Can you provide me any info/reference etc. on the accuracy level in HOMER?

The biggest inaccuracy is that HOMER assumes that operators will operate the system in an "optimal" manner. This refers to both the control and dispatch of a generator and also to maintenance issues.  For example, the PV output will decline if vegetation is allowed to grow and shade the panels.  Also, batteries will deteriorate if they are allowed to overheat or overdischarge.  It also does not consider component failures.  There are also a variety of minor simplifications in the modeling of each component.