Watts:
Total US NET electricty consumption in the year 2005 was approximately 4000 Terrawatt Hours (TWH).
There are 365 x 24 = 8760 hours per year.
So the NET electrical power requirements for the US are:
4000/8760 = 0.457 TW or 457,000 Megawatts.
However, integrated over all sources of power generation, we are about 50% efficient meaning that 914,000 Megawatts (0.91 TW) of power was produced.
Averaged over the entire United States, the typical power plant size for the generation of electricity is 300 MW (tho individually this ranges from 1 MW to 6000 MW)
Thus we have 914000/300 = 3050 or approximately 3000 individual powerplants that need to be hooked to the national grid.
And this is just for electricity production. We are not talking yet about heat or tansportation.
Note, also, for reasons to be discussed later, we are now annually losing about 10% of power plant generated electricity in our aging grid system.
This loss is equivalent to 300 power plants!
Clearly as our demand for electricity grows, we require more and more power plant construction. It is most cost effective to build a few large scale plants, rather than many smaller ones, due to grid limitations.
In the Pacific Northwest, the time history of power plant construction is shown here