One of the persistent comments about wind vs. solar is that solar has a better fit with time of use both time of year and time of day. Most everyone seems to repeat the same phrase that PV has a better match for time of use than wind. However, the frequency that those comments are made does not seem to make them universally true. While not as patently false as “weapons of mass destruction in Iraq” there does seem to be a sampling bias. RES Americas presented a paper at AWEA in 2009 that showed the lowest wind speeds at 60m hub heights in the afternoon (Time Of Day Correlations For Improved Wind Speed Predictions By Andrew Oliver, PhD aand Kristofer Zarling). The data set was dominated by wind farms in a band from Texas to the Dakotas.
There is another set of facts that tells a different story, even within the RES paper. RES made the point that the strength of wind by time of day depends on the height above ground. At 60 meters, wind picks up at night. Closer to the ground, the strongest wind is in the middle of the day.
Our wind turbines are on 30 to 37 m towers. They are for distributed generation and sized to fit in the landscape of schools, farms, factories, municipal buildings. At lower hub heights, wind energy peaks much closer to peak demand.
A UK Met Office Virtual Met Mast Report for a wind turbine at 37 meter hub height clearly shows the strongest wind from noon to 7 pm.
In addition to the time of use chart from a Virtual Met mast report, I ran hour to hour reports for one of our wind turbines operating in Vermont. Based on a sample of 72,000 rows of data with a time stamp and wind speed, it is clear that wind speed and consequently energy production is highest from 2 pm to 8 pm.
I could also suffer from a sampling error, so I found some longitudinal data sets. These charts for Rutland, VT and other cities show the wind is strongest from noon to 6 pm.
Here are similar wind distributions from sites around the country and the world. They show the same pattern.
Wind is lowest at night, strongest during the day.
Why does it matter? Electricity production from our 100kW turbines can more closely match the demand patterns than conventional wisdom would suggest as in Ontario, Canada.
This is an overlay of measured wind speed on one of our Vermont located turbines on the time of use chart above. The Blue line is wind speed. Green is summer demand and black is winter demand.
