Paper: Introduction

Solar thermal energy collection in its purest definition is the use of solar energy to generate work in the form of heat. This is different from photovoltaic cells in that photovoltaic cells use solar energy to directly create electricity. The most basic example of solar thermal energy collection is a solar oven. Solar ovens use mirrored surfaces inside of a container to focus solar energy to create enough heat inside the container to cook food. The use of mirrors to focus solar energy is common in solar thermal energy collectors, especially when high temperatures are required. Solar heaters are also commonly used in households to heat water and the air of the house. At the large scale, solar thermal energy collecting power plants use the focusing of sunlight to create steam and spin turbines to create electrical energy. This project is mostly concerned with these solar thermal power plants and evaluating their viability as a part of the greater power grid. In 2012, renewable energy produced eleven percent of all energy produced in the United States; only two percent of the renewable energy was produced using solar energy. In Arizona, state standards require that 15 percent of all consumed energy must come from renewable sources by the year 2025, in 2013 the 7.8 percent of consumed energy came from renewable sources most of which came from interstate imports from the Glen Canyon and Hoover Dams. Because of the desert climate and almost constant exposure to sunlight, many areas in Arizona are ideal places for the expansion of solar energy. In the year 2012, Arizona became the home of the world’s largest photovoltaic power facility. Solar thermal energy collection is another way that the collection of solar energy can be expanded both in the state of Arizona and in the United States; however, there are limitations that are being addressed to make growth possible.

Paper Outline

Evaluating the Viability of Solar Thermal Energy Collection

I. Introduction

1. What is solar thermal energy

a. background on solar energy, solar ovens, water heaters

b. solar thermal power plants, different kinds

2. Energy production in the united states

a. traditional fossil fuel plants

b. renewable energy in US

3. Energy production in AZ

a. Renewable energy goal

b. ideal place for solar energy

II. Advantages of Solar Thermal Energy Collection

1. Renewable, ideal in desert environments

2. collected energy can be stored as thermal energy

a. HTFs

b. methods of storage

c. allows energy to be generated at all hours

3. Most solar energy is collected because of concentration

III. Disadvantages

1. Cost

a. initial investment

2. inherent inefficiencies

3. problems with HTFs

4. Limited by location

a. Need for land, water, sunlight

IV. Development of New HTF

1. benefits of higher temperatures

2. Types of Heat Transfer Fluids

a. Molten Salts

b. Synthetic Oils

V. Work in the lab

1. Developing new molten salt

2. Describe the apparatus and procedure

3. Describe the data collected

4. Describe each step of analysis

5. Describe results

VI. Other areas of development

VII. Comparison to other methods of energy generation

a. fossil fuels

b. other renewable sources

VIII. Conclusion

Busy, busy, busy

This week has been unusually hectic.

I had to spend a lot of time working on a resume for the first half of the week, since I'm hoping to get a job over the summer.  Then I got my college decisions from Rice and Columbia, both of which denied me, so it looks like I'll be going to ASU in the fall (which I don't mind). Other than that I had to fully convert two days worth of experiments into only a few spread sheets on Monday, which took all day. All in all, I've had little time this week for supplementary research.

However, I have begun working on an outline for the paper that will be the "final product" of this project! With a few more hours of work I hope to have it all finished up and I'll be posting it here!

Congratulations to all of my classmates for the college acceptances! I hope you guys have a good time where ever you decide to go!

Thermal Energy Storage

As mentioned previously, one of the advantages of solar thermal energy collection is that the energy collected can be more easily stored. This is advantageous because it allows solar thermal power plants to store energy during the day so that it may later be used during hours of peak energy usage, the night, and on cloudy days.

Thermal energy can be stored in many different ways. Many home systems simply use water as a means of storage. The advantages of this comes from water's high specific heat, meaning that it is more difficult for water to gain and lose thermal energy. In an insulated container, hot water can be collected in the summer, and used in the winter to heat a house. However, water is limited in that it can only be heated to 100 degrees Celsius. Because of this, some systems use solids like rocks, concrete, or iron to store thermal energy. These solids are often immersed in water or synthetic oil and kept inside an insulated chamber. While solids have a lower specific heat than water, they can reach much higher temperatures. For Solar Thermal plants, the heat transfer fluid itself can be used to store thermal energy by keeping hot heat transfer fluid in an insulated tank.

sources:
  Glatzmair G. Summary Report for Concentrating Solar Power Thermal Workshop. Rep. no. NREL/TP-5500-52134. Washington D.C.: US. Dept. of Energy, 2011. Print.

