Use a panel to produce steam and electricity?

[Eccentric Dyslexic]

Just thinking out loud here, being as solar thermal panels are 80% efficient, could they be used to produce pressurised steam to then turn a small alternator?  I'm thinking this should be possible no?  You could capture and cool the steam after it has released its pressure and recycle the liquid...if the liquid is pure enough it wont scale up the manifold.

Just an idea!  Mite be worth an experiment....

Steve

[pdf27]

Problem is that they can only produce very low quality steam (if stagnation temperature is ~170 C, then any meaningful quantities of steam will be at well less than this). At 150 C, the Carnot efficiency of such a system would only be ~25% for a good condenser, and real efficiency will be around 10%. Solar thermal for electricity only really makes sense where you can spread the capital cost of the plant over a few megawatts and you can get the steam temperatures much higher.

[renewablejohn]

Just thinking out loud here, being as solar thermal panels are 80% efficient, could they be used to produce pressurised steam to then turn a small alternator?  I'm thinking this should be possible no?  You could capture and cool the steam after it has released its pressure and recycle the liquid...if the liquid is pure enough it wont scale up the manifold.

Just an idea!  Mite be worth an experiment....

Steve

The way to do it is by replacing the water with thermal oil which then gives max temperature of 230C which can then be used in conjunction with a thermal oil steam evaporator to produce steam upto a maximum of 25 bar pressure.

[ericw]

At stagnation temperature the losses equal the incoming energy so the efficiency is pretty well zero.
The high efficiencies quoted only apply at temperatures relatively close to ambient.

[renewablejohn]

At stagnation temperature the losses equal the incoming energy so the efficiency is pretty well zero.
The high efficiencies quoted only apply at temperatures relatively close to ambient.

If you use panels such as ritter stagnation temperatures are not reached until 270C so heating thermal oil at 230C is well within the efficiency range.

[EccentricAnomaly]

Solar thermal for electricity only really makes sense where you can spread the capital cost of the plant over a few megawatts and you can get the steam temperatures much higher.

The other way solar thermal for electricity can make sense is if you store the energy as heat, e.g., with phase change salts to generate electricity in the evening. Again the capital cost and efficiencies of storage (area to volume ratios, etc) only make sense for big plants.

[renewablejohn]

Dont know what you classify as a big plant but the numbers stack up for me at a modest 250kw.

[pdf27]

Can you give us some idea as to your cost per kWh?

[renewablejohn]

Can you give us some idea as to your cost per kWh?

I could but not going to.  Being a hybrid system its not quite as simple as biomass in compared to electric generated as the primary output of the superheated steam dryer is the drying of biomass material (woodchip or grass).

[pdf27]

So essentially you have a commercial use for the waste heat from the cycle? Since that'll be 80-90% of your usable output then it makes a lot more sense commercially than a domestic scale solar thermal steam setup as described in the first post...

[dhaslam]

It is possible to concentrate sunlight using a fresnel lens.   You  would also need a tracking system  to keep  the sun in focus.    It should be possible to power a small Tesla turbine.    It would be  quite tricky work. 


http://greenpowerscience.com/

http://www.youtube.com/watch?v=yk-_IGd4xYE

[renewablejohn]

So essentially you have a commercial use for the waste heat from the cycle? Since that'll be 80-90% of your usable output then it makes a lot more sense commercially than a domestic scale solar thermal steam setup as described in the first post...

Domestic scale systems such as this are already available

http://www.coolenergyinc.com/solar.html