(Due to technical problems, the complete report could not be posted on the internet; however it could be sent upon request)
Report:
Solar-Hydrogen Vehicle Project
Abstract
This project, to make a cleaner transportation vehicle, was motivated by the threats to our health and environment due to automobile-related pollutants. The hypothesis is that a vehicle can be powered by water and sunlight. The ultimate goal of this three-year project is to design and build a vehicle that is powered by hydrogen, which is generated on the vehicle from water and sunlight. The basic components of this system will include electrolysis cells, solar panels, a hydrogen purifying system and a storage system, all of which will be mounted on a vehicle with an internal combustion engine that has been modified to run on hydrogen. This project began in fall 2001 by building a 5-watt solar-hydrogen unit and researching many safety issues associated with this technology. During the 2002-2003 school year, I have built a 4-cell solar-hydrogen producing unit with over 320 watts of power and a purifying system. I am currently completing a pressurizing and storage system. Future work will include mounting the system in a vehicle and modifying an engine. It can be concluded that solar-hydrogen systems work well, and the next step will be to prove that a vehicle can be powered by water and sunlight.

TIMELINE: WHAT HAVE WE DONE?

So far, with the great help of a few people there has been steady progress on this 3-year project since fall 2001. Originally, it was planned to have a solar-hydrogen producing unit ready about a month before CARSEF 2003 (Central Arizona Region Science and Engineering Fair), and this has been accomplished. At this stage, the solar-hydrogen producing unit is ready and the designing of a pressurizing and storage system is underway. This pressurizing and storage system will be completed by the end of the current school year, so that next year efforts can be focused into designing an efficient hydrogen-powered engine and reaching the primary goal, building a solar-hydrogen powered vehicle.

Timeline

2001-2002 school year: During this period, great amounts of research were done on various sources of alternative energy. A new method was also hypothesized and tested. This was a plan for a possible electric generator created to make electricity to power the car with an electromotor. The plan consisted of 2 panels of different metals, cupper and zinc. It was hypothesized that if the metal panels were attached together and heated up, they would produce electricity. A small model of the system was built and tested but unfortunately, it did not work. Later on we learned that such a system would produce only a slight amount of electricity.

Having failed in our hypothesized system, all of the focus turned toward hydrogen technology. We learned about electrolysis and designed and built a small unit. During our research, one source of information was Home Power Magazine which had many articles on technologies of alternative energies. One system which seemed particularly interesting to us was designed by an engineer in California named Walt Pyle. We contacted him and he gave several good suggestions for how we might begin.

Rather than try to build a large scale electrolyzer from scratch, we decided not to “reinvent the wheel” and ordered an electrolysis cell from a small company in Iowa called hydrogen wind. During the spring of 2002 we built and tested a system around this cell.


2002-2003 school year: During the current school year, from September 2002-March 2003, there has been much progress associated with the Solar-Hydrogen Vehicle Project. We went from a hand-made electrolysis device powered by a 5-watt solar panel to a 4-cell solar-hydrogen producing unit with a total power potential of 320 watts. This unit is capable of producing, cleaning and purifying hydrogen by using solar energy. Unlike the earlier hand-made system, which was more of an experimental device, the new system is capable of actually producing hydrogen at a noticeably greater rate.


In addition to building the electrolyzing system, some basic experiments have been performed on the solar panels, such as arranging the panels in different configurations, attaching them to variable resistors and graphing their I vs. V performance. The Voltage vs. Current graphs all had a similar shape, and a few of these graphs can be seen below. In general it was found, as expected by previous knowledge about electronics, that the voltage decreased as the circuit resistance increased. Also it was found that for low currents, the voltage does not increase without limit, but it has a plateau as can be seen in the graphs. The maximum voltage of the panel is due to the semiconductor properties of the photovoltaic cells which will be discussed later. These results are also due to the fact that the panels have a limited amount of power and also due to the fact that for very low external resistance, when the current increases, there is some internal resistance in the solar panel. Later, the four solar panels were wired in parallel, and then connected to the electrolysis cells. Just like the prior tests, a total voltage of about 20 volts with no load on the panels (cells were not connected) was received. But unfortunately, after the connection of the 4 cells (increase in resistance), the voltage across each cell dropped to about 1.7 volts (which is about 6.7 volts across all of the cells).


