Shimizu's Luna Ring

Lunar Solar Power Generation - LUNA RING -, Shimizu Corporation.

They are proposing to install a photovoltaic array wrapping all the way around the moon's equator, 400 km wide and 10,921 km. long. The power would be radiated to Earth using microwave and laser transmitters. The lunar soil beneath the array would be covered with concrete made from lunar soil. The PV panels would be manufactured in automated, mobile facilities on the moon using lunar materials.

Critique:
1. Shimizu does not present a cost analysis.

2. The artwork shows the PV panels mounted flush pointing straight up. There does not appear to be any space to access panels for repair or replacement. Perhaps robots could access them from beneath.

3. An individual PV panel will be sitting in a vacuum under sunlight for a lunar day, about 15 Earth days, becoming incredible hot. Crystalline PV panels are inefficient at high temperatures.

4. For 15 days it will sit in a vacuum in darkness getting incredible cold.

5. Although the moon lacks atmosphere to carry and deposit dust, presumably the concrete surface is supposed to minimize dust kicked up from robots and astronauts and to make it easy for robots to move around.

6. To carry power from the far side of the moon to the side that faces the Earth, the power lines will need to be up to 5,500 km long which is approximately the east to west length of the United States. It ought to be cheaper and easier to electrify the long distance freight rail lines in the U.S. to interconnect dispersed renewable power generation.

7. To transfer power received from the moon to customers, it would be necessary to construct long distance transmission lines on Earth which would minimize the need to get power from the moon anyhow.

8. Microwave and laser transmitters could not handle the terawatts of power they are contemplating.

9. Transmitting energy by microwave and laser is rather inefficient.

10. Half of the PV panels will be in darkness half of the time and the illuminated ones should be getting less than 1360 W/m^2 * 3,476 km * 400 km = 1.9 PW spread out over 5,461 km of PV panels generating about 64% (2/PI) of their optimal power due to suboptimal pointing directions. That implies an overbuild of at least 3.1 times the continuous power. Combining that with power transmission and conversion efficiency of probably less than 30%, the overbuild of PV panels would be over 10 times. One could get a lot of power on a cloudy Earth day with that size of overbuild.

11. Imagine the difficulty of getting rid of all that waste heat in a vacuum at the transmitter.

12. For those thinking they would use GaAs PV panels like are currently used on satellites, I suspect there is not enough gallium on Earth and Moon to manufacture them all. My guess is Shimizu is imagining thin-film PV which is easier to automate manufacturing and whose efficiency increases with temperature.

13. How much natural gas would be consumed making the hydrogen to fuel the numerous rocket flights to the moon?

14. How much atmospheric o-zone would be depleted from the numerous rocket launches?

15. Assuming 8% efficiency of the PV panels, 1.9 PW of sunlight, 64% illumination factor, 99% due to lunar inclination and 30% transmission and conversion efficiency, I estimate 29 TW delivered to customers on Earth. Because total world primary energy consumption is ~17 TW, we do not need that much electrical power currently, so someone's estimate is faulty. Transmission and conversion efficiency could be much lower than 30%.

16. Shimizu is contemplating making water from moon dust and hydrogen brought from Earth. Imagine the price of making just the water to mix the concrete for a slab covering 4.4 million square kilometers.

17. Misaim one of those microwave or laser transmitters and everything in the beam's path on Earth would be vaporized. With a minimum communication latency between Earth and Moon of 1.2 to 1.4 seconds, a lot of damage could be done before an interrupted signal would shut down a properly operating system. With malfunction or sabotage, who knows how bad it could get.

18. The moon is not above the Earth's horizon at all times making the power sent from it intermittent at any given location on Earth. The idea does not even solve intermittentcy.

19. It's a corporate wet dream to own all the power used by every human on Earth.

I'll stop now.