Molten salt heat storage:
http://www.nrel.gov/csp/troughnet/thermal_energy_storage.html

Electrical storage:

http://electricitystorage.org/tech/technologies_technologies.htm

Fission & solar: That seems like a reasonable medium term approach.

Working fusion reactors: That's true, but nothing break-even, as far as I've heard.

Solar at night: off-grid systems manage that now with batteries. Of course then that makes the costs higher than grid-tie systems. I'd hope there'd be a better storage solution if we went much more heavily into solar.

Interesting to note, by the way-- solar and fission have similar problems with regard to needing a good storage solution. Fission is good for base load, but if fission were to provide more than base load, we'd need storage. I don't know if fusion will have that (hard to quickly ramp-up and ramp-down) characteristic or not.

So far noone has explained how we are going to run a solar society at night or shall we say after 6 pm.

We have been spoiled by having all of the energy we want available 24 hrs/day. As solar becomes the main thing available, we are going to have to adjust our lifestyles and our economy around its availability.

First and most importantly, we are going to have to adjust our lives to accomplish as much as we can during daylight hours. (Daylight is one form of energy not included in the above analysis, by the way. It won't be depleted, either.) Except for hospitals and emergency services, it just might not be possible to provide much artificial light after dark. Forget about shopping after dark. Industry will have to go back to a single daytime shift unless it is a continuous process that is so expensive and infeasible to shut down that the cost of nighttime lighting is worth it. Much industry will convert to daytime batch processing, though, powered by concentrating solar reflectors.

Households could use those wind-up lanterns to provide a minimal amount of interior lighting during the early evening hours, and people could use those wind-up flashlights if they have to be outside after dark.

We are also going to have to match a whole range of other tasks to available sunlight. Laundry and dishwashing and bathing will have to be done in late afternoon or early evening after solar water heaters have warmed the day's batch of water. The main hot meal of the day will be ready at the end of the day, after it has been cooking in the solar oven all day; we'll mostly be eating soups and stews and casseroles, too, because that is what works in solar ovens.

Rail transport will run during daylight hours and be idle at nights. If you are traveling a long distance, your trip will be a series of daily hops, staying each night in the "station hotel".

There will be rechargeable batteries to allow operation of electrical devices after dark, but these will tend to be device specific, just as they are now: radios, laptop computers, shavers, cordless power tools, etc. PV panels will supply the power to recharge the battery packs each day, and then battery packs are swapped out each night. The cost of a battery bank to keep an entire house running all night will be prohibitively high for most people. Maybe a small battery pack to keep the refrigerator running would be affordable; or maybe people will just have to adjust to keeping the refrigerator door closed after dark.

(What about wind, hydro, tidal, geothermal, biomass, etc.? I am assuming that they will be needed for all the other essential things not mentioned above, plus to provide backup on cloudy days.)

Obviously, what I am describing is a less prosperous society with a much lower per-capita GDP. At this point, I take that as an inescapable given for our future. The above is probably as good a way to cope with that fact as we are likely to get.

I suppose people could just go on a rampage and kill each other instead. The above seems to me to be a more reasonable and desirable alternative, though. . .