Chen, C. Julian. Physics of Solar Energy. Hoboken, NJ: Wiley, 2011. Print

Dinçer, İbrahim, and Marc Rosen. Thermal Energy Storage: Systems and Applications. Chichester: Wiley, 2011. Print.

They can't all be scientists...

For the past month, my bicycle has been an important part of my commute to the lab at the University (drive to a friends house, bike the rest of the way). Guess what happened today? The bicycle chain broke! Terrific! Wonderful! Applause!

It was probably my fault for riding around slowly on high gear, I was giving Joyce a ride home today so I was basically walking when it happened. For the rest of the way, about 2/3 of the leg I had to walk my bike while the pedals rolled around freely by their own momentum, frequently fitting my leg causing me great annoyance and misery. Joyce is probably going to talk about this too, and now theres a video of me uselessly trying to use the pedals somewhere in the internet.

They can't all be scientists, next weeks post will be cool and sciency and relevant.

P.S. Someone know how to fix a bicycle chain?

So, whats this all for again?

As cool as the lab work is, its meaningless without the context of what its ultimately being used for and the overall subject of this project, Solar thermal energy. Solar thermal energy collection comes in many forms, from solar ovens, solar water heaters, to solar thermal power plants, but all of them follow the basic principle of converting solar energy to thermal energy to eventually perform work.

The project is mostly concerned with the large scale solar thermal power plants. At such a large scale, almost all solar thermal power plants rely in some way on the concentration of solar energy to achieve maximum efficiency. Two of the most common ways are doing this are solar power towers and parabolic trough collectors. Solar power towers, also known as heliostats, use a massive field of mirrors to focus sunlight to the top of a tower in the center of the field, where as parabolic trough collectors use lines of parabolic mirrors to focus sunlight along a line that runs along them. The sunlight collected from all solar thermal power plants is used to heat a so called "heat transfer fluid" (HTF) to temperatures ranging from 400 degrees Celsius to 600 degrees Celsius. This HTF is then pumped to a heat exchange where the heat is transferred to water, creating steam to spin turbines like other fossil fuel based power power plants. While the conversion of solar energy to thermal energy of the HTF is very efficient, the second part of the process, the transfer of heat from HTF to water is not. This inefficiency is a major factor contributing to the high price of solar thermal power generation. The graph below shows how the efficiency of solar thermal power plants is dependent on the temperature at which they operate.

However, solar thermal power generation is promising because it allows energy to be stored in the form of thermal energy, allowing electricity to be generated during the night and while intermittent clouds are over head. There are many ways to store this thermal energy (which I need to research more), but the freezing of HTF must be avoided, which currently occurs at temperatures higher than room temperature.

Therefore, the development of better HTFs will both mitigate the limitations and heighten the advantages of solar thermal power generation. At temperatures approaching 1000 degrees Celsius, the efficiency of the heat transfer between HTF and water increases dramatically. At such high temperatures, heat transfer by radiation can be considered, potentially increasing the efficiency further. At higher temperatures, heat transfer fluid can be stored for longer periods of time, and research is being conducted to find a HTF that can remain liquid at lower temperatures, making it easier to store. The lab work that I am involved with is trying to develop these new HTFs and quantify the radiative properties of the fluid.

Citation
 Glatzmair G. Summary Report for Concentrating Solar Power Thermal Workshop. Rep. no. NREL/TP-5500-52134. Washington D.C.: US. Dept. of Energy, 2011. Print.

The Apparatus

I snapped some pictures of the experiment apparatus that is being used in the lab yesterday, so here goes my best attempt in explaining how this thing works. The metal frame allows us to easily manipulate the furnace (the white cylinder) and other components of the apparatus without touching the furnace itself. A pulley system allows us to lift the furnace and easily place the substance being tested inside. For the work being done now, that is salt compounds made in another part of the department. The furnace heats the substances to temperatures up to 600 degrees Celsius, melting the salts. These molten salts are the fluids that can be used in solar thermal power plants as heat transfer fluids. The salts are placed in a large cuvette that is placed inside the furnace.

An smaller cuvette is then placed in the metal holder that can be seen here above the furnace. This holder can be precisely lowered into the cuvette inside the furnace by a computer. By changing the position of the inner cuvette, the thickness of fluid can be changed.

Seen next to the outer cuvette holder in this picture is the output for a xenon laser (its the black speck thats connected to the wire). This laser is aimed inside of the inner cuvette and passes through the chosen thickness of the fluid being tested. Thanks to the Beer Lambert Law the absorbance of the fluid can be found by changing the thickness of the fluid that the light from the laser has to pass through. A collector below the apparatus collects the light that is not absorbed by the substance at each different wavelength that the xenon laser outputs. The absorbance of the substance affects how it absorbs light, converting that light energy into heat.