I responded to a question in an LED lighting thread on stock talk that may be of interest to others considering solar panels. This is based on one year's actual data from my three systems in SW WI.  In other areas your time to pay back may be shorter (south) or longer. I do think it is pretty consistent that putting money into PV Solar almost always has a much better/shorter payback than money in a bank savings account or most investments. In addition, after the payback period you are producing electricity basically for free.  My goal is net annual farm + home electric bill of zero.  This is a grid tie system and I do pay my share of maintaining the grid...

For anyone interested here is my ROI post:

I just did a presentation locally this week focusing on ROI in a PV Solar system. This was based on my actual output numbers for one year on my 3 different systems: roof top mount, ground mount and tracker mount.

There is a lot more to it than can be discussed here or in an email. Site possibilities, needs, local utility requirements and policies, etc.

However there are 2 websites with a lot of information and that offer complete systems for sale:

Here are two DIY grid tie systems I compared on a PER PANEL basis, no labor, freight, wiring from the array into your main panel, etc.

one central inverter system from AltEstore

one micro inverter system from Wholesale Solar

Note these include no electrician, install labor etc. You WILL need some knowledgeable local help.

On a per panel basis, based on my actual output here in SW WI over the past year, and based on either a home-made ground mount or a roof top mounted system (if you have a south facing roof at around 37 degree angle with a clear view of the sun through the day) here are my payback numbers on these two systems. A lot better than passbook savings in the bank and many other benefits.  My presentation was over 90 minutes. I can't get into any more details here. Sorry about the email but I had to take it off as I was getting more emails than I can possibly reply to while raising cattle, teaching physics, etc. Part of my spread sheet of results. Values in US $

edit to add: My optimum tilt angle for my location is 37.5 degrees. Yours may be different. Comparing my output from my 37 degrees ground mount and from my 4/12 pitch (18 degrees) hay shed roof top mount, the angle difference made a 12% difference in annual production, 37 degree being higher output.

Find your optimum solar panel tilt angle here. Someone did some great work on this.

Also, the numbers below are calculated at an 11 cents per KWhr electricity rate. If your utility rates are higher, payback will be quicker. My SolarWorld panels and Enphase micro inverters are guaranteed for 25 years. So for most of their expected life they are producing electricity for free.  They should last longer than 25 years. What changes is their output. Other components may deteriorate sooner.

I hope this helps.

further edited to add: I prefer the monocrystaline SolarWorld Panels and Enphase microinverters for performance, monitoring, snow tolerance, longevity...   However they are more expensive initially than the polycrystaline, central inverter systems but I have included both for payback comparison.  And yes I have simplified the payback. Installed costs will actually be a bit higher than shown but these numbers are in the ballpark for a partially DIY installation.