Yesterday, I talked about the very basics of how solar energy works and how it’s made.
CSP vs PV – Energy Storage and efficiency
CSP (Consentrated Solar Thermal) systems are capable of storing energy by use of Thermal Energy Storage technologies (TES) and using it at times of low or no sunlight, e.g. on cloudy days or overnight, to generate electric power. This capability increases the penetration of solar thermal technology in the power generation industry as it helps overcome intermittency problems; usually due to environmental fluctuations.
PV (Photovoltaic) systems, on the other hand, do not produce or store thermal energy as they directly generate electricity – and electricity cannot be easily stored (e.g. in batteries) especially at large power levels.
CSP systems are far more attractive for large scale power generation as thermal energy storage technologies are far more efficient than electricity storage technologies; CSP systems can produce excess energy during the day and store it for usage over the night, so energy storage capabilities can not only improve financial performance but also dispatchability of solar power and flexibility in the power network.
On a much larger scale, solar thermal power plants employ various techniques to concentrate the sun’s energy as a heat source. The heat is then used to boil water to drive a steam turbine that generates electricity in much the same fashion as coal and nuclear power plants, supplying electricity for thousands of people.
In one technique, long troughs of U-shaped mirrors focus sunlight on a pipe of oil that runs through the middle. The hot oil then boils water for electricity generation. Another technique uses moveable mirrors to focus the sun’s rays on a collector tower, where a receiver sits. Molten salt flowing through the receiver is heated to run a generator.
Other solar technologies are passive. For example, big windows placed on the sunny side of a building allow sunlight to heat-absorbent materials on the floor and walls. These surfaces then release the heat at night to keep the building warm. Similarly, absorbent plates on a roof can heat liquid in tubes that supply a house with hot water.
But solar energy doesn’t work at night without a storage device such as a battery, and cloudy weather can make the technology unreliable during the day. Solar technologies are also very expensive and require a lot of land area to collect the sun’s energy at rates useful to lots of people.
Despite the drawbacks, solar energy use has surged at about 20 percent a year over the past 15 years, thanks to rapidly falling prices and gains in efficiency. Japan, Germany, and the United States are major markets for solar cells. With tax incentives, solar electricity can often pay for itself in five to ten years.
The hope for a “solar revolution” has been floating around for decades — the idea that one day we’ll all use free electricity from the sun. This is a seductive promise, because on a bright, sunny day, the sun’s rays give off approximately 1,000 watts of energy per square meter of the planet’s surface, but we all like saving things for a rainy day and we simply can’t do that quite yet with solar energy.
How much sunlight energy does our PV cell absorb? Not as much as one might think. In 2006, for example, most solar panels only reached efficiency levels of about 12 to 18 percent. The most cutting-edge solar panel system that year finally muscled its way over the industry’s long-standing 40 percent barrier in solar efficiency — achieving 40.7 percent. So why is it such a challenge to make the most of a sunny day?
Visible light is only part of the electromagnetic spectrum. Electromagnetic radiation is not monochromatic — it’s made up of a range of different wavelengths, and therefore energy levels.
Light can be separated into different wavelengths, which we can see in the form of a rainbow. Since the light that hits our cell has photons of a wide range of energies, it turns out that some of them won’t have enough energy to alter an electron-hole pair. They’ll simply pass through the cell as if it were transparent. Still other photons have too much energy. Only a certain amount of energy, measured in electron volts and defined by our cell material is required to knock an electron loose. We call this the band gap energy of a material. If a photon has more energy than the required amount, then the extra energy is lost. (That is, unless a photon has twice the required energy, and can create more than one electron-hole pair, but this effect is not significant.) These two effects alone can account for the loss of about 70 percent of the radiation energy incident on our cell.
We have other losses as well. Our electrons have to flow from one side of the cell to the other through an external circuit. We can cover the bottom with a metal, allowing for good conduction, but if we completely cover the top, then photons can’t get through the opaque conductor and we lose all of our current (in some cells, transparent conductors are used on the top surface, but not in all). If we put our contacts only at the sides of our cell, then the electrons have to travel an extremely long distance to reach the contacts. Its internal resistance is fairly high, and high resistance means high losses. To minimize these losses, cells are typically covered by a metallic contact grid that shortens the distance that electrons have to travel while covering only a small part of the cell surface. Even so, some photons are blocked by the grid, which can’t be too small or else its own resistance will be too high.
The only question that occurred to me was if some that mass amounts of asphalt, metal, concrete, things like that are contributing to global warming, or at least warming around the area. My question was, wouldn’t solar panels do the same?
When I went out to try and answer the question, I had to keep in mind that local warming is not the same as global warming. While that may be true, I’m still wondering if any of the local heat would happen to spill into other areas. While I have no idea, I did find out that solar panels do not supposedly contribute to global warming or local warming. http://www.treehugger.com/clean-technology/ask-pablo-do-solar-panels-actually-contribute-to-climate-change.html This article lays it out quite nicely. And it even says that if roofs were replaced or were covered with these solar panels then that would reduce global warming some. I like that idea. Roof are supposed to be heat absorbent, so even if solar panels did contribute to that problem, it would only be replacing the roof and no more would be added. But the article says that it doesn’t
Then there is this article. http://voices.yahoo.com/solar-power-collectors-may-cause-more-global-warming-3176283.html?cat=9 . I’m not quite sure I follow or understand this guy’s logic. While some of it makes sense, most of it doesn’t and it doesn’t seem to be causing any problems that fossil fuel energy doesn’t cause. And at least with solar power, our air wouldn’t be toxic.
And now there is this article http://www.lowtechmagazine.com/2008/03/the-ugly-side-o.html . This isn’t the only article I found on this aspect, but the comments point out the things that are incorrect or miscalculated in the article. The article talks about how the production of solar panels contribute to global warming. The problem is that it takes extreme amounts of heat, fossil fuels, etc. to make these panels. The question is does the amount of emissions being let into the atmosphere outnumber the amount of electricity emissions you will save? If there is one thing that everyone is disagreeing about it’s the math. They all have different numbers. Who is right? I don’t know. I’ll never know. But they all seem to agree that solar energy is better than gas. They’re just trying to decide if the benefits are large enough to be worth it.
I’m giving you several production CO2 emission articles, so you check them all out. I don’t know whose math is right, but it’s there for you to decide for yourself. http://www.mnn.com/green-tech/research-innovations/blogs/how-much-co2-does-one-solar-panel-create
One thing I’d like to point out is that the numbers might be different because they come from different places. Not all factories are made the same so they don’t use the same amount of energy. Also, where people live is different. The sunnier a place is or the longer the sun is out, the more energy you’ll have and the pay off will be bigger.
The last and definitely least argument is that they’re ugly, but I’m not even going to get into this.
So that’s that. I’m sure that’s not all the finer details, but it’s the gist. Solar power isn’t perfect, but its evolving and it’s better than coal, fossil fuels, nuclear energy could ever hope to be.