Critical Chain Solar Project Management: Page 2 of 3

Why Use Critical Chain?

Between 2009 and 2013, national-scale residential solar businesses, such as SolarCity, Sunrun, Sungevity and Vivint Solar, attempted to standardize project delivery to support their growth ambitions. They developed and used project management software while predetermining acceptable site and project criteria. Unfortunately, solar projects—regardless of market sector—have more in common with custom home building or remodeling than with factory work in that each project is custom.

Timelines for some solar project tasks—such as receiving permit or interconnection approval or addressing special site conditions—can add anywhere from a week to a year to a project schedule. Delays can easily compound or threaten the budget. So how do project developers balance project payment milestones and task delivery schedules to minimize risks?

This is where a project management technique such as critical chain comes in. To illustrate, let us step through the mechanics of critical chain project management.

Mechanics of Critical Chain

Unlike traditional project management methodologies that evaluate project progress in terms of individual tasks, critical chain manages projects to your resource limitations, such as availability of engineers to produce permit-related documents, and substitutes individual task completion buffers with one large buffer at the end of the project. When a project experiences a delay, project managers can focus on the specific activities that most impact the buffer and intervene accordingly.

In this framework, the project management resources are people and their capacity limits for completing tasks. The role of the project manager is not to name tasks and line them up, but rather to understand resource capabilities and project completion requirements. Critical chain project management incorporates three types of buffers: an overall project buffer, feeding buffers and resource buffers.

Project buffer. Project managers use the overall project buffer at the end of the project between the final task and the completion date to monitor project timeliness, as shown in Figure 3. Ideally, delays on the longest chain of dependent tasks will eat away at the buffer but leave the completion date unchanged. Unlike a traditionally managed project that has time buffers built in to each task, the total project buffer allocated in a critical chain will be smaller than the sum of all individual task buffer times of that traditionally managed project.

Feeding buffer. Feeding paths are those tasks that are not on the critical chain. Delays from feeding paths can impact the project by delaying a subsequent task on the critical chain. To protect progress, project managers insert feeding buffers between the last task on a feeding path and the critical chain. The total duration of the feeding buffer should be half the size of the sum of safety time taken out of the feeding path.

Resource buffer. Project managers use resource buffers to account for the human elements of a project. This buffer addresses who is available to perform specific tasks, as well as any constraints they have in terms of skills, capabilities and tools. Resource constraints are the hardest project variable for project managers to change and are often what prevents completion of a project in the shortest possible time. Therefore, project managers must generally elevate resource management above other concerns and plan to take these constraints into account.

Once project managers set these buffers, they can monitor project health and timeliness by watching the buffer consumption rate rather than individual task completion to keep everything moving forward on schedule. This keeps a project manager from unnecessarily riding herd on feeding tasks that are running late but that will not significantly impact the critical chain.

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