Wind power is only available when the wind is blowing. Similarly, cloudy skies means less solar power.
The use of renewable energy resources for generating electric power is limited by the fact that renewable resources are not always available.
This is why renewable energy is commonly described as an "intermittent" energy resource.
Intermittency, or "variability," is renewable energy's Achilles heel.
Intermittent resources are considered potentially problematic because the output from individual units may vary widely in response to variation in available wind and solar energy, which can only be predicted to a moderate degree of accuracy.
The assumption seems to be that non-renewable energy resources – namely, fossil fuels – are not intermittent.
If the past three months have taught us anything, it is that not all fossil fuels are created equal in terms of availability.
Unlike coal and fuel oil, natural gas cannot be stored in large amounts onsite at power plants. The molecules that comprise natural gas move about 30 miles of pipeline every hour.
That may be why regional grid operators are creating new categories and classifications for gas-fired power plants.
Consider the new category – "Generation at Risk Due to Gas Supply Issues" – created by the Independent System Operator for New England in February for planning future capacity needs in the New England Power Pool in early 2015.
The category includes gas-fired generators "expected to be at risk during cold weather conditions or gas pipeline maintenance outages."
The ISO-NE projects that nearly 3.5 gigawatts of gas-fired power plants in New England will be at risk losing gas supply from one of the five interstate pipelines serving New England in January 2015.
During the afternoon of January 7, 2014, six natural-gas fired generators in New England, totaling roughly 1,500 megawatts (MW) of capacity, were unable to procure natural gas to generate electric power.
Despite a compressor failure on the Texas Eastern system at Delmont, PA, the other four pipelines were operating at or near capacity, with some recording record throughputs.
The graphic above shows the mix of generation by fuel type in New England during the evening peak load hour of January 7, 2014 arranged by percent of total generation.
Natural gas has become the primary fuel for generating electricity in New England over the past few years. Despite the rise in consumption, regional pipeline capacity has remained essentially flat and is projected to remain that way until 2017.
