NY's Dirty Power Secret

There's a dirty little secret in the New York City Power grid. Rather than build additional capacity for peak demand days (normally the hottest days of summer), Con Ed and the city have a deal to run backup diesel generators located at various city facilities to make up the shortfall. These generators were built for emergency backup during power outages, and are filthy, dirty polluting machines. The deal allows Con Ed and the city to avoid the expense of a new power plant, and all the political problems of siting one. But a new plant wouldnt add much to electricity rates, and would be substantially cleaner. Here's an easy opportunity for cleaner power generation, yet the rhetoric doesnt match the results