My recent experiences have included teaching solar energy conversion, developing tools for solar resource assessment, and leading a great team to design, build, and operate a solar-powered house (0 comments
Mar 21, 2009
What to do with solar in the economic turndown
As you may have noted, I am in the process of developing a new blog (Heliotactic.org). The reasons? First, the Sun allows for a plethora of possibilities, and I wanted to work with a bigger canvas! Second, I feel the need to open up the blog to entries from guests, to create a diverse perspective of all things tied to solar (including energy efficiency, green roofs, passive solar design, energy recovery and cogeneration). And third, and most frankly, PV is the most expensive solar investment for the individual. In this economic depression, we need to know what technologies are affordable and offer the highest rewards for the initial investment. I’ve been told again and again that solar hot water is the most obvious, no-brainer tactic in the solar arsenal. It’s cheap (< $6000 for everything), it’s easy, and by replacing/complementing your electric or gas (or fuel oil) water tank (with federal and state incentives), payback is often less than 5 years.
My recent experiences have included teaching solar energy conversion, developing tools for solar resource assessment, and leading a great team to design, build, and operate a solar-powered house (0 comments
My recent experiences have included teaching solar energy conversion, developing tools for solar resource assessment, and leading a great team to design, build, and operate a solar-powered house (0 comments
Dec 28, 2008
Solar Jobs = Green Collar Jobs!
As a researcher and instructor dealing with solar energy conversion, I am acutely aware of the immediate need (or ASAP) for a smart, flexible labor force--capable and trained to install and maintain our new solar technologies. Solar energy will be the heart of the new green collar job sector, as we will need to deploy PV and solar hot water technologies to residential and commercial buildings for a carbon-constrained future.
Analogy:
I want to use the familiar example of technologies for indoor air quality and thermal comfort: HVAC systems (Heating, Ventilation, and Air Conditioning). Think about how many air conditioning units are now an integral part of buildings in the country. Consider the labor force that is required for AC/heating installation, duct installation, monitoring and control systems (e.g. thermostats), and maintenance or repairs (hint: it is a huge industry). Now think about how little you think about these systems (because they just work). There is similar (perhaps even greater) potential for green collar jobs--earning a paycheck and helping society and the environment!
The Very Near Future:
Green collar jobs for solar technologies are here! Training is in full gear in states like California, New Jersey, and Florida, and is ramping up in Wisconsin and Pennsylvania. At Penn State, we are already working on a training course for PV installation, as well as an upper level college course in solar energy technology design.
Additional reading: NYT article on PV installers as the new wave of green collar jobs.
Analogy:
I want to use the familiar example of technologies for indoor air quality and thermal comfort: HVAC systems (Heating, Ventilation, and Air Conditioning). Think about how many air conditioning units are now an integral part of buildings in the country. Consider the labor force that is required for AC/heating installation, duct installation, monitoring and control systems (e.g. thermostats), and maintenance or repairs (hint: it is a huge industry). Now think about how little you think about these systems (because they just work). There is similar (perhaps even greater) potential for green collar jobs--earning a paycheck and helping society and the environment!
The Very Near Future:
Green collar jobs for solar technologies are here! Training is in full gear in states like California, New Jersey, and Florida, and is ramping up in Wisconsin and Pennsylvania. At Penn State, we are already working on a training course for PV installation, as well as an upper level college course in solar energy technology design.
Additional reading: NYT article on PV installers as the new wave of green collar jobs.
Dec 25, 2008
Solar technologies are really diverse
In preparing for my annual Spring course “Design of Solar Energy Conversion Systems”, I am reminded of just how many diverse technologies can be derived from our nearest large-scale fusion reactor. I will make exceptions to the obvious: horticulture and wind energy are derived from the sun too.
Here are some ideas beyond PV and concentrating PV (CPV):
1. Passive/Active Solar Water Heating Systems (in your showers, dishwashers, heating your floors)
Solar is very close to breaking out. Why not invest in solar tech?
Here are some ideas beyond PV and concentrating PV (CPV):
1. Passive/Active Solar Water Heating Systems (in your showers, dishwashers, heating your floors)
2. Commercial/Distributed Space Heating Systems (using Solar Walls, Phase Change materials, Pebble-bed hot air storage).
3. Solar Cooling (Yes! you can cool with the sun and heat pumps, dessicants, refrigeration cycles).
4. Solar Industrial Process Heat and Solar Ponds (Do you own a mine or a refinery? Look into ways that you could dramatically reduce your energy bills!)
5. Solar Thermal Power Systems (Also called Concentrating Solar Power--CSP--this is the technology with the best odds at being the next wave of electric power from the sun).
6. Don’t forget solar chemistry (not just growing plants) to make hydrogen and other fuels!
Solar is very close to breaking out. Why not invest in solar tech?
Nov 9, 2008
Educational Links on Photovoltaics and Solar Energy
Where would be the best place to get an update of solar energy conversion, and photovoltaics in particular? That would be in a classroom, where you can ask questions and sort through the multiple topics of materials, sources of photovoltaic action (drift, diffusion, electrokinetic phenomena), and the difference between a cell, module, and an array. You would also be able to see that PV is only a tiny segment of an otherwise broad portfolio of technologies to make use of the sun for heating, cooling, making chemicals, making electricity from turbines, and so on. I offer two core courses at Penn State that deal with these subjects, but obviously there is a larger audience out there that would like information. Thankfully, we will be producing a web-based course dealing with photovoltaics, but that will be about a year off.
Therefore, I would recommend two web-based books for the curious, right now! The first is an educational project that began as an international collaboration between the University of Delaware and the University of New South Wales, funded by an IGERT grant. The site is called Photovoltaics: Devices, Systems and Applications CD-ROM, and the authors are Christiana Honsberg and Stuart Bowden. This includes interactive diagrams, movie clips of the silicon manufacture process, and a good review of solar energy. You will need to download Shockwave from Adobe. Up until recently, the Shockwave addition did not work for Macintosh systems, so I was more hesitant at recommending the site. But now: go for it! You will be busy for weeks. Note that the site is dedicated to silicon devices, and will not provide a comprehensive description of thin film PV devices and the principles of operation. That being said, the site is a gem.
The second book is not as web savvy, but does contain fantastic fundamental information on solar energy conversion. The resource is Power from the Sun by by William B. Stine and Michael Geyer, at California State Polytechnic University in the USA and IEA SolarPACES in Spain. This text is more like the classic paper text by John Duffie and William Beckman: Solar Engineering of Thermal Processes, in which multiple solar energy conversion technologies are described.
There you go, solar energy enthusiasts! Go to school and get informed on solar energy. But if you are tied up with other things (like life), in the mean time do some winter reading and find out how much potential solar energy has as a sustainable technology!
Therefore, I would recommend two web-based books for the curious, right now! The first is an educational project that began as an international collaboration between the University of Delaware and the University of New South Wales, funded by an IGERT grant. The site is called Photovoltaics: Devices, Systems and Applications CD-ROM, and the authors are Christiana Honsberg and Stuart Bowden. This includes interactive diagrams, movie clips of the silicon manufacture process, and a good review of solar energy. You will need to download Shockwave from Adobe. Up until recently, the Shockwave addition did not work for Macintosh systems, so I was more hesitant at recommending the site. But now: go for it! You will be busy for weeks. Note that the site is dedicated to silicon devices, and will not provide a comprehensive description of thin film PV devices and the principles of operation. That being said, the site is a gem.
The second book is not as web savvy, but does contain fantastic fundamental information on solar energy conversion. The resource is Power from the Sun by by William B. Stine and Michael Geyer, at California State Polytechnic University in the USA and IEA SolarPACES in Spain. This text is more like the classic paper text by John Duffie and William Beckman: Solar Engineering of Thermal Processes, in which multiple solar energy conversion technologies are described.
There you go, solar energy enthusiasts! Go to school and get informed on solar energy. But if you are tied up with other things (like life), in the mean time do some winter reading and find out how much potential solar energy has as a sustainable technology!
Aug 31, 2008
More Photovoltaics to come...
It looks like there is interest in the principles of photovoltaics. I will be reviewing and revising my older posts on the subject in the next few days. Come back shortly for more!
Aug 2, 2008
Photovoltaics: Levels of Irradiance
Let’s talk about light interacting with a semiconductor to yield electricity. Today’s topic is to distinguish between low levels of irradiance and high levels of irradiance. Effectively, we are asking for an estimate of the concentration of photons being delivered from a high energy source to a low energy absorber/collector.
When we say low levels of irradiance, we are estimating a scale of light concentration that is typical of the diffuse and direct component of unconcentrated “global” or “total” solar radiation, or the light from a standard incandescent lamp or fluorescent lamp. This could be anywhere <1000 mW/cm2, or 10x the sun’s concentration (remember, this is just a crude scale, not a hard and fast rule--don’t take this back to your classes). The standard for testing solar cells inside the earth’s atmosphere is called Air Mass 1.5 Global (AM 1.5G), because the light from the sun passes through 1.5 lengths of a generic Earth’s atmosphere to generate a convenient irradiance of ~ 100 mW/cm2. Low levels of light such as this provide a sufficient number of photons (packets of light) to excite the electrons into an unoccupied level of energy (the conduction band). However, the population distribution of the majority carriers does not change significantly. That’s okay: the key player in a photovoltaic absorber is the minority carrier (n-type semiconductor: a hole; p-type semiconductor: an electron), and the population of minority carriers does change significantly with light absorption. Minority carrier transport gets the job done, in fact, because they are the limiting rate in the absorber reactor. You can find out more about charge carriers and carrier transport in the Photovoltaics CDROM from Honsberg and Bowden, Chapter 3 (although it doesn’t work completely for Macs, sadly)
What is high irradiance? You’ve heard the warnings about strong lasers pointing into others’ eyes? A laser is a coherent, collimated light source (the photons’ waves are in phase and heading the same direction), such that the photons can be very concentrated. If sufficient numbers of photons are absorbed by a semiconductor, the population of photoexcited charge carriers can be much greater than the majority carriers, and there a population inversion occurs, leading to stimulated emission (Light Amplification by Stimulated Emission of Radiation).
The photons from light bulbs and suns are neither coherent nor collimated, although they can be concentrated significantly to potentially cause a population inversion and stimulated emission (yes, there is the possibility for a solar laser). However, before that stage there are other phenomena that occur, making it a bit more complicated.
Concentrating cells allow an increased flux of photons to the smaller receiver/absorber using a larger aperture to collect the solar light. The geometric concentration ratio is the ratio of the area of an aperture to that of the absorber (C=Aapt/Aabs).1,2 For a perfect concentrator (as a point on the surface of Earth), the radiation from the Sun on the aperture-receiver assembly is only a fraction of the total radiation emitted by the Sun, given a half-angle subtended by the Sun of 0.27°. Assuming a blackbody, the absorber would have a maximum theoretical concentration ratio of 45,000 (for a circular concentrator) or 212 (for a linear,trough concentrator).1 The higher the concentration,the higher the photon flux (including increasing temperature),and the more precise the optics of the collector must be to deliver. This is an extreme energy flux for any semiconductor. Under high illumination levels, one will observe a decrease in minority carrier lifetimes and related diffusion path lengths. However, 45.6% of the suns power is contained in the infrared band (the part that makes things "hot"). Thermally, an imaging concentrator (C>> 10; analogous to camera lenses) can produce temperatures from 500 to 1500 °C at the absorber.2 This increased temperature can be used to drive thermal work (steam generation) or thermophotoelectrochemical reactions for concentrating solar power (CSP, not to be confused with CPV), but is not necessarily good for photovoltaic performance. High temperatures tend to decrease the efficiency of a photovoltaic device. In particular, this is why members of the microelectronics industry are getting into the concentrating photovoltaics field (CPV)--they know how to cool superhot microelectronics, and will do the same with CPV devices.
It is so interesting to see how this is all a great spread of possibilities that one can derive from our nearest fusion reactor!
Text sources:
1. Rabl, A. Active Solar Collectors and Their Applications. 1985 Oxford University Press, New York
2. Duffie, J. A.; Beckman, W. A. Solar Engineering of Thermal Processes. (3rd Ed.) 2006 John Wiley & Sons Inc, Hoboken, NJ, USA.
3. Andreev, V. M.; Grilikhes, V. A.; Rumyantsev, V. D. Photovoltaic Conversion of Concentrated Sunlight. 1997, John Wiley & Sons Ltd, Chichester, England.
When we say low levels of irradiance, we are estimating a scale of light concentration that is typical of the diffuse and direct component of unconcentrated “global” or “total” solar radiation, or the light from a standard incandescent lamp or fluorescent lamp. This could be anywhere <1000 mW/cm2, or 10x the sun’s concentration (remember, this is just a crude scale, not a hard and fast rule--don’t take this back to your classes). The standard for testing solar cells inside the earth’s atmosphere is called Air Mass 1.5 Global (AM 1.5G), because the light from the sun passes through 1.5 lengths of a generic Earth’s atmosphere to generate a convenient irradiance of ~ 100 mW/cm2. Low levels of light such as this provide a sufficient number of photons (packets of light) to excite the electrons into an unoccupied level of energy (the conduction band). However, the population distribution of the majority carriers does not change significantly. That’s okay: the key player in a photovoltaic absorber is the minority carrier (n-type semiconductor: a hole; p-type semiconductor: an electron), and the population of minority carriers does change significantly with light absorption. Minority carrier transport gets the job done, in fact, because they are the limiting rate in the absorber reactor. You can find out more about charge carriers and carrier transport in the Photovoltaics CDROM from Honsberg and Bowden, Chapter 3 (although it doesn’t work completely for Macs, sadly)What is high irradiance? You’ve heard the warnings about strong lasers pointing into others’ eyes? A laser is a coherent, collimated light source (the photons’ waves are in phase and heading the same direction), such that the photons can be very concentrated. If sufficient numbers of photons are absorbed by a semiconductor, the population of photoexcited charge carriers can be much greater than the majority carriers, and there a population inversion occurs, leading to stimulated emission (Light Amplification by Stimulated Emission of Radiation).
