NASA’s support for a prize competition to develop power beaming technologies, ostensibly for a space elevator, could also prove useful to Lunar solar power development. (credit: Spaceward Foundation)

Rectifying the case for beaming Lunar solar power

by Sam Dinkin
Monday, April 11, 2005

“The beam source is a 10 kWatt Xenon search-light (80 cm beam diameter, about 25% efficient), which should yield a climber power budget of about 500 watts.”
— 2005 Beam Power Challenge

Power beaming is an excellent way to send power into space. Rather than carting heavy power generation equipment and fuel, all of the mass can stay on the ground. The reference case for Earth to space elevators now utilizes power beaming. Power beaming can also be used to reduce the weight thrown to the Moon to begin scouting, pioneering, and settling. While important to make the cost of the administration’s Vision for Space Exploration reasonable and perhaps someday making space elevators feasible, the biggest value of power beaming may be beaming back to Earth after the Moon is industrialized.

An investment in Lunar industry can produce cell after cell that will have a very long life in the optimal conditions for electronics on the Moon. By producing vast farms of solar cells, power can be gathered without any clouds or atmosphere to get in the way. If the solar photovoltaic power cells are built out of Lunar materials, a small industrial base on the Moon can lead to enough power to export by radar beam back to the Earth. Lunar solar power (LSP) is a low pollution, low operating cost, high capacity power generation technology.

There are substantial questions that need to be answered regarding cultural, legal, financial, and political challenges before the more modest engineering challenges can be embarked upon. Dr. David Criswell advocates LSP as a panacea for global poverty, petroleum wars, pollution, US growth, Social Security, Medicaid, interplanetary travel, and colonization. Is it the real deal, or is it being thoughtlessly oversold like orbital solar, helium-3, and hydrogen? Criswell’s frontal assault on the academy has been going on for decades. Even as the economics and technology gets steadily validated through other projects, we are further from LSP now than we were in 1968.

Criswell is certainly too much of a Pollyanna (Webster’s 10th: a person characterized by irrepressible optimism and a tendency to find good in everything) to be a very good advocate for his case. I am probably too controversial to do it. Anyone else want to have a go?

As a commercial proposition, saying with a straight face you want to start a blue sky endeavor (black sky?) that will cost $400-500 billion to achieve breakeven will have commercial investors wondering why they took the meeting. If a space transportation startup cannot raise $1 billion (see “The ‘signal-to-noise ratio’ in financing new space startups”, The Space Review, February 28, 2005), then why would a power company be able to raise $400–500 billion?

For the United States Congress, this would be a major strategic undertaking. However, if we spread the cost over fifteen years, spending would be only $30 billion a year. As a percent of GDP it is only 0.3%, a bare two percent of the federal budget or about twice what we are spending on NASA today. After that, we would have an asset that is self-sustaining worth trillions of dollars to the world economy.

That level of investment of a one-time investment of 4–5% of US GDP would be a commitment on the order of the Apollo Project, the Manhattan Project, the Louisiana Purchase, the War on Terror, the War on Poverty, the War on Drugs, the invasion of Iraq, the tax cut, the prescription drug benefit, the student loan program, the residential mortgage program, and the list goes on.

Most of the early investment will be mirroring the administration’s Vision for Space Exploration (VSE) anyway, at least for most of the first $20 billion or so. The first expensive elements will be to establish sufficient Lunar infrastructure to embark on Lunar construction of a demonstration system.

Lunar solar is a boring, simple technology. Solar cells have been powering houses in sunny spots and call boxes for decades on Earth. As a solid-state technology, it is uniquely suited to the harsh Lunar environment. Radiation, heat, and cold are no big deal to a hunk of silicon. Broadcast radar power has been successfully demonstrated. If the engineering case for LSP is so simple, compelling, and boring as to be unbelievably easy if it can be validated, the main challenges associated with adoption and deployment are cultural, legal, financial, and political.

Validating the case

There is not too much mass represented by a solar cell. Almost all of the mass is taken up by silicon, which is plentiful on the Moon. The energy to refine the silicon is also plentiful. Thus the case for LSP is very robust to changes in the cost of transport. Even at ten times Criswell’s assumed cost to Earth orbit of $500/kilogram, building out the Moon would assure that the cost of energy never rises higher than it is today. That is a pretty good assurance. And once there is $500 billion a year or more in commerce on the Moon, it would be reasonable to assume there would be sufficient traffic for lower cost heavy lift to be affordable and fully utilized, making the low-cost case of Lunar development govern.

Obtaining the frequencies for broadcast could be a pricey proposition especially if band clearance is rushed. Clearing all the existing users from the primary frequency and the harmonics will be a tricky endeavor. Being right in the sweet spot of communication, it could cost another $100 billion to clear the relevant spectrum bands. Technically, it can be easily validated that power can be broadcast, and then rectified. The regulatory issue of obtaining the requisite frequencies and moving the existing users to other parts of the spectrum may be much more time consuming. Done over a decade like analog TV, it might not be too disruptive. Advocates should start figuring out the answer early so the frequency will be available when the broadcast antennae start sprouting on the Moon. If band clearance (possibly on the harmonics) is incomplete, perhaps geographic separation would be a substitute. Even without broadcasts near population centers, due to the difficulty of band clearance and interference with consumer electronics, power beaming economics would be affected little. It would be a shame not to put copper wire to better use, but we’ve already got it deployed in case we still have to ship power from outlying areas to population centers once it hits Earth. Even so, the frequency band plan may be the most critical item.

One benefit that cannot be banked on (at least not without intervention or a complete turnover of the capital stock) is reduction of carbon pollution. Cost of coal is about nil. It is between $10–40/ton delivered. That generates about 25 million BTU, which converts into about 7,300 kWt-h or about 2,400 kWe-h. That puts it right around $0.01/kWe-h. If the cost of Lunar solar generated electricity dropped to that, coal would still be burned in about half the plants in America if we discount operating and maintenance costs. Since there is nothing really to do with coal if we don’t burn it, the price of coal would drop if we stop. The prices would drop to microprices.

It is reasonable to expect that few new coal, nuclear or gas plants would be built if Lunar solar starts offering electricity at $0.01, but that would entail a huge drop in the cost of carbon and uranium. It might still be profitable to operate rather than close them after the capital is written off. The only way to stop the burning of coal in existing plants is to impose a tax or outlaw it. We can do either of those things without Lunar solar power.

Oil is a similar deal. There are still very-low-cost oil fields to work, especially in the Middle East. If the cost of electricity dropped to $0.01/kWe-h due to market saturation of solar, oil would likely drop precipitously until burning it became competitive since petrochemicals demand would take years to reach the same level of demand as burning oil as fuel for heating or transportation. There would be many expensive wells that would be capped. There would be few, if any, new wells drilled, but oil would continue to flow and be burned for years following such a price drop. Again, a steep carbon tax would be required to eliminate it.

Even if electricity is $0.01/kWe-h, that does not make the capital turnover to electric and hydrogen cars much less expensive, especially considering the drop in the price of oil if the transition usage drop gets ahead of the carbon electricity generation plant capital depreciation. Which do you think depreciates faster, cars or big steam boilers?

The math of industrial transition economics is not flattering to LSP. The total cost of the LSP would have to compete against the marginal cost of burning the carbon in order to make a profit.

page 2: building the capability >>