Re: Load calculation for elect lights
It's a bit more complicated than that.
To have a battery-based back-up power system you need not only the batteries, but an inverter to convert DC to AC. And you need a way to re-charge the batteries at the proper rate.
One example would be to use a small inverter, stand-alone battery charger, and batteries.
A step up from that would be to have an inverter with charger capability: it would take AC in and 'feed' your lighting circuits all the time while keeping the batteries up. Power goes down: batteries take over for that circuit only.
Since you're on grid and looking at buying panels, you might consider a grid-tie inverter with battery back-up. That way any time the batteries are fully charged and the sun is still shining you sell your 'extra' power back to the grid. I understand Florida has some pretty fair incentives for that sort of system.
If money is an issue, than a small, efficient generator might be your best choice for emergency power situations (although you have to keep fuel on hand and keep the gen maintained).
And yes, any back-up power system MUST disconnect from the grid when the grid goes down: you don't want to 'back feed' loose wires on the ground and risk electrocuting someone.
To start planning your system, get a Kill-A-Watt meter (or similar) and measure the actual loads you want to keep running in an emergency.
Don't worry: it takes a long time and a lot of posts to get this stuff all sorted out. We're here to help!
Four 175 Watt panels, OB MX60, 232 Amp hrs, OB 3524, Honda eu2000.
Ohm's Law: Amps = Volts / Ohms
Power Formula: Watts = Volts * Amps