The answer is always: it depends.
If all you're looking at is an economic viability of PV/battery for your home then you have to consider a whole array of variables to make the determination whether solar makes economic sense for a given situation and with a given known set of paramters.
Just to name the few critical ones:
1) Cost of the install. This is most easily expressed in $/W. It is one of the biggest variables. You also have to take a guess as to PV in the future will be less or more expensive. If PV prices will drop in 2 years time it might even make sense to postpone a purchase even if it was net positive to make that purchase today.
2) Total estimated annual production. It can vary widely by location anywhere between 4 hours to 6 hours of average production per day which can have the same effect on ROI where 6 hours would make sense but 4 hours would not. This variable can also be impacted by your individual situation ie. can you place all panels in an optimal southern facing location with no shading and ideal angle, or are you more limited to put them facing east/west on a less than ideal roof slope.
3) Life expectancy of the system. String inverters may last as little as 10 years, panels may go as long as 30. What is the estimated maintenance cost over the life expectancy of the system? Even if a part is guaranteed for 30 years, cost of repairs can be significant if you have to have someone come and replace microinverters on your roof or panels need swapping. What if you need to replace your roof during that time, did you account for the labor involved in removing and replacing the perfectly fine and working panels?
4) Price of electricity. If the electricity is cheap ROI will be much longer. If electricity is expensive, ROI will be much quicker. Do you anticipate prices going up or down in the future? If you do, by how much? Will it be matching that of inflation or significantly more/less?
5) Tax credits/subsidies? Is there some kind of government incentive on installing solar where you live? If yes, it can change your equation and net cost in a significant way.
6) Do you have Net metering? More than likely you no longer can expect watt for watt return on your solar production and you have to face the possibility that some or most of your production will not be of value to you, certainly not at 100%. If you do not have net metering, what is your estimated self consumption ratio? Do you get anything for power you're loading onto the grid? If you have peak demand pricing you might be coming out better if you put power on the grid when cost is higher rather than self consume/conserve. If you don't have net metering and you want to optimize self consumption you either have to go with a smaller system or you have to add some kind of battery storage for additional cost, also negatively impacting your ROI.
7) What is the opportunity cost of the money you're spending on solar? Could you get better ROI on your money had you invested it than purchasing the solar setup? Could you have avoided interest cost had you not financed it? These are all variables that should be considered from a financial perspective.
As you can see there are a lot of variables, many of you may not have the ability to control or even know making the simple question of whether solar is a wise economic decision far too difficult to answer.
Having said all this there are also other factors that are even harder to put a monetary cost/benefit to:
1) Are you DIY? Is the experience of installing and owning a solar setup a net positive or negative to your life? Is it a hobby that brings you joy, or is it an extra thing you need to worry about going forward?
2) How reliable is your alternate power source ie. generator or grid? Is the cost of having your own system benefits you enough in peace of mind of being partially or wholly independent from another source?
3) Do you feel good/bad about the environment and your own impact on it? Are you willing to bear some of the economic cost of a greener energy production, if there is a cost associated with it ie. your ROI is a net negative in terms of pure financials without accounting f or externalities?
I have created a spreadsheet that should allow everyone to play with their own numbers and see if the financial ROI is even there before they try to answer and put cost/value on the externalities and intangibles.
Sheet1 Solar Cost,3.4,$/W,This is the <a href="https://www.consumeraffairs.com/solar-energy/how-much-do-solar-panels-cost.html">installed cost of a Watt of PV</a> Average Solar Hours per day,4,hours,Number of hours of sunshine in a day, ranges between 4-6<a href="https://www.solar-electric.com/l...
docs.google.com
You should be able to make a local copy of the spreadsheet and play with your own numbers. The numbers in the sheet reflect what I'm expecting out of my system at my location based on my panels, their orientation, and my total cost including batteries. My ROI is about 14.2 years not accounting for inflation and about 10.7 years with a 3% inflation. This also does not account for all the other benefits I receive from having most of my consumption covered via my PV setup and the added resiliency and backup benefits.
