Solar sizing tool
This XLS file allow a quick look at scenarios for the financial viability and payback times of different solar photovoltaic systems.
Download ZIP file
Note that this is Version 7 of the tool, released on September 16th 2012, and now has an ability to input usage based on annual, quarterly, or monthly averages, an ability to adjust solar irradiation for specific regions, and also an ability to give estimates on key behavioral and equipment variables - namely, the number of occupants at home during sunlight hours, and the house's type of hot water system.
The first thing you may notice is that an 8c Feed in Tariff makes solar PV far less able to pay its way, particularly large systems on houses with low levels of electrical consumption.
Note that there are editable fields on the first workpage of the tool. Have a play with these to see what kinds of electricity charges, FiTs and system prices are required to allow systems to be paid-for within what most consumer consider viable, which is less than 7 years.
If you'd like me to include this or anything else - or if you have any other questions, comments, etc - please contact me and I'll do what I can to help out.
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