Renewable heating Systems

A flat black surface coating should be the best absorber for home solar heating projects. I would use a flat black paint that is high temperature rated similar to this one...

http://www.northlineexpress.com/itemdesc.asp?ic=5SA-8115

Black paint is not a particularly good surface for collectors.
I dissagree with this statement.

If it is not good, it is probably an unsuitable type of paint badly applied onto an inappropriate substrate.
Del

Flat black paint is slightly better at absorbing sunlight and turning it into heat. The high gloss stuff can in fact reflect some away. Also depending on how thick and what type of paint was used there may also be some slight thermal absorption and conduction variations from one type to another as well.

Black paint is not a particularly good surface for collectors because....

...although most commonly available black paint exhibits an desireable characteristic of high absorptivity... most commonly available black paint also exhibits an undesireable characteristic of high emmisivity.

The problem is that when the absorber gets hot, the surface coated with the black paint begins to radiate a great deal of energy that might otherwise be kept in the system.

Choosing a selective surface with a very high absorptivity to emmisivity ratio allows the system to keep a greater portion of the energy received.

Benbenben

Because I typically find myself the underdog, defending what is valid if unpopular and because I am a CR4 outcast, unable to log on for months.....links are provided below if you would like to understand...even if you prefer to remain safely with the majority and perhaps even attempt to heckle...

http://www.solarmirror.com/fom/fom-serve/cache/43.html

http://www.redrok.com/concept.htm

http://books.google.com/books?id=Xn8KbsgeFrwC&pg=PA212&lpg=PA212&dq=black+paint+emissivity+absorption&source=bl&ots=Rk_nJsm8mA&sig=CaxnPwfgkRKtLGyq4DxsrYfY29c&hl=en&ei=ghnySsbqCJLFlAeYlfy9Aw&sa=X&oi=book_result&ct=result&resnum=6&ved=0CCAQ6AEwBQ#v=onepage&q=black%20paint%20emissivity%20absorption&f=false

For commercial solar applications, black paint may not be a good choice (depends on the collector construction). If they can be used, one of the high aS/E coatings like Nickel Oxide or Black Sulfide could perform better.

For the home builder, flat black paint is really the easiest coating to use. If the painted surface is placed behind a sheet of low E glass or plastic (not an uncommon arrangement), the heat loss due to emissivity should be significantly reduced.

I agree with your statement that 'flat black paint is really the easiest coating to use'......... what could be easier than not putting any thought into it.

This thread seems to be asking more than, 'what is the very easiest.'

The funny thing is, many selective surfaces are relatively inexpensive and readily available to the backyard builder.

.... Have you ever noticed the black oxide layer that forms on stainless steel when it is heated sufficiently in air? Chromium and Nickel Oxides...highly selective and easy to make.

.... Most places that chrome plate, also plate with black chrome... another highly selective surface.

..... Galvanized steel and heavily oxidized low carbon steel are two more selective surfaces that are readily available. if you are concerned that the absorbtivity is not quite as high, just be sure to build the absorber with plenty of ridges and valley with intentions of any reflected radiation striking at least one more surface.....

Benbenben