solar losses

[windyknight]

I was wondering if the losses in pv panels being greater than calculated from cosine error is due to reflection from panel coating because I've noticed strong reflected light when sun strikes my solar water heater from an acute angle. It's difficult to quantify the loss though because when angle acute not much heat in sun and i cant easily rotate it for comparison.

Curved glass would help but is expensive so I wondered if a three faceted surface would be worth the effort of making it?

Shouldnt be too difficult to construct with silicon joins (like fish tanks) but would the extra surface area losses cancel out benefit?

Or what about using mirrors - local auctions always have loads which sell for little?

keith

[Clifford]

Hmmm...  interesting thought.

If you used curved (or fauceted) glass, you would need to have a large air gap under the glass, and the glass would have to extend far beyond the edges of your panel.  

With the mirrors and odd glass shapes, you are quickly approaching the subject of using mirrors and prisms to effectively increase the surface area of your panel.

For example, take your basic 6 foot satellite dish and mirror the inside, then point it at the sun.  It should focus a very intense beam about where the satellite reseiver should be.  However...   most "ordinary" solar cells wouldn't be able to tolerate that kind of treatment for long.

A solar oven does about the same thing.

Remember that for solar panels, heat is an unwanted byproduct.

Oh...

I was just thinking....  it might be worth looking up some of the research on diamonds.  If I remember right, the faucets on diamonds are generally designed so that wherever ambient light enters a diamond, it is reflected back up through the top faucet, thus adding to the brilliance of the stone.  And...  even light bouncing down through the top faucet tends to reflect back up through it...

The effect has to do with the angles that the light hits the faucets and whether the light is reflected internally or passes through the faucet.

Anybody have a cheap 10,000 ct clear diamonds available?

[windyknight]

Just want to clarify this is not a pv panel but a solar water heater.  I appreciate there is no advantage from 'concentrating' sun into one spot, indeed for more effecient heat transfer it is best over whole surface area - I was just really pondering not losing anything by reflection from surface glass!

k

[scottsAI]

Windyknight,

The simple answer is no.

Taking a look at the physics of optics, the smaller the angle the more reflection you will get. Look at the water in a pond. You can only see down for a short way out. Reflection is the reason you can't see further. (also dirty water:)

Adding a curved dome to the panel will make it worse. Think about it. Some points of the dome will be better, going along the entire surface, you can realize the angle becomes more acute on the far side of the dome. Not a good result.

The dome also increases the surface area, thus heat loss. Adding to cost etc.

Rotation of the panel is an option but the reality is the cost/complexity.

Mirrors are cheap, much cheaper than the panel.

To make mirrors work you must rotate them. The mirrors are light, easier to rotate than the panel. Down side to this is the area needed, not something your going to put on your roof.

In the past I thought large panels were the way to go. Materials were cheap.

Since the cost increase of copper and other materials, I'm rethinking the way to go. Panels have a limited temp range, higher is better for many things. I would like to use the heat to run my AC system. 175'f not high enough.

Now considering a trough solar collector.

A trough is a solar tracking mirror, either one or two axes, that generally reflects sunlight onto a linear receiver that is perpendicular to and is in alignment with the sun and the central axis of the linear parabolic mirror.

Using http://www.solar-trackers.com/tra-deci.jpg type of tracker, looks cheap.

Something to think about.

Have fun.

Scott.

[willib]

i believe windyknight is talking about reflecting the sunlight onto the surface of the solar waterheater correct??

if yes, then yes ,lol

it would benifit you to reflect the sunlight , with a mirror, onto the solar water heater ..

[GaryGary]

Hi,

I think that you could increase the amount of sun on your panels with fixed reflectors.  The following is from The Passive Solar Energy Book, Mazira.  It gives the most specific information for collectors that are mounted on a vertical surface, but indicates that you can also get good results for tilted collectors as well.

For a vertically mounted collector, the ideal place for a reflector is just below the collector, and slopped down about 5 degrees (ie nearly horizontal).  You keep getting gains as the reflector extends out from the collector until the reflector is about 1.5 times as long as the collector is high.  For lengths greater than this, the gains fall off rapidely.  The reflector should also be wider than the collector to work better in the pre and post noon times.  The graphs they provide show gains up to 50%.

They also show some reflector configurations for tilted collectors, and most of these have the reflector extending out from the top of the collector, and making an angle with the collector in the general ballpark of 90 degrees.  They don't give a lot of guidance on what the best angle is.  

You might try just experimenting with a not to large mirror in various positions, and just observing what kind of reflected sun pattern you get on the collector as the sun moves over.

I agree with the other poster on curved or angled glass.  I don't believe that it will help.  This seems like a variation on the idea that you can get more heat or power from a collector that has its east half angled slightly to the east and its west half angles slightly to the west.  This turns out to be not true -- the whole panel facing south receives more sun over a full day.

There are quite a few concepts in this:

http://www.builditsolar.com/Experimental/ShurcliffPart1/TOC.htm

that make use of reflectors postioned in varous orientations -- you might get some good ideas from it.  

Gary

[willib]

I didnt want to start a new topic so i thought i'd put it here.

Today i saw a house with 120 panels on his roof. i wish i had my camera with me , but it made me drool.. they were 10 panels from apex to overhang  x 12 panels wide .

The whole roof was covered .!!

they were those light blue ones ,not the dark ones..