An individual, grid-connected wind farm doesn’t need backup. On a larger scale Intermittent energy such as wind and solar requires 20% to 30% backup for short falls when these intermittent sources provide up to 20% of the grid’s energy. That backup doesn’t have to be built as it will come from neighbouring jurisdictions, passive hydro and existing natural gas peaking plants.
Studies on Wind Intermittency and Required Backup
In 2006 by the UK Energy Research Centre did a solid study. Formally established and overseen by a body of experts, it assessed 200 studies and reports from around the world about the actual and theoretical impact and mitigation of intermittency in power grids.
Here is the pertinent bit:
For penetrations of intermittent renewables up to 20% of electricity supply, additional system balancing reserves due to short term (hourly) fluctuations in wind generation amount to about 5-10% of installed wind capacity.
Current costs are much lower; indeed there is little or no impact on reliability at existing levels of wind power penetration. The cost of maintaining reliability will increase as the market share of intermittent generation rises.
A Finnish study says the same thing:
From the investigated studies it follows that at wind penetrations of up to 20% of gross demand (energy), system operating cost increases arising from wind variability and uncertainty amounted to about 1ñ4 Ä/MWh. This is 10% or less of the wholesale value of the wind energy.
It contains an excellent chart showing the value of widespread wind energy in reducing intermittency of supply garnered from data from multiple countries historical experiences:
Backup required for other generation sources
Some people look at this in an odd way. Let’s look at the Ardrossan wind turbine fire of December 2011. One of a dozen 1.2 MW wind turbines caught fire in a massive wind storm that swept Scotland, taking its 1.2 MW out of generation. The same wind storm knocked down transmission lines from the nearby Hunterston nuclear plant. It was offline for 54 hours for a loss of 17,000 MWh to the grid. That’s a lot more than one wind turbine’s generation.
Similarly, when an Australian 800 MW coal plant stopped delivering electricity to the grid recently, the wholesale price of power increased by a factor of 200 in minutes before returning to normal. This graph is leveled over 30 minutes so the peak price is masked, but the dramatic loss of power is readily apparent. As the linked article shows, loss of major generating assets is common and unpredictable, while loss of wind generation is common, but typically only a percentage of capacity and very predictable.
Grid managers have to maintain hot backup contingencies for failure of their largest single generation plants, typically coal, hydro or nuclear in the 1 GW range. Wind energy doesn’t rank as a grid management issue until you get into > 20% ranges, and even then it isn’t a particularly hard or sudden problem compared to dealing with a nuclear plant that suddenly isn’t there.
Ontario, as another example, generated 55% of its energy from its fleet of nuclear plants in 2013, which average around 850 MW per reactor at any given time. Ontario’s nuclear fleet has experienced many unforeseen shutdowns. One of these plants having a failure which takes it offline requires 100% backup for that contingency, or 850 MW of capacity.
Ontario has has a fleet of large hydro facilities, one of which generates 1500 MW by itself. While Ontario is only slightly geologically active, earthquakes registering 3 on the Richter scale have occurred and could cause a hydroelectric dam to be taken out of service.
Ontario has around 2.5 GW of wind capacity at present and is much lower than 20% of generation from wind (and does not currently plan to reach 20%). At the 20% backup, this would currently require 300 MW of backup generation, or about the size of a single large gas turbine generator.