The actual plan is to have 6 electrolysis cells, so that the overall voltage when they are all in series is as close as possible to the voltage associated with peak power (somewhere between 16-19 volts.) Power is basically potential difference multiplied by current. If we graph this relationship, it forms a curve. The area under the curve is power. In order to get the maximum, or peak, power we have the most area under the curve and in order to have the most area under the curve, the multiple of current and voltage has to be the greatest.



The next achievement was the assembling of the Double Bubbler was finished. The Double Bubbler passed the pressure test perfectly fine and there were no leaks. As it was planned before, a pressure relief valve was mounted on the Double Bubbler, which is now set at 60 PSI to prevent the system from building too much pressure. At this point Hydrogen is being produced at very low pressures by using two 5 gallon buckets and a water displacement method. Soon we hope to have metal storage containers but at high pressure there could still be a possibility for leaks, particularly at the fittings for the PVC pipe and tubing. In order to prevent the system from leaking at high pressure, with the aid of pressure relief valves and a pressure sensor, we will keep the system pressure below 60 PSI. A pressure gauge was mounted next to the pressure relief valve to monitor pressure as seen below on the double bubbler.


At this point, the last touches are being done on the purification train, which is believed to be one of the most critical parts of the system. The hydrogen that comes out of the electrolyzers is not perfectly clean and contains a small percentage of oxygen, which could be enough to make an explosion. Basically, this system uses a catalytic re-combiner, which causes free oxygen atoms to bond with 2 hydrogen atoms to form water, which is then collected by the water coalescors.


ASU’s Photovoltaic Testing Laboratory was generous enough to donate 2 solar panels to the project. Recently, ASU’s Photovoltaic Testing Laboratory announced that there would be more panels available for the project. Hopefully, the arriving panels would be able to generate the needed power by the system. Once there is a capability of producing a fair amount of solar hydrogen, it would first be used toward everyday applications. Once the final elements of the system are completed, a solar-hydrogen cooked hotdog party will be held for students at Central High School. This will be done during an Earth Fair celebration on May 2nd.

The plan for summer 2003 and next year is to focus the effort toward designing a safe and efficient way to use hydrogen to power a vehicle, and if everything goes well, the Solar-Hydrogen Vehicle would be finished no later than March 2004. It is understood that this unit may take long periods of time to generate enough hydrogen to drive only a short distance, but if the functional principal is demonstrated, perhaps future engineering and improvements in photovoltaic efficiencies will all make this a realistic technology. Another way to view this project and the fact that the vehicle in its initial stage will not be a practical alternative to the automobile is by noting that the first airplane only flew a few hundred feet!

WHAT STILL NEEDS TO BE DONE
At this point, with confidence, it could be said that almost 70% of the way has been traversed; however one of the greatest challenges, building the solar-hydrogen vehicle, is yet to be achieved.
In order to get to that point, according to project’s time line, the following tasks need to be accomplished:
1. Finish designing, building and testing the pressurizing and storage unit by May 2003
2. Design a small conversion system for an engine (to use gaseous hydrogen instead of liquid gasoline)
3. Do the conversion on a smaller gas-powered engine(perhaps a lawn-mower)
4. Do a safety analysis of the Solar-Hydrogen Vehicle (with outside technical evaluation assistance) and design a safe method to mount the Solar-Hydrogen system on a vehicle.
5. Convert the vehicle internal combustion engine from gasoline to hydrogen.
6. Test vehicle performance.

