An Experiment in Lowering my Carbon Footprint - Part 3

In my last post, I discussed the amount of CO₂ I prevented from being released into the atmosphere by increasing the thermostat setting in my house during the summer months in Dallas, Texas. I won't say it was a breeze to do; however, I am pleased by my results and by how much energy I saved.

In researching for my post, I discovered some interesting facts about US power consumption.

In 2007, the energy demand from the entire United States was 4.157 x 10¹² kWhrs; this includes energy used in transportation, utility electricity generation, residential and commercial and for industrial purposes. The total amount of energy demand for electricity generation was 2.5 X10¹² kWhrs. The types of fuel used to generate electricity in the US is provided below:

Breakdown of 2007 Energy Generation
Fuel Type	Energy Generated	Percent of Total
Coal	2.02 MWhrs	48.5%
Gas	0.9 MWhrs	21.2%
Nuclear	0.8 MWhrs	19.4%
All Other Sources	0.44 MWhrs	10.52%

Other sources of energy include that derived from solar, wind, biomass, hydroelectric among others.

The total amount of CO₂ released in 2007 from all sources was 2.5M metric tons (tonnes) or 2.7M tons. The largest contributor to this is from the generation of electricity and burning coal releases more CO₂ than oil or natural gas.

President Obama while attending the UN Climate Summit in Copenhagen, Denmark proposed a target reduction in US greenhouse gas emissions by 17% below 2005 levels by 2020. In order to maintain a somewhat pleasant lifestyle, I'll have to find additional ways in which to reduce my carbon footprint as I won't maintain the thermostat setting I used in my summer experiment in future summers.

In future posts, I'll share my thoughts on some of the ideas I came up with to lower my carbon footprint. I'm also going to start tracking my monthly energy consumption to see how effective my actions are and I'll share them periodically.

So why is reducing CO₂ in the atmosphere such a big deal? For most of pre-industrial humanity, the level of CO₂ in the atmosphere was approximately 275 parts per million (ppm); this is a ratio of the number of CO₂ molecules to all other molecules in the atmosphere. As we started to burn coal and oil to create energy, the amount of CO₂ in the atmosphere started to rise. Scientists have estimated the amount of CO₂ currently in the atmosphere to be 390 ppm and rising roughly 2 ppm per year. They have also stated that we need to curtail our activities and bring the number to a sustainable 350 ppm.

Most of the sunlight emitted from the sun is in wavelengths shorter than 4 μm, which pass through the atmosphere and gets either absorbed or reflected by the earth. When reflected from the earth, the wavelengths are stretched longer than 4 μm and the heat energy gets absorbed by the CO₂ molecules in the atmosphere. When a molecule of CO₂ absorbs heat energy, it goes into an excited and unstable state; to become stable again, it releases this energy. Some of the heat energy will fall back to the earth and some gets released into space.

If the amount of CO₂ in the atmosphere increases, the amount of reflected heat energy increases, which results in temperature increases. This is called the greenhouse effect and is similar to sunlight warming the interior of a car that has all its windows closed.

There are many things being done to combat this starting from greater use of renewable energy to generate electricity; higher gas mileage for cars; energy efficiency initiatives to name just a few. There are many initiatives being implemented at the local, state and national levels by many countries. I believe if we all work together, we can have combat climate change and at the same time intelligently meet our energy needs going forward.

Converting Solar Energy into Power - Photovoltaic Cells

My last post discussed how energy is created in the sun and arrive on earth via packets of energy called photons; it also discussed the amount of sunlight power that falls on the earth, also called irradiance. This post will discuss one of the ways in which we can convert the sunlight into usable power.

One of the ways it can be converted to usable power is via the photovoltaic effect. It was noted that semiconductor materials like selenium release small amounts of electricity when exposed to sunlight. When photons strike these materials, their energy is absorbed and transferred to electrons within the materials. With this energy, the electrons are able to break free from their atoms and flow as in an electric current. Further research into material science resulted in using silicon doped with impurities such as phosphorous and boron.

Adding these impurities to silicon required less energy from the photon for the electron to break free. Silicon doped with phosphorous forms a negative or n-type semiconductor material and silicon doped with boron forms a positive or p-type material. Placing an n-type material in close proximity to a p-type material creates an electric-field at their junction. If free electrons and holes happen to get close to the electric field, the field will send the electrons from the n side to the p side and positive charges or holes from the p side to the n side.

