PV Gap

Elizabeth Said:

Solar Cell concentration?

We Answered:

Hey Yoyo, Roderick and MTR are both correct on this one, but I'm not sure it gets to the heart of your question. You can concentrate photons onto any type of photovoltiac device and it will not increase it's efficiency one bit, but it will increase it's power output. It is like putting a larger fire under a water heater tank. It still has the same efficiency, but is getting much more heat. In the end, that small tank will probably burst. Multijunction panels are more efficient, that is, they convert more of the incoming energy to electricity by using many thin layers on top of each other, each one grabbing a slightly different wavelength of the incoming light. The real problem is as Roderick says, getting rid of the heat. The reason multijunction cell builders were experimenting with concentraters was because their devices were so much more costly per unit electricity produced, they were trying to find a way to make it pay off. You don't see them around for the same reason the single junction concentrators are not around today, they all burned out just a few years after they were put into service. Multijunction cells are very promising in space where heat is not the issue, and where space is limited by the size of the craft, or space station. In your yard or on your roof, none of this matters much.

Getting back to heat, some concentrators that were tested had cooling systems attached to wick off the extra heat, and then throw it out into the trash. Well if you've gone to such lengths to pile solar heat up in one place and it's causing a problem, it makes more sense to find a use for it. Hence today the Germans are putting their weight behind the North African Solar Project. If you google that exact phrase, you'll find some articles on what is happening, and by using the google images selection, some great pics. What they are planning on doing is concentrating sun to an air to oil heat exchanger, and heat oil to 600 degrees, then store it. The plant then uses the super heated oil to run through a oil to water heat exchanger to boil water and run a steam turbine. The throttle for the turbine is controlled by the steam output, and the steam pressure by the amount of oil introduced. In this way, we can take advantage of all the incoming wavelengths the sun has to offer and use the heat to our advantage, and additionally, store the hot oil for use at night, when the sun is not shining. Now there is an idea, a thermal battery. The project will eventually run all of Europe on the sun that is falling on a small corner of the Sahara Desert, minimally impacting wildlife, and in a location where nobody will have to look at it.

Multi junction cells are an interesting technonolgy, and may be commonplace one day, but not concentrated photovoltiacs, regardless of how many junctions they have, because they all have the same issue, too much heat. Maybe they could use them in the artic someplace. Take care Yoyo, Rudydoo

Tina Said:

ENGM Question HELP PLEASE!! :)?

We Answered:

Use your FEDEX excel provided by Prof.
change the tax and value of deduction by 50% of $1,850,000
means you'll use 950 000 on the FEDEX excel (on oak)
year property is 5, so cut the flow from 8 to 6
goodluck in submitting the homework tomorrow to me