Sasquatch: Three months ago I did a detailed analysis for my son and his wife to spend $35,000 for a Grid Tie Only system.
By training I am a CPA, Computer Systems Analyst and a Paralegal. My specialty was business analysis and turnarounds. I spent a lot of time building spreadsheets to forecast the financial future of decisions. I share this to tell you that I am not new at doing a mathematical projections/analysis.
My advice to them was that to project out 30 years of future power costs in today's world of financial fraud was impossible. I could not advise them that in 30 years they would recover their investments, especially factoring in damaged equipment, added insurance costs, unknown repair rates, Value of the dollar changing and crazy interest rates, etc.
Instead I convinced them to invest in silver because that could be calculated out and gave a much GREATER return on investment than just hoping to get your original solar investment back.
So instead they drew out $45,000 from a pension fund, used some to pay taxes and penalties to IRS and the balance was invested in silver. This should yield them $2 to $4 Million on the backside of the financial reset, whatever it is going to be.
And to my surprise, they added to the solar system equipment and installed a $50,000 Grid Tied system with a Tesla battery back-up system in the event of the grid going down.
In your case the Cash Flow Projection is even more difficult when you factor in the age of the system, higher repair frequencies and lower power production due to older technology. You must realize that if it is grid-tied, as PGE(?) raises power rates so too will they raise the "Buy Back rate" they will charge you for nighttime power.
So what does all this mean to you? If you are buying a grid tied system only, you are just tying up your purchasing power each year and gambling that that investment will never get you anywhere and instead will probably harm you. In other words there is no gain to be had but may be a loss in the long run. If you purchase the real estate I suggest you reduce the value of the Solar note by reducing the real estate purchase price or take back cash from the seller for the devalued solar system. Maybe you can use this cash to purchase silver!
I hope this helps in some way. Best of luck to you.