Interesting data. Your solar sensor may be a bit "optimistic." The maximum value is essentially equal to the accepted value for solar incidence at the top of the earth's atmosphere. At sea level, for overhead sun the value is usually taken as 950 - 1000 W/m². Since it is never "overhead" at your latitude, the number would be slightly lower. (If you were on top of a substantial mountain, it could be a little higher, but not at your altitude). On the wind data, even your highest 10 minute value would put you well down in the cube law region and at roughly 7.5% of rated power (usually generators require 12 - 14 m/s for rated power).
--- On Fri, 9/18/09, James R. Frysinger <[email protected]> wrote: From: James R. Frysinger <[email protected]> Subject: [USMA:45842] Weather data for solar and wind power calculations To: "U.S. Metric Association" <[email protected]> Date: Friday, September 18, 2009, 10:46 PM I have a Davis Vantage Pro2 weather station and console, read out and archived with WeatherLink software. Here is some actual weather data that might interest those concerned with harnessing solar or wind power. The data was collected on my farm in Middle Tennessee. To four places, the weather station location then was 35.9785N, 085.5087W; it has since been moved to a better, nearby site. This old site was somewhat shielded by nearby buildings, but still the data is interesting (at least to me). The data is collected every few seconds and recorded in 10 min bins. Each bin's value then represents an average over that 10 min period, but a few channels also record "instantaneous" high and low values during that period as well. I have pulled the 52599 bins (10 min each) of data that I obtained for 2008 into a spreadsheet, in which I have started some additional statistical analysis. My data follows, without regard to significant figures. Note that wind speed data is sensed and transmitted in 1 mi/h intervals. The logger is set up to convert those to kilometers per hour and it then rounds it to the nearest 0.1 km/h. Thus wind speeds are archived in 1.61 km/h intervals to the nearest 0.1 km/h. Solar (essentially no effective shadowing by nearby structures): minimum insolation 0 W/m2 maximum insolation 1180 W/m2 (10 min average) maximum insolation 1331 W/m2 ("instantaneous") average insolation 165.02 W/m2 (10 min average) Wind (two one story buildings in the south to northwest sector): minimum speed 0 km/h maximum speed 20.9 km/h (10 min average) maximum speed 57.9 km/h ("instantaneous") average speed 1.66 km/h (10 min average) Wind bin data: speed freq. log frequency (km/h) 0.0 27658 4.44 1.6 10401 4.02 3.2 6681 3.82 4.8 3920 3.59 6.4 2033 3.31 8.0 1036 3.02 9.7 488 2.69 11.3 218 2.34 12.9 90 1.95 14.5 42 1.62 16.1 21 1.32 17.7 7 0.85 19.3 3 0.48 20.9 1 0 The best fit straight line for the log frequency data is log f = 4.55 - 0.21v/(km/h) Those who love to play with numbers can cube the speeds (I recommend converting to m/s first), then doing a numerical integration using the above frequency data to determine the mean power available in the wind here. Or the regression equation above can be used to do the integration if you're a hard-core mathematician. Either some more information will be needed. The elevation here is 375 m above sea level. The average sea level pressure (obtained by altitude correction to sea level by the logger) was 1017.8 kPa (min 981.3 hPa, max 1046.4 hPa). The average relative was humidity of 71 % (min 17 %, max 98 %). The average temperature was 14.54 °C (min -13.4 °C, max 35.0 °C). These are all 10 min bin averages. You will need these numbers to correct to actual barometric pressure and to calculate the density of air here (on the average, sort of). Hopefully this will give someone some interesting real-world numbers to play with. Jim -- James R. Frysinger 632 Stony Point Mountain Road Doyle, TN 38559-3030 (C) 931.212.0267 (H) 931.657.3107 (F) 931.657.3108
