White Box Technologies has historical weather data for all years between
2001 and 2016 for 62 locations in Poland, including Warsaw
(POL_WARSZAWA-OKECIE_123750). Just go to the web site shown in my
signature, click on "Historical" on the left panel of the home page, and
then search by country and year.

WBT Weather is a commercial web site, so the data is not free. However,
all weather files are processed from raw weather station data, and so
have all the meteorological elements needed for an energy simulation,
including solar radiation, which is almost never measured and needs to
be computed by various methods, including empirical and analytical
models, satellite imagery, etc.

Joe

Joe Huang
White Box Technologies, Inc.
346 Rheem Blvd., Suite 205A
Moraga CA 94556
yjhuang at whiteboxtechnologies.com
http://weather.whiteboxtechnologies.com for simulation-ready weather data
http://www.whiteboxtechnologies.com
(o) (925)388-0265
(c) (510)928-2683
"building energy simulations at your fingertips"