We're still living in complicated times when it comes to figuring what's best in terms of energy usage and storage.
If the goal is to become purely fiscally self-sufficient, I think ben's answer is really good. Sell your excess for cash. Then use said cash to exchange it for 'cheap' (relatively speaking) storable energy sources like a propane tank + generator.
Whether we like it or not, fossil fuels are still the cheapest way to store energy for extended use.
If the goal is to help the environment, then ideally you are never drawing power from the grid at all if the grid is powered by fossil fuels. On the other hand, if the grid is powered by wind or solar (or, arguably, nuclear) then it actually may be better for you to draw from the grid rather than storing it yourself.
If the grid is fossil fuel based, then you're back to finding a device to store energy with.
Options:
- chemical energy = batteries (likely most common for household usage)
- kinetic energy = flywheels (my favorite concept, but not really affordable or practical at a household size)
- kinetic energy = compressed air (already mentioned)
- kinetic energy = water pumping
- heat energy = ideal if a large part of your energy needs are for heating
and plenty more options: http://en.wikipedia.org/wiki/Energy_storage
Based purely on your 3 bullet point needs, I'd say the propane tank + generator are your best bet.
You have 2x6 joists 16" o.c. and lets assume #2 fir- the MAXIMUM spam (where they are supported underneath - bearing the weight) for a 20 lb dead load is 9'10" and for 10 lb dead load: 13' 2"
You show 11' +- in photo but it is unclear if there is support at that point.
you can check span table at:
https://www.awc.org/pdf/codes-standards/publications/wfcm/AWC-WFCM2018-ViewOnly-1711.pdf
There is some interesting framing in that attic: The 2x4 at the peak of the triangle which is set on top of the ceiling joists is very odd, in my opinion. It is transferring a load from the roof to the ceiling, and unless there is a wall underneath: you probobly have a bow in the ceiling at that point below.
Soooo: minimal storage, depending upon support at the 11' 3/4" point - Once you put a floor downs there even with the intentions of keeping it light up there - people forget in time.. . . .
As to the beefing up the joists with 2x8s that is an option - but the total span is more important. Is the entire width unsupported? and if so what is that total span?
Best Answer
For our home, we simply used a draping thread-curtain. The curtain is made of individual strings which we hang on the staircase itself. The strings will drape down and we cut the remaining threads according to the height that we require. Previously the storage underneath there was open and look a bit unsightly too. But with the "door" guests will not be too surprised like previously they had before.