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I recently had fun tinkering with solar radiation data. There are a few helpful resources available although they're usually kind of buried; also, the depth of the data varies by region.  If it's third-world, tropical data you're looking for, you can find an estimate based on the latitude band on this Solar Energy World Distribution link. If you're interested in the reflectivity (albedo) of the ground and atmospheric absorptivity for tropical climates, it's at the Intensity of Solar Radiation link. If, on the other hand, you're interested in United States data for your own home solar project, the Renewable Resource Data Center at NREL has neat maps; by clicking on the lightning bolt, then on a location, you can get a text file giving the average, maximum, and minimum solar radiation hitting a collector (stationary tilted south-facing or tracking, and others) by month. Also hidden in this text file is average climatic data for the location -- handy if you're sizing a heating system, and a lot easier than trying to find the information you need in an ASHRAE handbook.

Neat spreadsheet feature : Did you know that Excel can filter lists for you? The feature is called "Data Autofilter." I use this tool all the time to (try to) make sense of data quickly without having to do any real programming. To try it, set up a list with each row containing one data point, plus a header row. You'll need to record the data and other information about it in separate columns. For example, for my students' grades, I have the name in one column, the major in another, the year in a third, and so on. Set up at least a couple of rows and select a cell in the list. Then, when you turn Autofilter on (it's a toggle; go to the "Data" menu item and select "Filter/Autofilter"), you'll see little buttons with arrows appearing next to the column headings. Hit the button, and you get a drop-down list where you can select the filtering criteria. The criteria include blanks, nonblanks, specific values already in the list, top 10, custom, and so on. Select one of the filtering choices, and the rows not conforming will magically disappear!

The key to making really productive use of this tool is to use a built-in feature of Excel whose name I haven't been able to determine. First select a column of interest, or at least two cells. Then look at the bar across the very bottom of the screen (on the left-hand side it will probably say "Ready"; look to the right). On my screen, this is usually under the horizontal slider bar. You'll see some text there; I think the default is "Count". By right-clicking on that text, you'll get a list of other choices. In my grades example, you could choose "count" if the column contains letter grades, or "average" if the column contains numerical information.  Filter the list different ways, and track how the number changes to get an idea of how the aggregate data looks.

Of course, this is just a quick and dirty way to get an impression of the variations. To do the job right, you'll want to use Database functions -- a topic for another time.