Space vs Ground Panels

This is the first in a series of articles published published on www.solarfire.org reviewing the idea of solar panels in space compared to ground based alternatives.

Part 1. Space vs Ground Panels: Increasing the impact of Space Solar Panels … by placing them on the ground

It seems to have suddenly become common knowledge in ecological and peak oil (media) circles that solar panels in space would solve our energy and environmental problems, or if not all at least a large chunk. If there has been any serious critique of this idea in the media I have yet to come across it (though there’s plenty of comments). Though “solar panels in space” sounds cool … they may be literally too hot to be practical, as we shall discuss in the next article.

Historically, “neat and clever” ideas that suddenly become taken for granted (in the media), then implemented by governments without any actual thorough study of the feasibility or environmental impact of the plan (i.e. biofuels, nuclear, shale gas to name a few), have generally lead either to great disasters or great expense, often both simultaneously.

Hopefully, solar panels in space won’t be the next great blunder. And probably they won’t be, as this plan is so unfeasible even governments aren’t lining up to try (correction: California is making an attempt.).

So what’s the problem with space based PV?

Below is the basic claims and argumentation of Keith Henson piece “Space Solar Power – Recent Conceptual Progress” published on TheOilDrum. It claims Space solar panels would:

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1. A system of power satellites scales to human civilization’s needs (tens of TW).
2. They don’t need storage since their location (the 24 hour orbit, geosynchronous or GEO) is illuminated 99% of the time. [7] (Satellite TV antennas point to a location on that orbit.)
3. No day-night cycle and no clouds or air gives power satellites an average advantage of about nine times over the same area of solar collectors on the ground.
4. Power satellites use relatively little material. Being in orbit (zero gravity), and no wind they can be much lighter per kW than collecting sunlight on the ground.
5. They have a very short energy payback time.

They have some disadvantages, however:

1. For optical reasons, they don’t scale down to small sizes; 5 GW is about as small as you want to make one. [8]
2. At 50% loss electricity-in space to electricity-on-the-ground, the cost is doubled from one cent per kWh to two. On the other hand, that’s 40 times less cost than transmitting the same power over wires for the same distance.
3. They take a large investment to get the cost of transporting parts to GEO down to where they make economic sense.

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Though these claims seem advantageous and the caution of “assuming a cost effective space launch system can be found” is thrown in there, they ignore some basic facts about humanity’s energy system.

It should be noted that the article only discusses concepts, but does make the argument that with cheap enough space launch space launch would become profitable.

To begin with we can note that:

Thermal energy is the foundation of modern society, not electricity

This is a concept I develop at some length in the “Thermal Problem – and the Solar Thermal Solution”, so I will only resume it here. But basically, if you are convinced that the thermal problem is far greater than the electricity problem, then space solar panels are largely irrelevant to solving major energy related problems to begin with.

But to recap, most energy consumption is thermal energy either for heating things like space, water or industrial processes, or for running thermal engines, such as the internal combustion engine. So electricity from space based solar panels only addresses about 15% or our actual energy consumption (in Western nations) and less everywhere else.

Though we could imagine simply doing everything with electricity: it makes no thermodynamic sense to do so, as electricity is a high quality energy (needing energy to make) and so it will be always cheaper to use low quality energy for low quality energy tasks (which represent most energy consumption).

Converting sunlight directly into heat can be easily 60-80 % efficient and extremely cheap, from technologies such as the window to the solar water/space heater to the industrial use of solar thermal energy. Not only is the solar thermal device itself cheaper, it doesn’t require wires, transformers, and a host of other electricity equipment. So, beaming solar energy down from space (actively … rather than letting the sun do it for free) we can seriously doubt would be cheaper than a window, roof top solar heater, or industrial process thermal concentrator.

Now, since ground based solar thermal technology actually addresses the bulk of human energy consumption (and more so actual energy needs), and is a technology that exists and can be (and is being) easily deployed, it should be the priority at the very least. Conversely, since space based PV can’t address the world’s thermal needs it cannot be considered a global solution (in the "short term" of within decades), not to mention electricity grids being far from universally accessible to begin with. Finally, since it’s also possible to create electricity with solar thermal, while using the waste heat generated for thermal applications, this would leverage the massive deployment of solar thermal needed to address thermal needs (factories, technicians, know-how, etc.). It’s reasonable to assume this would be far cheaper than space based PV, if it is feasible at all, which is far from established as this series aims to explore.

However, if you dismiss the Thermal Problem and are convinced everything could be done with electricity, or you are still wondering about solar panels in space as an answer to the relatively small use of electricity that is beneficial, then we can understand the potential of this technology in terms of a series of hurdles it must pass to be considered feasible and effective, the first of which is the premise that panels in space would be superior to those on the ground to begin with.

Hurdle 1. Space vs Ground Panels

The first hurdle is of course whether such a system would be desirable in space at all. For if there’s no clear reason why panels situated in space would be superior, it’s of only hypothetical interest of whether it’s possible to install and maintain them there. For, regardless of technical feasibility, advancements in photo-voltaic technology, space launch, or whether electricity can displace a large portion of thermal consumption, proponents of space panels have to demonstrate a clear advantage over the same panels on the ground.

