[NH.Solar]

Descant,
If you already have an automatic whole house generator then battery backup to a solar system probably wouldn't make sense for you. You already have a bought and paid for backup system in place and all the solar storage would gain you is 10 kWh of daily self consumption. At the current 16 - 19 cents/kWh that the local utilities charge, the extra cost to add a battery, specialized inverter and the needed peripherals just wouldn't be worth it. If you didn't already have the whole house generator and were gaining both the advantages of self consumption and backup power, that would be quite a different story.
The bump to add 10 kWh of storage to a solar system is about $11K. I don't sell generators but my understanding is that a 10 kW automatic generator installed is somewhere around $8K, so the upfront cost is less for a generator if you are only looking for backup capability. The additional ability to harvest energy from the sun daily, store it, and consume it directly in the home during the evening is where the solar storage has an advantage over an emergency generator and can be financially justified.
The LG RESU10H battery we last installed has a warranty or 10 years or 27.4 mWh of energy. At the current rate of 16 cents/kWh that the Co-op charges the battery should produce $4,384 of energy in its warrantied life, about 2/3 of the current cost of the LG battery. But bear in mind that the battery will not require any fuel or maintenance, and that the utility rates will in all likelihood rise as time goes on. Plus it has the additional benefits of being a silent and non-polluting source of energy. I would imagine that there would be some sort of recycling charge when it comes time to replace the battery, but also suspect that by then the cost to purchase a new one will be half of what it is today. Plus this assumes that the battery fails on the exact day the warranty expires, but I would hope that it would continue to function well after that date.
A solar system with battery backup makes sense for a home that doesn't already have an existing backup system. For a home that already has the emergency backup in place (yours??) a simple solar array with no storage other than the grid is usually the best option. As PeterG well explained the utility companies charge you about 25% to store and return your excess solar production, but you are still well ahead of the cost of purchasing purely grid provided power. The least expensive installs are roof mounts and if you have a favorable southern exposure the payback for a simple solar system would be about 8-9 years at the current utility rates and discounted net metering ratios.