Managing PV Installations with a Gantt Chart: Page 3 of 3

Using the Gantt Chart

Now you can start putting the schedule to work as part of your project management plan. You can use the dates on the schedule to accurately schedule equipment deliveries, crews and subcontractors.

Updating the schedule. Since large projects rarely go exactly as planned, you should expect that you will complete some activities ahead of schedule while others fall behind. You therefore will need to update the schedule periodically to account for actual progress. If you change or update one date or duration, all the other activity dates automatically adjust according to the relationships you have defined. With just a few clicks, you can see how a delay in one activity affects the start and finish dates of other activities and the overall project, and you can then adjust the timeline accordingly.

Following the critical path. When managing your project, you must focus on the schedule’s critical path, the series of activities that determines the finish date. A delay of one day on a critical path activity results in a one-day delay in finishing the project. For example, “Install PV modules” is a critical path activity for PV installations. If rain delays the module installation two days, that has a two-day impact on the project’s projected completion date.

Some activities not on the critical path have float or slack time, which is the number of days you can delay a noncritical path activity before it becomes part of the critical path. For example, if an activity has 5 days of float, it can take 5 days longer than scheduled without affecting the overall project. If the activity is delayed past 5 days, it becomes part of the critical path, and additional delays push back the project completion date accordingly.

Since the critical path determines the project’s finish date, the project manager must understand which activities are on—or may become part of—the critical path and ensure that they finish on time. As the project progresses and activities finish early or late, the critical path can change, which is why updating the schedule is important.

Crashing the schedule. Just as a delay on the critical path can cause a delay in the schedule, if you complete the critical path activities a day early, the project can wrap up a day early. Project managers can use this to their advantage and crash the schedule, applying additional resources to an activity to complete it faster. You can assign more crewmembers or have the current crew work overtime to finish it earlier.

However, crashing is not usually the most cost-effective way to manage a project. Doubling the number of people on the roof probably will not cut the activity’s duration in half because crewmembers will be bumping into each other, which slows down productivity. In addition, overtime pay rates increase the project’s direct costs. That said, if the contract has a liquidated damages clause, the cost of crashing may be less than the cost of paying penalties for project delays.

If your project is behind schedule and you decide that the additional cost of crashing is warranted, it is essential to know the critical path and understand which activities to focus on. Only crashing the critical path activities will get you caught up. If you spend a weekend working on noncritical path activities, you increase the cost of the project but do not catch up to the schedule.

Earned value analysis. Scheduling software can take your schedule to the next level by analyzing project performance using metrics such as earned value analysis (EVA). Enter the actual project time and expenses into the scheduling software to compare planned to actual progress. You can determine whether you are falling behind schedule or going over budget. If an activity or work package is only 25% complete, but you have already used 75% of its allotted resources and funds, an EVA will show you that the project is going over budget and allow you to take corrective actions.


The Gantt chart is an essential tool for any solar installer or project manager. The schedule allows you to plan your crew assignments, schedule accurate material delivery dates, track actual against planned progress, give advance notice when a project is at risk of going over budget or falling behind schedule, and identify where you should focus your resources to correct issues or delays. At the end of each project, you can compare the actual schedule to your estimated schedule, and use that information to plan and estimate your next project more accurately.

Richard Ivins / Pure Power Systems / Hoboken, NJ /

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