Science Journey: Fueling the World Engine: Chemistry for Solar Fuels

Great question! I'm going to assume you mean to ask how much area would we need to cover to generate that much power.

If we can use the entirety of the Earth's surface, we need about 5% of the surface covered by modern-day solar panels to generate 100% of the Earth's power demand. If we can't use the oceans (because transporting power from the middle of the ocean is hard) then we need about 15% of the world's land. Which is a lot!

You can offset this somewhat by using rooftops but realistically we'd need an improvement in technology to make this feasible. Fortunately, there is room for improvement! Plus, we don't necessarily need to generate 100% of our power from solar. We can incorporate wind, hydro, nuclear, and of course, hydrogen! Storing solar energy reduces the area we'd need to cover with solar panels to meet our needs.

Reference: Sandia National Laboratories

Yes, nuclear can be used to generate hydrogen, but modern reactors use steam turbines to harness that energy because it's more efficient.

Your question on safety concerns with hydrogen is a very important one. Hydrogen can indeed be very dangerous if improperly handled. In fact, it is not unheard of for explosions to occur when scientists attempt water splitting without proper safety controls. As a result, there has been considerable research on safely containing and transporting hydrogen. Most of that has been worked out already. Industry has safety controls so that filling a rocket with literally tons of hydrogen is a regular occurrence and accidents at hydrogen generation plants are extremely rare.

One of the current areas of research is storing hydrogen in porous solid materials for applications such as hydrogen-powered cars to prevent detonation should the storage unit suffer damage. It's similar to how batteries work. To my knowledge that has not yet been commercialized but it is an active area of research!

References:

• French Ministry of Ecology, Energy, Sustainable Development and Town and Country Planning
• NASA
• Chemistry World

Thanks for your question! Unfortunately, we probably won't be able to get all of the energy from the Sun because we are so far away. Think about how a flashlight looks really bright from close up but you can hardly see it from far away. To get as much energy from the Sun as possible we need to use chemicals like semiconductors to absorb a lot of light and turn it into electricity. Though we should also use wind power because wind energy is solar energy too! Winds are caused by the Sun heating the Earth unevenly so if we want all the energy from the Sun we should harvest the winds too.

I'll start by saying that there are not an infinite number of atoms in the observable universe. There are a lot, but not an infinite number.

That equation you are referencing calculates the energy of a resting particle, which for atoms is only recoverable by nuclear processes which is very hard to do for most atoms. I should also point out that we aren't really facing a shortage of power! We have a lot of fossil fuels left, though not an infinite amount.

What we are facing is environmental pressure which makes continual burning of carbon undesirable, at least at our current rate. Similarly, we have lots and lots of solar power available, but we don't have enough solar technology to harness it all. That's where research into solar energy and solar fuels comes in. Think of it like trying to collect water from the ocean to fill a swimming pool using only a coffee mug. The problem isn't that we don't have enough water, it's that our cup is too small!

References:

• U.S. Energy Information Administration
• United Nations Development Programme

Electric cars are a very cool technology! I focused on hydrogen-powered cars because my talk was about hydrogen, but I'd be happy to expand on it a little. In my opinion (emphasis on "opinion"), battery-powered electric cars are more likely to be the vehicle of choice in the future than hydrogen powered cars. However, that doesn't mean solar fuels would have no impact on cars.

A factor to consider when looking at "clean" technology is where the electricity is coming from. And for electric cars, the answer is the same as it is for your house: carbon! So while the car itself doesn't burn any carbon, the power plant it uses to charge up probably does. Perhaps they would be better for the environment if the power plants burned hydrogen!

Great question! You are absolutely on the right track. We will definitely need to use wind and hydro to help out with our nighttime problem. However, even putting those together doesn't quite solve our problem because both of those are what's called "intermittent" power sources.

For example, what do you do if you live in a place where you can't make hydro power because there's not enough water and one day the wind doesn't blow? You'd have no power! We don't want that situation to happen so that's why we want to store the power as hydrogen. But you are absolutely right that power sources like wind, hydro, and even nuclear could be used to help us with the nighttime problem.

That's wonderful to hear! There are all sorts of cool semiconductors out there. I work with gallium arsenide a lot because it is more efficient than silicon, but also more fragile. There's indium phosphide, germanium, strontium titanate, tungsten oxide, titanium dioxide, lead-halide perovskites and so many more! Each has its own properties which make them useful for one thing or another.

Germanium was used to make the first transistor and is still used today (though silicon is more common), strontium titanate is one of the only materials known which can split water all by itself, indium phosphide is good for lasers and high-frequency tech, titanium dioxide can be used for white paint or solar windows, tungsten oxide changes color with electricity, and perovskites are one of the more promising solar materials out there. There are so many semiconductors with unique and interesting properties!

For a more in-depth look at how semiconductors work I recommend PV Education.

Hydrogen has an extremely high gravimetric energy capacity, meaning it stores lots of energy per unit of mass. It is also relatively easy to make!

The second part of your question is a little tricky for me to answer. I think the most basic answer is that "we use the Sun and semiconductors to put the energy in". The reason this is tricky is that we are not adding any energy to the hydrogen, we are adding energy to the system. Consider the slide where I showed how plants store energy as sugars. Water is quite stable — a chemist might say it has "low free energy" — so it sits on the bottom of the graph. Hydrogen is relatively unstable — it has high free energy — and sits in the valley higher up in the graph.

What we are doing when we perform water splitting is putting in enough energy to rip the water apart and then form new bonds which are more unstable (H-H bond is less happy than O-H bond). Now I have the exact same atoms (same system) arranged in a new way that has more energy than it used to. That's what we need the Sun for: adding that energy. Then we just need a little nudge like a spark or something to push it out of the valley and break these new bonds which re-forms the more stable bonds. This releases the energy we put in earlier so we can use it now.

References:

• https://rmi.org/run-on-less-with-hydrogen-fuel-cells.
• https://labs.chem.ucsb.edu/zakarian/armen/11---bonddissociationenergy.pdf