Thursday, May 18, 2006

Hull wind facts

The following is from the Hull wind website:
Hull Wind 2, a Vestas V80 - 1.8 Megawatt turbine has been installed in Hull!
The new turbine will produce 5 million kWhs every year.
And right below it are data from Hull Wind 1 that call into question that claim:
May 8, 2006
6,853,738 kWhs
Capacity Factor: 27.1%
Days Commissioned: 1594
Total Hours Generating: 25403
After more than 4 years (1,594 ÷ 365), Hull 1 has generated electricity only 66% of the time (25,403 hours ÷ [1,594 days × 24 hours]) and its capacity factor is 27% (6,853,738 kWh ÷ [1,594 days × 24 hours × 660 kW]), yet in complete denial of that fact, a capacity factor of 31.5% is projected for Hull 2 (5 million kWh ÷ [1,800 kW × 365 days × 24 hours]).

The 15% exaggeration may not seem like much, but with such a marginal power source it is indeed significant. In fact, 27% is the average capacity factor voluntarily reported by wind facilities in the U.S. to the Energy Information Agency, and since those reports apparently allow discounting turbines that are temporarily broken down the actual capacity factors are lower. Yet promoters continue to claim that new facilities will have capacity factors of 30-40%. Then when the turbines are up and running, it's on to the next project and if the actual output actually becomes known, why, new technology will have a much higher capacity factor, yes, don't dwell on the past, let's move on.

And let us return to the other aspect of that output that is problematic on the grid (where large-scale storage is impractical): the fact that one third of the time wind turbines are idle (from either too little or too much wind). Related to this is the fact that from the "cut-in" wind speed up to the "rated" wind speed -- at which the generator's output reaches its full capacity, typically around 30 mph -- the output is cubically related to the wind speed. That is, if the wind speed doubles the power output increases by 8. The result is that in addition to being idle a third of the time, another third of the time wind turbines produce power below their already low average rate.

In other words, whatever the capacity factor is (from historical experience it would be expected to be 20-30%), that level of output is seen only one third of the time.

wind power, wind energy, wind turbines, environment, environmentalism