It might be easy to dismiss as a sci-fi fantasy, but a recently published Pentagon report claims that beaming solar power from orbiting satellites to the earth could soon become commercially viable.
The National Security Space Office (NSSO) predicts such a service will be in operation between 2017 and 2020. The spacecraft, the report argues, would be equipped with a microwave or laser beam, which could supply energy to remote locations facing high costs to generate or import electricity.
However, despite the fact an array of solar panels in geo-stationary orbit would be exposed to roughly eight times as much sunlight as it would on the ground, the orbiting array would still need to measure one and a half square miles across to generate 1 gigawatt continuously, the capacity of a traditional power station.
Consequently, Lt. Col. Damphousse of the NSSO believes that the technology remains some way off large scale commercial viability. "As of today we cannot close the business case," he says, but quickly adds that that could soon change. "The price of oil is going to continue rising," he argues. "If SSP [Space Solar Power] can go through a scaling up process over the next few decades it could generate ten percent of US baseload power by 2050."
But while the Pentagon reckons the technology is decades away from commercial use there are several private companies aiming to launch a prototype SSP platform within the next two years and one of these companies, California-based start-up Space Island Group, predicts it will supply space-generated electricity to the UK domestic market at competitive rates as early as 2012.
Advocates of the technology reckon recent advances in ion thrusters and thin-film solar cells have made such a prototype project viable today. Wireless energy transmission over distances of up to one mile has been successfully demonstrated since the 1970's, and some experts argue that subsequent improvements in transmission efficiency mean it would be perfectly feasible to beam power down from orbital solar power stations.
One approach would be to use a laser for transmission that could beam continuously to existing photovoltaic panels, cutting energy storage costs. However, the infra-red beam would experience interference on overcast days and as a result a microwave-based system that would be far less sensitive to distortion from the atmosphere looks the likeliest solution. The ground antenna array used to collect the energy from a microwave beam would also be far more efficient than solar cells, leaking less heat to the surrounding area and ensuring that a 10 megawatt operation could in theory cover just one-tenth of a square kilometre.
As for potential health risks, Damphousse insists that "by the time the beam has reached the surface, it has spread out considerably. The energy density is one-sixth that of the noon-day sun."
The major remaining commercial obstacle is the high cost of space transport. However, according to various viability studies a ten-fold increase in launches per year would create an economy of scale that would make SSP competitive with other renewable energy technologies. The US and Europe each currently launch around 10 to 15 space flights a year, but Space Island Group CEO Gene Meyers thinks his company alone will soon be launching close to one rocket a week.
The company has almost completed financing for a prototype system that it claims will be in orbit within 18 months, at a total cost of $200 million. "The satellite will deliver between 10 to 25 megawatts of power," says Meyers. "It will 'site-hop' across base stations in Europe, beaming 90 minutes of power to each one by microwave."
If the test proves successful, a 1 gigawatt installation for the UK domestic market would be the next step, he adds.
However, Space Island Group is not alone in its ambitions for an orbital power station. Kevin Reed, chief marketing officer at Welsom Space Power, a recently-formed consortium including a large US aerospace company and a leading Swiss thin-film solar cell manufacturer, says the company is planning to put a 1.2 megawatt satellite in orbit by 2010 with an eight megawatt operation scheduled for 2012.
"Smaller versions of our thin-film solar cell arrays will be tested for space heritage first," says Reed. "We are talking to the government of Palau about Helen Island as the test area for the service. It sits next to a coral reef, which is very sensitive to heat, so it's an excellent test area."
The test satellite will be situated in a low 'Molniya' orbit and will pass over a number of islands during a daily cycle. The plan is to have one base station connected to the grid on Helen Island, and an additional one thousand handheld rechargers distributed among the populace. "They can use them to power their cellphones or laptops," Reed says. "The amount of power required is very minimal, something like 2 watts."
Supporters of SSP argue it is particularly suited to small island nations that typically pay high prices to power their generators with imported diesel, coal and other fuels. Similarly developing nations are interested in the concept as a means of distributing power to rural communities without the need to invest in massive grid infrastructure. Meyers says Space Island Group has talked to almost every department within the Indian government about the potential of SSP, but no contracts have yet been signed.
However, some observers are far less than optimistic about the technolgy's chances of short and even medium-term success. Leopold Summerer, head of advanced concepts at the European Space Agency (ESA), remains conservative about the prospects for SSP. " Space solar pops up every ten years or so; it generates a lot of enthusiasm, then fades away," he says. "Presently we are still far from a commercial proof-of-concept. I think we'll see some plants in orbit, but not until 2050."
But Reed insists that if the technology can be proven and is competitive against the alternatives then it has the potential to scale up very quickly. " Once a system is in place, people in Tokyo will look at the people in Palau powering their laptops or even their cars this way, and they'll ask why they can't do it themselves," he predicts.
