Department of Energy Argonne National Laboratory Office of Science NEWTON's Homepage NEWTON's Homepage
NEWTON, Ask A Scientist!
NEWTON Home Page NEWTON Teachers Visit Our Archives Ask A Question How To Ask A Question Question of the Week Our Expert Scientists Volunteer at NEWTON! Frequently Asked Questions Referencing NEWTON About NEWTON About Ask A Scientist Education At Argonne Solar Panels, Electrolysis, and Feasibility
Name: Jon
Status: Other
Grade: Other
Location: MI
Country: United States
Date: April 2006


Question:
Energy: the feasibility of a vehicle with solar panels used for electrolysis in separating water into hydrogen for fuel. Say, drive to work and panels sit in sun all day producing hydrogen. Would hydrogen production be fast enough to supply daily energy needs?



Replies:
At present, the direct use of hydrogen as "the perfect fuel" is far from practical reality for a number of reasons. 1. The cost and energy required to produce hydrogen exceeds the energy of combustion of hydrogen in air.

2. Solar panels are not very efficient. They convert only a few percent of the sunlight into electricity. Existing solar panels are too large to produce an adequate amount of electricity. Direct conversion of sunlight to electricity is more efficient than electrolysis.

3. There are not many parts of the surface of the earth where the sun shines bright all day long -- but you being from Michigan do not need to be reminded of that.

4. The hydrogen / air combustion temperature is high enough to produce nitrogen oxides, so that pollution problem would not be eliminated.

5. The hydrogen / air reaction speed is so very fast, a different sort of engine than a conventional internal combustion engine would likely have to be used -- possibly a Sterling engine -- but that would have to be developed.

6. Storing hydrogen safely in a vehicle in case of an automobile accident is a difficult issue that has not been solved.

7. One very important issue (my opinion) not being adequately addressed by hydrogen fuel advocates, and possibly the most important issue, is that water vapor is the most efficient of all the "greenhouse gas". It has the highest concentration in the atmosphere of all the "greenhouse gases" by far. It is essentially transparent to ultraviolet radiation. It absorbs far more infrared radiation than carbon dioxide or hydrocarbons. It has three very intense infrared absorptions, a rich overtone/combination spectrum in the near infrared, and a prolific pure rotational spectrum in the far infrared. In contrast, carbon dioxide has only two infrared absorptions, fewer infrared active absorptions in the near infrared, and no pure rotational spectrum at all, since it does not have a permanent dipole moment, which is required for a molecule to have a pure rotational spectrum.

8. The effects of adding large amounts of additional water into the atmosphere are not known.

9. Electrolysis, in particular, has a very fundamental thermodynamic problem. Think about the process. Water is converted to hydrogen by some energy source. This conversion is at best 100% efficient and free. The hydrogen is burned to produce work. The efficiency of the conversion of heat to work is absolutely limited by the Second Law : Efficiency = (Thot -Tcold) / Thot, where Thot is the hot temperature of any theoretical engine and Tcold is the ambient temperature. Efficiencies seldom exceed 50-70%. The exhaust is liquid water. So what has been done is to convert water at ambient temperature to water at ambient temperature. That's a closed cycle -- an identity -- water-to-water. And there is an energy cost somewhere in between.

Hydrogen is far from the "perfect fuel" some dream of. The more dramatic positive impact on the "greenhouse effect" is to take vehicles off the road by moving "work" nearer to "home" and by various transportation forms such as "light rail" to move substantially more people from place to place with very little increase in the use of energy. But these are sociological and demographic issues which are far more difficult problems than chemistry and physics. It is clear this lesson has not been learned, because we at least in the U.S. continue to subsidize "sprawl" with longer wider highways from where people work to where they live.

Vince Calder


Hi, John. Presuming the array is large enough, this is theoretically possible, but let me raise some points:

First, let us consider that the amount of energy required to power a vehicle (200 to 300 Watt-hours per mile) would require several hundred square feet of solar panels. It is not feasible to carry them along on a vehicle. They could be set up in a stationary location, however, and used to store energy (either in the electricity grid, in batteries, or by cracking hydrogen) for later refueling/recharging.

The setup you propose (presuming we use a stationary array) converts solar energy (about 25% efficient) to potential chemical energy (hydrogen), which has to be compressed and stored, and delivered at high pressure into a storage vessel on the vehicle. Then it is either 1) converted it to mechanical energy by burning it in an internal combustion engine (about 30% efficient) or converted to electricity in a fuel cell (about 70% efficient). If you use the fuel cell, then you have another 80 to 90% efficiency factor added into the mix by going through a controller for an electric motor.

Handling hydrogen requires a filter, dryer, and a compressor that uses electricity, further taking away from the overall conversion efficiency.

Each energy conversion involves losses that makes the required array larger. There are also equipment issues with handling the hydrogen in such a way as to minimize loss of the gas.

How far are you driving everyday? A typical commute is less than 50 miles a day total. In this case, it is simpler, cheaper, and more efficient overall to use an electric vehicle (www.evalbum.com showcases hundreds) for the commute. The array can then be placed on a residence and used to generate electricity to run the home and recharge the vehicle in a few hours after you get home. If the array is connected in a "batteryless grid-tie" arrangement, then you are essentially using the electricity grid as a storage unit, reducing system cost. If you have excess solar array capacity, it is used to power your home. A "battery grid-tie" arrangement will keep the home powered during outages as well. Some people even take advantage of peak and off peak rate differences, selling power back at peak rates and charging during off peak rates.

The particular advantage of this arrangement is that it is available using technology that is easily available to the general public at reasonable cost. Adding hydrogen cracking, compression, storage, transfer equipment, and a fuel cell into the mix increases cost by orders of magnitude, if you can actually lay your hands on the fuel cell.

So it is possible, but not practical or feasible as you describe. by modifying the setup to use a stationary array and equipment, it could be made to work more readily.

David Brandt


I suppose that for some people, such a vehicle could be possible. Unfortunately, there are other factors that would come into play. How far does the person drive to work? How is the traffic on thier drive? Even their driving habits can play a huge role. (aggressive drivers burn more fuel) Lastly, Unless you live in a particularly arid climate, the weather may also come out to get you. After all, who wants to be stuck at work, just because it got cloudy and they're out of fuel because of it?

Weather and traffic can be mitigated to some extent, by providing the vehicle with a larger fuel tank, (thus ensuring an ample reserve), although such a vehicle would still probrably need some external means of fueling.

Ryan Belscamper



Click here to return to the Engineering Archives

NEWTON is an electronic community for Science, Math, and Computer Science K-12 Educators, sponsored and operated by Argonne National Laboratory's Educational Programs, Andrew Skipor, Ph.D., Head of Educational Programs.

For assistance with NEWTON contact a System Operator (help@newton.dep.anl.gov), or at Argonne's Educational Programs

NEWTON AND ASK A SCIENTIST
Educational Programs
Building 360
9700 S. Cass Ave.
Argonne, Illinois
60439-4845, USA
Update: June 2012
Weclome To Newton

Argonne National Laboratory