I am looking to get current and historical sun radiation or illuminance data for given locations around the globe. I've had a look at the wunderground API as I also need generic weather data but it appears that it doesn't include that info even though some weather stations do provide it. The ticket requesting it is 1 year old and doesn't seem to have moved very much in that time so it doesn't give me confidence that this will be made available any time soon. Does anybody know of any good alternative source for such data?

Note that in terms of location, I would prefer an API that has a worldwide cover. Failing that, my highest priority is UK data followed by Europe and then the rest of the world.

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    You mention given times ... are you looking for specific dates, averages for the year, or averages for a given month, or a given time of day? Some older monthly averages are available for the US from DOE NREL : nrel.gov/gis/solar.html – Joe Aug 28 '13 at 14:32
  • Not really, what I meant was that I need to be able to obtain historical values as well as current values. I will re-phrase the question to clarify. – Bruno Girin Aug 29 '13 at 15:04
  • Presently, solargis.com offers the services for your needs. Long-term average data is basically free, time-series data paid. – jurajb Sep 13 at 8:46
up vote 5 down vote accepted

As no one's given anything else so far, so might as well make this an official answer.

I'm not aware of any free APIs specifically, but there are various data sources that might be able to give you what you need:

The US Department of Energy's National Renewable Energy Lab offers maps of solar radiation in the US, both annual and monthly averages, although the data is only through 2009:

NOAA offers data from 1991 to 2010 from 1500 ground stations in the US, with nominally hourly cadence:

OpenEI (Energy Information) maintains a registry that lists 43 'irradiance' datasets and 26 maps. (some are the NREL ones I already mentioned):

SolarGIS might have it, as they sell products that look to have more granular information, but their only free (attribution required) offerings are annual averages of two types of 'irradiation'. (I'm not sure how that differs from 'irradiance'):

And the company that specifically markets an API (not free) for this data is 3Tier. If those other resources aren't sufficient, you might have to look at their pricing:

  • Thanks, that's a brilliant summary! I should add that in terms of locations, I would prefer an API that has a worldwide cover and failing that my highest priorities are the UK and Europe. – Bruno Girin Aug 29 '13 at 15:15

For UK & Europe solar data, I've used Photovoltaic Geographical Information System (PVGIS) before. This may be more of a "typical meteorological year" as opposed to a climate database/almanac/normal. It's also data, not an API.

PVSyst has a good resource on finding solar data: Meteo data sources.

A great list can be found at:


Solcast offers free access to this type of data for researchers and students, which is a great for my research group. I hope this helps!

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