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Light to create power
To begin to understand the ability of light to generate electricity with photovoltaics, a useful resource is posted on Worldwater and Solar'sEntech website.
The wavelength of light visible to the human eye is equivalent to less than one frame in a roll of film 2,500 miles long.
If you have time, watch a lecture by University of Berkeley, Richard A Muller, on the properties of light.
Triple junction cells
There is a new innovative cell for PV electricity generation called a triple junction, 3J cell, which has been adapted from space application solar cell technology. Current standard photovoltaic technology is designed to harness a single band of the suns energy. If you look at the spectrum of light generated by the sun, you will see that the predominant bands are the blue, green and red spectrums.
This photovoltaic technology differs from silicon or Cadmium Telluride flat panel in that instead of capturing and utilizing only a single band of the spectrum, it actually captures 3 bands - the Red, Green and Blue - instantly increasing the energy available for use by around 300%. Emcore and Spectrolab are market leaders in the development and production of these triple-junction cells. The current best efficiency levels of these cells was around 39%, but most recently has crossed over the 40% mark and with further development will lead to significantly higher efficiencies.
Emcore, one of the 3J cell developers has a target of 45% efficient cells by 2010. This may not sound like much, but when you consider that it is in fact a 20% increase from the current 39% efficiency here alone (think utility scale 1000MW to 1200MW), it starts to add up. Now to give a brief example of where PV technology is currently at, I will use First Solar's (FSLR) last annual report as a guide. 457,000 panels to produce 30MW of power equates to 65 watts per panel. First Solar’s efficiency is currently at 10.6%. With others, such as Sunpower (SPWR), obtaining efficiencies up to 23.4%. As you can see from the graphic below, 1m2 of sunlight at higher efficiency has a significant impact on the output of a solar panel.
Sunrgi graphic showing the benefit of increased sunlight conversion efficiency
Concentrating sunlight
The second innovation involves harnessing more photons by using a larger collection area and redirecting light. Most of the traditional terrestrial (on earth) means of photovoltaic electricity production from the sun rely on a 1-1 ratio. That is the glass used is simply a means to enclose and protect the silicon (or Cadmium Telluride) cells underneath from the elements. The area of silicon to produce 1 watt of power is dependent on the sun on the day, the quality of the silicon used, direct or non-direct exposure to the sun and of course the technology used and its respective conversion efficiency.
To understand concentration, think about a magnifying glass or the inverse affect of a lighthouse lens or a car headlight. The goal in these instances is to manipulate light. In one case to a focus on a single point, in others from a single point.
In the case of concentrated photovoltaics, there are a number of ways this is done. The first is by utilizing what is called a Fresnel Lens. Many of the current CPV developers have adopted this method ofconcentration achieving ratios upwards of 1000 suns. For an idea of what I am referring to, take a look at the diagram on Sol3g’s site showing a how the lens redirects light to a secondary lens.
To get an idea of what happens to the power generation of a photovoltaic panel by using a form of fresnel lens concentration, please watch the youtube video below.
Now you may now be thinking that the production of these cells would be more expensive than standard silicon, and this would be a correct assumption. But then if you consider that a) these cells are designed to operate with over 1000 times the energy input into them with the concentration technology, and b) they are 40% efficient, the numbers start to look a little better. For interest sake lets look at 1cm2 of this type of cell. Raw material cost is lower than standard PV as instead of using silicon as the base, it uses Gallium Arsenide or GaAs.
Gallium is extracted primarily from the residue obtained during the processing of aluminum and secondly via electrolytic zinc. Other sources include fly ash collected from burning coal.
Now consider the ratios. Instead of one sun's concentration, we have 1000 and better sun concentration. Instead of 10.6% efficiency, we have 40% efficiency. (I’ll round down to 3 ½ times). So for the same 1cm2 area of a CPV cell versus a standard flat plate cell, we get 3500 times the power generated. Even using Sunpower, a silicon based PV manufacturer, as a base efficiency of 22%, we still get 1500 times the watts from the same area of cell. Now if you think this can't be right, please take a look at the diagram comparing PV flat plate vs the CPV cell size.
In other words you would need to produce 3500cm2 or 1500cm2 the amount ofsilicon/CdTe panel to compete with 1cm2 of a CPV cell. So on a strictly capital base for machinery and sq ft factory space you need to produce the same output of MW off the production line vs standard PV, this in itself will make available substantial capital cost savings. With a touted figure of a 1GW production line utilizing triple junction cells and Suncube/Sunryder technology the cost is approximately $120-$150M USD. For an equivalent sized flat panel production line it could be as much as $1200 M USD.
For a video of how concentration works, please visit Amonix website.
The two leading developers of triple junction cells are Emcore and Spectrolab.
Tracking the sun
The third innovation concentrated photovoltaics has introduced is a two-axis sun tracking system. This ensures the photovoltaic array is fully exposed to direct sunlight from the moment the sun rises to the time when it sets. The tracking systems Emcore and its development partners use have been field tested and refined over the last two years to a point where power usage, breakdown and manufacturing costs have been optimized.
Concentrating Photovoltaic Consortium
Co-contributors to ISFOC CPV installation - ISFOC, PARC, IES, UPM, Isofoton, Concentrix, Emcore, Azur Solar, Solfocus, Spectrolab, Arima Eco, Concentracion Solar La Mancha, Sol3g. CPV Presentation On Tuesday 1 April and Monday 2nd April the consortium members above, are presenting the developments of the last 12 months research at a collaborative 3MW installation in Spain. CPV presentation schedule
Attendees of the conference include the who's who of major industry.
Consider this fact: China's energy economy is growing significantly - China added 90GW of electricity generation capacity last year to December 2007 this is on top of 102GW in 2006. Compare this against the total united States installed generation capacity for electricity of 1,075GW. China is adding to their grid per year an amount of power equivalent to around 10% of the total installed US grid which has taken well over 50 years to build up. In fact taking an older figure of 391GW as of 2004 and adding 100GW per year, China will come close to meeting the installed capacity of the US in terms of electricity infrastructure within a short time frame.
The fact that China is able to do this so quickly is quite a feat of Engineering and logistics. In fact the capacity of this country to build large scale infrastructure and process plants is at such a stage now that China is developing a potential competitive advantage over the Western world.
Taken from the BHP report above, where the Western benchmark for building generation capacity takes around 3 and a half years, China is able to do this in a quarter of the time, in 10 months.
What this demonstrates is that China's essentially brand new power grid is being built in record time and adding to fossil fueled power generation at unprecedented rates. So to reduce the carbon footprint of coal fired power stations, what if China and the US were able to shift a larger proportion of new generating capacity to Solar based power.
By 2007, total photovoltaic installations in came to a grand total of 2,826 MW or a very small 2.8 GW. And although growth in solar photovoltaic installations grew by 62 % from 2006 to 2007, with manufacturing capacity from 2, 026 MW (2.2GW) in 2006 to 3,436 MW (3.4GW) in 2007, this is still less than 4% of China's demand alone, excluding the rest of the world. SOURCE - Solar Buzz
We have a couple of issues here: If the Western world is to maintain its standard of living, what can we do? How do we shift to renewable forms of energy, keep manufacturing jobs, construction jobs and heavy industry jobs growing in the US as well as China, reduce emissions without impacting the economy, and if possible, bring the cost of electricity down by eliminating an ongoing, highly volatile input, the fuel (coal, gas, oil)?
Well it all depends on how well we can concentrate....
And BTW China are already building CPV systems
Note: It is not intended to infringe on copyright material. Any content used will be removed on request. Email Brad Ross - info@unenergy.org
