Irradiation evenness... getting better by a bunch

Thought I'd tease a bit of the recent findings from the optics team:

Earliest proof of concept:

takeaway... not good but the photons do get there... and I learned a lot.

Knowing where the trouble comes from (and rethinking many other tangentially important elements) gets us this:

these are not the same scale (btw) what we care about is the evenness of the light and of the image. The low value (or more precisely intensity) yellow smear is easily corrected (nearly a column above.) The cell size can now drop to about 1/5 the original intended size. I've not tiled it as a hexagon (an even better fit if you hope to grab circular images with fewer wasted margins. ) Hexagons should fit even better on parent wafers... quick estimate 500 per 156mm pseudo square... that is a tiny bit of Silicon serving a very large aperture.

I am trying to characterize the packing factor (how much margin is lost by the space between cells). Or in my case the space between individual mirror "wells." It is better for the heat (.95 or so) than for the PV but if those smears above get into the center they might scavenge  us up to 92 or so. Which would add aperture-efficiency to our list of accomplishments.

Stay tuned!

Study from the Thermal side of the house...

Thermal Plant .(com) is my new internet crush!

Here are some compelling figures on hybrid PVT systems from a thermal perspective. Optimization of the thermal fraction is their agenda and they pound TRNSYS to get some insight. Cool.

here is some of it:

The performance of the PVT system consists in the renewable energy production, net of auxiliary devices’ consumption. