TRNSYS is a flexible graphically based software environment used to simulate the behaviour of transient systems. TRNSYS is made-up of two parts. 
The first is an engine (called the kernel) that reads and processes the input file, iteratively solves the system, determines convergence, and plots system variables. The kernel also provides utilities that (among other things) determine thermo physical properties, invert matrices, perform linear regressions, and interpolate external data files.
The second part of TRNSYS is an extensive library of components, each of which models the performance of one part of the system. The standard library includes approximately150 models ranging from pumps to multizone buildings, wind turbines to electrolyzers, weather data processors to economics routines, and basicHVAC equipment to cutting edge emerging technologies. Models are constructed in such a way that users can modify existing components or write their own, extending the capabilities of the environment.

Price TRNSIS 17 (2014) : 4500 €
TRNSYS Solar simulation software