sometimes smaller internal work packages—required to complete all work for that package. A work package is considered finished once the team has completed all of the activities and work packages inside it. You should assign a descriptive noun to each work package. Figure 1 shows the location by level for the three major components that make up a WBS.
Activities are the individual tasks the project team performs. Each activity has associated time and cost estimates. In Figure 2, graphical bars depict activities in the schedule, and thinner graphical bars with triangles at each end represent work packages. You should describe each activity with a verb, since activities consist of actions.
You can divide a work package into successively smaller work packages. The process of subdivision must follow the 100% rule, which dictates that the subitems of a work package must add up to 100% of the work package. You should define and organize activities so they do not cross over to other work packages. If an activity does not fit into one of the work packages, then you need to add another work package or redefine the existing ones to ensure that they capture all aspects of the project. The 100% rule ensures that nothing slips through the cracks and that you account for all time and resources when planning the project.
Refine the work packages and activities so you can practically track and manage each level. The structure varies depending on the project and the company doing the installation. Smaller, more refined work packages give the project team more control and visibility, but at the cost of greater overhead. In theory, you could refine work packages all the way down to individual PV modules, with detailed activities such as installing a bolt, tightening a nut and so on. However, you would then need to estimate, track and record the data for each of these activities. Trying to manage at this granular level would put too great a burden on the project team and would drive the installers crazy. With practice, you will find the sweet spot that offers the right level of management and control for your company.
Figure 3 shows the WBS for a 100 kW rooftop PV installation. The first level is the overall project; the second level divides the project into three work packages (project management, structural installation and electrical installation); and the third level shows the activities in each package.
Project managers may be tempted to forego the WBS and just define the project activities in a simple list. This approach limits the effectiveness of the schedule and does not allow you to use the planning and control methods described here.