How Do We Get Electricity From The Sun?

You can see solar energy powering your calculators and tax dollar funded NASA satellites, but imagine your house and cars powered by the sunshine! There are two main ways to generate electricity from the sun: the main groups being "Photovoltaics" aka "PV" and "Thermal solar".  In layman's terms, "PV"= sun hits solar panels and electricity is produced. "Thermal solar"= sun hits solar panels and heat is produced in a working fluid to provide hot water or create steam that's used to generate electricity.


I want to talk about PV solar because its what most people think of when they hear solar power!





What solar cells are made of:


The basic idea is that photons of light are absorbed by a solar cell and electric current is produced.  However the full picture is much more complicated.  Silicon, Si, which makes up the majority of the solar cell structure is a semiconductor.   The main concept is that the silicon alone would not be able to form a productive electrical field, thus "impurities" are added to create an effective solar cell.  Addition of impurities is also known as "doping" the Si.  The top layer of silicon is doped with Phosphorus (n-type layer), and the bottom layer of Si is doped with Boron(p-type layer), where the two layer meet is called the "p-n junction".  Additionally, there is a solid conductive backing on the bottom, and conductive metal collector comb on the top, sandwiching the doped Si layers.  An external circuit that connects the metal comb and conductive backing.

  


How they work:


Atoms are a lot like people in that they don't want to be lonely. Every atom has an outer ring of electrons called valence electrons that keep them stable, like our friends keep us from going crazy sometimes. However, the valence electron spaces are not always fully occupied, and atoms hate going without a full team of valence electrons.   An atom that has less than the full # of possible valence electrons tries to attract additional electrons.  The phosphorus doped silicon layer has an extra electron (not complying with my earlier analogy about loneliness , this makes the phosphorous doped silicon layer "Negative", n-type layer).  The boron doped silicon layer has an incomplete valence shell, we refer to this as an "electron hole". The boron doped silicon layer has a positive charge, thus it is referred to as a p-type layer.

When a photon hits the solar cell, an electron-hole pair may be split in the upper n-type layer resulting in mobile electrons and electron holes.  The electrons move to the upper metal comb and the electron holes travel down towards the p-type layer, contributing to a flow of current through the external circuit.  Electrons will want to travel the external circuit from the n-type layer to the p-type layer where there are holes for the electrons, producing work along the way.  This work is converted from DC to AC, stored and distributed for use as electricity. Solar cells are commonly connected to form panels, which are connected to make larger solar arrays, like the one seen below.

Right now solar energy is way less than 1 percent of our electricity produced in the U.S.  So why then should we be concerned with it?  Well, I'm glad you asked... there are billions of dollars invested in this stuff!!   We are getting a move on cleaning the way we make electricity!




Please comment about solar!

Is Compressed Air Power the Future for Cars?

I made the mistake of going on youtube this morning for no apparent reason, but it landed me in an interesting place.  I started at the old spice man on a horse to Michael Franti to an interesting video on compressed air cars!  Now, the car video looked like it was made in the 80s and I must say the car was unimpressive, but the technology is what interested me.  So, as a responsible environmental engineer I thought I should briefly analyze the possibilities of compressed air technology and form some sort of opinion on it.

Advantages:

 -Air is free!

 -Cost of refueling compressed air is inexpensive compared to gasoline

 -gasoline is running out so this is a potential alternative

Environmental/Human Health Advantages:

-Air is a renewable resource

-Emissions from car engine will be 100% clean air!

-Emissions from the whole process of compressing the air and firing the small gas combustion engine in the car total to about half the carbon dioxide when compared to toyota Prius, equivalent to 106 mpg.

Disadvantages:

 -Cars don't have the power of our current car fleet (I saw a model with top speed of 43mph).

 -Car must be be very light, and thus there are questions about their safety

 -Production of compressed air at refilling stations and homes will require electricity.

 -from what I studied in thermodynamics I know that not all energy produced in reactions is useful energy, thus the two      reactions necessary to create compressed air results in a lot of wasted energy!

 - the range on a full tank and 8 gallons of gasoline or ethanol is about 100 miles

 -compressed air fill-up stations are uncommon, making long travels difficult

 -potentially dangerous because the tanks are at such a high pressure.

Now I wonder, is this a good long-term solution for our dependence on fossil fuels?  Looks to me that it may be, especially with possibility to have a near zero emissions vehicle (possible with the increasing amount of research in renewable energies for electricity generation needed to compress the air).  Also, for future success the air engine must eventually be independent of the small gasoline engine that it currently requires.

The only issue, and this is quite an issue, is the safety of this proposed car.  Will the cars be too light, and potentially get squashed by larger SUVs and trucks, like a middle school kid playing tackle football with the neighborhood college graduate? Also, is it possible that these tanks can explode if impacted? 

Regardless, there are companies working on selling cars with this technology, although many have recently been having various setbacks.  There was word a few years ago that India's Tata Motors was going to have these in production now, but that obviously hasn't happened.  Who knows if this is the best option for our future, but I think its worth a shot.