Pros
If you have great ideas for R&D, there are a number of ways to capture funding. This is with the caveat that your research has to align with DOE and NREL goals.
Cons
NREL is also a place where, for many people, where careers go to die: 1) Few opportunities for advancement 2) The office politics are ridiculous, especially when funding gets tight. I've never met a more insecure group of people then when dealing with scientists and engineers. 3) If you make a mistake, then forget about advancing your career. 4) NREL will pay for you to get a graduate degree, but don't expect a salary boost. I know managers that have told people that a degree earned while at NREL is worth less than if you had it at the time you were hired. Bottom line -- If you are in R&D, position yourself to become a line manager or a task leader. If you miss, then your career will stall.