It is with joy and some trepidation to report that White Box
Technologies (WBT) is updating all its historical weather files
with satellite-derived solar radiation. Joy because this overcomes
what has been the most significant question mark with weather
files; trepidation because of the amount of work needed to carry
out and maintain this effort. To show that this is more than
marketing hype, I need to give a rather long explanation about
this development.
The bane of weather data over the past three decades has been the
solar radiation (global horizontal and direct normal) which are
not measured parameters, but derived using various solar and sky
models. All the familiar "typical year" sets, i.e., TMY, WYEC,
IWEC, etc., let alone the historical weather files, have modeled
solar radiation. Although a lot of
work has gone into such models (see M. Iqbal,"An Introduction to
Solar Radiation", Academic Press, 1983), there remain an almost
intractible problem of the lack of good measured solar to tune any
of these models. For example, in the ASHRAE IWEC2 weather files,
my team was able to find one or two years' measured data for less
than 50 locations,
from which were derived 28 sets of regression coefficients then
used for all 3,012 IWEC2 locations.
For the past decade and a half, researchers around the world have
been working to derive solar radiation from weather satellite
imagery, driven largely by the needs of the solar power industry
for the siting of solar power plants and getting "bankable" solar
estimates for their arrays. Our little building energy simulation
sector can of course benefit by hanging on the coattails of the
solar power industry, but the downside has been to be totally
priced out, since the commercial cost for one year's solar data
for one location (grid cell) typically runs around $1,000.
A welcome development over the last five years is that various
government offices or affiliated consortia are now beginning to
also providing access to satellite-derived solar radiation at
minimal or more acceptable costs under various conditions. Over
the past three years, WBT has obtained access to such data and
permission for its use in WBT weather files.
WBT is now either replacing the solar radiation on its historical
weather files, or using satellite-derived radiation to develop
custom solar coefficients for each location to extend the
satellite-derived solar to time periods outside the available time
window. With the exception of polar locations above or below 60/66
degrees, island nations in the Pacific and Indian Ocean, and a few
unfortunate "blind spots", the entire land mass is being covered
with at least 10 years up to 18 years of hourly solar records.
Starting in 2018, WBT historical weather files in the following
areas will all have satellite-derived solar radiation for the
following time periods: Europe, Africa, South America east of 66
West, i.e., Brazil and Uruguay (2004 to date), Australia (1999 to
date), and East Asia (2007 to date, access pending). WBT
historical weather files in the following areas will have
satellite-derived solar radiation for the indicated time periods -
North America and Central/South American down to 20 South
(1998-2015), South Asia (2000-2014), with modeled solar radiation
from 2016 on that has been individually tuned to the past
satellite-derived solar.
Another benefit to the satellite-derived solar is to increases the
number of available weather stations, which in many places has
been limited by the lack of cloud cover data needed to model the
solar radiation. For reasons that are not immediately
identifiable, several English-speaking Commonwealth countries has
seen a marked drop in the number of available stations due to the
decreases in the reporting of cloud cover (see plot, ZAF = South
Africa). For example, the number of stations in the UK has dropped
by almost 2/3s between 2001 and 2017 (174 to 64), but with
satellite-derived solar, it will go back up to over 180, while in
Australia and South Africa the comparable numbers are from 175 to
well over 500, and from 37 to over 100, respectively.
If interested, customers who have purchased a historical weather
files from WBT over the past five years can get an updated weather
file at no cost. Lastly, although it will take at least a month to
update all 10,000 2017 files, it's very quick to do for any
specific location or even 50 or so locations. Therefore, if you
have an urgent request please e-mail me and I will put that at the
beginning of the queue for that day.
-- Joe Huang White Box Technologies, Inc. 346 Rheem Blvd., Suite 205A Moraga CA 94556 yjhuang@xxxxxxxxxxxxxxxxxxxxxxxx http://weather.whiteboxtechnologies.com for simulation-ready weather data (o) (925)388-0265 (c) (510)928-2683 "building energy simulations at your fingertips"