What are pros and cons of using concrete as absorber in a solar panel?

[flying penguin]

I have recently replaced my patio doors and saved the double paned glass.

I plan to use them to build solar panels. My plan is to build a frame (wood),

run some pipes through the frame and cover it with the glass. My question

is would concrete (painted black) make a good absorber plate? There

is the obvious drawback of adding weight which could make roof mounting

problematic. I believe an advantage might be that it could hold heat

longer than a sheet of metal possibly providing heat later into the

evening (when people will actually be in the house). I have two

possible ideas. One is to pour a flat slab into the frame between .5 and

1 inches thick and lay the pipes over the top of it. The other idea is

to actually cover the pipes in concrete so that the pipes are complete

encased in the slab (disadvantage here is not being able to fix possible leaks).

The slab might get as thick as 1.5 to 2 inches thick in this case.

Does anyone have any thoughts that I should consider before going this route?

Thanks for any info.

[joe4324]

Ack.. this is a  tough one,  I mean,   well it "would" work.  there is no doubt about that.   But the more mass inside the collector the longer it will take to get heat out the other end,  AND the more of that heat will be lost in the evening and night as the collector bleeds it off while not in use,  I think you could be more effeceint, if you could keep as little heat as possible in the collector, and move it to another form of storage that is more insulated, like a tank inside your home...   OR you could go the oppostie direction, and do a Batch water heater.   Instead messign with concreate or anyt of that stuff,  find a 55gallon drum,  build a box to hold it,  with that glass on it, super insulate it, SUPER insolate it,  then just let it sit on your roof, in the summer it would probably get 130F inside that box when you werent using much water.  and just plum the output down to your hot water heater,  you could possible coast sometimes using nothing put sun heated water

but I'm no expert!  

[joe4324]

Ack.. this is a  tough one,  I mean,   well it "would" work.  there is no doubt about that.   But the more mass inside the collector the longer it will take to get heat out the other end,  AND the more of that heat will be lost in the evening and night as the collector bleeds it off while not in use,  I think you could be more effeceint, if you could keep as little heat as possible in the collector, and move it to another form of storage that is more insulated, like a tank inside your home...   OR you could go the oppostie direction, and do a Batch water heater.   Instead messign with concreate or anyt of that stuff,  find a 55gallon drum,  build a box to hold it,  with that glass on it, super insulate it, SUPER insolate it,  then just let it sit on your roof, in the summer it would probably get 130F inside that box when you werent using much water.  and just plum the output down to your hot water heater,  you could possible coast sometimes using nothing put sun heated water

but I'm no expert!  

[skravlinge]

It will work, but you might be home during early morning, and just want to save  surplus heat fr the night.

But if you want to save heating for the night, you can melt wax in an

insulated container, when it becomes solid, it gives back the heat, which is

about 6-8 times than storing in water.

The insulation do not need to be extrme if you just save for the next night.

Jorgen  in Sweden

[flying penguin]

Just wondering if there is any toxicity or explosion

hazard with the melted wax.   Are there any precautions

necessary?   Can I just load up a 55 gal drum with the

wax and run pipes through it?    Should the drum be sealed?

Thanks

[skravlinge]

You should not have it more than just meltet. The toxic risk depends  of what stuff you use, there is harmless some even patented,

55 gallons will save a lot of heat, and it will stay at the melting temperature until it all are solid. If the salt or wax you use melt at 60 centigrade, it will keep the temperature  steady  whitout any regulator.

Look for phasechanging  in books or on the net as I do not know which is the best and cheapest at your place.