Off-world Power Generation

Given:

• earth to moon: 238,900 miles
• there are four lagrange points that provide constant sun exposure at predictable locations
• l1 to earth/moon: 1 million miles
• the sun primarily produces visible light (not microwaves or gamma...)
• laser transmission is more efficient than microwave, except where earth's atmosphere interferes
• current status: A Gigawatt-range microwave system would weigh ~80,000 tons (prohibitively expensive) more lots more
• Solar cell efficiency

Premises:

<Earth> <-microwave-- <Earth-orbit satellite> <-laser-- <Earth's moon> <-laser-- <L1 solar array>
<Earth> <-clearsky-burst-laser-- <Earth's moon> <-laser-- <L1 solar array>
<Earth> <-clearsky-burst-laser-- <L1 solar array>

• <Earth> <- <Earth-orbit satellite>

Laser transmit antenna in space: 1 meter diameter per GW Receive: Several hundred meters across

• <Earth-orbit satellite> <- <Earth's moon>

• <Earth's moon> <- <Earth-Sol Lagrange-point solar array>

Targeting the energy requirement of NYC:

• Power is measured in Newton-meters per second or Joules per second or Watts.
• ~3000 trillion BTU in 2016 = 3000 trillion btu / 365 days = 3.4E+11 btu/hr = 1.0036680479e+11 watts = 100 GW

PV energy collection

• PV power stations collect more power than solar thermal power stations. They seem to average ~3 MW/km^2 (throwing out 2 ridiculous outliers).
• Traditional single-junction cells have a maximum theoretical efficiency of 33.16% more. In reality it is around 18.7%.
• A 65"x39" (1.64 m^2) solar panel made in 2018 produces ~320W.
• About 48% of solar energy hitting the Earth reaches the surface. Perhaps optimistic, but we will divide by .48 to get energy-in-space vs on-earth.
• Approximate energy absorbable by a solar panel in space: 320W / 1.64m^2 / .48% = 400W/m^2 in space
• Approximate required size of a solar array "near Earth" (including l1) to power NYC: 100GW / 400W/m^s = 250 sq km
• Dan: 1 out of every 811 humans on earth live in NYC, so 250 sq km dish * 811 (assuming every human uses as much energy as a New Yorker) requires a solar array of only around 200,000 sq km - the size of Nebraska - to power the globe.