HOW DOES IT WORK?
The Solar-Hydrogen producing unit consists of several sub-units:
Solar panels> Electrolysis Cells> Double Bubbler> Purification Train> Pressurizing and Storage System


Solar Panels:
The element of silicon is what over 95% of today's solar cells are made of and other solar cells work by basically the same principal as Si solar cells. A silicon atom, with the atomic number of 14, has four valence electrons, meaning they are freer to interact with other atoms. In a pure silicon crystal, each atom shares these valence electrons with four neighbor atoms in covalent bonds. The electrostatic bond between an electron and the two atoms it is helping to hold together can be broken by a minimum amount of 1.1 electron volts. This energy can be obtained by a photon of light of wavelength 1.12µm or less, which includes all colors in the visible spectrum, and a significant part of the infrared.


After the electron is freed, it would travel through the crystal similar to a way that an electron travels in a metal, freely, not attached to any one atom. Now an electric field would accelerate this electron; that is to say it takes a part in the conduction of electricity. This transition causes the electron to leave behind a "hole", a place lacking an electron. Now electrons from other atoms can leave their bonds to fill the hole. This effect, which is called the photoconductive effect, takes place throughout the crystal.

If nothing is done, within a certain time t, called the minority carrier lifetime, the electron would fill a hole, giving off its gained energy during the excitement stage, producing a photon (heat). This certainly is not useful for creating electricity. The ideal situation would be that the electrons and holes are separated so that they don’t recombine in the crystal. There should also be a path to guide the electrons out to do work on a load. This is achieved at a semiconductor junction between two semiconductors with different electrostatic charges and by metal contacts to the cell on opposite side of the junction.

Doping

If a small amount (on the order of one part per million) of phosphorous was added to the silicon crystal as it is forming so that the phosphorous atoms fill sites in the silicon crystal lattice, then the crystal would be 'doped' with phosphorous. Phosphorous is in group V on the periodic table of elements. In other words, it has five valence electrons – one more than silicon. The phosphorous nucleus and inner electrons settle into the lattice site, and four of phosphorus’s electrons participate in the covalent bonding with electrons from the four neighboring silicon atoms. But in the crystal the fifth electron is very loosely bound to the phosphorous atom, as a matter of fact, at room temperatures it is thermally excited into the Free State. This type of doping, doping with elements such as phosphorous with one valence electron more than the original atom is called n type doping (n for 'negative'), and the dopant is called a 'donor' because it easily gives up electrons.

On the other hand, doping silicon with boron has the opposite effect. On the periodic table of elements, boron is group III, so it only has three valence electrons – one less than silicon. Boron would fill a silicon lattice site, but it only has enough electrons for three covalent bonds with neighboring atoms, leaving a hole. This hole, identical to the photo generated hole explained above in the discussion on photoconduction, is thermally excited at room temperature into freedom to travel throughout the crystal. For silicon, boron is a p type (positive) dopant, and called an acceptor because its unfilled bond (hole) readily takes in free electrons.

Diodes

Photovoltaic cells are nothing but diodes with a large surface area exposed to the sun. A diode is basically an n - type layer attached to a p layer. The space where the two layers meet is called the junction. Almost instantly after the diode is formed, billions of free electrons near the junction in the n-type material rush over to fill the holes in the p-type material, leaving the n side (which had originally been neutral) positive. At the same time, holes on the p side migrate to the n type material, leaving the p side of the junction negative.

Almost instantaneously, the process reaches equilibrium as the statistical force pushing electrons on the n side to fill holes on the p side is balanced by the force from the electric field created by the electrons and holes when they have moved from their original materials (this process occurs within milliseconds). The n and p sides can be demonstrated as two regions with a high "electron pressure" and a low electron pressure (n side with high electron pressure and p side with low electron pressure). Forming the junction lets the electrons to flow in to the region of lowest pressure. The electric field of the junction presents a barrier to further crossover of majority carriers: in the n type material, electrons are the majority carriers, and in the p type, holes are the majority carriers. The junction does not stop the flow of minority carriers; if there are electrons in the p side (and there won't be many because holes are so common there) and they wander into the junction they will be accelerated across to the n side. Actually this wandering is not entirely random: those electrons on the p side which make it to the junction are whisked across, and their absence on the p side near the junction encourages a drift of electrons from farther in the p side to take their place. This current is called a diffusion current. Vice versa for holes (minority carriers on the n side).

