The Space Reviewin association with SpaceNews

SPS illustration
Solar power satellites have promised to provide cheap, clean power for decades, but we have made very little progress on the concept in over 30 years. (credit: SSI)

Whatever happened to solar power satellites?

At the end of June, a conference about space based solar power generation was held in Granada, Spain. The conference provided progress reports from groups in Europe, the US, and Japan who are working on concepts and plans for building solar power plants in orbit that would beam electricity down for use on Earth.

It sounds like the perfect solution for our future energy needs. The Sun is constantly sending energy to the Earth and all we need to do is catch it and then use it. Unlike current energy sources, we are not going to run out of sunlight anytime soon, it wouldn’t contribute to global warming, and it is available everywhere (or to put it another way, we don’t need to get most of our sunlight from a politically unstable region).

The idea of generating power in space has been around for a while, but has never really gotten off the ground. Concepts for solar power satellites were being discussed in the 1960s and they have received varying amounts of interest since then. If solar power satellites are such a great thing, why haven’t more people been more excited about them? The theory of the concept is sound, but there are a number of hurdles that are holding development back.

Earth based solar power

Why bother putting solar panels on a satellite when you could generate electricity by putting them on the ground or on rooftops here on Earth? The obvious problem is that any point on land is in the dark half of the time, so solar panels are useless during the night. During the day clouds can also block sunlight and stop power production.

The idea of generating power in space has been around for a while, but has never really gotten off the ground.

In orbit, a solar power satellite would be above the atmosphere and could be positioned so that it received constant direct sunlight. Some energy would be lost in the process of transmitting power to stations on the Earth, but this would not offset the advantage that an orbiting solar power station would have over ground based solar collectors.

There are also opportunity costs associated with both options. On Earth, land used for generating solar power is not being used for other things. Rooftop space may not be valuable, but acres of farmland are. There is also only a limited number of available slots in geosynchronous orbit where a satellite could be placed to continuously beam power to a specific receiver. Where land is at a premium, a satellite would have an advantage over a ground-based system.

For places with plenty of sun and available land, satellites couldn’t compete with generating solar power locally. It would be difficult to argue for the need of an orbital system if every place had San Diego’s weather and climate, but since this isn’t the case there would be demand for beaming solar power to locations that couldn’t generate it otherwise. Using solar panels here on Earth though is far easier and less expensive, so much of the focus on renewable energy solutions is not on satellite systems.

High cost of launching

Another barrier is that launching anything into space costs a lot of money. A substantial investment would be needed to get a solar power satellite into orbit; then the launch costs would make the electricity that was produced more expensive than other alternatives. In the long term, launch costs will need to come down before generating solar power in space makes economic sense. But is the expense of launching enough to explain why so little progress has been made?

There were over 60 launches in 2003, so last year there was enough money spent to put something into orbit about every week on average. Funding was found to launch science satellites to study gravity waves and to explore other planets. There are also dozens of GPS satellites in orbit that help people find out where they are on the ground. Is there enough money available for these purposes, but not enough to launch even one solar power satellite that would help the world develop a new source of energy?

In the 2004 budget the Department of Energy has over $260 million allocated for fusion research. Obviously the government has some interest in funding renewable energy research and they realize that private companies would not be able to fund the development of a sustainable fusion industry on their own. From this perspective, the barrier holding back solar power satellites is not purely financial, but rather the problem is that there is not enough political will to make the money available for further development.

In the long term, launch costs will need to come down before generating solar power in space makes economic sense. But is the expense of launching enough to explain why so little progress has been made?

There is a very interesting discussion on the economics of large space projects that makes the point that “the fundamental problem in opening any contemporary frontier, whether geographic or technological, is not lack of imagination or will, but lack of capital to finance initial construction which makes the subsequent and typically more profitable economic development possible. Solving this fundamental problem involves using one or more forms of direct or indirect government intervention in the capital market.”

Competing with other options

Even if a solar power system was built and launched there would still be the economic problem of producing electricity at a cost that is comparable to other options. Government subsidies can help get this new industry on its feet but it will need to compete in the market in order to survive. This is a challenge for all emerging renewable energy solutions.

Current non-renewable energy supplies are cheap. Even with the recent increases in the price of oil, it is still historically low. Adjusted for inflation, gas prices are still much lower than they were during the oil crisis in the 1970s. With current prices there is little incentive for customers or producers to pursue alternatives. Even if oil prices continue to increase, it is not likely that this will be enough to drive demand for alternatives. Although we will eventually run out of oil, coal, and other non-renewable energy sources, in the short term rising oil prices will simply generate more oil.

There are large amounts of known reserves that are too expensive to profitably develop when oil is below a certain price. As soon as the price increases past a certain threshold, a given field can be developed at a profit. From an economic standpoint, energy producers will take advantage of this and will make use of their existing infrastructure to extract, refine, and distribute as much oil as possible regardless of how high the price of a barrel of oil goes.

Again the problem is more of a political one than an economic one. There will not be a financial reason to start creating a solar power system in space unless we reach a decision to include the hidden environmental costs of our current non-renewable sources of energy into the equation. In the near term we certainly can afford to keep burning more oil, but are we willing to start investing in alternatives so we don’t have to?

A very big problem

A fully-operational solar power satellite system could end up needing to be enormous. Some designs suggest creating rectangular solar arrays that are several kilometers long on each side. If we assume that enough money could be found to build something like this and that it could be run competitively against other energy options, there is the very real problem of figuring out how to get it into orbit or how to build it in orbit from separate smaller pieces.

Starting the development of such a system by building small proof of concept satellites is completely within our reach.

The largest solar panels ever deployed in space are currently being used on the International Space Station. They cover more than 830 square meters and are 73 meters long and 11 meters wide. These large panels make the ISS one of the brightest objects in the night sky. Scaling up from there to something much larger would be challenging, but the good news is that we can take one thing at a time.

For a proof of concept satellite it makes sense to use the station’s solar panels as a baseline. By taking advantage of improvements in solar cell technology we could launch a demonstration satellite of the same size that generates up to 3 times as much power. The station’s solar panels are 14% efficient, but recent advances with solar cells and solar concentrators could allow us to build panels that are up to 50% efficient.

If this demonstration system validated the theory behind generating power in space and beaming it down to Earth, the next step would be figuring out how to put even bigger solar panels in space. It may be that with our current launch options it simply isn’t possible to launch an operational solar power system into orbit. If that were the case, the concept would need to be put on hold until other lift options, such as a space elevator, are available.

What’s next?

There are a number of reasons why we won’t be seeing huge orbiting solar collectors beaming us lots of energy anytime soon. Starting the development of such a system by building small proof of concept satellites is completely within our reach, though. There are economic, political, and engineering hurdles in the way, but none of these should be enough to stop the idea if we choose to pursue it. Once a successful demonstration has been achieved, there may be enough interest in government or in private industry to continue working toward fully-operational solar power satellites.