If I mount a flat surface which points to certain constant direction. At certain place of the world. I now need to estimate the maximum amount of Solar radiation energy which this surface can get during certain time.
Is there a PC program or an algorithm that can make this estimate for me?

The actual problem.
I need to know how much maximum energy can I get during a year, if I put solar cells or solar collectors on my house tilted roof?

Is there anyone who can somehow help me?

Thank you in advance.