Sunlight into Electricity

The photoconductive effect occurs when a photon of light hits an atom and frees an electron leaving behind a hole. When the electron and hole are created they can travel around the crystal. At this point, I still do not understand all of the specific semi-conductor properties that allow these free electrons to be used by an external load. As you will see later in this report, this area of research will be addressed in the future.
(Chris Greacen. “How Photovoltaic Cells Work.” Home Power Magazine 1991) (http://www.homepower.com/files/hp23-37.pdf)

Electrolysis Cells:
Water is a polar molecule, meaning that its hydrogen is positive and oxygen negative. Positive charges tend to be attracted to the negative side in an electric field and negative charges to the positive side. Creating an electric field through water (using KOH as an electrolyte to increase the conductivity) causes the water molecules to break down into hydrogen (H2) and oxygen (O2) atoms. Hydrogen (+) will be collected at the negative side, and oxygen (-) at the negative side.


(Miller, Marion Francis. ”Acid-Base Titrations.” Chemistry Structure and dynamics, McGraw-Hill inc., 1984. 481-491)
(Wilbraham, Anthony, Dennis D. Staley, Michael S. Matta, and Edward L. Waterman. “Aqueous Solutions.” Addison-Wesley Chemistry. Prentice Hall, 2000. 482-489.)

Double Bubbler:
The hydrogen gas that comes out of the negative side is not perfectly clean and contains a fair amount of electrolyte (KOH). Since the mixture of hydrogen and KOH is heterogeneous, one way of cleaning hydrogen is to easily pass the gas through water, where the electrolyte gets left behind in water. The mixture of KOH and hydrogen can be described as a mixture of water and coins. When the mixture is passed through a filter, coins get left behind in the filter. The Double Bubbler works upon the same principle. KOH particles, or imaginary coins, get left behind in water, filter, and hydrogen, water, would easily pass through.
Hydrogen gas enters a chamber, half-filled with water, and pushed the liquid to a second chamber that was also half-filled with water. Now the first chamber is full of gas and second chamber is full of water. After this point gas would enter the second chamber and pass through water and leave the electrolyte in the water.


(Pyle, Walt, ed. Solar Hydrogen Chronicles. Richmond, California: H-Ion Solar Inc., 1998)

Purification Train:
After leaving its electrolyte behind at the Double Bubbler, Hydrogen enters the purification train. The first place hydrogen goes to in the first water coalescors. We do not exactly know how this part works but basically, what it does is that it removes moisture from hydrogen. After that, Hydrogen passes through the flashback arrestor. This component prevents the system form explosions cause by a flame. After that hydrogen will pass through another part called catalytic re-combiner. This component finds free oxygen atoms and bonds each of them with 2 hydrogen atoms. Hydrogen will carry these H2O molecules to the next section, the second water coalescors, where the water molecules will be collected.
(Pyle, Walt, ed. Solar Hydrogen Chronicles. Richmond, California: H-Ion Solar Inc., 1998)

Pressurizing Unit:
There are several methods to pressurizing hydrogen. Earlier in this project, we used the water displacement method, in which the pressure of the gas was related to the height of the water column. Since we need the gas to be at a high pressure and our system to be as light weighted as possible, that method was not a practical solution for our project. After spending a few months on research, we learned that the process of electrolysis can itself cause great pressure. We are currently designing a system to utilize this pressure in our system by using a float valve.

First Hydrogen enters a chamber that is filled with water. In the middle of this chamber there a tube with one open ending that floats in the water. First hydrogen flows into the tube. After the tube is completely filled with hydrogen, it becomes less dense than water; therefore it floats up to the top of the chamber where a small hole is located. Then the tube blocks the whole. Meanwhile, gas is filling the tube and after the tube is completely filled with gas, hydrogen starts to enter the chamber, where it would push down on water. This causes the water to enter the tube; therefore the tube becomes denser than water and opens the whole and that lets the hydrogen to exit the chamber and enter the storage tank.
(Pyle, Walt, ed. Solar Hydrogen Chronicles. Richmond, California: H-Ion Solar Inc., 1998).
(Pyle, Walt. Telephone Interview. 12 Nov. 2002.)

