Quote from: lamontagne on 11/28/2016 02:55 amSo the colonists need 3 MW of photosynthesis, i.e light. But since plants are not 100% food, you will probably need 5 to 10 times more. So now your base is overheating because of the lights required for plant growth...? But where to get 15 MWin winterat nighton Mars?
So the colonists need 3 MW of photosynthesis, i.e light. But since plants are not 100% food, you will probably need 5 to 10 times more. So now your base is overheating because of the lights required for plant growth...
Quote from: lamontagne on 11/28/2016 02:55 amSo the colonists need 3 MW of photosynthesis, i.e light. But since plants are not 100% food, you will probably need 5 to 10 times more. So now your base is overheating because of the lights required for plant growth...? But where to get 30 MWin winterat nighton Mars?
Quote from: wstewart on 11/28/2016 03:15 amQuote from: lamontagne on 11/28/2016 02:55 amSo the colonists need 3 MW of photosynthesis, i.e light. But since plants are not 100% food, you will probably need 5 to 10 times more. So now your base is overheating because of the lights required for plant growth...? But where to get 30 MWin winterat nighton Mars?Build near the equator, as I suggest. Melas Chasma in Valles Marineris is a good spot, nice and low with a great view and available water. Don't need 30MW at night because you'll have daytime and a lot of thermal inertia. And you'll have a lot of batteries.
A final point about thermodynamics of underground bases. Conduction equation is Q=AdT/R.dT is the temperature difference between the interior of the base and the soil. R in the insulation value of the materials.Now, as your soil heats up, the thickness of the warm soil around the base and the original cold soil gets thicker and thicker. Eventually, you will have a few meters of warm soil, and it will now serve as insulation.Any underground base that is sufficiently deep will reach an equilibrium where the heat loss becomes negligible, and eventually overheat. The only exception is if the heat reaches the surface and starts radiating away.The Earth is a perfect example of this. 12-20 km of Rock, with an overall R value of many thousands, has been keeping the core hot for billions of years... (plus the radioactive materials in the core, of course).
Quote from: LMT on 11/28/2016 03:15 amQuote from: lamontagne on 11/28/2016 02:55 amSo the colonists need 3 MW of photosynthesis, i.e light. But since plants are not 100% food, you will probably need 5 to 10 times more. So now your base is overheating because of the lights required for plant growth...? But where to get 30 MWin winterat nighton Mars?Build near the equator, as I suggest. Melas Chasma in Valles Marineris is a good spot, nice and low with a great view and available water. Don't need 30MW at night because you'll have daytime and a lot of thermal inertia. And you'll have a lot of batteries.
And don't grow the food at night, never a good idea!
Sabatier waste heat (which is optimally 300-400C)
Quote from: Robotbeat on 11/28/2016 04:05 amSabatier waste heat (which is optimally 300-400C)Sabatier reaction is exothermic, but it can't run at a scale to heat Hew Thermopylae in winter because the energy input required to maintain the reaction is far too high, as I think you know. It's more efficient to heat electrically, from PV, and skip intermediary processes. But in winter the PV for tunnel heating just isn't there.
Quote from: LMT on 11/28/2016 11:54 amQuote from: Robotbeat on 11/28/2016 04:05 amSabatier waste heat (which is optimally 300-400C)Sabatier reaction is exothermic, but it can't run at a scale to heat Hew Thermopylae in winter because the energy input required to maintain the reaction is far too high, as I think you know. It's more efficient to heat electrically, from PV, and skip intermediary processes. But in winter the PV for tunnel heating just isn't there.As you stated the Sabatier reaction is exothermic. It does not need any energy input to run except the initial energy to get it to operating temperature.Needeed is hydrogen from water electrolysis, this indeed needs a lot of energy. You can produce the hydrogen during the day and keep the Sabatier reaction going all night.
Quote from: wstewart on 11/08/2016 06:36 amQuote from: Robotbeat on 11/08/2016 04:59 amPerchlorates are both an energy and oxygen source.This is not a microbial astrobiology thread, Senior Member Robotbeat. I'm not talking about astrobiology.
Quote from: Robotbeat on 11/08/2016 04:59 amPerchlorates are both an energy and oxygen source.This is not a microbial astrobiology thread, Senior Member Robotbeat.
Perchlorates are both an energy and oxygen source.
How to survive the winter?
And his hydrogen comes from a bottle, gratis.
Quote from: guckyfan on 11/28/2016 12:04 pmQuote from: wstewart on 11/28/2016 11:54 amQuote from: Robotbeat on 11/28/2016 04:05 amSabatier waste heat (which is optimally 300-400C)Sabatier reaction is exothermic, but it can't run at a scale to heat Hew Thermopylae in winter because the energy input required to maintain the reaction is far too high, as I think you know. It's more efficient to heat electrically, from PV, and skip intermediary processes. But in winter the PV for tunnel heating just isn't there.As you stated the Sabatier reaction is exothermic. It does not need any energy input to run except the initial energy to get it to operating temperature.Needeed is hydrogen from water electrolysis, this indeed needs a lot of energy. You can produce the hydrogen during the day and keep the Sabatier reaction going all night.The reaction needs hydrogen, heat and pressure, yes, and exothermy doesn't get us there, unfortunately. As example, Zubrin's unit is predicted to output 1 kg/hr, while requiring 700 W electrical, continuous.And his hydrogen comes from a bottle, gratis.
Quote from: wstewart on 11/28/2016 11:54 amQuote from: Robotbeat on 11/28/2016 04:05 amSabatier waste heat (which is optimally 300-400C)Sabatier reaction is exothermic, but it can't run at a scale to heat Hew Thermopylae in winter because the energy input required to maintain the reaction is far too high, as I think you know. It's more efficient to heat electrically, from PV, and skip intermediary processes. But in winter the PV for tunnel heating just isn't there.As you stated the Sabatier reaction is exothermic. It does not need any energy input to run except the initial energy to get it to operating temperature.Needeed is hydrogen from water electrolysis, this indeed needs a lot of energy. You can produce the hydrogen during the day and keep the Sabatier reaction going all night.
Quote from: LMT on 11/28/2016 12:38 pmAnd his hydrogen comes from a bottle, gratis.No it doesn't. Half of the hydrogen goes into water and needs to be recovered by electrolysis.Edit: Some power is needed for controlling gas flow and pumping the process products but that is miniscule in comparison to the amounts produced.
PV or not PV?Just to quantify the winter PV problem at Hew Thermopylae:1 ton of state-of-the-art PV produces ~ 100 kW, summer high-noon max.Hew Thermopylae is at 34° N, where winter sunlight intensity drops to ~ 15% of summer max.So in winter, that's 15 kW max, maybe 22 million Joules / sol.If that energy were stored and released on-demand with 80% efficiency, that's 18 million Joules/sol of heat energy.And with a hypothetical 8 MW conductive heat loss, the uninsulated tunnels would need 700 billion Joules / sol.So 40,000 tons of PV, just for heat.