Ian Stirling wrote:
wrote:

ok theres a proven system a bit like this using shade cloth. 2 or more
layers of shade cloth, just one of glass. The air flow is from near the
outer glass towards the inside, through the cloth, and efficiency is
very high, far above any black or selective absorber system. And the
cloth is cheap, unlike glass.

Interesting.

IIRC The solar barn uses it at
http://builditsolar.com/Projects/Spa...rn_project.htm


Possibly - there is an obvious tradeoff (for non evacuated panels)
between power output, and maximum temperature.
Obviously, adding another layer of glazing will always increase the
maximum steady-state temperature, but due to absorbing some light, will
decrease the power output.

only above a point. Double glazing will give more power out than
single, as conduction losses are less. Triple may not. Extending the dg
layer below the first glazing layer also provides reduced heat loss.

To restate.
Adding another level of glazing will increase the maximum temperature it
will reach at 0 flow.

yes

It will reduce the maximum power output at a reasonable flow to below
the temperature without an extra pane, due to the lower power due to the
losses from the first pane.

I still am not seeing how you can conclude that, since an extra layer
of glazing has 2 opposite effects, not just one. First there is 5% or
so absorption reducing the power output, then there is the double
glazing effect reducing convention losses, which increases power out.



Instead of having a 1m^2 radiator, in a 1m^2 panel, you have a 0.5m^2
radiator in a 1m^2 panel, and a fan, to circulate the air to the
radiator.

ahh I dont think youd need a fan. Why dont you run this past
alt.solar.thermal? Lots of expertise there. When I calculated something
similar, small collector plus plenty of space yielded more than the
small colelctor in small box but less than the bigger in the bigger
box. I think small rads in bigger boxes would make good sense, long as
youre not short on glass.


NT