Posted by mpate on January 23, 2009, 3:22 am
> The Carnot efficiency limit is 1 - (Tc / Th), where Tc is the cold head
> temperature and Th is the hot head temperature (both in Kelvins). A 70F
> cold head and a 725F hot head yield a theoretical maximum efficiency in
> the area of 54%.
> A parabolic trough can easily provide the 725F, but to calculate the m2
> or ft2 needed we'd need to know the efficiency of the absorber - which I
> don't have a handle on, and won't until warmer weather (it was -14F and
> windy last I checked, and that's too cold for this geezer to play outside).
> --
> Morris Dovey
> DeSoto Solar
> DeSoto, Iowa USAhttp://www.iedu.com/DeSoto/
I was thinking about the fluidyne at when I started reading the
thread, glad you mentioned it here.
I found the solar constant in btu/hr and then a conversion from btu/hr
to horsepower here:
http://raenergy.igc.org/btu.html so assuming this is correct
the solar constant per sq ft at 428 btu/hr and then the conversion 1
btu/hr to 0.0003929 HP
428*0.0003929 give us 0.168 HP/sq ft which means we need about 6 sq ft
to get one HP collected.
Say the optics might be 80% efficient on average (I know they can do
better clean and fresh).
The absorption of the collector pipe say is 50% so now we need 15 sq
ft per HP.
Take it from here.
Posted by Morris Dovey on January 23, 2009, 9:16 am
mpate@oscintl.com wrote:
> I was thinking about the fluidyne at when I started reading the
> thread, glad you mentioned it here.
>
> I found the solar constant in btu/hr and then a conversion from btu/hr
> to horsepower here:
> http://raenergy.igc.org/btu.html so assuming this is correct
> the solar constant per sq ft at 428 btu/hr and then the conversion 1
> btu/hr to 0.0003929 HP
> 428*0.0003929 give us 0.168 HP/sq ft which means we need about 6 sq ft
> to get one HP collected.
> Say the optics might be 80% efficient on average (I know they can do
> better clean and fresh).
> The absorption of the collector pipe say is 50% so now we need 15 sq
> ft per HP.
>
> Take it from here.
Thank you. I'll still need to test this thing before I dare do any
bragging...
What I know so far is that the light reflected from the hot head is so
intense that I can't look at it without dark glasses - and I'm thinking
that welding goggles might be a lot safer. That's a lot of light being
reflected and, at the moment, I'm hoping that your 50% number isn't
wildly optimistic.
I'm still /hoping/ to squeeze a full horsepower out of my 4x8 mirror -
but before I get too bound up in dealing with all of the various loss
mechanisms (interpret as: spending more of my meager resources), I just
want to see it oscillate decently.
I'm eager for spring to arrive! :)
--
Morris Dovey
DeSoto Solar
DeSoto, Iowa USA
http://www.iedu.com/DeSoto/
Posted by EskWIRED on January 16, 2009, 8:47 am
Does anybody in a.e.h have an opinion about whether the problem of storing
electricity for home use has been solved by the invention of pumped
storage with two ponds, as discussed below?
What are the economics, compared with, say, selling excess output into the
grid?
> Curly Surmudgeon wrote:
> > Y.Porat wrote:
> > >> knews4u2c...@yahoo.com wrote:
> > >> >http://www.enn.com/top_stories/article/39077
> > >>
> > >> > A Wind Turbine for Every Rooftop?
> > >>
> > >> The worst possible place to have one.
> > >>
> > >> In urban areas, trees and homes act as a big windbrake You will get
> > >> little power. There is also a danger of structural damage to your home.
> > >>
> > >> To get decent results, wind turbines need to be in unobscured areas and
> > >> at least 25m (80ft) above ground level.
> > >
> > > -------------------------
> > > another problem that has to be resolved reasonably is
> > > **storage of the electric output**
> >
> >
> > That's been solved for a long time but it requires hilly land, two ponds,
> > a pump and water-powered generator. One pond downhill, the other as high
> > up the hill as you can. Pump the water uphill during generation and
> > generate power when you let it flow down to the lower pond.
> Fine if you have hilly (ideally mountainous) land. Surprisingly few suitable
> locations exist.
> Graham
--
The whole problem with the world is that fools and fanatics are always so
certain of themselves, but wiser people so full of doubts.
-- Bertrand Russel
Posted by RED on January 17, 2009, 12:12 pm
> Van Chocstraw wrote:
> > Ever heard of a pole? Go go vertical you know.
> Ever heard that a pole of that size needs supports (guy lines) or building
> with expensive high strength materials ?
That problem has been solved for a long time.
Utilities use telephone poles, so that must be a complete solution for
everybody.
Posted by Ulysses on January 18, 2009, 12:55 pm
> Yes, that's currently a missing element. First the upper pond. I've
> arranged with a local contractor to excavate the pond and dig a well.
> Then I'll fence it in and put pigs in for two years to seal the bottom.
> After that the pipeline & generator.
Please tell me the story of the little piggies. I've heard of bentonite for
sealing a pond but not pigshit. How do you keep the pigs from drowning when
it rains and the ponds fill up?
> --------------------------------------------------------------------------
----
XML site map
> temperature and Th is the hot head temperature (both in Kelvins). A 70F
> cold head and a 725F hot head yield a theoretical maximum efficiency in
> the area of 54%.
> A parabolic trough can easily provide the 725F, but to calculate the m2
> or ft2 needed we'd need to know the efficiency of the absorber - which I
> don't have a handle on, and won't until warmer weather (it was -14F and
> windy last I checked, and that's too cold for this geezer to play outside).
> --
> Morris Dovey
> DeSoto Solar
> DeSoto, Iowa USAhttp://www.iedu.com/DeSoto/