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Cost/performance
Tradeoffs
Imagine a system consisting only of
wind turbines and natural gas combined cycle generators. The initial configuration starts
with all natural gas, then wind is added to reduce CO2 emissions.
The solid blue line in the figure below shows the resulting cost as a function
of grid emissions. Cost increases sharply as wind penetration increases (to low
emissions) due to curtailment. At certain times with low load, wind is
generating too much power. At that time all the natural gas generators are shut
down, and wind needs to be curtailed (shut down some turbines). Also note that
we cannot reach zero emissions at any cost with just wind and natural gas
generators.
The analysis uses hourly wind and load
data for the PJM system in 2012. Cost data is from the US Department of
Energy’s Energy Information Agency’s Annual Energy Outlook (AEO) for 2015 based
on new 2020 installations. The red square reference (100% CO2
emissions) is the cost of an all natural gas system
assuming that the system needs 15% reserves. The black X is existing PJM grid,
25% dirtier than all natural gas and at today’s retail price slightly higher
than AEO’s cost estimate for the cost of a new 2020 all natural gas installation.
If we had perfect storage (zero cost, 100% efficient, infinite size) we would
get the blue dashed line. The line slopes slightly up to the right because with
AEO2015 costs, the discounted capital cost of the wind is slightly greater than
the cost of natural gas saved. But real storage is expensive. More realistic
storage (red line) is based on Bath County Pumped Hydro Storage, $200/kWh and
80% efficient. Storage reduces system costs modestly but only at very high wind
penetration. The green square is a system consisting of nuclear base load (AOE2015
costs) plus natural gas to manage diurnal variations and reserves. The green
diamond is a system consisting of nuclear plus domestic hot water storage (like
the French system) to manage diurnal variation plus natural gas reserves. These
cost/performance tradeoffs are being documented in more detail in a series of
papers starting with an ASME conference in 2014.
