# Calculate potential of solar radiation on rooftops (without LiDAR data)

I'm trying to calculate the solar radiation for rooftops, but I have a big problem, I don't have LIDAR data. I need to give the buildings the information of height. I've tried to do these, but for a building I'm going to get for example three types of heights when I should only get one.

So, I want to ask if anyone could suggest another way to calculate the buildings height and the surface of rooftops, so that I can calculate the potential of solar radiation for rooftops without using LiDAR data.

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Hi, This sounds like you might need to do some primary data collection! Can you get to the physical location that you're trying to analyse? Failing that, do you have any other information on the buildings in your area of analysis - numbers of storeys etc? I don't know where your looking at, but a general rule of thumb is 1 storey ~3 metres - you could apply this to the z value if you have the building foot prints already. – Andy TIce Feb 10 '13 at 5:23
Hello Andy! Thank's for answered. Well i have the physical location and the information about the storeys too. I applied the rule of three metera.But my doubt is that when i process the area solar radiation i should have the information on my raster about the buildings height and the surface. If i had LIDAR data it should be a surface digital model that combines te surface with the elements in it like buildings, trees, etc. So not having these information, it is right to process the solar radiation to buildings height? Thank's Mónica – user15002 Feb 10 '13 at 18:24
@user15002 please try to correct your question. We think we may understand, but there are inconsistent sentences with negatives used incorrectly, like.. "without using LIDAR data because I can get it". If you "can" get it why would you "not" use it? My understanding is you have building height and solar information. – Brad Nesom Feb 11 '13 at 3:37
@BradNesom - that was my take on it! Mónica had my sympathies as I remember having to digitize a tree coverage for an entire city about 15 years ago ... think I went blind during the process - old school digitizer puck and A0 1:10,000 hard copy base maps. – Andrew Tice Feb 11 '13 at 5:39
Hello Brad Nesom, you're right i'm sorry about the errors what i wanted to say was "without using lidar because i dont have it." Thank's – user15002 Feb 11 '13 at 13:02

Since you don't have LIDAR you'll need to think about how best to represent the spatial information you have.

I'd suggest starting off with just the building heights (using the 3 meter rule) - generate a raster from this - and conduct initial analysis based on buildings only (mainly to make sure your calculations work).

Next you'll have to think about introducing vegetation cover to the analysis. Again, without LIDAR this is going to be trial and error (and, how it used to be done before LIDAR!)

A suggestion here might be to digitize (manually - or via something like this Determine density or cover from a raster layer that has been clipped by a polygon) a coverage for your area based on a aerial image - if you have one to hand. Failing that you could get hold of QGIS and derive a layer from a Google Earth aerial image (http://qgis.spatialthoughts.com/2011/12/digitizing-in-qgis.html) and import the resulting coverage into Arc.

Here is a screenshot of what I mean - NOTE that I'm only concentrating on vegetation cover above the visible roof line of the buildings, that way I'm reducing the amount of digitizing needed to be done:

Since you will have derived the building heights under the tree cover you could set each digitized polygon to be above the underlying building heights as the aerial image validates this.

The reason why I was suggesting getting out to your Physical location is to get an understanding of how dense / high the vegetation level is - does the majority the tree canopy sit high above the roof tops, or very close to it - you'd might want to adjust the digitized layer based on your observations.

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Hello Andy!! Well i'll try what you suggested. Thank's for your attention and sorry about the english (i'm not used to write in english all the time :) – user15002 Feb 11 '13 at 13:05
Not a problem ... having had to do the same in the past I could understand your problem! It might be worth your time to ask around your colleagues, or put a general request out, to see if you can get an aerial image of your location and to do the work directly in Arc. – Andrew Tice Feb 11 '13 at 21:58

Weather underground has a solar calculator.

http://www.wunderground.com/calculators/solar.html

This can also be used with the API (on special request)

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