4 ms·

Total mass for a fuel cell system still wins against any battery system. And solar panels go up to 200 W/kg these days (UltraFlex/MegaFlex design), with up to

by jhgb 5y ago

Total mass for a fuel cell system still wins against any battery system. And solar panels go up to 200 W/kg these days (UltraFlex/MegaFlex design), with up to 300 W/kg in labs. They're the least of your worries.

Retric 5y ago
For non tracking panels at 100% efficiency and 200W/kg assuming an optimistic 1/2 of total weight for solar collection is panels runs around 50 kg per MWh per month on the moon. Batteries at ~90% bump that to 55kg/MWH. Fuel cells at ~30% bump that to ~170 kg or another 110kg /MWh, not that significant but still important.
- jhgb 5y ago
  How does panel efficiency go into this? Those 200 W/kg are post-conversion, so whatever efficiency they have is already included. > assuming an optimistic 1/2 of total weight for solar collection is panels What does that even mean? 200 W/kg is system efficiency, so not just cells but all the structures involved. > runs around 50 kg per MWh per month on the moon. I don't get it. "MWh per month" is 114 watts. A 50 kg array at 200 W/kg has 10 kW peak. At the south pole, a non-tracking unifacial horizontally mounted and elevated array will have at least a ~30% capacity factor, a bifacial array will have a ~60% capacity factor. That's 3 kW or 6 kW on average, respectively, far from your 114 watts. EDIT: Should have really been 1.4 kW instead of 114 watts - I calculated with 1 MWh per year by a mistake. Still a substantial difference from 3/6 kWh. > Fuel cells at ~30% A round-trip from a fuel-cell system will be at ~40%. Maybe ~50% if you use top equipment. But even bog-standard fuel cells are at ~50-55% (LHV) efficiency and bog-standard PEM electrolyzers are at ~80% efficiency, which should give you no less than a 40% round-trip.
  - Retric 5y ago
    > How does panel efficiency go into this? It doesn’t but a measure of output from solar panels ignores the storage efficiency which is what we care about here. > 200w/kg is system efficiency. You listed that as the panels in your post. First actual array output falls over time. Whatever it would be new is irrelevant you scale for how long it’s in use. Panels on the moon need to be mounted at an appropriate angle for maximum efficiency, cooling, they need wires to move electric from the panel to your power conversion, electronics to handle that power etc. You also get losses from lunar dust, etc. Simply saying all that doubles weight is a reasonable ballpark. Don’t forget the moon is dealing with days of full sun panels need to maintain low temperatures for efficiency and you can’t just dump all that heat into the moon. > I don’t get it A 50kg array consisting of 25kg of solar panels, at 30% efficiency produces: 25 different 0.2kw panels for 30 percent of the time over 28 days times 24 hours = 25 * 0.200kw * 0.30 * 28 * 24h = 1008 kWh or 1.008 MWh. Edit: 1.4kW * 28 days * 24h/day = 940 kWh or 0.94 MWh. > A round-trip from a fuel-cell system will be at ~40%. I have yet to read about an actual working system over 30% water to hydrogen to water. Do you have any citations or is this assuming some unknown breakthrough?
    - jhgb 5y ago