The photons from light bulbs and suns are neither coherent nor collimated, although they can be concentrated significantly to potentially cause a population inversion and stimulated emission (yes, there is the possibility for a solar laser). However, before that stage there are other phenomena that occur, making it a bit more complicated.
Concentrating cells allow an increased flux of photons to the smaller receiver/absorber using a larger aperture to collect the solar light. The geometric concentration ratio is the ratio of the area of an aperture to that of the absorber (C=Aapt/Aabs).1,2 For a perfect concentrator (as a point on the surface of Earth), the radiation from the Sun on the aperture-receiver assembly is only a fraction of the total radiation emitted by the Sun, given a half-angle subtended by the Sun of 0.27°. Assuming a blackbody, the absorber would have a maximum theoretical concentration ratio of 45,000 (for a circular concentrator) or 212 (for a linear,trough concentrator).1 The higher the concentration,the higher the photon flux (including increasing temperature),and the more precise the optics of the collector must be to deliver. This is an extreme energy flux for any semiconductor. Under high illumination levels, one will observe a decrease in minority carrier lifetimes and related diffusion path lengths. However, 45.6% of the suns power is contained in the infrared band (the part that makes things "hot"). Thermally, an imaging concentrator (C>> 10; analogous to camera lenses) can produce temperatures from 500 to 1500 °C at the absorber.2 This increased temperature can be used to drive thermal work (steam generation) or thermophotoelectrochemical reactions for concentrating solar power (CSP, not to be confused with CPV), but is not necessarily good for photovoltaic performance. High temperatures tend to decrease the efficiency of a photovoltaic device. In particular, this is why members of the microelectronics industry are getting into the concentrating photovoltaics field (CPV)--they know how to cool superhot microelectronics, and will do the same with CPV devices.
It is so interesting to see how this is all a great spread of possibilities that one can derive from our nearest fusion reactor!
Text sources:
1. Rabl, A. Active Solar Collectors and Their Applications. 1985 Oxford University Press, New York
2. Duffie, J. A.; Beckman, W. A. Solar Engineering of Thermal Processes. (3rd Ed.) 2006 John Wiley & Sons Inc, Hoboken, NJ, USA.
3. Andreev, V. M.; Grilikhes, V. A.; Rumyantsev, V. D. Photovoltaic Conversion of Concentrated Sunlight. 1997, John Wiley & Sons Ltd, Chichester, England.
Jul 23, 2008
Surfing more and more photovoltaics!
In just a few years since returning from France in 2006, I have noticed some significant improvements in the world of PV within the United States. In fact, it seems that there is a wave of solar development and deployment that is rolling across the country!
Let me preface this glowing remark by commenting that not all was so great even two or three years ago. I had been working for a year in a laboratory in France that specialized in basic research for silicon and eta-cell (extremely thin absorber) thin film photovoltaic devices. While there, I was working with members of industry, the French government and power company, and the French national lab system. It seemed that there was a great vertical integration of research, industry, and deployment in France (and even more occurring in Germany). It was therefore a bit of a let down to return and learn how far behind the US was in terms of this integration. Yes, there are two major centers for research in Colorado (NREL) and Florida (FSEC), but as a national whole, the system seemed a bit worn, frumpy, and patchwork in nature. In truth, the USA went through about a 25 year period where not much was visible at all in solar research. The funding had dried up, leaving room only for the biggest four or five names in materials research and computer simulation (who supplemented their funding with studies in refrigeration). Now, many of the notable solar researchers are either retired scientists, microelectronics specialists, or emeritus professors.
However, in the two years since I returned there has been a dramatic bootstrapping occurrence. Just as we are looking to “next generation” PV technology, so are we seeing “next generation” researchers, educators, and industrial developments! Gunther Portfolio is a great blog for keeping us informed about developments for investing, and SolarBuzz and PVNews/Greentech Media also have regular installments of more and more PV industry growth.