If we add leads to either sides of the semiconductor material and connect them to a load, a circuit is created and electrons can flow through the circuit. The electron flow provides the current, and the cell's electric field results in a potential difference or voltage between the two material types. PV-cells develop direct-current or dc voltage.

The original PV-cells were made from materials such as selenium. These cells were only 1% efficient, meaning only 1% of the sunlight that fell on the material was converted into power. Research using doped silicon yielded cells with efficiency as high as 6%. Current manufactured cells have efficiencies in the range of 14 – 18% and laboratory tests on new cell-designs have shown efficiencies as high as 42%.

A standard solar panel is made from interconnected cells housed in a metal frame and protected with anti-reflective glass; they are typically 1200mm by 600 mm in size. A standard condition for testing solar panel rated power is under an irradiance of 1000W/m², at 25 ºC and a sunlight attenuation factor of AM1.5. This represents the typical conditions in the 48 contiguous United States at noon in the spring and autumn with the solar cell aimed directly at the sun. A panel rated at 14% efficiency is rated to deliver approximately 100W under the standard test conditions.

Currently, the most prevalent material used to make solar cells is crystalline silicon. Silicon is a well-understood semiconductor material with good stability, physical, electrical and chemical properties. Furthermore, silicon cells have benefited from the enormous economies of scale achieved from the semiconductor and microelectronics industry. However, the manufacturing process used to make silicon wafers is complex, which makes them expensive in solar power applications. Furthermore, demand for silicon from the microelectronics and semiconductor industry has driven up material costs.

There is considerable research and development into so called thin-film PV-cells, which use less silicon material. Some of these new types of thin-film PV-cells include CdTe (cadmium telluride), a-Si (amorphous silicon) and CIGS (copper indium gallium selenium). Solar panels formed from these materials have efficiencies in the 11 – 12.2% range, which are lower than that of silicon based panels; however, are much cheaper to manufacture and have higher manufacturing yields. Efficiency advances through continued investment in R&D and in manufacturing techniques could get efficiencies that are comparable with silicon based technologies over time.

Solar Energy is poised for high growth especially with issues related to climate change, a strong desire to diversify sources of energy and from national security concerns. In my next post, I'll continue discussing photovoltaic power and applications for it.  

An Experiment in Lowering my Carbon Footprint - Part 2

In my last post I discussed an experiment I ran over the summer months of 2009 in Dallas, Texas where I attempted to reduce my carbon footprint. In this post, I discuss my attempt to determine how much CO₂ I prevented from being released into the atmosphere and contribute to climate change.

In order to do so, I had to first determine two pieces of information: 1) estimate how much energy I saved over the duration of the experiment; and 2) determine the sources of power being delivered to me and the amount of CO₂ they emit.

To get the first piece of information, I went to my account on the TXU website and compared my energy usage for the summer months in 2009 to what I used in 2008; TXU is the energy company that bills me for the electricity I use. I assumed all other factors are equal and the only major contributor to the differences in energy usage result from my experiment. Below is a summary of my findings.

Table I. Energy Usage Data

Month	2008 Energy Used, kWhr	2009 Energy Used, kWhr	Difference, kWhr
June	1,025	716	309
July	1,820	1,128	562
August	1,690	1,212	608
September	900	473	427
Total	3,529	4,750	1,906

As a result of my experiment, I saved approximately 1,906 kWhrs of energy. In order to determine the second piece of information, I first had to determine how the power that was distributed to me was being generated. There a number of ways in which power is generated and each emits carbon in different amounts in the generation process. I had to determine for example, what percentage of my power was being generated from a coal-fired plant, from a natural-gas plant, etc.

I first contacted TXU and inquired as to how the power being delivered to me was being generated. They referred me to Oncor as TXU provides metering and billing functions to their customers. I then contacted Oncor who referred me to Luminant as Oncor provides transmission and distribution services. I never got a response from Luminant, the power generating company that serves me. I went to their website and did some digging around. I found that Luminant generates electricity using coal-fired plants, natural-gas plants and nuclear plants.

