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  • Writer's pictureAlison Brown

10% Preliminary Design Milestone

Updated: Nov 17, 2022

As discussed in last month's post "Design Milestones", integrating engineering into project development milestones helps reduce risk and increase the likelihood of success for portfolios of projects. Over the next few weeks, we will review how each major engineering milestone, 10%, 30%, 60%, 90%, IFC and As-builts, can be planned around major schedule

The 10% Design Milestone is the preliminary stage of design. It is typically used to understand the high level feasibility of a project. It seeks to answer the following questions:

  1. Does the available land provide space for adequate power generation?

  2. Is the layout compatible with the zoning code and land owner’s requirements?

  3. What type of equipment will be needed to satisfy the project’s needs?

  4. What type of upgrades must the utility perform to support the change in power on the local grid?

A preliminary 10% layout is frequently completed years before final project commissioning, and with the rapid pace of technology improvements, it is inevitable that the solar panels, batteries or EV charging equipment will change multiple times over the course of the project. This means the exact make and model of the equipment does not need to be defined. However, for all technologies a few questions need to be defined:

  1. Where is the project going to be located? A site address, or latitude and longitude coordinates is enough to make assumptions about property boundaries.

  2. Where is the intended point of interconnection? This will define gen-tie lines and any interconnection facilities likely needed.

  3. What is the product type? Fixed tilt or tracking solar? Containerized or individual battery stacks?

With answers to these questions, experienced project designers can draft an initial site plan and single line that will be constructable and accommodates future design modifications. While many developers rely on internal resources to put together these preliminary designs, we think that engineers who are getting constant feedback on designs under construction will create initial deliverables that ultimately save time and money. Once the 10% plan is completed, a few processes can get started.

  1. The layout can be included as an exhibit to the land option agreement

  2. The drawings can support the interconnection application as soon as site control is established.

  3. An RFP can be issued to equipment integrators for preliminary quotes.

  4. The site plan can be presented for a pre-application review with the local planning department.

Do you need a 10% design completed for your project? If so, contact us at! We would love to support your projects with informed, quality engineering. Even if we are not the perfect fit for your needs, we will introduce you to our many other engineering contacts in the industry.


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