# Solar Energy Terminology

**URL:** <https://boards.straightdope.com/t/solar-energy-terminology/717928>\
**Category:** Factual Questions\
**Created:** [April 17, 2015, 5:37pm UTC](https://boards.straightdope.com/t/solar-energy-terminology/717928 "2015-04-17T17:37:18Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![Jinx](https://avatars.discourse-cdn.com/v4/letter/j/c6cbf5/32.png) [@Jinx](https://boards.straightdope.com/u/Jinx)\
**Post date:** [April 17, 2015, 5:37pm UTC](https://boards.straightdope.com/t/solar-energy-terminology/717928/1 "2015-04-17T17:37:18Z")

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Trying to work through some simple solar energy calcs, but the terminology may be misleading me. One starts with finding the solar energy available at their location. If I understand correctly, let’s say “Fig 1” provides a table of “average cumulative daily solar radiation on a horizontal surface” which is broken down by month for various parts of the US. On a seemingly-related note, let’s say “Fig 2” shown as a map of the US divided by sections of equal values of “annual mean daily solar radiation in the US”.

Shouldn’t the total monthly averages (from Table 1) correspond to the annual average values (from Table 2) for the same area? …assuming both are expressed in the same units? Or, are they not really the same thing? (If not, why aren’t they the same thing)? Thanks, all!

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**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\
**Post date:** [April 17, 2015, 6:22pm UTC](https://boards.straightdope.com/t/solar-energy-terminology/717928/2 "2015-04-17T18:22:28Z")

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One of them is by month, while the other is averaged over the entire year. You’ll get more sun in June than December, but how much more depends on your latitude.

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**Author:** ![Jinx](https://avatars.discourse-cdn.com/v4/letter/j/c6cbf5/32.png) [@Jinx](https://boards.straightdope.com/u/Jinx)\
**Post date:** [April 20, 2015, 2:58pm UTC](https://boards.straightdope.com/t/solar-energy-terminology/717928/3 "2015-04-20T14:58:16Z")

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Chronos, I realize that should be the case, but I’m finding the annual average of all monthly averages (of my Fig 1)) is like 2:1 compared to the annual average for the same latitude. I was expecting it to be relatively close, but it’s not. Perhaps the two figures use two different ways of measuring solar collection?

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**Author:** ![LSLGuy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lslguy/32/5813_2.png) [@LSLGuy](https://boards.straightdope.com/u/LSLGuy)\
**Post date:** [April 20, 2015, 4:36pm UTC](https://boards.straightdope.com/t/solar-energy-terminology/717928/4 "2015-04-20T16:36:01Z")

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Clearly the devil is in the details. Give us cites to your actual sources and we have some hope of resolving the difference. If not, not.