Thank you very much for that graph. It is perfect. I looked for about an hour and a half for something like that and all I got was mathematical formulae. Actually WRONG! (I am editing right now) I did find that graph but was too much in a rush and didn't appreciate what it showed. Thanks again.

Now I can do a rough comparison of a lean-to and lean-away with evening light to see if the bonus is significant. Can I have permission to repost the image? With thanks to Usbport on CR4 in the image if you like.

It is useful to the solar cooking and solar tracking people too.

Actually one thing to clarify while I am editing. The glass has 2 surfaces, so do we have to double up on the graph stuff? Because it reflects a bit from both surfaces of the roof and then it reflects a bit from both surfaces of the front window too. Thanks Brian

You're welcome. At times I've generated the same graph using MathCad, but in this case I just grabbed the image off Wikipedia, so give that source credit.

You are right that you'd need to average the graph for both surfaces. The glass will have a small amount of absorption and internal scattering, but those can probably be ignored from what I saw on the video. Those terms would be small except at really steep angles - and anyway you'd need to know the spectral transmissivity of the glass to computer them, which you may not have. So just assume that transmission + reflection = 100 per cent when you compute the average.

I did a guestimate with a little angle finder I have and the difference between a lean to and lean away at one stage in the late evening is incidence light at about 80 degrees for the lean to and about 65 degrees for the lean back. According to the graph, (if I am reading it right) about 20% of the light gets reflected from the lean away and about 70% from the lean to at that point. I think that is highly significant! I just looked at lean-to greenhouse images on google search. Not a single one leans away! Yet in summer here at just below 50 degrees north, lots of direct sunlight arrives form the northeast in the morning and northwest in the evening.

Thanks again Usbport for the graph. It is only a guestimate but it was made possible from usbport's graph. Also, I did not count in the sine effect. The amount of glass that gets hit by the evening light in the lean away is HUGE compared to that that gets hit by the evening light in a lean-to.

Brian

Cool. Glad I could help.

Brian - I don't have any useful comments regarding angle effects/light transmission but did want to comment on your cool project.

Looks like USB provided some great info though!

Can't view the u-tube where I am now but will check it out tonight.

Keep us updated!

Regards - KJK

I added a modification of the image that Usbport showed to a facebook album about the greenhouse. http://www.facebook.com/media/set/?set=a.10150925789340767.477288.736625766&type=3&l=05cab04462 Anyone like to check that I explained stuff correctly? Anyway, I have it down that about ight 3 times more of the light passes through the glass of the lean away at about 7.30 pm as would pass through a lean to. Approximate incident angles about 10 degrees for the lean-to and 25 degrees for the lean-away. I reversed the numbers off the wikipedia thingy because 90 degrees means at right angles to where they had it at zero. (Which makes no sense to me).

Brian

I just found a very useful sunlight map it is at http://www.sollumis.com/ I think the map shows 3 rays of light per hour. (36 for the equinox)

The really useful thing about the sunlight map is that it shows the direction of light as a part circle and shows some of the potential for catching the inbound sunlight from the northwest and northeast in summer with the lean away greenhouses. It is a very visual demonstration. Even though I have seen it with my own eyes, it never crossed my mind that you could catch sunlight coming from the northwest or northeast.

Brian

I made an instructable about the greenhouse. It shows the light transmission issue, the light reflected to the back wall in the evening and a couple of construction techniques to save the lumber from rot and termites. Also a few screenshots of solumis to help people plan theirs.

http://www.instructables.com/id/Design-your-greenhouse-Lean-away-Better-than-l/

I don't know if you need to be a member to see them.

Will put them on the facebook album too at http://www.facebook.com/media/set/?set=a.10150925789340767.477288.736625766&type=3&l=05cab04462

Brian

The project about the greenhouse design is on the instructables homepage today. Just one major thing to clarify. Quite a lot of direct sunlight comes from north of the east west line in summer in my area but I haven't found a site yet that shows how much time (in hours) before the sun gets to exactly east. Lots of sites tell sunrise time, sunset time and noon time for any location. What I want to find out is how many hours before the sun reaches exactly east and how many hours after it gets to exactly west?

I had a little physical model that could help but I destroyed it when i moved.

Thanks Brian

Anyway Usbport used the program 'starry night" and found that for 26th or 27th June in Nottingham, the figures were "Total daylight hours is 16 hours, 37 minutes. The Sun spends 10 hours and 37 minutes in the 'South' part of the sky, between 90 and 270 degrees azimuth. It spends 3 hours and 33 minutes in the Northeast part of the sky and 3 hours and 35 minutes in the Northwest part of the sky." So it was 7 hours and 8 minutes in the northern half of the sky and 10 hours and 37 minutes in the southern half. So of course, the northern light is not of great quality but I question the logic of putting a house between it and your greenhouse.

It has been interesting, at least for me. The early nasty comment threw me for quite the loop. Nearly as bad as being mugged.

Thanks Brian.

Video is at http://www.youtube.com/watch?v=PBbTLUahWHc Includes the input from Usbport. Much appreciated.

Only big mistake is I put in 44. something as Victoria Latitude instead of 48.4

Thanks Brian