SAFTY ISSUES:
There are many public misconceptions about the dangers of hydrogen. Athough it can be explosive and deadly, if proper precautions are used, hydrogen is not as dangerous as most people think, and in some ways is more safe than gasoline. Many people may recall the bitter accidents of hydrogen-filled zeppelins, but the fact that is more likely not realized is that most people did not die due to the explosions; they died because they fell from the zeppelin, and others died because of inhalation of toxic fumes.

Having said that, there is still no reason to prevent us from using every single safety component. Combustion occurs with the presence of oxygen and when hydrogen is pure and contains almost no oxygen, it is not combustible. In the purification train, hydrogen could become better than 99.9% free of free oxygen atoms. After that, pure hydrogen would be pressurized and stored, where no oxygen can get in. Even if there were a leak in our system, it would not be dangerous to us. Since hydrogen is lighter than air, and the experiments are performed outside, it will go up in the air.

Since we use KOH, which is a heavy base, as our electrolyte, we should also be extra cautious. Heavy bases on skin, if not treated immediately, will result in chemical burns. In order to prevent our selves from getting chemically burnt, we always wear thick lab aprons, face shields, eye goggles and thick gloves. We also perform our experiments out side of the lab, in an open area, behind a thick plastic shield to prevent our selves from getting burnt. Since KOH is a base, it could be neutralized with an acid. That is why we always keep some vinegar and fresh water near the site at where we work to avoid any chemical burns.
(Gjertsen, Andrea. Personal Interview. 15 Oct. 2001)
(Pyle, Walt, ed. Solar Hydrogen Chronicles. Richmond, California: H-Ion Solar Inc., 1998.)

Future experiments:
There will be more experiments in the future associated with this project, some of which include:
• An experiment to find the system’s rate of production
• Design a sun-tracking system for solar panels
• Compare time of charging vs. time of running
• Vehicle’s fuel efficiency
• Vehicle’s performance
• Cost analysis comparing this technology to conventional systems
QUESTIONS THAT STILL NEED TO BE ANSWERED:
1. How can we best utilize the electrolysis cells?
• How would increasing the resistance by changing the concentration of KOH in the electrolyte effect gas production?
• How can we get more power out of the solar panels (refers to graphs, we need to get the most area under the curve to get the most power)
2. How can we store hydrogen into a metal hydride, and is this better for our project?
3. How can we use a water eliminator valve instead of a float valve in our pressurizing system?
4. How does the catalytic re-combiner work?
5. How does the flashback arrestor work?
6. What are the semi-conductor properties of photovoltaic cells and how do they allow free electrons to be used to generate power in an external load?


References:
• Pyle, Walt, ed. Solar Hydrogen Chronicles. Richmond, California: H-Ion Solar Inc., 1998.
• Serway, Raymond, and Jerry S. Faughn. ”photoelectric effect, plank’s equation.” Holt physics. Holt, Rinehart and Wilson, 1999. 831-839
• Chris Greacen. “How Photovoltaic Cells Work.” Home Power Magazine 1991. (http://www.homepower.com/files/hp23-37.pdf)
• Wilbraham, Anthony, Dennis D. Staley, Michael S. Matta, and Edward L. Waterman. “Aqueous Solutions.” Addison-Wesley Chemistry. Prentice Hall, 2000. 482-489.
• Miller, Marion Francis.” Acid-Base Titrations.” Chemistry Structure and Dynamics, McGraw-Hill inc., 1984. 481-491.
• Gjertsen, Andrea. Personal Interview. 15 Oct. 2001
• Pyle, Walt. Telephone Interview. 12 Nov. 2002.
• Pyle, Walt. Telephone Interview. 26 Feb. 2003.
(Due to technical problems, the complete report could not be posted on the internet; however it could be sent upon request)