      > It doesn’t but a measure of output from solar panels ignores the storage efficiency which is what we care about here. So why even mention panel efficiency? > First actual array output falls over time You always compensate for it, it's not hard. > Panels on the moon need to be mounted at an appropriate angle for maximum efficiency, cooling, they need wires to move electric from the panel to your power conversion All included in that figure. > electronics to handle that power That is admittedly not included in that figure but PPUs are still fairly lightweight these days. > Don’t forget the moon is dealing with days of full sun panels need to maintain low temperatures for efficiency We've already dealt with these things for geostationary satellites, and those are almost always insolated thanks to their orbit. > and you can’t just dump all that heat into the moon On the south pole you most likely can, since even though there's lots of sunlight, the extreme incidence angle means that the surface is disproportionately cool. > A 50kg array consisting of 25kg of solar panels, at 30% efficiency produces: 25 different 0.2kw panels for 30 percent of the time over 28 days times 24 hours = 25 * 0.200kw * 0.30 * 28 * 24h = 1008 kWh or 1.008 MWh. Heh? A 50 kg array at 200 W/kg produces 10 kW peak and even at 30% capacity factor generates ~2 MWh in a lunar month: 100.324*29.5 = 2.124 MWh. > consisting of 25kg of solar panels I already said that the ~200 W/kg for UltraFlex/MegaFlex arrays includes structures, so there's no "25kg of solar panels". There are in fact no panels at all - on UltraFlex/MegaFlex, individual "naked" cells are attached to the flexible substrate of the array directly. > I have yet to read about an actual working system over 30% water to hydrogen to water. Do you have any citations or is this assuming some unknown breakthrough? No, it assumes perfectly standard system components. But here you have NASA's RFC demonstrating 50% efficiency in 2006 (already fifteen years ago!): https://ntrs.nasa.gov/citations/20060008706 https://ntrs.nasa.gov/citations/20060008706
      - Retric 5y ago
        > UltraFlex/MegaFlex arrays Those fit on satellites in zero g. The moon has gravity so you support them at an angle you need bracing on something else, or for extra long panels connected to a structure you need bracing inside these ultra flex panels. In space panels can radiate from their back sides into space, but that doesn’t work on the moon as it hits 260 degrees Fahrenheit in the day. Look up panel efficiency curves with temperature. Cooling during the day is a major concern for a long term lunar base, but also needed for panels. Further you need cables from wherever they are to where up your using power. Lunar dust again is an issue for solar panels on the moon vs satellites. All added up doubling weight may be generous. > https://ntrs.nasa.gov/citations/20060008706 https://ntrs.nasa.gov/citations/20060008706 Sure, and that worked wonderfully a lab. But, production systems need to worry about a great deal of stuff that doesn’t apply in a lab setting. I don’t mean this dismissively yes I completely agree in theory it could work, but it’s just not working technology yet. I haven’t looked recently so hopefully there is a system demonstration out there.

