The answer to all energy conversions?

[dcasto]

As viewers know, i'm a skeptic on wierd stuff coming out (radio frequecy to burn water). Our local news paper had an editorial on this link and NREL.

http://www.stirlingenergy.com/whatisastirlingengine.htm

Through out the literature they quote effiecies of 25% to 29% for conversion to electricity of the sunshine. What I guess is that they mean the units will produce electricity at the rated capacity for about 25% of the time. Any guesses anyother way?

The editorial says that instead building a new 1500 MW power plant, the builder should put these in. at 10 to 25 KW per unit, thats 100,000 of the units and they only work in the day time, so at the 25%, thats 600,000 sets of mirrors and generators.

Final question, have we all gone nuts over this? The units in the article will work and use proven technology, but why do we look at these things as a savior?

 

[Sailor53]

Rather than being based on the amount of time that the sun shines, I would think that efficiency is input power divided by output power. The sun delivers a certain amount of watts per square foot, which varies according to latitude, time of day, etc. Multiply this by the area of the mirror will give you the input power. Your output power is either the mechanical power output of the Stirling engine, or electrical power output of a generator connected to the the Stirling engine - your choice.

Efficiency does play a part in determining how many generators you need to supply a certain load, but keep in mind that your power output is always going to be zero at night.

 

[stevenal]

Efficiency is defined as output power over input. It would a pretty good trick if the inverse was 25%.

I see no reason to be skeptical of using radio waves instead of electricity to separate H2 from water, and burning the result. The only thing to be skeptical of is the idea that this will somehow save the world.

 

[IRstuff]

Not sure what the issue is. The Stirling engine has a theoretical efficiency of >40%, dependent on inlet temperature, while an electrical generator can have efficiency above 80%. A net of 30% sounds plausible.

This would be nearly double the efficiency of a typical solar cell, so there would be a plausible argument that such a system would be more productive than a solar cell array, particularly since such a system could put out AC line power directly, without the need for an inverter.

The big efficiency loss is areal, since there's a line of sight limitation on mirror reflections that does not exist for solar cells directly viewing the sun.

TTFN

FAQ731-376

 

[BJC]

Why put in in space when we have plenty of deserts?

When you factor in the cost of putting the plant in orbit, maintenance in orbit etc. it's probably just as economical to use half of Arizona, New Mexico and Southern Utah and Arizona.
I have not reasearched it but can't you use a solar cell to reflect the thermal enery in sunlight to the Sterling engine and use part of the spectrum for generation photovoltaic powerer?

 

[IRstuff]

Not sure if anyone suggested a space-based system. The initial cost and maintenance would be prohibitive, as you suggest.

My discussion covered a weak point of a thermal vs photovoltaic approach in that mirrors have a more limited coverage compared to a direct-view solar panel.

TTFN

FAQ731-376

 

[davefitz]

IRSTuff:

applied commericial stirling solar engines are now commercially available at Infinia , with a net efficiency of about 20%. They used a tracked , focused reflector to focus the sunlight onto the hot end reciever of the stirlig engine. see:

http://www.infiniacorp.com/applications/clean_energy.htm

another solar thermal effort is by Ausra- they have large array of fresnel focused (?), tracked , flat plate reflectors that focus the sunlight onto a common hot water pipe , which boils water and sends the 2 phase mixture to a saturated steam tank , for expansion across a sat steam turbine. So long as they limit themselves to sat steam, they would be better off using the system in a hybrid mode with a gas fired combined cycle plant: the gas turbine exhaust would only heat the superheaters and economizers, while the evaporator duty would be provided by the Ausra solar fresnel evaporator.

 

[IRstuff]

I understand the concept.

But, if you consider the reflectors closest to the direction of the sun during late afternoon, you'll find that their capture cross-sections diminish greatly, reducing the overall efficiency.

So, if you consider total kWh generated per day, you might find that solar furnaces are THAT efficient compared to solar cells.

TTFN

FAQ731-376

 

[davefitz]

The hybrid combined cycle I suggdested using the Ausra fresnel focusing solar collector is similar to the now announced solar combined cycle by Alstom. The Ain Beni Mathar project will integrate steam generated by the solar collector in the HRSG .

 

[davefitz]

Alsa, solar thermal/steam and biomass fired boilers can be used to offset the rate of coal fired in large coal fired central stations. A simple method is called" parrallel power combined cycle" , where the steam produced from the solar or biomass fired evaporator is used to heat the feedwater of the coal fired plant. This ( renewable) steam would be inducted to the feedwater heaters, which offsets normal steam extraction from the steam turbine. At max implementation, the coal fired boiler can reduce MCR firing rate by 15% yet still make 100% MCR steam turbine load.

Although using a large array of reflective mirrors next to a coal pile would imply a lot of Windex and paper towels used to clean the mirrors