Would South Tyneside survive on wind driven energy?

Via Trixy

I’ve had a ridiculously busy day tearing around, not much time for getting my thoughts down onto a keyboard, other than that Junior is enjoying yet another day off school because a fuse has blown and therefore they cannot get any light or heat, and yes it is a bit cold out there. I guess temperatures in South Shields have been a little higher than those enjoyed in the greater parts of inland England over the past seven days, the little coastal area is warmed by the sea so we’ve probably averaged three degrees or so during the daytime, whilst others have struggled to get above freezing point.

I’ve noticed during these periods when we have “enjoyed” high pressure (i.e. blistering hot in summer when you need the fans and the air conditioning, mind numbingly cold in winter when you need heat) that the wind turbine at Middlefields, Tyne Dock, and the huge things at Nissan’s Washington plant just don’t turn. No wind = no electricity, seems like a sensible conclusion with wind turbines.

So, if we had to rely on them solely for energy we’d be pretty much stuffed, and with the Russian’s playing around with the gas taps and the EU stipulating that by 2020 we need to be producing 15% of our energy from renewables, we face a bit of a problem! (We were only producing 1.3% of our energy from renewables in 2005).

Perhaps instead of waffling on about insulation (which most of us have coming out of our roofspace) Labour ministers could instead be insisting that all new buildings be fitted with solar panels, and that power stations be allowed to use modern clean carbon capture methods and share out their heat locally.

Here’s a video from UKIP MEP Godfrey Bloom showing how it is down the road.

Does our government have an alternative energy strategy? You know, one that doesn’t humble itself to the climate scientologists.

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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,¹ 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!

1. Duffie, J. A.; Beckman, W. A. Solar Engineering of Thermal Processes. (3rd Ed.) 2006 John Wiley & Sons Inc, Hoboken, NJ, USA.

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=A_apt/A_abs).^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.

Posted by: Karl Ramjohn

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Acciona Energy has put into service its photovoltaic (PV) power plant in Amareleja (Moura, Portugal). The Company has invested around 261 million euro (US$367 million) in the 46 MWp plant, one of the largest of its kind in the world. Amareleja is capable of producing 93 million KW/h a year. The plant was constructed in the record time of just thirteen months.

Acciona already has an installed capacity of 68 MW of PV in Spain, with a further 100 MW of Concentrated Solar Power (CSP) currently under construction. In the USA, Acciona owns the largest CSP plant built in the world in the last seventeen years (Nevada Solar One, 64 MW).

The plant covers a total area of 617.8 acres , located in the parish of Amareleja in the municipality of Moura, in Portugal’s Alentejo region, not far from the border with Spain. It has 2,520 Buskil trackers (Acciona in-house technology), that support a total of 262,080 PV modules. The trackers can follow the sun throughout the day, boosting the output of the solar modules over the output of a stationary system.

The first 3 MW were installed at the end of 2007, and were connected provisionally in March 2008. This year has seen the installation of the remainder of the plant’s solar field and the construction of the evacuation line, and last week the plant was finally connected to the grid.

At the same time, the municipality of Moura has launched the Sunflower project, which involves a network of eight municipalities from eight different countries in Europe (Bulgaria, Britain, the Czech Republic, France, Greece, Italy, Portugal, and Spain) that seek to transform their towns into what the EU calls “Zero Carbon Communities” under its Intelligent Energy – Europe (IEE) programme for the promotion of alternative energy sources.