I determined the power generating capacity from all their plants and then determined what percentage of total the type of plant represents; they are summarized in the table below.

Table II. Luminant Power Plant Data

Plant Type	Generating Capacity, MW	Percent of Total
Coal	6,396	38.27%
Gas	9,018	47.97%
Nuclear	2,300	13.76%
Total	16,714

I was able to find the amount of CO₂ released per thousand-Watt-hours (kWhrs) of power generation from various fuels used in power generation systems from the US Government's Energy Information Administration website; they are summarized in the table below.

Table III. CO₂ Emissions Per Fuel Type

Power System Fuel Type	CO2 Released, lbs/kWhrs
Coal	2.117
Natural Gas	1.314
Nuclear	0

Note that nuclear fuel used to generate electricity produces no CO₂; however, a small amount is released from processing the uranium that is used in the reactors. I decided to ignore that fact as it wouldn't be meaningful in my estimates.

I assumed the power delivered to me was generated in the percentages shown in Table II. I then calculated the amount of CO₂ I saved by the following:

CO₂ = ((2.117)(38.27%)+(1.314)(47.97%))(1,906) = 2,743lbs.

This is equal to 1.37 tons or 1.24 tonnes of CO2 not released. I think that's pretty good and in future posts, I'll try to comment further on this.

I believe there is increasing scientific evidence showing our burning of fossil fuels such as coal, oil and natural gas are contributing to climate change. Burning fossil fuels in generating electricity is responsible for 39% of all carbon emissions.

In 2007, the per capita emissions in the US was 19.1 tons/CO₂; this represents approximately 20% of the total emitted by all nations in the world. The average American in their daily routine emits roughly 9.44 tons/CO₂. Assuming I fall into the average camp, by my experiment over the summer, I reduced my CO₂ emissions by 14.5%. I'll provide more details and analyses in my next post.

Getting Power from the Sun

I wanted to learn more about solar energy and I decided to start from the sun because that's where it all starts. The sun, our star is central to all life on Earth! Current theories state that the sun and everything else in the solar system formed from the leftover clouds of gas and dust from a massive star that went supernova. The cloud was mostly hydrogen and helium with trace amounts of other materials.

The sun formed from the coalescing of the materials in the clouds due to their mutual gravitational attraction. After a period of time as the proto-sun continued accumulating more material, it started to collapse under its own weight and build up pressure at the core. As the pressure increased, the temperature at the core started to rise. The pressure at the core is 340 billion times that of the earth at sea level and temperature is approximately 13,600,000 ºC. The present state of the sun is such that the inward pressure of all the material in the outer layers is matched by the outward pressure at the core.

The sun is enormous: it's diameter is approximately 864 million miles and equal to about 109 earths; it's volume is equal to approximately 1,300,000 earths. It is so massive that it comprises approximately 99.9% of the total mass of the solar system including that of the planets, moons, proto-planets, asteroids and comets. It is comprised of about 75% hydrogen, 24% helium and small quantities of other elements like oxygen, neon, iron, carbon and silicon.

At the very center of the sun, the pressure and temperature conditions are favorable for nuclear fusion to occur. Nuclear fusion is the process by which atoms are able to overcome their repulsive electrostatic force and bind to another atom by their attractive nuclear force and release tremendous amounts of energy in the process. The only place this can happen is at the core of stars. 

In this process the mass of four hydrogen atoms fuse into a single helium atom and release roughly 0.7% of the combined mass as energy per Einstein's famous equation E=mc², where E is the energy released, m is the mass lost in the conversion process and c is the speed of light in a vacuum. In one second, the sun converts 600 million metric tons (tonnes) of hydrogen into 595.8 million tonnes of helium; the missing 4.2 million tonnes are converted into energy. Every second, the sun releases approximately 386x10²⁶W of power; the sun releases more energy in one second than used by man in our entire existence!

In the mass-energy conversion process at the core, photons or "packets of energy" are released. It takes anywhere from 10,000 to 170,000 years for the photons to get from the core to the outer edge of the sun called the corona. This is due to the photons continuously being deflected from their path by electrons. Once free of the corona, the photons reach the earth, about 93 million miles away, in about 8.3 minutes. The photons are received by the earth as light and heat.

