PJM Interconnection has based its argument for the need for PATH entirely on stresses on the transmission system at times of peak demand. Peak demand is not the same thing as overall demand for electricity.
Peak demand is the maximum demand that is put on a part of the electrical grid only a few times a year. This could be in the hottest part of the summer in warm climates when workplaces and homes have their air conditioning on full blast. It could be in the coldest part of winter when everyone has their electric heat and supplemental heaters going full blast.
Grid planners must plan the overall capacity of the electrical grid for these few peak times of the year plus a margin of safety, usually around 15%. This is particularly true of the centralized, inflexible grid that exists in the PJM region today.
Electrical load, the demand for electricity that is created whenever lights or air conditioners or refrigerators or industrial motors are turned on, must be met by generation of new electricity, or the entire transmission system becomes unstable as voltages drop below their operating requirements.
The current electrical power system in the PJM region relies on a power technology that is rapidly becoming obsolete. The PJM system, especially since AEP and its massive coal-fired plants joined PJM in 2004, relies on large power plants located hundreds of miles from the customers who need power in times of peak load.
PJM’s current system is very inflexible because it relies on huge coal-fired plants that must continue to burn coal and produce electricity even when their power is not needed. This highly centralized system must be built to meet peak demand that may only happen a few times a year. For most of the rest of the year, PJM’s generating and transmission system operates far below its peak load capacity.
Peak loads can be managed in a much more flexible and economical way, without rate payers paying for lots of expensive equipment that is only fully used a few times a year. PATH is just more of this wasteful equipment.
The Power Line 