As an approximation solar flux is about 1kW / m^2. Last time I looked the efficiency of panels was about 20% so we can generate about 200W / m^2 for at most 6 hours a day. The USA power usage / day is 4^15 W.hr.<p>As 1km^2 = 1,000,000 m^2. So taking the power usage, we divide by solar flux, by number of hours of high solar input, by 200 W / m^2, by area conversion, and get approx 3,000,000 km^2. Since the USA is 10,000,000 km^2, we would need to cover 1/3 of the country with solar panels to generate enough electricity, mostly down south where the sun shines the most. Alaska would be spared.<p>Since we use power 24 hours a day and can only expect to generate at peak rate for 6 hours, we need to store the power in batteries. Not to mention that not every day is sunny. It sometimes rains, panels get covered in dust and need cleaning, stuff breaks down, etc.<p>A Tesla PowerWall stores approx 120KWhr / m^3. So 4^15 / 120^3 = 33^9 m^3 just for the batteries, not including cabling, racking, etc. To get an idea of how this compares, Trump Tower in Chicago is approx 80,000 m^3. So we'd need 400,000 of them to house the batteries and this only for one day's worth of power.<p>Of course, none of the foregoing considers the power required to make the solar panels, the mounting hardware, the batteries, the housing and new power-lines. The math just gets more complicated. But if you were to consider every step from beach sand to working solar panels you will find that the lifetime energy produced by solar panels is less than that which was used to produce them in the first place. I read an article to this effect once, but can't find it. Google is your friend if you are interested to research further.