Development of fuelless powerplants?

As Charisian industry develops, the need for more and more fuel will compete with iron production very rapidly. Iron production itself is very fuel-intensive due to the high temperatures required. However, with the discovery of really large silver deposits now available to Charis, there is another option.

The proposed plant works as follows;


1) Create lots of solar troughs using silver and glass, both of which Charis has.

2) At the focal line of the solar troughs you have a (preferably ceramic) pipe filled with Tin/Lead alloy for its really low melting point and comparatively high boiling point.

3) The solar troughs start melting the tin/lead alloy once they hit a bit over 200 C in temperature so you now have a liquid that can be moved around, melt a bit more of the alloy and slowly increase the amount pumped into the system in a liquid state. Over the course of a day, the solar troughs can reach very high temperatures, easy exceeding 600 C, with 3000 C being possible (though the latter is ill-advised; the pipes will burst)

4) You store the high-temperature molten tin/lead in an accumulator, like the ones normally used for water. A sufficiently large accumulator with a bit of insulation will take many days or even weeks to fall again below the melting point. That can be used to store the energy with higher energy densities than batteries for much cheaper, easy and simple to produce materials. Of course, you don't let it to cool down over days - you use most of the heat over the day and night in your industrial needs until the mix is low-temperature but still liquid the next day when you send it into the solar troughs to be reheated.

5) You can feed the high-temperature mixture into a boiler to heat water and produce steam without burning fuel. You can feed the mixture into a modified furnance to heat it to 600 C or more, reducing the fuel requirements by 30-40% (or even higher, with a bigger solar plant that gains higher temperatures)


6) Once the proscriptions are lifted and the Rakurai is gone at a later date, upgrading the plant to electricity production is really easy.






Essentially, it is a solar power plant that uses no modern technology whatsoever and, once constructed, obviates the need for fuel for many things. Charisians know the sun heats things up. They have a lot of sun. They know mirrors. They know accumulators. They know that a liquid takes time to cool down. So it's a viable technology that doesn't really introduce anything new.

Except for solar power, that is.

From my liberal arts MA point of view it seems as if you're increasing the capital and maintenance/operation costs and reducing (weather dependency?) the carbon fuel costs. Depending on the availability/costs of carbon fuels you may not have a winner here.

Good out of the box thinking!

EdThomas wrote:Good out of the box thinking!

Can't take the credit for that - the first commercial solar plants with thermal accumulators have recently appeared in real life. Though they use liquid salt as the accumulation medium rather than my proposed tin/lead mixture - I preferred the tin/lead mix due to its significantly lower melting point, higher density and thus energy density; liquid salt OTOH has higher melting point but better insulation properties.

it seems as if you're increasing the capital and maintenance/operation costs and reducing (weather dependency?) the carbon fuel costs.

Solar plant needs:
Mine the silver for the mirrors and tin/lead for filling.
Make the mirrors, pipes and accumulator.
Polish mirrors every so often.
Reorient mirrors seasonally.
Replace worn ceramic pipes.
Coal plant needs:
Build the furnace, intakes and exhausts.
Build major coal mine, often in another country.
Mine significant quantities of coal.
Transport quantities of coal thousands of miles over land and sea.
Feed the coal into the furnace via muscle power or build automated machines for it.
Clean furnace every so ften.
Replace worn ceramic bricks.
As you can see, the solar plant requires higher capital investment and is harder to make BUT its operational costs are insignificant in comparison. Not only does coal have intrinsic value but the sheer amount of workforce required to mine it, transport it from the mine to the sea, transport it overseas to your power plants, and feed it to your plants is staggering. And coal-burning furnaces are extremely maintenance-heavy if you want to keep their efficiency up.

availability/costs of carbon fuels

Expected annual capacity is around 150 GWh per square mile of plant - that figure is taken from real life solar plants near the equator, not theoretical calculations. That's the equivalent of over sixty thousand tons of anthracite burned in a furnace with 30% thermal efficiency (probably higher than what Charis has now). That figure goes up if less efficient fuel is used.



