This is a critical oversight of the analysis indeed - you have to normalize all of your $ figures to present value (or future value, or whatever point in time that you choose) otherwise they're not really comparable.
1) All needs to be done on a present value basis. Take what you are paying out today and then take each of the future year's savings back to today's present value.
As was mentioned in quite a few other comments, the financial viability of this project will heavily depend on local state incentives.
From what you are mentioning there are, however, two important factors that could impact your decision:
1) Volume: your overall consumption volume is based on a 5 people household with four staying at home all the day. Without knowing your particulars, it seems that from here on your consumption would most likely fall. Your kids probably moving out would be a big factor here. Once again I don't know the particulars of your household, but it's unusual to have 80% of its members at home and in the future if things were to change it would most likely go down (once again, a rough and general assumption). What about the house in which you will install the system - have you done renovations a while ago or are you planning to do this soon? That could have a big impact on how energetically efficient your home is.
2) Habits: in order to reap the full benefit of solar, it might potentially be interesting to look into changing some of your habits. As was mentioned in previous comments, if you go down the road of un-locked power prices things can get pretty wild: negative prices are, for example, a common feature of most power markets nowadays (though as an end-consumer you are usually protected from those wild swings). Every state/country has different generation profiles (for example California has a deep "duck shaped" price curve heavily dependent on solar, but the Midwest has stronger generation at night due to wind, and Northwest depends a lot on hydro) so that what you might be able to save varies quite a lot. For example, if you have an electric car, charging during the day when sun's actually out might save you quite a bit. Same for running dishwashers/washing machines. Once again a lot of local factors come into play here.
Statistics: Posted by tdgb — Mon Nov 18, 2024 3:30 am