10 year old Laura was bored. Sitting in their fuel cell vehicle, they had to queue at the “petrol” station. Not that there was any petrol anymore, prices above $50 per liter had convinced even the hardiest advocates of “ye good old times” to change to other means of transportation.
She was sitting in one of those means. Not that her father had had any second thoughts, having being one of the first ones to change to fuel cell driven automobiles. Waiting in line for the alcohol, methanol and ethanol, she watched the other type of fuel cell cars being automatically refueled with hydrogen without the drivers ever having to exit their cars. That was one of the reasons that particular type of fuel had become so popular in the US. Elsewhere, though, stimulated discussion about the abysmal energy efficiency for creating hydrogen in the first place usually prevented wide spread of direct hydrogen cars.
After a short time, however, the display of the automatic refueling process got boring. She looked around, being drawn to the silent glittering insect-like vehicles whizzing by on the street. She especially liked their vario-colored exteriors and sparkling light effects in sunlight.
“Dad, why do these insect cars not have to stop and refuel?” Being on the way to her swimming training, she did not want to wait around at an alcohol-hydrogen refueling station. Grown-ups were always involved in so much waiting all day. And they did not even seem to notice, or much less comment on it. Aggravating her current situation was the fact that the old-fashioned car radio she liked so much was broken and she could not play around with it. Either she or her genitor had to tweak around with it later. At home. After training. After waiting.
“Are you even listening to me?” She looked up into a face that featured a knowing, warm smile. The well-prepared answer was easily out, “Of course”.
“Ah, I will repeat what I just said nonetheless,” her father continued. “Your insect vehicles are solar powered cars. Installed in the frame are solar cells. They convert the incoming solar energy into electric energy which in turn drives an electric motor not much different from that in any other car nowadays. The glittering colors derive from the materials that are being used in the solar cells. The old-school glittering blue ones still use silicon…” She did not know why these blue cells should be somehow connected to her old school, or exactly what silicon was, but she remembered another similar talk in which the explanation led her to believe that silicon was somehow connected to sand. The nice white sand. Why it became this glittering bluish hue she had no idea, but she had long ago decided that she liked the color. Definitely nicer than these dark non-descript panels they had atop their roof at home.
“… The newer ones utilize organic materials and have all kinds of colors. Their development took much longer as the lifetime of polymers under constant solar radiation is rather limited. Research was further set back when oil products necessary to produce most polymers got exceedingly expensive with the ending of the oil age.”
“So how comes we humans are not automatically moving while we are in the sun like those cars?” she wondered aloud.
Another by-now well practiced smile by her begetter preceded his answer. “Well, although our skin produces certain vitamins while we enjoy ultraviolet solar radiation, the energy inherent to these rays unfortunately also dissipates in our bodies by destroying tiny molecules called proteins in our skin cells.”
More cells, everything was cells these days, battery cells, fuel cells, kitchen cells, body cells, solar cells. At least her radio was still a radio. And it was almost their turn in the queue now.
“Solar cells, in contrary”, her father continued, “are semiconductors like the chips that are incorporated in all intelligent machines from fridges to computers these days. By using certain atoms in a process referred to as doping, they sport a large region called positive-negative, or short p-n junction, but forget about that name, it is not important.” She agreed wholeheartedly. “What it means is that when sunlight arrives in this p-n part of the material, it separates an electron from an atom and creates a hole. Not a hole like a hole in the ground, but rather like an anti-electron.” He thought that particle physicists would probably get goose bumps when they would hear that explanation, but then again there happened to be no such people in his car at that particular moment. “Both, electron and no-electron-there hole, travel through the material in opposite directions and, just like whenever electron movement is involved, create an electric current that can be used for example to drive a motor. Since we neither have semiconductors on our skin nor the capability to use raw electricity, we do not automatically move when we are standing in the sun. And now I have to refuel our liquid sunlight.”
Having said so, he set out to the task of pumping ethanol into their car. That left Laura ample time to reflect upon what she just heard while watching more of the glittering mobiles silently whizzing past. She knew that electrons were tiny invisible things that traveled through the wall at home to arrive at a plug. There, they seemed to wait for her to extract them whenever she plugged something in. She had learned from her father, and still did not believe him entirely, that electrons were somehow usually whizzing around much larger, but still invisibly tiny atoms. According to previous explanations she had enjoyed, atoms had certain shells like an egg in which these electrons traveled in a very defined distance. Or not so defined, but her father’s explanation of probability density function something-or-other had contained the footnote to better be ignored. If these shells were large enough, the electrons could be extracted, she liked to think of it like a harvest, and transported somewhere else. They were not created or destroyed, just moved, and that was electricity. That seemed to happen in the solar cell, too. Sunlight somehow provided the energy necessary for the electron harvest.
“So the solar cell drinks sunlight and converts it into electrons?” she ventured once he returned.
“Nicely put, yes.”
“So why do we not have such a car? Our car could drink sunlight all day and not have to drink alcohol anymore. That’d be awesome.”
Chuckling, he replied while filing into the semi-automated traffic, “That is true, but you mentioned a slight drawback. All day. At night or on dark days, the incoming solar radiation energy is insufficient to facilitate adequate energy conversion. “Raising an eyebrow, she interrupted “What does that mean in English?”
“Ah, yes, it means that in the beginning, when these cars became more prominent on the streets, they were bound to travel mostly on sunny days. They could not drink enough sunlight at other times. Advances in solar cell efficiency and intelligent chemical energy storage systems have made it possible that a large chunk of the energy produced by the solar cells during the day is now stored in batteries to be used at night and whenever else sunlight is scarce. The opening of the ozone layer, which makes it dangerous to be outside unprotected for longer periods of time these days, admits more high-energy ultraviolet radiation to our planet’s surface. Thus, there is usually sufficient energy for those solar machines even on a cloudy day.”
The purpose of the ultraviolet light shield installed over the outside yard of her school and the dangers of exposure to ultraviolet light had been explained to her early enough, this was the first time she heard of a real positive effect. And if glittering solar cell powered cars were not getting thirsty, that qualified it as a good effect in her view. She certainly did not like getting thirsty herself. That reminded her to drink some water before being completely immersed in that same element for the upcoming two hours.
Waiting at a fuel station had at least the positive side-effect that her father had bought her a large bottle of fresh mountain water, a rarity these days. Ever since the vanishing of the last glaciers, mountain water had become a rather seasonal commodity. And she had already heard about areas where water was so scarce that the exhaust of fuel cell engines, pure water, was filtered and used for drinking. Her father had mentioned that that had also been done in the early manned space missions in the 1970s, but she could never get her head around what that had to do with the arid regions of earth.
At the time she had been occupied with plans. Now she was making plans of how to help her father repairing the radio, as they arrived at the swimming pool entrance. The roof of the indoor facility was, like the roofs of all public buildings, completely covered in solar cells, powering the whole block while doing nothing more but drinking the sunlight. After watching the roof for a while, imagining how the incoming sunlight created electrons that only she was able to see with her mind, she rushed inside. Maybe if electrons could be made larger, they would be more effective? Maybe not. Time to start training anyway. Completely human-powered. Or was it? Didn’t she get her energy from food that in one way or another grew in sunlight, drinking the sun’s energy to grow? This would be a good question to ask her father on their way home…