This 'informal white paper' authored by the renewable energy industry and the Electric Reliability Council of Texas addresses the impact of wind's intermittency on the need for the development of comparable capacities of reliable sources that can be called upon when the wind is not blowing. It contains a particularly interesting chart that characterizes different energy sources as 'base load', 'peak load' and 'intermittent' with their associated benefits and drawbacks. Wind is deemed 'intermittent' with the following benefits (no emissions, no fuel costs, stable cost, low operating cost) and drawbacks (not dispatchable, not responsive, transmission needs, low peak value).
This report begins with a list of "facts" about wind energy and the grid; of particular interest:
• Wind production is an intermittent resource and is not always fully available. In order to ensure reliable electric service to customers, substantial wind development must be accompanied by development of comparable capacities of other generation resources that can be called upon when the wind is not blowing.
o In West Texas, wind produces more power during low load times than during high load times.
o In coastal areas, wind may produce more power on-peak than off-peak.
• Wind energy can be expected to increase the amount of generation reserves needed to operate the system reliably. The costs of such "ancillary services" are assessed on all energy scheduled in the ERCOT market. The magnitude of any increase in ancillary service costs depends on a number of variables that are not known at this time. Estimates range widely. Diversity of locations and installed amounts over a wide area may help this situation.
The report identifies the need for up to $3-billion in new transmission lines to accomodate 10,000 MW of new renewable energy generation (wind), and estimates that this level of development would raise the average electricity bill of TX resident by about 2% to pay for just the new transmission lines. It also estimates the cost of generation for wind turbine electricity - based on windplants built in TX since 1999; the cost of wind energy ranged from $39/MWh for windplants operating at a 40% capacity factor to $53 for windplants operating at a lower 30% capacity factor.
Also possibly of interest:
"In addition to meeting the state’s energy needs (MWh), the electric system must also meet expected peak demand (MW). Generation resources other than wind will be needed to meet most of the projected growth in peak demand, as maximum output from wind resources does not correspond to system peak demand. ERCOT currently assigns 10% of the installed capacity of wind turbines to its calculation of the ERCOT peak capacity reserve margin. Based on a review of historical data of actual wind turbine generation during ERCOT system peaks (from 4 p.m. to 6 p.m. in July and August), the average output for wind turbines was 16.8% of capacity. However, the data also showed that for any hour during these months, the output of the wind turbines could range from 0% of installed capacity to 49% of installed capacity. Stakeholders comprising the ERCOT Generation Adequacy Task Group have expressed concern that use of an average number (i.e., 16.8%) was too optimistic because it fails to adequately recognize the intermittency of wind generation. Accordingly, the group is working to assign a peak capacity value for wind using an appropriate “confidence factor.” While the group has not yet formally made a recommendation to the ERCOT Technical Advisory Committee, it is currently considering recommending a wind capacity value of 2%. In summary, in order to reliably meet system peak demand, dispatchable resources (such as gas, coal, biomass) would be required to replace the wind resources when wind is not blowing."