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Re: Feasible new approach to solar power use? - Metal bars thermal - Page 2

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Posted by daestrom on January 13, 2009, 12:30 am
FKohler wrote:

So, as I understand your idea, the sun heats a bar and causes it to expand.
Then, after about maybe 10:00 AM, the bar is no longer expanding and the
sunshine for the rest of the day is wasted?  Unless you find a way to shade
the unit after it stops expanding, and then remove the shade after it stops
contracting.  Or tilt the collector away/towards the sun each time.

Seems like if you go to all the trouble of creating a parabolic collector,
you'd want to actively use it for more than just a couple hours a day.

Absolutely.  So the question simply is, how much energy for how much $$.

In your 10m rod example, how much force can a rod of that exert?  We know
the distance (0.07m).  So let us *guess* that the rod can exert 100 tonnes
of force (9.8e5 Newtons).  That would be an energy of 68 kJ for each cycle
of operation.

Even expensive photo-voltaic, at $/watt in only two full-sun hours
equivalent, would take about $7 worth of PV to generate that same 68 kJ.

I doubt the rod with a collector alone could be had for $7, much less the
ratchet and something that uses the output of the ratchet to make the energy
into a useful form.  Yet PV would supply it in nice DC electricity for that.

P.S.  A 10m long rod would have a great tendency to bend/buckle.  So a
lattice-work supporting several bearings along its length would probably be
necessary.  This structure alone would probably cost more than the energy
output is worth.

Posted by FKohler on January 13, 2009, 7:29 pm

Hello Daestrom,

Well, lets say that so far all I got is a rough idea of what to do,
how to do. After many contributions and your support here, I glad to
know what do improve, right before any serious calculation....

Certainly, to cool the metal is a hefty improvement on efficiency, and
how many times it can be done a day depends on how to do it. Somthin I
didnt figured out yet. Maybe shade the bar is a solution, by using the
parabolic trough turned upside down or any other mechanism. I really
didn figured out but its not an impossible thing I suppose (but will
take some time for sure).

However, as you used in your example, Im not so sure if 02 hours of a
standard PV panel beats up this alternative. Ill work on this
carefully and I appreciatte the comments, but I need more data of
effective cost of both systems. Even considering an active system.

Is there anyone here with any material/opinion/data on the comparison
of steam/stirling solutions x standard PV panel cost of energy?

Thank you

Posted by FKohler on January 13, 2009, 7:52 pm

I guess if we work out on realistic payback time for each solution
would be nice. Ive seen many different sources talking about 4 to 13
years payback time on PV (which depends on the technology, grid energy
cost, etc.), as well as some talking about 50 years (I dont believe).
But I didnt found yet some decent figures on steam and stirling
solutions (using solar concentrators).


Posted by azuredu on January 13, 2009, 8:13 pm

Solar concentrator plus thermoelectrics:

Heat and power cogeneration, realistic and cost effective.

Posted by Mauried on January 14, 2009, 1:58 am


Whats the cost of the thermoellectric generators per watt output.

No costings at all on the Web Page.

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