Welcome to day 3 of this short 5-part series following the progression of a utility solar project from idea to interconnection. Today we touch on Detailed Design.
“It all works until you get down to the details”, that is what my dad used to say. Hopefully once you have passed through the Feasibility and Preliminary design phases you won’t come to a point in the Detail Design phase that kills the project (see day #2 for some important helps with that).
Detail design is where drawings, written specifications, etc. specify the final configuration and layout of the equipment, the materials with their quantities, and very importantly specifying information used during construction.
It all Looks Good on Paper
I learned early in my engineering career that just because it looks good on paper, it doesn’t mean that that it can be built. I also learned that sometimes it’s better to let the construction contractor follow best practice rather than for me to dictate all the details.
The detail design in a solar project carries the characteristic that a single “error” can have the multiplying effect. It can impact of thousands of connections, or pieces of equipment. One example is a simple thing like specifying the type of wire tie-wrap. One type will last for years, one will degrade in a matter of months. Since there can be 10,000+ tie wraps, if they embrittle in the sun and need to be replaced, that simple error can lead to large rework and warranty costs. Specifying a structural bolt that carries with it the need for specific testing can lead to huge costs, not because the bolt won’t do the job, but because the bolt specification requires testing. The wrong corrosion code for the steel piles is something we have seen. Imagine finding that once you have 8,000 piles in the ground. Easily overlooked is specifying cable cuts to minimize the leftover cable on the reel. This is a “real” problem in cases where splicing is not allowed for underground cables. If this isn’t considered when the cable is being purchased, the entire construction schedule can stretch out waiting for more cable from the vendor. Delaying construction is very costly. The list goes on and on.
Who’s on First?
One of the difficulties in our industry can be that projects are “piecemealed” together. One company will do the Feasibility, another Preliminary Design, and yet another Detailed Design. Because different engineering companies have different ways of doing things, specifically how all the different drawings and specifications work together, having a properly integrated final design package can be a problem. If one drawing refers to another drawing, or one specification refers to another, someone needs to verify the validity of the reference.
Successfully completing the Solar Detailed design phase requires experience engineer working with people who have installation and construction experience. Often companies will send their engineers to the field to get a good dose of reality. Some companies lean heavily on standardization of design, some are very good at capturing lessons learned and maintaining a knowledge database. All are good strategies and have their pros and cons. There is little substitution for experience and not rushing through the Detailed Design Phase. You can, but likely will pay a big price in the construction phase.