Engineering, procurement, and construction (EPC) costs are hard to estimate. Changing a major supplier for racks, mounts, or converters means recalculating part of the project's cost estimate. The shakeout in commoditized solar module providers has not ended. The future bankruptcy of some mount maker means replacement parts will not be available after a localized system failure. The cost of procuring some potentially incompatible mount that requires further customization is a variable adding potential cost to a project's out-years.
One large solar tech provider, who shall remain nameless, argues that cost of capital is a major factor in solar's levelized cost of electricity (LCOE). I think that was true up until the 2008 financial crisis when the Federal Reserve lowered its interest rate target to less than 0.25% and kept it there. I also think developers in a low-rate era should concern themselves more with how soft costs detract from a solar project's bankability. Developers who apply the DOE EERE SunShot Initiative's soft cost best practices have a leg up in getting those estimates under control. Of course, if the Fed raises rates or loses control of the yield curve during hyperinflation, then capital costs will matter once again. Solar developers with long-term supply contracts will progressively reduce their inventory costs during a hyperinflationary period.
Free public resources help developers learn about project finance. The DOE EIA Annual Energy Outlook Documentation and Assumptions section has an excellent reference for estimating LCOE. Developers need good references to make robust estimates. The DOE's NREL Renewable Energy Project Finance site is loaded with tips on securitization and credit enhancements. The Solar Energy Industry Association (SEIA) policy page keeps developers current on tax credits and other incentives that mitigate project costs. Solar Industry Magazine's October 2013 edition had an excellent primer on preparing project finance. The article's coverage of the PPA's relationship with site details and off-taker financial strength is noteworthy.
Solar project finance help is as close as a Web search. You can all thank me later. I'll take my bow right now for keeping the best solar financing references out in the public eye.