Here are a couple public free downloadable programs for properly designing a solar array and other renewable energy projects.
Both are government sponsored and have loads of capability including photovoltaic and concentrating systems, wind, geothermal and energy efficiency measures. The first is from NREL (The National Renewable Energy Laboratory) and is called SAM (System Advisor Model) and is available for Mac & Windows. The second is called Retscreen International, a Windows-only package built by the Canadian government. Both have selectable sun hour data from various sources and include financial calculations built beyond common man capability.
Of course, you could spend some dollars by purchasing a program like CPFTools, Ongrid or PVsyst, but before you do, give the free programs like SAM a whirl. You’ll be surprised at what they offer for the price!