Anti Solar Panels?

[James M]

Addressing the news of the recently developed anti solar panels, I was wondering if maybe the devs could add them into the game as an earlier (Or later!) alternative to RTG's. I was imagining they'd be put somewhere in the middle of the tech tree (Experimental?), would be somewhat expensive each, would generate a decent amount of heat (Perhaps requiring some radiators ), and would weigh significantly less than one RTG. As far as the wattage goes, I was thinking along the lines of a small amount when the sun goes down over the horizon and slowly maxing out at the coldest hours of night (It should also be more useful further from Sol.) The only problem I can see from here is having these compete with our current fuel cells. Any thoughts?

[The Aziz]

I read the article on that.

Aside from being extremely confusing (what is the source of energy here?) I read one important line

"Essentially this form of passive cooling uses the night sky as a massive heat sink, drawing warmth away from the earth once it gets dark."

So it kinda is a radiator itself, and needs a power source, in this case, the heat in the ground accumulated through the day. Can't see how this is gonna work in space.

[RizzoTheRat]

They appear to be a kind of heat pump, relying on being warmer than the night sky so generating some electricity as they transfer heat from the warm earth to the cold sky.  To operate in space at night I guess you'd need a big heavy heatsink to absorb heat during the day and then use that heat to generate electricity at night.  Probably not the most efficient way of storing energy.

However presumably you could use them as radiators to dump excess heat during the day by projecting it out the shaded side.

[AHHans]

3 hours ago, James M said:

I was imagining they'd be put somewhere in the middle of the tech tree (Experimental?), would be somewhat expensive each, would generate a decent amount of heat

Please try to understand the physics of such things before making such suggestions. The thing is that "anti solar panels" - or "thermoradiative cells" as the working part in them is called - don't generate heat, they generate electricity by radiating away heat.

These are interesting things btw. I didn't know that such things are a thing. As far as I understand it, they are essentially photovoltaic cells, but at the hot side and not the cold side like PV cells. I think I understand now how they work, but I'm not 100% sure. Where I am sure is that they are heat engines and thus follow the same rules of thermodynamics as all other heat engines.

Thermoradiative cells work with a radiation temperature of at best the 300 K average earth - or spacecraft - temperature. That means that the amount of power per radiating surface is strictly limited. In space you might be a bit better than the 50 W/m² quoted in the articles about the "anti solar panels", but not much! On Earth (or Kerbin I guess) you don't need to worry about where the heat is coming from because the planet is a huge reservoir, in space you cannot just radiate away heat - i.e. cool down your spacecraft - indefinitely before the craft stops working. So you'll need a source of heat: solar radiation -> Why not use PV and batteries? Chemical fuel -> Fuel cells. Radioactive isotopes -> RTGs?

Using them for thermal control might work and generate some electricity along the way, but they are less efficient at radiating away heat than "simple" radiators (or they'll be even worse at generating electricity) so you'll need more m² to get rid of the same amount of heat. And they will be heavier than the same area of "simple" radiators (in addition to the structure that spreads the heat you need the parts that generate the electricity). So what do you think about thermal control systems that are 10 times as heavy and twice as bulky as the current stock ones, but instead of using ECs they generate ECs at about the rate that the stock ones use ECs? While they actually need to work!

In real life I could imagine that this technology is used in spaceflight. E.g. to increase the efficiency of RTGs: make the whole RTG assembly more heavy and bulky but have it use less radioisotope for the same electricity output.

1 hour ago, RizzoTheRat said:

They appear to be a kind of heat pump,

Not heat pump, heat engine! (Heat pumps use non-heat energy to transport heat to a higher temperature.)

[James M]

Hm AHHans may be right. I was just thinking that since Kerbals are already verified as being more technologically advanced than us, they could have found a way to generate heat through electricity that was extremely efficient or something? I dunno.

Was worth a try 

Edited February 8, 2020 by James M
Correction?

[AHHans]

1 hour ago, James M said:

I was just thinking that since Kerbals are already verified as being more technologically advanced than us, they could have found a way to generate heat through electricity that was extremely efficient or something?

Errr.... You do know that a simple resistor is 100% efficient in converting electrical energy into heat? (That does not mean this it is smart to do this to heat your home, but that is another topic.)

P.S. But thanks for point these things out to me! I didn't know that thermoradiative cells exists and learning to understand how they work was quite interesting.

[kerbiloid]

Irl this is simple.
Two water reservoirs (a water tower and a pool, or two lakes one above another).
A pump, fed by a daytime power source (say, from those solar panels).

Day: you power the pump with the solar panels and pump the water from the lower reservoir to the upper one.
Night: you stop the pump and let the water from the upper reservoir slowly drain down to the lower one, rotating a turbine and producing the electricity.

Instead of two reservoirs and water you can use a heavy weight and a column or a chain.
Day: lift the weight with electric motor.
Night: switch off the motor, let the weight slowly go down, rotating a generator.

Water is better, as it's easier to manage the flow rate to let it work all the night.

Instead of water you can of course use, say, mercury, as it's more dense and compact, but it's exotic.

