tim.... wrote:

Expected output 2928 kWh per year.


Expected on what basis? (tell us the panel area, roof slope and approx.
location (nearest city) and someone will be able to check the numbers)

What's the cost of capital? (lost interest)

If she has a mortgage the interest rate on the capital is of course the
mortgage rate. IMHO this will soon rise and she may prefer to pay off
the mortgage and know where she is, rather than effectively borrow money
to buy the panels.

Andy