The answer, assuming your primary energy source is solar, is "when the sun is out". Easy answer but you need to understand why.
A battery is not 100% efficient. That is, the amount of energy you have to put into a battery to recharge it is more than the amount of energy you took out.
Earlier this month, some economic luminaries in the United States Congress introduced a new bill, H.R. 2835. The bill intends to “establish a joint select committee of Congress to report findings and propose legislation to restore the Nation’s workforce to full employment…”
Great idea, fellas.
What if there is no choice?The first and most obvious is that you may not have a choice or even if you do have a choice, the initial investment for a grid connection may be more than for a system to allow you to be off-grid. Where I currently live extending the grid would have cost about $17,000. My PV solar system cost $12,000.
When selecting batteries the two big considerations are:
Yes, there was an official investigation of sorts. It was funded with less money than the one to determine if Bill Clinton had sex with that woman but, more important, it just didn't seem to want to find the truth.
The first is where you are starting and where you see the future of your system. If, for example, you have an existing 120VAC system (either grid connected or just things you run off a generator), 120VAC is more likely the right answer. On the other hand, if you are just starting, 12VDC is probably the best choice.
SIP is a standard for establishing calls over the Internet. The trick is to use SIP to make inexpensive calls. Not like Skype which is proprietary and expensive but open and cheap. I am going to point you at one particular vendor, http://callwithus.com, but I am just a satisfied customer of their service.
The good news is that LED lighting is efficient and becoming inexpensive. A few years ago you couldn't find much that would serve as useful home lighting but today you can and at fairly reasonable prices. The trick is to shop carefully.
If you have an off-grid system, take a look at what is available to run on 12 volts.