installed capacity

Installed capacity is a measure of equipment, not of output. It is the maximum electrical power a generator can deliver under the conditions its manufacturer specifies, added up across every unit on a system and usually quoted in megawatts. The United States Energy Information Administration defines a generator's nameplate capacity as its maximum rated output under those specified conditions, a figure normally shown on a plate physically attached to the machine. A country's installed capacity is the sum of all those plates.

This is why capacity figures and electricity figures rarely match. A 100 megawatt coal plant and a 100 megawatt solar park have the same installed capacity, but the coal plant can run through the night and the solar park cannot, so across a year the two deliver very different amounts of electricity. Capacity tells you what has been built. Generation tells you what it produced. Both are needed to describe a power system honestly, and treating the first as though it were the second is the most common way a clean energy statistic gets overstated.