corina,
there's a lot of variables that go into this type of calculation. A few pointers:
watts = amps x volts
so a 60 watt bulb on 120V house current will use "only" 0.5Amps of current. A 60 watt bulb via 12V will use 5 amps (yes a 10x difference) - still the same 'power' used (wattage and kwhours), but still, hence the allure of LED and ultra low wattage items when on DC power in off-grid power from solar or wind.
**you'll 'save' more by reducing load requiring a larger system. the panels cost, the wiring costs, the charge controllers cost, and the battery banks cost** lower load = lower costs at every stage. for most people, buying a 'kill a watt' meter and measuring every device in your house and putting it in a spreadsheet to know your draw is step 1.
Regarding the comment above about electric
being too much draw - imagine one of those 1500watt free standing electric oil heaters, they pull 12-13 amps on 120V wall power. so they'd draw 120-130amps of current on a 12V system. eeek.
All electricity as friction type devices - think iron, coffee maker, hair dryer use a lot of electrons (current).
you also need to think about 12v, 24v, 48v - closing the gap to 120V has advantages in fewer amps = less thick cables from your solar array to the electronics in your home.
with solar panels, the wattage rating is under ideal circumstances, depends on the efficiency of the panels, efficiency of your charging controller and whether it's a battery system or no batts and grid tied only. And there's number of hours of daylight you actually get per day.
in short, 300Watts of solarpanels will not run 300 watts of actual draw constantly. think of the batteries as a reserve you can draw from with your usage and will refil from the solar panels - assuming you have enough sun+panels vs. your 24 hr draw. ergo, the 'watt-hours' - in the spreadsheet above, the wattage of an item should be factored by how many hours per day you use said item. resulting in a watt-hour value. add them all up and you know how much power per day you need, then you size a system to fit. (and this is when most people go: "oh, i will work on how to cut down my draw).
try this link:
https://homepower.com/articles/what-solar-electricity to pick up the fundamentals.
my suggestion: buy a 12V battery, a 3Amp 12v charge controller, a 15W solar panel - all at amazon for under $120 to then have some 12v testing (led lighting, charging laptop, etc) from this you'll learn the basics and see it in action.
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