ImageNico Hotz, a Duke University researcher, discusses solar power generation research that involves using hydrogen as a vehicle for creating electricity.

 Full Transcript:

Ben Lack:  You’ve got some pretty interesting findings on trying to get more generation capacity out of solar panels.What’s the problem that you were trying to solve and how you came across the research.
Nico Hotz:  The problem or the question that we wanted to address is how can we use sunlight or other renewable sources to power a house or building like, for example, a single-family household.  How can we generate enough electricity for such a building?  One of the big problems obviously is sunlight and some other renewable sources, as well as the storage.  You don’t really get the power when you need it exactly.  You might get the sunlight during the day, but you need power obviously 24 hours in your home.  So, I was thinking of different options and the different  technologies that we can combine to use sunlight maybe in combination with a biofuel, biomasterized fuel, like an alcoholic fuel, and convert that to electricity in a way that we can also store it on sight.  So, we basically can produce the electricity on the man hour we need it or power the whole thing with sunlight and a biofuel.  So, I compared different solutions.  One would be what people are doing already today, to buy photovoltaic cells, put them on your house, on the roof.  These photovoltaic cells convert to sunlight and to electricity. But then you need obviously some electricity storage system like a battery. For example, generate a lot of electricity during the day, store some of it for the night.  I didn’t really like that option or that system that much because batteries, at least at the moment, are expensive, they are quite big.  It’s not really easy to store enough electricity for a family house, for example, that lasts for a couple of days.  It’s expensive.  So, one option that we came up with since and that I that I since then I’m testing and analyzing in more detail is the following. Can we store the energy initially in an energy-dense fuel like, in this case, a biofuel, methanol, for example; convert it to hydrogen and use that hydrogen then directly in the fuel cell to convert it to electricity and, at the same time, can produce more hydrogen then we need at that moment and store that excess hydrogen in a very intermediate tank, for example, for the night, or maybe for the next day it’s very bad battery or something like that.
Ben Lack:  Why did you choose hydrogen as your element of choice for storage?
Nico Hotz:  Hydrogen has a few huge advantages.  First of all, it has a very high energy density per mass. So, you don’t have a high mass that you have to store somewhere.  You can convert it very efficiently in a very clean way into different useful forms of energy. For example, in fuel cells, even very conventional, low-temperature fuel cells that you can buy already today, convert hydrogen very quickly, very efficiently into electricity directly, and the only exhaust that you produce in that way is water, so it’s completely harmless.  You cannot use the hydrogen in combustion engines and so on, but that way you don’t really get electricity, but it has a big problem.  The reason why I and nobody in the world really uses hydrogen directly in your home or your car is because it is difficult to store volume-wise.  It has a very low-energy density per volume. So, you would need a really big tank to store enough energy in the form of hydrogen, for example, a few days to power your house.
Ben Lack:  And that’s where you get into using hydrogen for fuel cells?
Nico Hotz:  Exactly. What I want to do is I want to store the energy in a very easy form in the long-term; that’s my methanol tank.  The idea would be, and obviously that does not work now but would be in a few years, maybe people use this system, is to have a big tank in your house where you fill it up with methanol, that gives you enough energy for several weeks or months to power your house. And, every day, whenever you have enough sunlight, you convert some part of the methanol into hydrogen, you use it immediately to some degree and to some degree you store that just intermediately just in this market.  The advantage of that hydrogen is then you can convert the hydrogen into electricity instantaneously.  These fuel cells you can turn them on and off very quickly, so if you suddenly turn on some electricity-consuming device in your house, the fuel cell basically follows that load immediately; that’s the advantage of hydrogen.  You basically can turn it on and off the hydrogen-consuming fuel cell immediately.
Ben Lack:  Do you have any specifics that show you know energy loss from converting sunlight to hydrogen to electricity?
   
Nico Hotz:  One big problem of methanol to hydrogen conversion is that it’s so-called endothermic correction; that means a need to provide heat to the reaction all the time.  You have to keep it at a reaction temperature, which is in this case around 200-250 degrees celsius.  So, when some people say, well, we could do that in a way that we take methanol, burn part of it to generate heat, we use that heat to heat up our system, and the other part of the methanol we actually convert to hydrogen.  If you calculate the efficiency to produce hydrogen that way, you might be somewhere at 40%, 50% of the energy conduit of the methanol goes actually to hydrogen.  The rest you lose due to heat loss, due to the combustion of part of the methanol cell.  That section, however, of this project is that at 250 degrees celsius, we can achieve that without burning any of our very precious fuel.  We can just make a very good, very efficient solar collector, put it under the sunlight and that heats it up to 200-250 degrees.  In that case, if you basically say your sunlight is for free, you don’t have to pay for it, you just get it, the conversion efficiency for methanol to hydrogen is pretty much 100%.  It’s, of course, cheating because you add another energy source to it.
Nico Hotz:  In the form of sunlight, but if you say, okay that’s for free.  The methanol to hydrogen efficiency is pretty much 100%, so all your losses you’ve compensated with the sun, basically.
Ben Lack:  Now that you’ve tested your design, what are the findings?
Nico Hotz:  So, when you speak about testing, what we are right now doing is we have experience with pretty much all the similar components of this system. I have students in my lab working on the fuel cell and hydrogen storage and so on.  So, we have experience with all these components, but what we are doing right now is actually putting them together  and setting up an entire system where we really have, from the start, a sunlight and methanol going through the whole system with hydrogen fuel cell electricity where we set up everything as one.
Nico Hotz:  System integration is what we are doing now and that’s what we are working on.
Ben Lack:  Assuming, you know, that the system proves itself out, are there any major changes in the cost for either installation or in the actual design itself or even in the project for designing and installing these on roofs.
Nico Hotz:  That’s always a difficult question, especially for me.  I’m more the scientist who works with the chemistry and thermal aspect of the system.  When I did and I guess that’s where you were at, as well, some analysis of the system, including some prices, I look basically at how many solar collectors that you can buy already today and fuel cells that you can buy already today and hydrogen source systems that you can buy already today.  How much do they cost?  And if you use them in one system, how high would this total system cost then be?  Obviously, once we are running it now, basically starting this summer and hopefully getting good results within the next year or so.  We want to be able to optimize the system solar collector and so on, so that this can be commercialized in a few years or so.  We can give hints to the industry how they can produce these collectors, these reactors and so on in a cheaper way.
Ben Lack:  Nico, why are you interested in the space?  And why have you chosen to research this industry and to try and find solutions to many of the problems that this industry faces.
Nico Hotz:  On the one hand side, I have been interested in this topic in energy and green sustainable renewable energy since I was a kid. So, it was kind of obvious for me always to go in this direction.  The other thing is I believe this specific system could be very interesting because I believe its technology that is not too far away.  It’s not a technology that we might be able to use in 10 to 20 years.  I think we can use that already in a few years.  I think that customers, including you and me, could potentially be able to buy such a system, install it in your house, and you have your small power plant in your house.  I kind of like that idea of having decentralized, small power plants in your house, and you produce electricity when you need it.  Maybe, you can even produce on good days more and sell it back to the grid and actually make money on the system.  I kind of like that idea, applying renewable sustainable energy solutions on a daily basis because it’s not just high-tech that nobody can afford, but in a way that hopefully we can afford it economically.


Front photo by graur codrin.