Advancing Your Solar Utility Project, Part 2, Preliminary Design

Welcome to day 2 of this short 5-part series following the progression of a utility solar project from idea to interconnection.  Today things get real with Preliminary design.  (For Day #1, click here)

Jumping Into The Deep End

Preliminary design is where excitement and dread start to come together.  It’s like that moment when you jump from the high point of a cliff towards the deep lake below.  Things get very real very fast.

Preliminary design in the renewables industry is often termed 30%.  Some clients however ask us to jump from 10% directly to 60% design as the preliminary phase.  Either way the intent is the same.

Roughing it Out

The preliminary design of a solar project is focused on solar collector layouts, locations for major pieces of equipment, roads, storm water control, and the like.  This work primarily involves Civil and Electrical engineers.  It pre-supposes that the Land Survey information and Geotechnical Report are accurate.  Often an initial PV panel layout is used as the starting point.  Sometime other land constraint information must be considered such as environmental zones, setbacks, etc.

Risks and Rewards

What we typically see are requests for preliminary design work that is only focused inside the fence line.  We also see incomplete survey or geotechnical information.  Sometimes this is acceptable, sometimes it presents a lurking risk.

Transmission Lines: Permitting and approvals outside the fence line is overlooked in a large majority of what we see.  A significant risk exists if the transmission line needs to pass through a parcel where access is denied.  Because the T-Line to the utility interconnect substation is typically long, overhead lines are best.  However overhead lines may be denied by local authorities then requiring costly buried lines.   Similarly examining the need for a local substation, or a project substation adjacent to the utility connection substation is often overlooked until later in the design process which can be a costly mistake.

Solar Racking Piles: The information gained from a geotechnical investigation and report is very important for many aspects of the site design, however there is a significant reward (cost savings) that can be realized by adding on-site pile driving and pull-testing.  This is something seldom done at the 30% stage but something that can save hundreds of thousands of dollars in the cost of the steel solar piles.

Boots on the Ground:  We highly recommend sending qualified, multi-disciplined individuals to the site at the 30% design stage whenever possible to visually verify the 10% information and look for things that have been missed.  This is roughly equivalent to sending out an engineering inspector to a commercial building that you might be considering purchasing.   

Some of the stories that come back from these trips never cease to amaze.  Stories like, “we found out that the owner who leased the property also signed a contract to allow cattle to graze” remind us that developing a solar project can be full of surprises.