If you step back and think about it, installing a solar system (PV or Solar Thermal) requires a strong knowledge or trade experience in structural design, roofing & waterproofing, electrical and/or plumbing, and probably carpentry.  Sometimes even steel work.  But I think a lot of folks forget mobilization, which is arguably the most important aspect.

Mobilization is really the lead-up to working on a site.

It can include a lot of aspects of the project.  I like to include things like the morning safety meeting and cleaning up the site at the end of the workday.  It also includes travel, planning for safety, putting up and taking down the ladder every day.  Basically the little stuff.  And it adds up. Accounting for it just requires a little diligence: thinking through a whole day.  I once bid a solar project that was complicated and I thought I had accounted for everything.  I spent a fair amount of time on it.  After it was complete, I reviewed the build data and found I had bid under.  

Further investigation showed that the mobilization costs were almost double my estimate.  It turns out that despite being new construction, just getting to the roof was a bit of an ordeal.  Mostly because the array was spread out on 5 different roof planes over 4 different stories.  Talking to the crew, I learned the simple act of getting from the truck to the roof took 10 minutes (absurdly there were things like walking to the other end of the building, climbing out of a window, walking around a corner to a ladder, climbing up the ladder, walking to almost the other side of the building to climb another ladder to get to the top).  A crew of 4, 10 minutes each way, twice a day they each make the walk, translates into about 2.5 hours every day.  Double my estimate.

Keep Transitions in Mind.

Bringing us back to the aspects of trades, you must keep in mind transitions.  My crew does their best to foresee the tasks ahead.  But when juggling 4 different trades and the tools that go with them, trips back to the truck are going to happen.  The bigger the project, the less that kind of cycling occurs.  That’s because the team gets on the roof, or in the field, and they do one trade at a time;  Installing all the racking or all the posts.  Unless the project is phased.  Roof 2 gets all the posts while roof 1 is already in the module installation phase.  

Ever since the crazy roof project, I take a peek at the access to the roof and how many levels it will be.  It turns out it can impact your costs more than you think!