Future development
Great Britain had over half a million coal miners for a period of nearly a century (1880-1960, though that figure almost doubled in the 1900-1930 period). A comparable number of workers producing the required mirrors and ceramics could cover a 100-mile-square in solar plant in less than a decade.
The annual generation of such a plant would exceed 15 PWh. That is equivalent to 65% of the annual total energy consumption for the USA.

Belial666 wrote:

it seems as if you're increasing the capital and maintenance/operation costs and reducing (weather dependency?) the carbon fuel costs.

Solar plant needs:
Mine the silver for the mirrors and tin/lead for filling.
Make the mirrors, pipes and accumulator.
Polish mirrors every so often.
Reorient mirrors seasonally.
Replace worn ceramic pipes.
Coal plant needs:
Build the furnace, intakes and exhausts.
Build major coal mine, often in another country.
Mine significant quantities of coal.
Transport quantities of coal thousands of miles over land and sea.
Feed the coal into the furnace via muscle power or build automated machines for it.
Clean furnace every so ften.
Replace worn ceramic bricks.
As you can see, the solar plant requires higher capital investment and is harder to make BUT its operational costs are insignificant in comparison. Not only does coal have intrinsic value but the sheer amount of workforce required to mine it, transport it from the mine to the sea, transport it overseas to your power plants, and feed it to your plants is staggering. And coal-burning furnaces are extremely maintenance-heavy if you want to keep their efficiency up.

availability/costs of carbon fuels

Expected annual capacity is around 150 GWh per square mile of plant - that figure is taken from real life solar plants near the equator, not theoretical calculations. That's the equivalent of over sixty thousand tons of anthracite burned in a furnace with 30% thermal efficiency (probably higher than what Charis has now). That figure goes up if less efficient fuel is used.

For all the complaints about the efficiency of external combustion, coal is one of the better fuels, as it has a very high energy density, the plant can be used to produce useable power where and when needed, not something your solar plant can do. Also you are wrong about the ideal location of said plant, it is not the equator, you actually want to locate a solar plant under the Hadley cell high (on Earth ~23 degrees latitude)due to the lack of clouds. This brings in problem number two, these latitudes are normally very sparsely populated, so who is going to be using the power generated. It is the intermittentcy of Solar and Wind power that make them unsuitable for use as intensive power sources, they will actually break grids when used to provide electric power.

Thermal accumulators counter the fluctuating output of solar power plants. They can store the heat of the concentrated sunlight for extended periods, allowing the plant to produce at whatever output is needed at a given time rather than how much sunlight is available.


Basically, you take the heat from the sun and store it in a really large tank when there's sunlight. Whenever you need to produce power, you take the heat out and use it at the rate of power demand rather than the rate of power supply.
You can have the same average output at night and day
You could store in sunny days against demands in cloudy days.
You can meet peak demands that exceed the plant's maximum output for a time, by storing up when demand is less than the plant's output.




Unlike batteries, thermal accumulators use no chemical reactions, require no complicated manufacturing to produce, use much cheaper base materials, have no upper limit on recharge cycles and directly store thermal energy rather than electricity.
The downside is that they can't store indefinitely - the larger the accumulator and the better insulated it is the longer the discharge period - but eventually you will have to use the stored energy or lose it.

Belial666 wrote:

EdThomas wrote:Good out of the box thinking!

Can't take the credit for that - the first commercial solar plants with thermal accumulators have recently appeared in real life. Though they use liquid salt as the accumulation medium rather than my proposed tin/lead mixture - I preferred the tin/lead mix due to its significantly lower melting point, higher density and thus energy density; liquid salt OTOH has higher melting point but better insulation properties.

Another reason molten salts are preferred is that they are stable in both solid and liquid phases without going near gaseous state or degrading and/or unmixing.

A tin/lead mix will degrade if in presence of oxygen at any point and lead will create vapors even early in the liquid phase. Not really a big deal but still imply maintenance because slag and degradation products will appear. Any impurities will produce nasty vapors and the tubing will tend to clog.