The major advantages of ground based Solar PV would be:

1. Can be situated at point of use and so no huge distribution system is required (no one serious, for the time being at least, is suggesting microwave space earth transmission to all points of use).
2. Decentralized system is far more robust against total failure.
3. Incremental deployment with incremental improvements.
4. Can be more easily maintained.
5. Can be more easily recycled.
6. Can co-produce low-grade thermal energy.

Central electric distribution system isn’t free
One factor space-PV proponents seem to have ignored altogether is that the electric distribution system from centralized generating (or in this case receiver) points costs money and energy. It costs to build the infrastructure, to maintain it, and to move electricity over it, all of which generally represents about half the cost of grid based electricity in today’s mega-grids. One advantage of ground based solar, whether thermal or PV, is that it can be decentralized to point of use, thus immediately reducing the distribution cost.

So it’s not even clear cut whether space PV would actually be more efficient, or at least I don’t see how this assumption can be taken for granted. The claim for transmitting the energy down to earth is said to be 50 percent efficient, if then half the cost continues to be distribution from these central gigawatt energy receivers, then the transmission cost could be about 75 percent of the cost (assuming transmission to the ground is 25 percent the cost and the actual panels 25 percent) so compared to same panel on the ground placed at point of use we could place 4 for the same price (assuming the larger bulk of ground-PV costs the same as development and launch costs of space-PV).

Now it is claimed that the space panels will produce 9 times more energy per square meter per day than ground panels, but already the installed systems we can assume at least 75% losses, so the panels only really provide 2.2 time the energy of ground panels. If the cost of putting the panels in space is the same as the panel themselves, then the cost-effectiveness of ground panels is about the same. Ground-panels of course have aluminum packaging and glass cover, but these are a relatively small part of the cost and can be recycled, and we can surely find plenty of hidden costs in space PV panels.

Though this isn’t an exact comparison, as no space-PV system exists in which to compare price, my point here is only that we can’t automatically assume panels in space would be more cost-effective once put into orbit. For even if the space panels produce 9 time but there is a 75% transmission loss (in terms of cost), then it seems to come out even with local solar energy, except of course for the installation cost which would be far greater for space deployment.

So, since it is certain to cost more to blast solar panels into space the transmission cost compared to local solar shouldn’t be dismissed lightly.

So already we can cast some serious doubt about whether space based PV would actually be more efficient than ground based thermal or PV alternatives.

Debate
Now, there are of course plenty of more details to debate. A likely counter critique is that panels at point of use may wasted a lot of energy if there is no consumption or battery capacity to use the electricity as it’s produced. To this ground-PV proponents could rebuttal that a local grid could reduce this and would be cheaper than the large mega grids of today, and that “smart appliances” and basic user awareness can increase harmony between energy generation and consumption. Certainly, space-PV proponents may have further arguments. To be absolutely clear, I’m not trying to settle this debate here, only show that there is a debate and it’s far from clear space-PV automatically wins the efficiency context in the narrow operating system sense.

Point
My point here is only to bring these issues up and argue that the advantages of solar panels in space vs. on the ground can’t simply be taken for granted and the matter cannot be reduced to simply whether they can be blasted into space cheaply or not.

However, even if some reasoning is presented that space based panels would be superior in the narrow sense discussed above, the issue is far from over.

Life-cycle and risks
For instance, we could go on to consider life-cycle costs, such as it’s probably easier to recycle panels on the ground rather than in space, that distributed generation and consumption is far more robust against total system failure than a highly sophisticated space technology of which we can imagine plenty of total failure situations. Ground-PV can also co-produce low grade thermal energy, which though cannot answer all thermal needs is still value added that must be considered in comparing technologies.

We can also note that all current commercial photo voltaic cells degrade proportional to the light hitting them. So, in terms of the life of the panel, a ground panel may produce just as much electricity in it’s life-time as a space-panel, if wear of the semi-conductor is proportional to total light impact. There are of course other wear issues on the ground such as wind and rain, but in space there is also space junk and micro-meteorites.

In both electro-magnetic and physical wear, as with the other issues, it’s far from clear who has the advantage.

Furthermore, we have to weight each issue as to it’s importance. For instance, do we value system material costs, which would presumably be lower for space-PV, over system stability, which would presumably be higher for decentralized point of use solar energy. So these questions would also require a political component to answer.

Now, proponents of space based solar panels may have answers to some or all of these issues, this series of article is not written to try to "exclude the possibility outright" but rather simply establish the issue is more complicated than whether a cost-effective space launch is attained or not.

But the above issues are simply the first hurdle. Other hurdles must also be passed both in a technical and systems perspective, from the cost of robots, to the mentioned space junk, environmental factors, to lead in times, to not only space launch costs but projected space launch costs (i.e. what if fossil fuels become more expensive and we need them to grow and maintain the space PV system directly or indirectly). These issues and more will be discussed in the next parts.