[0]http://www.greenrhinoenergy.com/solar/technologies/pv_manufa... [1]https://www.sciencedirect.com/science/article/abs/pii/S00380....
It's not like we have huge space constraints for small starts, I reckon?
The real challenge with solar power on the Moon remains the two-week day/night cycle, which means either massive batteries (impractical) or awkward polar cliff locations to minimize the hit.
https://www.nasa.gov/mission_pages/LADEE/news/lunar-atmosphe...
Now you just need to bring big enough batteries to survive 14 days in a row with no sun.
[0] https://en.wikipedia.org/wiki/Solar_irradiance#Irradiance_on...
A 10 ton rock, lifted up to 50m high, will store up to 810M Joules at moon gravity
Wrong prefix? I think you meant 810K Joules.
For Earth gravity: 10,000 kg times 9.8 m/s^2 times 50 m = 4.9 megajoules, 1.36 kilowatthours. (Anker sells a 2.04 KWh battery pack for US$1999: https://www.anker.com/products/a1780)
Again, that's for Earth gravity. Lunar gravity: 10,000 kg times 1.62 m/s^2 times 50 m = 0.81 megajoules, 0.225 kilowatthours.
Gravity storage isn't economical on Earth, and it's really not economical on the Moon, where gravity is lighter.
https://space.stackexchange.com/questions/34025/moon-polar-d...
There's no shortage of places to put solar panels, and nothing that will reduce the amount of light getting to them (except the rotation of the Moon itself), so actual efficiency isn't that important.
This... may or may not matter. When it comes to solar power on the Moon, there are significant advantages and some serious disadvantages. The most obvious advantage is that there is no weather and no atmosphere. This means a lunar solar cell has way more potential power generation than an terrestrial solar cell. The big disadvantage is the long day night cycle. The Moon is tidally locked with Earth with an orbit of 28 days so that's basically 14 days of day and 14 days of night.
You have to work around this problem with batteries, which add a ton more mass, having panels (and settlements most likely) at the poles or running a network of solar cells around the Moon with power cables.
Settling the poles makes sense as this is where the most water is.
But having a network of panels probably makes a lot of sense too. For one, aluminium is abundant so making electrical cables should be entirely possible.
> Another big question is how much mass needs to be shipped up from earth to manufacturer solar cells.
Yes, this is a huge factor, probably way more than efficiency is. Or at least we should look at power generation per unit mass shipped from EArth.
They can make batteries out of moon rocks [1], use fly wheels, melt lava, etc. None super efficiently, but as a start.
It's only a problem if you want to use the energy for systems that must be always available. If you intend to use it to power a factory, let's say to make more panels, you just operate 50% of time that, without clouds or any atmosphere filter, is actually better than on Earth.
For continuous support, take a nuclear reactor or build a wired net near a pole so when night comes to one station, you receive power from another.
Oh, of course this is terrible now. It would have a very, very large required scale to come out ahead compared to just shipping power or power generation some other way (if this is true at any scale). It is also surely not fully baked yet.
On the other hand... it's a notable step towards being able to build "big" in space and might be worth doing to learn more about the practical aspect even if it's higher risk and more costly than shipping a bunch of PV.
The bigger problem is how practical is it to use PV at all on much of the moon.
I think part of the solution will involve using "regular stuff" (which can be sourced from lunar atoms) like batteries.
Don't use lithium batteries to continuously power an oxygen generator. Instead, have an enlarged oxygen generator and store half the flow for use at night.
Don't use lithium batteries to power a heater at night, instead "pre-charge" heat in a dirt thermal mass during the day.
Don't use lithium batteries to power a continuous CO2 scrubber, instead use a liquid amine scrubber and recharge the fluid tanks during the day.
Etc etc
Obviously you need to do in-depth tradeoff math for each case, but my napkins say "the system is the battery" wins in many cases.
Storing 14+ days worth of <everything> is going to mean massive amounts of storage.
...which is why you want to be extra careful in how mass-efficiently you're storing it.
A tank of liquid oxygen masses only a few percent of its contents, and its contents store more chemical energy per mass than a lithium battery. Later on, insulated tanks are vastly easier to produce from lunar materials vs batteries. These are all nice leverage multipliers.
Nuclear is a popular notion, but the real-world economics don't favor it. Effectiveness beats elegance.[0]
Making liquid oxygen (as opposed to gaseous oxygen) is not a terribly efficient process.
You have to do the trade between liquefaction and storing oxygen as a pressurized gas. Reusing a single Starship's propellant tanks, for example, at 6 bar would hold ~14 metric tons of oxygen, enabling a continuous lunar population of over 1,000 people.
The compression or liquefaction energy isn't a show-stopper necessarily, it just works into the total energy efficiency of the storage system. Compression is nice because practical isothermal compressors are now being demonstrated.[0]
Both liquefaction and compression require cooling. I do think it probably makes sense to do the thermal storage trick in reverse also, storing up a bank of "cold" at night to be used during the day. The thermal radiator panels still provide (derated) cooling in the day, but the thermal storage pool time-shifts the natural oversupply of cooling power at night.
[0] https://newatlas.com/good-thinking/carnot-centrifugal-air-co...
Care to elaborate? As an interested layperson I always thought the major factor for losses in open air was radiation into space. As such an atmosphere's thermal mass would be benfitial, no?
A tactic I've used in Dyson Sphere Program is to build an equatorial belt around the entire moon so that some % of panels are always in sunlight. On our actual moon that would be approximately 7.2m panels, assuming they were a single tightly packed row of 5' x 3' panels.
This sounds like an insane amount but several of the largest solar installations on Earth each have more than that, with Bhadla Solar Park in India having over 10 million[1]. It's a dumb solution but is one which requires no shipment of energy storage. If you're able to mass manufacture panels in-situ, it may be simpler to do something like that than to ship large batteries to the Moon in order to use them as storage.
[1]: https://www.aljazeera.com/gallery/2021/11/3/india-solar-rene...
If you take the linked page at face value, it explicitly states:
> without special substances brought from Earth.
(I suspect, like most press releases, some important details aren't being provided. Maybe dopants aren't considered "special substances")
If it's not included, then the extra energy available could raise the output to an equivalent of a 12-18% efficiency cell on Earth's surface, wouldn't it?
[1] https://earthobservatory.nasa.gov/features/EnergyBalance/pag...
Another big question is how much mass needs to be shipped up from earth to manufacturer solar cells. Dopants will still need to be shipped up as they cannot currently be obtained with this method, but the mass per area solar cell is practically nothing. More concerning are the electrodes for their electrolysis cell.
They are literally electrolyzing molten lava. Molten silicates are a very good solvent and the hot oxidizing environment of the anode is quite harsh. We do have materials which can withstand this environment, but how long will they last? How much power can the whole set up produce and would it be more than landing the setup's weight in solar cells?
Regardless this is still a major advance. Materials processing of this level suitable for the lunar environment has not been previously demonstrated.
[0]https://www.niac.usra.edu/files/library/meetings/annual/jun0...