A nitrate salts (potassium, calcium, sodium) mix is usable in the 270-550 °F (130-290°C) storage range, can be heated north of 1000°F (540°C) and is non flammable and non toxic. A lot easier to use than a metal mix and dont need high tech to produce. 2 are common forms of salpeter, the third is extracted from limestone with nitric acid and is also an intermediate of a common low tech method of producing fertilizer (odda process) so could even be in one of the writ recipes. Drawback is though that the lower accumulation density means quite big insulated tanks.

higher temps mix exists but are often quite caustics (eg fluorides).

How about using pure tin? It has a very low melting point for a metal (230 C I think), and a relatively high boiling point (well over 2000 C). It should be better than most salts for energy density and every culture everywhere knows of its existence. Also, it is not nearly as corrosive as most ionic liquids.



BTW, anyone know how good an insulator brick is? I'm trying to calculate how soon a spherical accumulator containing 20 kilotons of tin would cool...

Belial666 wrote:How about using pure tin? It has a very low melting point for a metal (230 C I think), and a relatively high boiling point (well over 2000 C). It should be better than most salts for energy density and every culture everywhere knows of its existence. Also, it is not nearly as corrosive as most ionic liquids.



BTW, anyone know how good an insulator brick is? I'm trying to calculate how soon a spherical accumulator containing 20 kilotons of tin would cool...

Problem with heated pure tin is the pure part in a non technological Safehold. Most of antique and medieval tin was retrieved using placer mining in rivers down current of tin rich granites, retrieving pellets where tin is mixed with bismuth, antimony and mercury. While the first one is about as harmless as tin, the latter 2 are quite dangerous in vapour form. In solid form, they are mixed in the matrix and mostly neutralized, but once heated they are likely to be released.

Frankly, molten salts are easier below 900°C unless you use positive pressure neutral atmosphere (which is out of reach of Safehold right now).

For your insulation question, most bricks are rather dense and in fact a good heat conductor. This is why well built brick houses normally use a double layer with something else (straw is ideal) in between.

Fire bricks (high alumina content) are porous and refractory so are very good isolators. But they have little structural integrity at high temperature and cannot touch the molten tin or salt.

The usual design of high temp thermal storage tanks is a dewar bottle with a stainless metal or ceramic lining. Even the best of refractory material will conduct a bit of heat whereas vacuum dont.

Purity should not be an issue with enough mirrors. Tin has a boiling point nearly a thousand degrees higher than antimony or bismuth and well over two thousand higher than mercury. So you apply a distillation technique and from the mix you get highly-pure mercury, antimony and bismuth, leaving the tin behind.
There must be a good use of those metals somewhere - projectile manufacture, medicine, solders, dirty bombs to drop on Church cities.



For the insulation, I never even thought of vacuum bottles. With the Delthak plant producing steel at such quantities it could be done.
Hell, the way things are progressing on Safehold, a decade or two down the line they might even produce some tantalum hafnium carbide bricks. Just in case someone decides to take a swim into the surface of the sun or something.

While I think your idea is interesting, you might consider the reasons why a similar technology has not been commercially developed and deployed on Earth, even though we are far better equipped to do so.

After all, most of the technologies you describe have been well known for many years, if not centuries, and variations of these designs have actually been built in prototype form since the oil crisis of the 1970's.

The basic problem is the length of time it would take to "start up" your system (i.e. fill the accumulator with enough molten whatever to start powering things), the intermittent nature of the system (won't work at night, during cloudy weather etc.), the capital cost of the land needed for the mirrors and all the supporting equipment, along with the capital costs of the mirrors and plumbing itself and the amount of time needed to build the thing.

Frankly, I could probably build several coal plants far faster and cheaper, plus put them right where they are needed in the same time you got your solar plant up and running.

One thing which might be worth while is to tap the waste heat of a thermal generator to "pump up" a thermal accumulator of the type you describe, to release extra energy during peak hours.