China's Space Program News Thread

[siegecrossbow]

It seems to me any need to deliver solar energy around the clock using space installations would be much cheaper to meet if the principle is to simply to use large thin film reflectors in orbit to reflect sunlight down to pre-existing ground based solar farms in remote areas, then to build orbital PV facilities that would generate power in situ and then transmit it down to earth and requiring additional ground based receiving antenna of the required scale.

A square kilometer of .4 mil commercially available aluminized mirror finish film weigh about 8 tons. Even if we assume we can do no better, and the supporting and positioning structure required to maintain mirror shape, counter solar photo pressure and maintain position and orientation would weight 5 times as much, a single LM9 launch can still lift 3 square km of such reflectors.

current solar PV technology allows about 40 MW of solar peak output per sq km.

So a 3 sq km reflector in space could roughly double the output of about 120MW of ground based solar generating capacity.

Current cost of solar PV is roughly $2 per Watt of capacity, installed.

So if LM9 class rocket can launch 120 tons into space for $240 million or less, or any rocket for launch at $2 million per ton, then mylar mirror in space might be a economically viable solution to allow solar farms to generate cover night using just existing solar PV technology without any need to beam microwave from space.

I think the primary draw of space based solar is that weather/day night cycle will be less of a factor. The greatest hurdle for solar energy today is that energy generation is not stable, which causes problems when integrating with the grid.

 

[Nutrient]

Agreed. Solar panels placed on earth will be so much cheaper than any launched into space.

Solar panels on the ground will need some way to store some energy for nights; this may need a new technology, one that can be scaled up to terawatts. Are you feeling lucky enough to bet the future of the planet on a roll of dice?

Alternatively, we could have an enormous global grid, which would allow the sunny half of Earth to feed the dark half. But I am not holding my breath waiting for global friendliness and harmony.

There's energy models which look at how wind+nuclear can supply the night-time baseload, with other sources such as solar and hydro also providing for day-time supply.

Nuclear power may work. But the INS Arihant, a nuclear submarine, has shaken my faith: a crew presumably of the best and brightest of India's navy forgot to close a hatch before a dive, and nearly sank the sub. Do we want such people anywhere near a nuclear reactor? If there were no alternatives, I might reluctantly support an atomic future of fast neutron breeders. But there is an alternative: the SPS.

Also note that new solar plants today, are deliberately sized so that excess electricity during very sunny days is simply left to waste, because solar electricity panels are so cheap.

And probably because there's no feasible way to store a vast amount of excess solar power; we are talking terawatts here.

 

[Richard Santos]

I think the primary draw of space based solar is that weather/day night cycle will be less of a factor. The greatest hurdle for solar energy today is that energy generation is not stable, which causes problems when integrating with the grid.

weather effect can be mitigated to a considerable degree by selectively concentrating solar generation capacities in area with relatively reliable sun shine, and interconnecting regional sized grids to ensure deliverability from some sources when others are covered by bad weather.

day-night cycle is much harder to mitigate by siting of PV facilities and interconnection. The transmission network required to serve night night load from PV facilities on the daylight side of the planet would be global in scale, and many countries would not not allow most of their power use to depend on transmission lines running through potentially unfriendly neighbors.

Orbital mirrors provide a means to mitigating the day night cycle of sun light at solar facilities.

Orbital mirrors provide another potential advantage. Modern solar panels are relatively inefficient in part because solar flux at earth is considerably below the level at which they are most efficient. If the panels are cooled they can generating considerably more in proportion to the flux they receive if they receive more light flux. hence development of PV cells with integral lenses to intensify flux onto a smaller area.

Orbital mirrors can potentially greatly increase the economy of ground based PV by doubling the times when they receive sunlight by reflecting light to it at night, it can potentially also more than double their energy output during the day, provided the grid interconnection for the PV facility is sized accordingly.

 

[Nutrient]

Orbital mirrors can potentially greatly increase the economy of ground based PV by doubling the times when they receive sunlight by reflecting light to it at night, it can potentially also more than double their energy output during the day, provided the grid interconnection for the PV facility is sized accordingly.

Orbital mirrors -- at least the cheap and billowy ones -- don't focus. Rigid mirrors that do focus somewhat could be heavier than an SPS's thin-film solar panels.

 

[Richard Santos]

Please. Things don’t billow in space.