The sun also emits charged particles (electrons and protons) through its corona as the solar wind. Every second a million tonnes of these charged particles are emitted by the sun as the solar wind; we detect these particles as they interact with the earth's magnetic field as polar auroras or the northern and southern lights. The matter-energy conversion process also release neutrinos, inert particles that aren’t affected by and pass right through matter.

The sun has so much mass that even with the tremendous mass loss through the matter-energy conversion process and through the solar wind, it is estimated it has enough material to last for another 5 billion years. And it is estimated our sun has been in existence for approximately 4.6 billion years!

The photons or sunlight received by the earth is used by plants for energy in synthesising carbon into sugars and releasing oxygen, a process called photosynthesis. We can also use sunlight to create energy using various techniques. The estimated amount of power that the sun deposits on the earth is approximately 1300W/m²; however, due to atmospheric effects, the power is approximately 1000W/m². It is estimated that amount of energy that falls on the earth for an hour could satisfy the entire energy needs of the world for a year!

As this abundant source of energy will be available for a very long time, we should find ways to utilize it. It is free, clean and with our ingenuity, could satisfy all of our energy needs. My next post will discuss some of the ways in which we can use this energy to create usable power.

An Experiment in Lowering My Carbon Footprint

With all this talk about climate change, carbon footprint, renewable energy, green living, energy efficiency and the like, I decided to try an experiment over the summer of 2009 to see what I changes I could make in my lifestyle to lower my carbon footprint. Sure I did the usual things like change most of my light bulbs to CFL bulbs, consolidate my automobile outings to as few as possible, recycle more, bring my own bags when grocery shopping, unplug as many electrical items as I could and run most appliances with a full load and during off-peak hours. But I wanted to try something drastic that could have more of an immediate impact.

I live in Dallas, Texas and the summers here are brutally hot and living without an air-conditioner is pretty much impossible; this summer had been hotter than usual with July having almost two weeks of above 100°F (37.7°C) days. I usually turn my air-conditioner on in June and turn it off after September; I also turn it off when leaving for work during the weekdays. Normally I set the thermostat at 80°F (26.7°C).

The daily summer weather here is such that it gets really hot after noon and stays so until well into the evening; during this time the air-conditioner continuously operates because it never gets the internal house temperature below the thermostat setting. Regardless of the actual internal temperature, the house is quite comfortable as long as the air-conditioner is running and continues to pump in cool air.

My experiment was to see if I could live comfortably during the summer months with the thermostat set higher and use ceiling fans for supplemental cooling. My thought was that with the higher setting, my air-conditioner would turn on later in the day, turn-off earlier in the evening and operate continuously in between. I arbitrarily chose a setting of 85°F (29.4°C) during the daytime and a setting of 82°F (27.8°C) at night, which I would set before I’d go to bed and change back to 85°F in the morning. I should point out that I live by myself and only maintained these settings when I didn’t have invited guests.

The month of June was tolerable; I was able to go a week into the month before having to turn my air-conditioner on. When I was in my house, I wore a tee shirt and shorts during the daytime and used a ceiling fan in any room I happened to be in; during the night I slept with the window in my bedroom open, which allowed relatively cooler air in and with the ceiling fan, made it comfortable enough for sleeping.

The months of July and August were admittedly tougher; there were days, especially in July, when I was tempted to forego this experiment and turn the thermostat down, but I was determined to get through to the end of summer. During these months I found myself checking weather reports and would look forward to cloudy or rainy forecasts as that would make for a cooler day. On those hot and sunny days, I kept the ceiling fans running on high, which made it bearable if somewhat uncomfortable. I was able to get through these two months, which made getting through September a relatively breeze.

What conclusions can I draw as a result of this experiment? First, I am under no illusion that I would have been allowed to even contemplate this experiment were I not the only occupant of my house. And second, the electric utility companies charge the same rate for peak and off-peak energy usage, i.e., they provide undifferentiated pricing so there is no incentive for me to reduce my peak-electricity use other than for altruistic reasons, which is still a good reason!

So I made it through the summer! But the experiment was to see if I could reduce my carbon footprint and live comfortably. June and September were comfortable while July and August were somewhat uncomfortable. Would I do it again? Perhaps, but with lower settings than what I had used for July and August! I’ll provide an estimate of my reduction in carbon emission from the experiment in my next post.