Power options for a Mars settlement

[lamontagne]

Greenhouses would reduce this by some significant fraction,

Only if there aren't additional energy costs elsewhere, due to thermal issues (for example). Or additional infrastructure costs to solve those issues (such as day/night counter-cycling heat-sinks, deployable insulating night covers, etc) that add to the ISRU-materials and energy-of-production demands on the early settlement.

Given the alien environment, and lack of reasonable analogies on Earth, IMO people should take the numbers from fully artificial grow-rooms (as you did) and assume that's the minimum for any ag on Mars. (The reasoning being, as I said earlier, if your numbers don't work without assuming near-free agriculture, then your margins are too slim for the unexpected realities of Mars.)

Grow rooms with staged growing patterns might allow for a nearly constant demand

You'll almost certainly need supplemental lighting in greenhouses -- even if you're not trying to maximise productivity, you will still need to mimic natural seasonal variation to trigger key stages of growth (such as flowering/fruiting). In which case, you can have staged growing in greenhouses just as you can in grow-rooms. It's not a "trade" between the two.

Should have added, ' if greenhouses are built at all, they will need to provide food for less energy overall'
As for the trade in growing times, I agree, however some grow rooms could operate all night, leveling out demand for a nuclear reactor.  Otherwise you would need to have a number of reactors idle at night.

[lamontagne]

If somebody was serious about nuclear power on Mars and in space, but did not have access to nuclear materials, could they build 'the rest' of the reactor to test our components and add in the actual core at the end?  I believe Kilopower did something like that, using a core simulator in some of their testing?
You could have a 5 MW electrical heater element, at 1200°C, for example, mimicking a core for a 2 MWe reactor?
Or are the nuclear elements of a design more important that purely thermal loads?
Perhaps the electrical conductors might significantly alter the geometry of the core?

[Vultur]

Taking LMTs numbers in the image 100 kWh/day for 2500 kg per day feeds about 2.5 persons per day if they eat only wheat.  100 kWh/day divided by 2.5 = an average power of 40 kW per person.
Most foods hold less power than wheat. 

Maybe calorie density per pound of food, but per growing area wheat is actually rather poor as staple crops go.

There's a reason Andy Weir picked potatoes...

[lamontagne]

Taking LMTs numbers in the image 100 kWh/day for 2500 kg per day feeds about 2.5 persons per day if they eat only wheat.  100 kWh/day divided by 2.5 = an average power of 40 kW per person.
Most foods hold less power than wheat. 

Maybe calorie density per pound of food, but per growing area wheat is actually rather poor as staple crops go.

There's a reason Andy Weir picked potatoes...

All here: https://marspedia.org/Food
It tends to average out but potatoes are 80% edible, rather than 50% for wheat.
Winners are beans and bananas, but potatoes are very good.

[LMT]

...per growing area wheat is actually rather poor as staple crops go.

There's a reason Andy Weir picked potatoes...

All here: https://marspedia.org/Food

The values are high but remain below record yields...

Your table actually states the record yield for wheat, from Bugbee & Salisbury.  That's not "theoretical" or "below record", but the achieved record, with calorie density an order of magnitude beyond potatoes, in your table.

Most foods hold less power than wheat.  However, there are biological reactors that have higher yields.

Calories = energy.  Do any reactors truly have higher yields?  What are the facts?  They should be in your article.

[lamontagne]

...per growing area wheat is actually rather poor as staple crops go.

There's a reason Andy Weir picked potatoes...

All here: https://marspedia.org/Food

The values are high but remain below record yields...

Your table actually states the record yield for wheat, from Bugbee & Salisbury.  That's not "theoretical" or "below record", but the achieved record, with calorie density an order of magnitude beyond potatoes, in your table.

Most foods hold less power than wheat.  However, there are biological reactors that have higher yields.

Calories = energy.  Do any reactors truly have higher yields?  What are the facts?  They should be in your article.

The article doesn't actually cover bioreactors much.  They have a separate entry.  The reactors seems to be able to use thermal energy to produce food, so they are quite efficient.  I have the paper but I haven't used it for a few years.

Yes, they achieved those numbers with a lot of lighting and multiple trays.  the tables are mostly for single layer growth, unless otherwise stated.
The correlation between lighting and growth seems pretty direct. Energy to energy with the conversion efficiency of photosynthesis.  More light =more food.

Density is important in a space ship or a space station, somewhat less in a surface installation, IMHO, and useless at more than one layer for natural lighting due to shadowing.

[LMT]

All here: https://marspedia.org/Food

The values are high but remain below record yields...

Your table actually states the record yield for wheat, from Bugbee & Salisbury.  That's not "theoretical" or "below record", but the achieved record, with calorie density an order of magnitude beyond potatoes, in your table.

Most foods hold less power than wheat.  However, there are biological reactors that have higher yields.

Calories = energy.  Do any reactors truly have higher yields?  What are the facts?  They should be in your article.

they achieved those numbers with a lot of lighting and multiple trays.  the tables are mostly for single layer growth, unless otherwise stated...

No, their single-layer plots are plain in Fig. 1, with guard areas marked and excluded for accuracy.

The reactors seems to be able to use thermal energy to produce food, so they are quite efficient.  I have the paper but I haven't used it for a few years.

Those aren't the yield facts.  OT now.

