Sep 15 2015

Solar Hydrogen and our Energy Infrastructure

We are at an interesting point in our civilization. It seems pretty clear that the fossil fuel infrastructure on which our technology is largely built is not sustainable. Pulling massive amounts of conveniently stored energy out of the ground fueled the industrial revolution, and continues to be the primary source of our energy. Currently fossil fuels produce 82% of the worlds energy.

However, putting all that sequestered carbon back into the atmosphere is having unintended consequences on the climate. A recent estimate indicates that if we burn all the remaining known fossil fuel reserves the Antarctic ice sheet will essentially melt raising the oceans by 60 meters. Even if they are off by an order of magnitude, a 6 meter rise in sea level will dramatically alter the coastlines of the world.

Even if we put aside climate change, burning fossil fuels produces pollution. Beijing’s atmosphere is a good example of what happens when you try to fuel an industrial revolution with coal. Further, fossil fuels are finite. We can argue about how much there is available in the world, but it’s not infinite.

There is an interesting debate occurring about what the energy infrastructure of the future will and should look like. Some think the only way to wean ourselves off fossil fuels is to go massively nuclear. They make a compelling argument. Nuclear has the potential to produce large amounts of energy on demand without releasing carbon. Next generation reactors we are building right now can burn fuel more efficiently and produce less waste – and even burn the waste from older reactors. Some think we should develop a thorium reactor cycle.

There is the promise of fusion reactors, but that hope has always been 30 years away, and we’re still 30 years away by optimistic estimates, which could mean we’re 50-100 years away. Fusion is likely to be a major component of our future energy infrastructure, but we just cannot predict how long it will take.

Renewable energies therefore garner a great deal of attention, primarily wind and solar. These sources of energy are becoming cost effective with fossil fuels (although the price of a barrel of oil fluctuates considerably, and is currently quite low). One year ago Nadine May published a graduate thesis in which she calculated that if we covered a square in the Sahara desert with solar panels 158 miles x 158 miles (c. 25,000 square miles) we could power the world with current solar panel efficiencies. This was not a proposal, just a demonstration of the land area needed.

The primary drawback of solar and wind technology is that they are not on demand. This is not close to being a problem yet – the US, for example, does not produce enough solar or wind to exceed demand, so we don’t have to store the energy. We just use it and offset power plant production, reducing peak demand which improves the efficiency of the entire system.

The intermittent nature of solar and wind will only start to become a problem when they represent a significant portion of our energy production, essentially when peak wind and solar production exceeds current demand. That would be a nice problem to have. Building lots of batteries is a problem not the solution, especially given current battery technology. There are other ideas floating around for how to store unused energy, including compressing air in deep caverns, spinning up flywheels, and using the energy to produce hydrogen. That latter solution may become viable quickly.

Solar energy can be used in several ways. Most people think of photovoltaics, which turns sunlight directly into electricity. Sunlight, however, can also be used to heat water tanks, either for direct use as hot water, to heat buildings, or to produce steam to run a generator.

There is another use – artificial photosynthesis, or using solar energy to convert water into oxygen and hydrogen. Hydrogen is not a source of energy because we do not have any significant free hydrogen on Earth. Hydrogen, however, is very energy dense and therefore might be a good medium in which to store energy.

If you recall the coming of the hydrogen economy that was discussed 15 years ago – it never really panned out due to technological hurdles. It turns out that it’s really hard to store large amounts of hydrogen in a stable form that can be released quickly in a light and small container. These are the features that would be necessary for a hydrogen fuel cell car.

If we forget cars, however, hydrogen can be an excellent fuel storage medium. If we don’t care about weight and size is not a critical factor, we have ways of safely storing hydrogen, which can then be burned with oxygen to make on demand energy for buildings. We may see a hydrogen economy yet.

A home, for example, could have solar panels on the roof that convert water into hydrogen, the hydrogen is then stored and burned on demand to make energy. Centralized power factories could also mass produce hydrogen for distribution.

Right now one limiting factor for this kind of energy infrastructure is the efficiency of devices that convert solar into hydrogen. The record for efficiency, which has stood fro the last 17 years, was 12.4%. However, a team from TU Ilmenau, Helmholtz-Zentrum Berlin (HZB), the California Institute of Technology as well as the Fraunhofer ISE has just announced that they have finally exceeded this record, with a device that produces hydrogen from solar with a 14% efficiency.

The authors estimate that this process will be cost effective with fossil fuels at an efficiency of 15%, so we’re close but not there yet (but of course this is dependent on the current price of oil). If the process can be improved in terms of stability and efficiency even incrementally, it seems likely we will get to cost effectiveness.

Conclusion

At this point no one really knows what the energy infrastructure of the future will look like. The broad picture is that we are slowly weaning off fossil fuels, and many think we need to dramatically increase the rate of this weaning.

What percentage of future energy (and when) will be met by fission, fusion, solar, wind, or other energy sources, and what role if any will hydrogen play as an energy storage medium, is still anyone’s guess. That makes it pretty exciting, to see how this will unfold.

It can also get a little frustrating. I read about amazing advancements in solar, battery, and other energy technologies on a weekly basis. We are making incremental advances, but it always seems like we are not quite there, and optimistic projections of future advancements, of “scaling up” technologies, or overcoming a major limitation, need to be taken with a huge grain of salt.

I guess I should stop waiting for the news release that a new technology is fully developed and ready to deploy. We need to be patient and allow for the incremental advances to accumulate. I do think we would all benefit if the process were accelerated by making energy research a higher priority and increasing funding.  It seems like it would be a cost-effective investment.

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