In education, Penn State launched a new Spring 2008 course from the Dept. of Energy & Mineral Engineering, focused on solar energy conversion (with emphasis on photovoltaic conversion). Penn State also has plans to develop another more hands-on course in photovoltaics for extended education in the near future. Prof. Tonio Buonassisi of MIT has also announced a course in photovoltaics set for this Fall 2008 semester. The students have spoken, and they want more information on the current state of the art in solar and photovoltaics!
In the federal government realm, we are still sadly lacking a signal to encourage PV via incentives. The residential tax credit is slated to expire at the end of this year (following an extension). You will find much better luck for incentives on a state by state basis (see DSIRE). However, we did just receive a call to action by former Vice President Al Gore that may put more senators and representatives “in the mood” for renewable electricity generation. Also, the Solar Decathlon is to continue until 2015, the projected year for levelized cost of electricity generation from PV to be competitive with coal-fired electricity generation. The sponsor (DOE/NREL) projects half a billion visitors to the Mall area over a three-week period in September 2009, and anticipates global exposure to the Solar Decathlon concept to over one billion people. The Solar Decathlon is also exerting a viral effect on solar engineering and design, as it is inspiring similar competitions globally. Even now, a Solar Decathlon Europe is planned for 2010 in Madrid, Spain. The city of Beijing will be holding the 2009 Delta Cup – International Solar Building Design Competition, where the winning homes will be deployed in the earthquake-hit areas of Sichuan.
Keep up the good work, solar community! Let’s continue to work together to provide more information and more incentive for the broad public to adopt solar renewable energy. Of course, if a major component of that is photovoltaics, I would be pretty ecstatic!
Let me preface this glowing remark by commenting that not all was so great even two or three years ago. I had been working for a year in a laboratory in France that specialized in basic research for silicon and eta-cell (extremely thin absorber) thin film photovoltaic devices. While there, I was working with members of industry, the French government and power company, and the French national lab system. It seemed that there was a great vertical integration of research, industry, and deployment in France (and even more occurring in Germany). It was therefore a bit of a let down to return and learn how far behind the US was in terms of this integration. Yes, there are two major centers for research in Colorado (NREL) and Florida (FSEC), but as a national whole, the system seemed a bit worn, frumpy, and patchwork in nature. In truth, the USA went through about a 25 year period where not much was visible at all in solar research. The funding had dried up, leaving room only for the biggest four or five names in materials research and computer simulation (who supplemented their funding with studies in refrigeration). Now, many of the notable solar researchers are either retired scientists, microelectronics specialists, or emeritus professors.
However, in the two years since I returned there has been a dramatic bootstrapping occurrence. Just as we are looking to “next generation” PV technology, so are we seeing “next generation” researchers, educators, and industrial developments! Gunther Portfolio is a great blog for keeping us informed about developments for investing, and SolarBuzz and PVNews/Greentech Media also have regular installments of more and more PV industry growth.
In education, Penn State launched a new Spring 2008 course from the Dept. of Energy & Mineral Engineering, focused on solar energy conversion (with emphasis on photovoltaic conversion). Penn State also has plans to develop another more hands-on course in photovoltaics for extended education in the near future. Prof. Tonio Buonassisi of MIT has also announced a course in photovoltaics set for this Fall 2008 semester. The students have spoken, and they want more information on the current state of the art in solar and photovoltaics!
In the federal government realm, we are still sadly lacking a signal to encourage PV via incentives. The residential tax credit is slated to expire at the end of this year (following an extension). You will find much better luck for incentives on a state by state basis (see DSIRE). However, we did just receive a call to action by former Vice President Al Gore that may put more senators and representatives “in the mood” for renewable electricity generation. Also, the Solar Decathlon is to continue until 2015, the projected year for levelized cost of electricity generation from PV to be competitive with coal-fired electricity generation. The sponsor (DOE/NREL) projects half a billion visitors to the Mall area over a three-week period in September 2009, and anticipates global exposure to the Solar Decathlon concept to over one billion people. The Solar Decathlon is also exerting a viral effect on solar engineering and design, as it is inspiring similar competitions globally. Even now, a Solar Decathlon Europe is planned for 2010 in Madrid, Spain. The city of Beijing will be holding the 2009 Delta Cup – International Solar Building Design Competition, where the winning homes will be deployed in the earthquake-hit areas of Sichuan.
Keep up the good work, solar community! Let’s continue to work together to provide more information and more incentive for the broad public to adopt solar renewable energy. Of course, if a major component of that is photovoltaics, I would be pretty ecstatic!
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