One sees occasional anomalies in "raw" data, John. Yes, that one
instantaneous insolation number is nearly the theoretical maximum at the
top of the atmosphere AND at the Sun's declination. I have not searched
the table of numbers; that value might have been recorded at night! It
is impossible to say what caused the instrument to record that
particular value: a reflection, electronic noise, a flash of lightning, ...
The data does show that our farm would be a very poor candidate for
harvesting the wind. Just looking at the large fraction of time in which
the winds are below or just at minimum turbine needs dissuades such
notions. Our low solar average insolation likewise does not encourage me
to erect large solar arrays to ease TVA's load, but of course it
suffices for powering remote electric fences.
Jim
John M. Steele wrote:
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
--
James R. Frysinger
632 Stony Point Mountain Road
Doyle, TN 38559-3030
(C) 931.212.0267
(H) 931.657.3107
(F) 931.657.3108
