Solar thermal heat exchanger to run a steam turbine?

SolaRevolution

I recently saw an old (now defunct) heat exchanger steam turbine system at a farm in Covelo , CA.

As the owner described it to me:
It had, perhaps, 100 sqft of mirriors mounted on a tracker which focused the sun on steel coils. The coils had oil pumped through them and down to a 500 gallon storage tank. The oil would get to 400 deg F. Water was then put into a heat exchange coil in one end of the oil storage tank and steam came out the other side. This was used to drive a turbine and then used for ag water pumping in lieu of about 5 kW of grid power.

Aperarantly it was in use for several years but is now burried in blackberry bushes. The concept is great! The energy storage potential of hot oil would be considerable. It seems to me the problem is in maintenance and safety. It would take many diciplines of expertise to keep it running. A maritime mechanic could do it. Hot oil, steam, and electricity! Oh boy!

Are there any practical residential or farm scale systems like this in use now?

BB.

Re: Solar thermal heat exchanger to run a steam turbine?

The problem is the "boiler"... Many people have been killed over the years by steam explosions--So even if you are willing to take the gamble, there are probably enough laws and inspectors out there to make a large system pretty much an easy target.

One of the "issues" with storing heat is that there is generally lots more "heat" in the transition temperatures (from solid to liquid, from liquid to vapor)--So that a simple oil based system that raises the temperature of the oil from 300-400 degrees F does not store nearly as much heat as a similar sized system using ice/water or molten salts.

So--from what little I have read about, mostly would use the oil as a transfer fluid rather than as the thermal storage media itself.

-Bill

mike95490

Re: Solar thermal heat exchanger to run a steam turbine?

Sounds a lot like Solar One, run by SCE, till it caught fire and burned in a spectacular blaze
http://www.nrel.gov/csp/troughnet/power_plant_data.html#segs_i
Newer plants use a molten salt as the working fluid.

story
http://www.digitalstoryteller.com/BTV99/hartley/0303.shtml

SolaRevolution

Re: Solar thermal heat exchanger to run a steam turbine?

Yea Bill, it's scary as heck to think about what could go wrong.

It's just a bummer to see how small scale off-grid just keeps comming back to batteries. There seems to be no (practical) escape unless you have an ideal hydro site.

-Alex

peakbagger

Re: Solar thermal heat exchanger to run a steam turbine?

Study up a bit on the Carnot cycle and you will see why small scale solar thermal electric power generation is not going to be economic. It just takes too much expensive hardware generating at low efficiency to make sense.

SolaRevolution

Re: Solar thermal heat exchanger to run a steam turbine?

A pic of the ruins of the reflector array for an old 5 kw system.
Many of the mirriors are still there. The oil storage and the steam turbine are somewhere under all of the blackberries.
Attachment not found.

Ralph Day

Re: Solar thermal heat exchanger to run a steam turbine?

Talk about some robust racking for a pv tracking system! I can hear the wheels turning already...a few changes to sensors, swap out mirrors for pv panels, make lots of jam then cut out the berry bushes. Has nobody seen the potential of this hardware yet? The heck with old satellite racks and actuators.

Oh yeah, a wire brush and some rust paint too.

SolaRevolution

Re: Solar thermal heat exchanger to run a steam turbine?

Here is an article about the new The Torresol Energy Gemasolar plant in Fuentes de Andalucia, Spain.

http://www.physorg.com/news/2012-03-thermosolar-power-station-spain-night.html

From the article:
"Energy is stored in a vat filled with molten salts at a temperature of more than 500 degrees C (930 F). Those salts are used to produce steam to turn the turbines and produce electricity.

It is the station's capacity to store energy that makes Gemasolar so different because it allows the plant to transmit power during the night, relying on energy it has accumulated during the day."

Not quite residential scale.;)

techntrek

Re: Solar thermal heat exchanger to run a steam turbine?

So if the dangerous part is the steam turbine, what about just keeping the molten salt part or another medium and using that for various thermal uses? Air/water heating, heat-driven A/C, etc. Any more or less efficient than a run-of-the-mill solar thermal system using water as the storage medium? At the home scale of course. From a safety standpoint I guess water is the only option - dense for thermal storage but not too dangerous (unless it gets above 100 C).

peakbagger

Re: Solar thermal heat exchanger to run a steam turbine?

Dump the stream turbine and switch it over to organic Rankine Cycle system. Its basically a heat pump that runs backwards. ORC boils refrigerant rather than water, the pressures are lower. ORC is still constrained by Carnot cycle so dont plan on a lot of effiency.

jagec

Re: Solar thermal heat exchanger to run a steam turbine?

techntrek wrote: »

So if the dangerous part is the steam turbine, what about just keeping the molten salt part or another medium and using that for various thermal uses? Air/water heating, heat-driven A/C, etc. Any more or less efficient than a run-of-the-mill solar thermal system using water as the storage medium? At the home scale of course. From a safety standpoint I guess water is the only option - dense for thermal storage but not too dangerous (unless it gets above 100 C).

At the home scale, thermal uses don't really need the high temperatures of molten salt, and so a large, well-insulated water tank really is the cheapest and most effective option. High temperatures are more efficient for running heat engines, but if all you need is the heat itself, then the safety issues, greater thermal losses, and cost/complexity bring us right back to "standard" solar thermal.

Plus you can build it with stuff that you buy at the local hardware store.