I purchased one and was so happy with it, that I bought a second one. So I have two on my balcony leaning against the house facing southwest (in Los Angeles.) These go into separate, independent 30 amp Sunforce controllers. Normally they are both charging two marine deep-cycle batteries hooked in parallel to a 2KW (square wave) inverter which stays on all the time. Since the inverter draws so little power when not being used, I see no reason to turn it off and on all the time. I use it to power mostly lights at night in my bedroom, but occasionally my vacuum, laptop, and such. I also power several items directly from the batteries 12 Volt taps, including cell phone chargers and the like designed to run on 12 volts. Works great. When the marine cells are fully charged, I also switch one controller to GEL CELL and charge some gel cells I use to pump shower water onto my lawn. We have water restrictions here in Los Angeles, and I see no sense it just letting mine go down the drain. I use less than 25% of my water quota every month, and as a result, don't pay higher rates for the water I do use. Since these solar panels can put out nearly 10 amps each, they make quick work of charging two marine batteries. I wouldn't count on powering your house directly from just two panels unless you have a way to store the power like batteries.
A watt is a watt so you can add up the wattage that you use in your home and double it (safety margin and you can't expect your panels to pump out 100% power all the time.)
The formulas, if you care, are:
P=I x E where P is the power in watts, I is the current in amps, and E is the electrical voltage soooooo...
123 watts = 10(ish) amps x 12 volts
So you can get up to 10 amps at approximately 12 volts.
That translates to 1 amp (assuming 100% efficiency) at 120 volts.
123 watts =1 amp x 120 volts. (I am fudging the math ever so slightly because, obviously 123 does not equal 120)
So if your house pulls 50 amps of power all the time (yeah right - only if you are running air conditioning all the time with 4 TVs on and your freezer with the door open) you would need 50 panels (working at 100% rating ha ha ha) to power your house during the day. Now account for the fact that you will probably not get 100% out of your panels for numerous reasons, account for the transmission loss, general inefficiencies in conversion to AC, and general, 50% engineer's markup insurance, you would probably want between 75 and 100 panels to meet your electrical needs. When it gets to that kind of cost, you are better off buying wholesale, and taking the deductions and cash from your electric company.
Just remember that your house would probably only pull more than 50 amps at peak times and if you also use battery backup for storage, not only will you also have power at night, but the juice from the batteries will help buffer any surges from starting up your A/C, hot tub, washing machine, table saw, or other unreasonable industrial machinery you might be playing with in your garage.