NREL is now the National Laboratory of the Rockies (NLR), and its tools have moved to nlr.gov. The links on this page point to the new addresses.
The System Advisor Model is NLR’s free techno-economic modeling application. It couples a physical performance model with a financial model, so the same run produces both an hourly production profile and a set of project returns. It covers photovoltaics from residential through utility scale, battery storage, concentrating solar power, wind, geothermal, biomass, fuel cells, marine energy, and solar water heating.
On the financial side SAM includes behind-the-meter residential and commercial cases, grid-connected PPA projects, and third-party ownership structures. That combination is the reason it shows up in so many analyst workflows: you can change an engineering assumption and immediately see what it does to the returns, without exporting a production file into a separate spreadsheet model.
How it gets used on a real project
SAM sits between PVWatts and a full commercial model. It is the right tool when you need defensible production plus economics and you do not yet have a bankable energy assessment or a lender-reviewed financial model. It is also the most accessible way to build real intuition about how tilt, DC/AC ratio, degradation, and a PPA escalator interact, because you can move one input and watch the whole chain respond. Analysts and engineers use it heavily; it is free, well documented, and backed by NLR.