The Oil Drum

Electricity - production: 3,892,000,000,000,000 Wh (2003)   https://www.cia.gov/cia/publications/factbook/geos/us.html

Coal is ~50% of the mix.  So 1,946,000,000,000,000 Wh attributed to Coal.

http://www.eia.doe.gov/cneaf/coal/page/acr/table4.html
68% of mines appear to be "surface" mines, so 1,323,280,000,000,000 Wh attributable to surface mined coal.

If a 1,400 MW (continuous duty plant) consumes roughly 13,200 tons of coal per day, which is (33,600 mWh/13,200 tons) or (2.54 mWh/ton).

(1,323,280,000,000,000 Wh) X (tons/2,540,000 Wh) = 520,976,378 tons of coal per year for "surface mined" coal.

Which best case 110,000 tons/acre: (520,976,378tons)X(acre/110,000tons)= 4,736 acres/year

Worst case 3,000 tons/acre (18" seam): (520,976,378tons)X(acre/3,000tons)= 173,659 acres/year