A solar plant that's worth its salt

[Kevin Rooney]

That's the title of a headline which appears in today's online version of the LA Times.

This alternative method of producing "green" electricity has the advantage of being able to generate power even when the sun isn't shining/water flowing/wind blowing, as the molten salt can be stored and later used to convert water into steam.

The devil's in the details. In arid sections of the country where sunshine is plentiful, water is not. So, the questions which will arise will include - what is the source of the water powering the turbines, and will that use negatively impact upon other users.

 

[TCD]

Interesting article. The power generation method is not really as "futuristic" as the article glams it up to be. Basically, we're using mirror concentrated solar energy to heat a heat transfer medium to run a generator. What they seem to be claiming is new or different about this is the ability to store the molten salt for long periods without losing energy.

As someone (I think it was DougPaul) said in another thread, energy is difficult to store. I'd like to know more about how they can keep this hot salt hot. The mirrors and towers and all that stuff are no big deal. What's not glamorous, but I want to know more about, is how are they insulating the salt tank?

That's why I advocate making Hydrogen as the first step in energy conversion. You can store Hydrogen more easily than energy.

TCD

 

[Little Rickie]

They could ship in washed potatoes, fry them in the hot salt, cooking and salting the chips at the same time. Then capture the moisture cooken off the potatoes as the salt heats up again and cycle it back into the salt to run the turbines. Ship out the potato chips. Hopefully the fuel used to ship potatoes in and chips out would be less that the fuel to fry them. Even if it wasn't with goverment subsidies it would "look" energy efficent.

To wild to believe. Them look at farm and energy subsidies for converting corn into alcohol for fuel.

 

[Kevin Rooney]

... What's not glamorous, but I want to know more about, is how are they insulating the salt tank?
TCD

The same question struck me when I read the article.

As you point out - using mirrors to focus sunlight is not new, especially parabolic mirrors. There's a large facility not too far from the LA Times article's reference (Barstow, CA) on US 395 in Boron, CA which focuses the sunlight on an oil-filled tube a few feet above the mirror's surface. The mirrors track the sun's position during the day. A similar installation is slated to be built within 10 miles of where I now live, and there's been discussion of using a nearby town's effluent for cooling.

 

[Little Rickie]

I mean no offence to the science of this, I think the science is cool and like hydrogen best, but the outcome, in all likelyhood, will be determined by politics and economics.

 

[DougPaul]

The power generation method is not really as "futuristic" as the article glams it up to be. Basically, we're using mirror concentrated solar energy to heat a heat transfer medium to run a generator. What they seem to be claiming is new or different about this is the ability to store the molten salt for long periods without losing energy.

You are correct: this is just a heat engine driven by direct solar heating. Heat engines have to dump large amounts of waste heat*. This is usually done by dumping the heat in a local body of water or river (very damaging to some aquatic life), evaporation (consumes large amounts of water), or into the air with dry towers (large (~500ft tall), but probably the least damaging). In cities, the waste heat can be used for building heating (cogeneration) but we tend to site power plants away from people.

* Nuclear and fossil fuel plants have to dump ~2/3 of the input heat.

As someone (I think it was DougPaul) said in another thread, energy is difficult to store. I'd like to know more about how they can keep this hot salt hot. The mirrors and towers and all that stuff are no big deal. What's not glamorous, but I want to know more about, is how are they insulating the salt tank?

The laws of scaling work in their favor. The volume (proportional to the heat capacity) increases with the cube of the size and the surface area (proportional to the heat loss rate). Thus the rate of cooling will be less in larger tanks.

So I presume the answer is to use a large tank with some appropriate amount of insulation.


The article also makes light of any salt spills. Salt is a persistent poison for many species of plants. Hot salt will also kill simply from the heat.


Mirror based solar power plants make a tradeoff: they are cheaper because mirrors are cheaper than the actual light absorbers, but require a clear sun so that the light can be focused. Non-focused solar power plants (eg an array of solar cells) will work under a cloud cover as well as under a clear sun.

Doug

 

[peakbagger]

With enough govenrnment subsidies, large scale solar thermal is worth building. There were several plants built during the first energy crunch and they survived as long as subsidies existed. The subsidies are back, so there is rush to build the plants with mandatory carbon trading, these plants will have permanent subsidies so more will most likely be built.

The solar tower plants are the most efficient but also most expensive. As reported they can store thermal energy for limited times. They dont have to use a lot of water, but if they do closed loop cooling the efficiency of the plant goes down.

The solar trough plants are less efficient but cheaper to build. They also can do closed loop cooling with the same consequences. These plants can store power for limited off peak.

There is another recent solar thermal design that mounts sterling cycle engines on indivdual tracking dishes (looks like a high tech satelite dish)that are strictly air cooled. Pretty slick but the cost is higher than the solar trough plants. They dont have storage capacity.

Unfortunately in New England, solar thermal isnt in the cards except for small home applications. About all we have are winds, tides and trees.

 

[DougPaul]

As you point out - using mirrors to focus sunlight is not new, especially parabolic mirrors. There's a large facility not too far from the LA Times article's reference (Barstow, CA) on US 395 in Boron, CA which focuses the sunlight on an oil-filled tube a few feet above the mirror's surface. The mirrors track the sun's position during the day.

This is a cylindrical mirror and focuses in only 1 dimension. The mirror only needs to be moved in 1 dimension (rotation along its axis) to aim its focus at the sun. The system in the article requires the mirrors to be aimed in two dimensions to approximate a large parabolic reflector. (The more complex mirror aiming is likely to require computer contol.)

A similar installation is slated to be built within 10 miles of where I now live, and there's been discussion of using a nearby town's effluent for cooling.

Sounds like the fish will be very happy... (Fish can be very particular about water temps so this can effectively dam the river for the fish.)

Doug

 

[Kevin Rooney]

...Sounds like the fish will be very happy... (Fish can be very particular about water temps so this can effectively dam the river for the fish.)

Doug

Fish are the least of the concerns where these facilities typically are sited. There are no brooks, streams or rivers. And as for salts as with the LA Times articles - impact on plants from salts would be negligible as it is sited in a very area area (upper Mojave). And, if vegetation does need to be planted, there are salt grasses which do quite well.

 

[Little Rickie]

With enough govenrnment subsidies, large scale solar thermal is worth building. There were several plants built during the first energy crunch and they survived as long as subsidies existed. The subsidies are back, so there is rush to build the plants with mandatory carbon trading, these plants will have permanent subsidies so more will most likely be built.
.

But at what cost? If this was a competitive energy alternative then the tax payers wouldn't carry the load.

Now if the minds of people really focused of improving the technology then this could be a great thing, but no...self interests, greed and politics will screw this up.

 

[Dr. Dasypodidae]

Unfortunately in New England, solar thermal isnt in the cards except for small home applications. About all we have are winds, tides and trees.

And, shallow geothermal energy. The free pdf at the link below is European and a bit dated, but many architects in the New England area are working SGE into their building designs. I have heard that the payback periods are typically less than 20 years, and some times as low as 10 years.

http://www.docstoc.com/docs/2198805/Some-history-of-shallow-geothermal-energy-use