Wow, that's a great question! I had to look up some figures to answer...
According to the Wikipedia (who quotes the IRS
http://www.irs.gov/pub/irs-drop/n-99-18.pdf), a "BOE" which is a "Barrel of Oil Equivalent" , is 5.8 million BTU.
That is equal to 6.117 Tera-Joules or 1.70 MWh. (
http://www.engineeringtoo...at-units-d_664.html)
Now we look at the solar source. According to
http://apps1.eere.energy....ves/resources_nj.cfm
A "flat plate" solar collector in New Jersey should be able to collect about 3500-4500 W-hr per Sq m (more in the south) (more in the summer, less in the winter)
That means then a 100 square meter collector should average 0.35 to 0.45 MWh per day, which is about 0.2 - 0.265 barrels of oil per day. Time 365.25 days in a year gives
73 - 96.7 Barrels of oil per year equivalent. If a Barrel of oil is $100, that means saving up to $10,000 per year in oil, enough to pay for the solar cells in a few years.
Calculating another way, 0.35 MWh per day times about $120 (cost per MWh of electricity, on average) gives an electrical energy savings of $42 a day, or $15,340 a year! However, transferring from DC to AC will give a loss, storage will give a loss, etc.
Most houses average 2-6 KW rate, or 48-144 KWh per day, so 100 square meters is more than a typical household would need, but they would need to be able to store it during the day to use it overnight (or sell it back to the power companies, reversing their meters). In the South, our usage is highest in the summer when the solar energy is high; but in New Jersey, your usage is highest in the winter when the sunlight is less, so again you'd need storage or selling it to the power companies. This is called "Co-generation". However, 100 square meters is big for the rooftop of an average house - fortunately an average house would need less.
According to that same web site, the entire energy use of the US could be satisfied with 9% of Nevada - a plot of land 100 miles on a side. You'd still have to move it around the country and store between day and night and summer and winter.
http://apps1.eere.energy....es/photovoltaics.cfm