by jhgb 5y ago

Retric 5y ago

For non tracking panels at 100% efficiency and 200W/kg assuming an optimistic 1/2 of total weight for solar collection is panels runs around 50 kg per MWh per month on the moon. Batteries at ~90% bump that to 55kg/MWH. Fuel cells at ~30% bump that to ~170 kg or another 110kg /MWh, not that significant but still important.

jhgb 5y ago
How does panel efficiency go into this? Those 200 W/kg are post-conversion, so whatever efficiency they have is already included. > assuming an optimistic 1/2 of total weight for solar collection is panels What does that even mean? 200 W/kg is system efficiency, so not just cells but all the structures involved. > runs around 50 kg per MWh per month on the moon. I don't get it. "MWh per month" is 114 watts. A 50 kg array at 200 W/kg has 10 kW peak. At the south pole, a non-tracking unifacial horizontally mounted and elevated array will have at least a ~30% capacity factor, a bifacial array will have a ~60% capacity factor. That's 3 kW or 6 kW on average, respectively, far from your 114 watts. EDIT: Should have really been 1.4 kW instead of 114 watts - I calculated with 1 MWh per year by a mistake. Still a substantial difference from 3/6 kWh. > Fuel cells at ~30% A round-trip from a fuel-cell system will be at ~40%. Maybe ~50% if you use top equipment. But even bog-standard fuel cells are at ~50-55% (LHV) efficiency and bog-standard PEM electrolyzers are at ~80% efficiency, which should give you no less than a 40% round-trip.
- Retric 5y ago
  > How does panel efficiency go into this? It doesn’t but a measure of output from solar panels ignores the storage efficiency which is what we care about here. > 200w/kg is system efficiency. You listed that as the panels in your post. First actual array output falls over time. Whatever it would be new is irrelevant you scale for how long it’s in use. Panels on the moon need to be mounted at an appropriate angle for maximum efficiency, cooling, they need wires to move electric from the panel to your power conversion, electronics to handle that power etc. You also get losses from lunar dust, etc. Simply saying all that doubles weight is a reasonable ballpark. Don’t forget the moon is dealing with days of full sun panels need to maintain low temperatures for efficiency and you can’t just dump all that heat into the moon. > I don’t get it A 50kg array consisting of 25kg of solar panels, at 30% efficiency produces: 25 different 0.2kw panels for 30 percent of the time over 28 days times 24 hours = 25 * 0.200kw * 0.30 * 28 * 24h = 1008 kWh or 1.008 MWh. Edit: 1.4kW * 28 days * 24h/day = 940 kWh or 0.94 MWh. > A round-trip from a fuel-cell system will be at ~40%. I have yet to read about an actual working system over 30% water to hydrogen to water. Do you have any citations or is this assuming some unknown breakthrough?
  - jhgb 5y ago
    > It doesn’t but a measure of output from solar panels ignores the storage efficiency which is what we care about here. So why even mention panel efficiency? > First actual array output falls over time You always compensate for it, it's not hard. > Panels on the moon need to be mounted at an appropriate angle for maximum efficiency, cooling, they need wires to move electric from the panel to your power conversion All included in that figure. > electronics to handle that power That is admittedly not included in that figure but PPUs are still fairly lightweight these days. > Don’t forget the moon is dealing with days of full sun panels need to maintain low temperatures for efficiency We've already dealt with these things for geostationary satellites, and those are almost always insolated thanks to their orbit. > and you can’t just dump all that heat into the moon On the south pole you most likely can, since even though there's lots of sunlight, the extreme incidence angle means that the surface is disproportionately cool. > A 50kg array consisting of 25kg of solar panels, at 30% efficiency produces: 25 different 0.2kw panels for 30 percent of the time over 28 days times 24 hours = 25 * 0.200kw * 0.30 * 28 * 24h = 1008 kWh or 1.008 MWh. Heh? A 50 kg array at 200 W/kg produces 10 kW peak and even at 30% capacity factor generates ~2 MWh in a lunar month: 100.324*29.5 = 2.124 MWh. > consisting of 25kg of solar panels I already said that the ~200 W/kg for UltraFlex/MegaFlex arrays includes structures, so there's no "25kg of solar panels". There are in fact no panels at all - on UltraFlex/MegaFlex, individual "naked" cells are attached to the flexible substrate of the array directly. > I have yet to read about an actual working system over 30% water to hydrogen to water. Do you have any citations or is this assuming some unknown breakthrough? No, it assumes perfectly standard system components. But here you have NASA's RFC demonstrating 50% efficiency in 2006 (already fifteen years ago!): https://ntrs.nasa.gov/citations/20060008706 https://ntrs.nasa.gov/citations/20060008706
    - Retric 5y ago
      > UltraFlex/MegaFlex arrays Those fit on satellites in zero g. The moon has gravity so you support them at an angle you need bracing on something else, or for extra long panels connected to a structure you need bracing inside these ultra flex panels. In space panels can radiate from their back sides into space, but that doesn’t work on the moon as it hits 260 degrees Fahrenheit in the day. Look up panel efficiency curves with temperature. Cooling during the day is a major concern for a long term lunar base, but also needed for panels. Further you need cables from wherever they are to where up your using power. Lunar dust again is an issue for solar panels on the moon vs satellites. All added up doubling weight may be generous. > https://ntrs.nasa.gov/citations/20060008706 https://ntrs.nasa.gov/citations/20060008706 Sure, and that worked wonderfully a lab. But, production systems need to worry about a great deal of stuff that doesn’t apply in a lab setting. I don’t mean this dismissively yes I completely agree in theory it could work, but it’s just not working technology yet. I haven’t looked recently so hopefully there is a system demonstration out there.