The film mirror in space only needs to be in slight tension to hold its shape. There is no need to make it rigid. Tension can be created as easily as by slowly spinning the mirror. A more sophisticated mirror can have a flexible wire perimeter frame around its edge also held in tension by centrifugal force. Such a frame, stiffened with some weights, can be used as anchor for a network of catenary wires that can pull the mirror into a slight parabolic shape.

 

[AndrewS]

Solar panels on the ground will need some way to store some energy for nights; this may need a new technology, one that can be scaled up to terawatts. Are you feeling lucky enough to bet the future of the planet on a roll of dice?

Alternatively, we could have an enormous global grid, which would allow the sunny half of Earth to feed the dark half. But I am not holding my breath waiting for global friendliness and harmony.



Nuclear power may work. But the INS Arihant, a nuclear submarine, has shaken my faith: a crew presumably of the best and brightest of India's navy forgot to close a hatch before a dive, and nearly sank the sub. Do we want such people anywhere near a nuclear reactor? If there were no alternatives, I might reluctantly support an atomic future of fast neutron breeders. But there is an alternative: the SPS.



And probably because there's no feasible way to store a vast amount of excess solar power; we are talking terawatts here.

You missed the point I made before.

The models have night-time baseload provided by a combination of wind + nuclear.
Solar doesn't enter the equation for night-time use.

And I'm happy to roll the dice on this, because the probability is 90%+ in my analysis.
The question is the timing in how many years it will take, which is based on how fast the cost-curve drops.

 

[Nutrient]

Please. Things don’t billow in space.

By "billow" I meant that your orbital reflector won't hold its shape without some active, continuing intervention. I was in a hurry and neglected to explain the intended meaning.

The film mirror in space only needs to be in slight tension to hold its shape. There is no need to make it rigid. Tension can be created as easily as by slowly spinning the mirror. A more sophisticated mirror can have a flexible wire perimeter frame around its edge also held in tension by centrifugal force. Such a frame, stiffened with some weights, can be used as anchor for a network of catenary wires that can pull the mirror into a slight parabolic shape.

Are you contradicting yourself? First you said that your orbital mirror won't billow, and here you are suggesting ways to counteract the billowing.

Your spinning idea won't work anyway: the mirror's angle to the sun will change as the mirror orbits the Earth; the constantly changing solar radiation vector will eventually distort your mirror's shape. Once distorted, your mirror will spread the reflected sunlight far beyond the bounds of the receiver on Earth, diluting the energy available to it.

Of course, you might think of making the mirror spin two ways: one to keep the mirror stretched, and another to keep the mirror facing the Sun as the construct orbits the Earth. However, if the mirror is always facing the Sun, the light that the mirror reflects -- even if somewhat focused -- will miss your Earthly receiver most of the time.

So you have a choice: maintain the mirror's shape by always making it face the Sun, in which case the reflected light will be useless most of the time; or make the reflected light hit the same spot on Earth throughout the night, in which case the mirror's shape will be destroyed by the changing solar radiation vector.

But you make an interesting point: an SPS's farm of solar panels will need some way to maintain its shape against the radiation pressure from the Sun. The farm will also need some constant station-keeping thrust to counter the same pressure; an ion engine might work.

 

[Nutrient]

The models have night-time baseload provided by a combination of wind + nuclear.

If you're going to have nuclear power for the night, you may as well use it during the day.

Remember, global power consumption is roughly 18 terawatts. To replace all of that with nuclear, we would need eighteen thousand one-gigawatt plants. It's not impossible, but I am frightened by the risk of that many plants run by the same people who nearly sank India's nuclear submarine. Why roll the dice when you don't have to?

 

[Richard Santos]

come on. billow has a specific meaning. it means filled with air. you’ve been so obviously bluffing and blustering all alone this entire thread as if talking down from a position of ignorance create the appearance of knowledgeability.

Any mirror focusing from orbit would be very close to being flat. for a flat mirror it doesn’t matter which direction the parallel rays of sun light comes from, the photo pressure vector would be the same across the mirror so there will be no distortion.

 

[by78]

A paper on structural design of a new 'heavy lift rocket', presumably Long March 9. Specifically, it deals with dissipating and evenly distributing various concentrated loads over the rocket's body. The PDF is unfortunately inaccessible for me. I would like to provide a translation, but this is far beyond my limited Chinese.