Also you can use a heavy flywheel to store the daytime energy.
You rotate it in daytime, then let it rotate the turbine in night time.

Edited February 8, 2020 by kerbiloid

[James M]

9 hours ago, kerbiloid said:

Irl this is simple.
Two water reservoirs (a water tower and a pool, or two lakes one above another).
A pump, fed by a daytime power source (say, from those solar panels).

Day: you power the pump with the solar panels and pump the water from the lower reservoir to the upper one.
Night: you stop the pump and let the water from the upper reservoir slowly drain down to the lower one, rotating a turbine and producing the electricity.

Instead of two reservoirs and water you can use a heavy weight and a column or a chain.
Day: lift the weight with electric motor.
Night: switch off the motor, let the weight slowly go down, rotating a generator.

Water is better, as it's easier to manage the flow rate to let it work all the night.

Instead of water you can of course use, say, mercury, as it's more dense and compact, but it's exotic.

Also you can use a heavy flywheel to store the daytime energy.
You rotate it in daytime, then let it rotate the turbine in night time.

This is too op.

[RoninFrog]

On 2/8/2020 at 2:21 AM, kerbiloid said:

Irl this is simple.
Two water reservoirs (a water tower and a pool, or two lakes one above another).
A pump, fed by a daytime power source (say, from those solar panels).

Day: you power the pump with the solar panels and pump the water from the lower reservoir to the upper one.
Night: you stop the pump and let the water from the upper reservoir slowly drain down to the lower one, rotating a turbine and producing the electricity.

Instead of two reservoirs and water you can use a heavy weight and a column or a chain.
Day: lift the weight with electric motor.
Night: switch off the motor, let the weight slowly go down, rotating a generator.

Water is better, as it's easier to manage the flow rate to let it work all the night.

Instead of water you can of course use, say, mercury, as it's more dense and compact, but it's exotic.

Also you can use a heavy flywheel to store the daytime energy.
You rotate it in daytime, then let it rotate the turbine in night time.

Um, isn't that basically a battery?

[kerbiloid]

2 minutes ago, MunsterIII said:

Um, isn't that basically a battery?

It's a hydraulic or mechanical accumulator which allows to distribute the daytime generation power between day and night.
So, it's a usual replacement of the "anti-solar panel".

[RoninFrog]

8 minutes ago, kerbiloid said:

It's a hydraulic or mechanical accumulator which allows to distribute the daytime generation power between day and night.
So, it's a usual replacement of the "anti-solar panel".

Batteries are chemical accumulators which store charge from solar panels during the day so that the power can be used at night.  It seems like the same thing to me.

[kerbiloid]

28 minutes ago, MunsterIII said:

Batteries are chemical accumulators which store charge from solar panels during the day so that the power can be used at night.  It seems like the same thing to me.

It's same thing in sense of purpose, but with higher capacity and more simple technologically. They are used for decades.

Edited February 15, 2020 by kerbiloid

[Starman4308]

As I understand this, the "anti solar panels" are existing technology with a headline-grabbing name and zero commercial potential. There's two elements to the majority of power generation systems:

1) The fuel, or power source. This can be fossil fuel combustion, the Sun, nuclear fuel rods, etc. Often, the energy from this fuel comes out in a high-entropy form like heat.

2) The generator, which converts some other form of energy (often heat) into some other form of energy (often electricity), where that second form is often a lower-entropy form of energy.

In this case, the fuel is heat from the Sun. This... is hardly a technological breakthrough. The generator is a commercially available thermoelectric generator (TEG), the same technology used in radioisotope thermal generators (RTGs).

TEGs, though, are very inefficient ways of converting heat differentials to electricity; they're primarily used in small systems where their solid-state nature makes them more reliable and lighter than more efficient systems such as turbines and Stirling generators. You'd need a lot of exposed area to collect the solar heat and a huge heatsink to store it.

Now, there are actual, legitimate proposals that approach making sense to use collected solar heat for nighttime power generation. The one I've seen is to use a large mirror array to focus light onto a tower with liquid sodium as the heatsink, used to drive a large high-efficiency turbine similar to those used at fossil fuel plants. This actually solves two of the biggest issues with renewable power supply: not only does it provide consistent power through many weather conditions (assuming you don't get a long stretch of multiple cloudy days), but it gracefully handles moment-to-moment power surges and drops.

One big advantage of fossil fuel and nuclear plants is the sheer inertia present in the turbines. If power load goes up unexpectedly, the turbines' rotation rate drops minutely, but the sheer rotational inertia gives the plant operators time to feed in a bit more fuel. Same thing when the power goes down: the actual power distributed goes up very little, the turbines gain a little excess energy, and the plant operators can reduce the fuel feed. Solar panels and wind turbines, however, have much less of this inertia, much less capacity to buffer these moment-to-moment fluctuations.

[sturmhauke]

This tech might be useful for planetary bases, but I don't see it being much use on most spacecraft. They require thermal mass to draw heat from, and mass is something you want to minimize. Maybe it could be used on a colony ship or large space station or something.

[James M]

Can someone close this thread please? Thanks in advance. 

[Geonovast]

Thread locked at OP's request