[LMT]

A perovskite (methylammonium lead iodide perovskite) thin film solar cell has been validated after 10 months in space:

"A lot of people doubted that these materials could ever be strong enough to deal with the harsh environment of space," McMillon-Brown said. "Not only do they survive, but in some ways, they thrived. I love thinking of the applications of our research and that we're going to be able to meet the power needs of missions that are not feasible with current solar technologies."

This result would seem to open the door for commercial space applications of roll-to-roll printed perovskite PV.

With perovskite thin films rated at 10-30 kW/kg, and this particular perovskite offering over 20% conversion efficiency (Hoye et al. 2020), the prospective numbers for a space-rated R2R printed perovskite PV system are looking very good.

Refs.

Li, Y., Hoye, R.L., Gao, H.H., Yan, L., Zhang, X., Zhou, Y., MacManus-Driscoll, J.L. and Gan, J., 2020. Over 20% efficiency in methylammonium lead iodide perovskite solar cells with enhanced stability via "in situ solidification" of the TiO2 compact layer. ACS applied materials & interfaces, 12(6), pp.7135-7143.
 

[Twark_Main]

The reactors seems to be able to use thermal energy to produce food, so they are quite efficient.

Holy thermodynamics, Batman!!

Obviously a biological system can't exceed the efficiency of a Carnot engine, so presumably you're talking about some temperature difference between hot and cold. Or are they actually claiming to turn Brownian motion into usable energy?

Can we see the paper?

[Lampyridae]

Nature article just dropped:

Assessment of the technological viability of photoelectrochemical devices for oxygen and fuel production on Moon and Mars

https://www.nature.com/articles/s41467-023-38676-2

[wes_wilson]

Some thermites are used for metal refining and welding. My dad used thermite to weld a cracked tractor engine block, a method he picked up  during WW-2 to repair Jeep & aircraft engines, and I guarantee you it's hot enough 😨

The oxide he used was iron oxide, rust,  and I believe Mars is awash in it. Fuel: powdered aluminum.

Fe2O3 + 2 Al → 2 Fe + Al2O3

Liquid iron, on the half-shell, with gobs of residual heat for other uses.

Historically this was SOP for railroad welding repairs.

Of course the problem is where you get the raw Aluminum powder from in the first place, which is even more energy intensive than Iron, and can't be reduced using coke.

Thread necromancy. 

Anyway, was reading Ukraine news about thermite drones, got to pondering thermite at Mars, remembered this old thread, found the earlier talk of thermite, and here I am. 


TLDR?: Sending 1 starship full of Aluminum for use in a thermite reaction would yield 2 starships equivalent of iron plus about 400,000 kWh.  Minus losses, probably lots.   

Thinking
Mass: 2Al + Fe2O3 = 213.651 = 53.964 + 159.687
Mass: 2Al = 53.964 = (26.982 * 2) or 25.3%
Mass: Fe2O3 = 159.687 = (55.845 * 2) + (15.999 * 3) or 74.7%

   907,185 grams per ton
90,718,500 grams AL per starship flight (100 tons)

Wikipedia Says: 3,956 J/g
https://en.wikipedia.org/wiki/Thermite#:~:text=Thermite%20(%2F%CB%88%CE%B8%C9%9C%CB%90rm,temperature%20in%20a%20small%20area.

Mixing 1 starship of AL with 3 equivalents of locally sourced Fe2O3 from Mars would give a total of 362,874,000 grams of Thermite (90,718,500 * 4) which reacted would yield 1,435,529,544,000 joules of energy (362,874,000 * 3,956).

A joule is 1 watt for 1 second or 1/3600 of a watt hour --> 398,758 Kwh

Since it starts with 2 Al and yields 2 Fe which is roughly twice the molecular weight it has the added equivalent of giving 200 tons of iron for every 100 tons of Al transported. 

[Eka]

Borosilicate glass is more resistant to thermal shock, but soda lime glass Pyrex(tm) casseroles routinely go from a 225C oven to a 20C room so it has some resistance to thermal shock.

Air is a lousy heat conductor, particularly when it's still (still air is basically an insulator). If you remove a baking dish from the oven it doesn't cool down that rapidly so it's not being over-stressed, and also any food/liquids in the dish are absorbing some heat so that regulates the temperature a bit. On the other hand, water is an extremely good heat conductor so if you took the dish right out of a hot oven and dumped it in a sink full of cold water, it will fracture. That's why ice cubes crack when put in a glass of water but not when you remove an ice cube tray from the freezer and just set it on the kitchen table at room temperature. They will gradually thaw and melt, but do not crack as the temperature change is much less sharp.

That's why standing outside on a 65F day feels perfectly nice and comfortable but you would not enjoy swimming in 65F water very much. Air doesn't conduct heat that much, water does.

Of Pyrex glass baking dishes: The old Corning ones used to all be made of borosilicate glass. After Corning sold the line decades ago, they started being made from soda lime glass. There have been many shatter incidents with the latter when they were put in a hot oven (500F/260C) from room temperature or colder, or removed from a hot oven and placed on something cold, like a wet drainboard. The old borosilicate glass ones can go from the freezer to a hot oven with no issues. Don't try that with the soda lime glass ones. I won't use soda lime glass bakeware above 165C (325F), and I always place a hot one on only silicone or cloth hot pads. New soda lime glass may be good in a hot oven, but after it has been beat around a bit, no way. It's thermal stress handling limit is too close to the advertised operating conditions.

Safe working limits for a material are usually under ideal conditions. They nearly always require derating for your use.