I have to assume net metering may change, to be less advantageous to homeowners, not soon but eventually. It may be that solar homes are grandfathered (for 20 years?) with the net metering terms in place at the time of installation.
I'm asking, not telling. But it's a factor in breakeven analysis.
Yes.
In some places in the US, the UK, and Australia, they are dropping the old way of allowing the homeowner to pump electricity into the grid and then to be able to pull out the same kWh later. The reason for that is sound, that is peak solar production does not coincide with peak demand periods. One hour you have more electricity than anyone can use, and the next hour you do not have enough. One cannot bank the surplus power this way.
When there were few home solar systems, the above was acceptable, but they now have the situation where California had to pay Arizona to use some of the surplus electricity. I posted about this several times in the past.
Existing home systems are grandfathered, but with newly installed systems the homeowners may be paid only the wholesale price of their surplus power, at the time that is pumped into the grid.
With a home battery storage, instead of getting peanuts for their surplus power produced in the early hours of the day, the homeowner can store it himself for use later in the day, when electricity cost is higher. Thus, he gets more dollar value out of the same kWh that his panels produce, by saving it when he cannot use it, and using it later when it is worth more.
Some places including California have a rate schedule where the homeowner pays an additional penalty if his usage exceeds a certain threshold. The battery can be used for "peak shaving" by absorbing the power at low usage periods like at night, and releasing it in the mid-afternoon to offset the AC usage.
The only problem with using batteries for storage and peak-shaving is that the lithium battery wears out with each charge/discharge cycle. Tesla guarantees its Powerwalls for so many kWh of throughput, and the hardware has a built-in metering system to keep track of that, and to report back to Tesla.
Figuring out the cost effectiveness will take a bit of work. However, if one is using such a system for emergency power during periods of PSPS ("Public Safety Power Shutoff") because of high winds, the availability of the backup power is worth a lot more than the cost of the kWh. It is even harder to put a price on that.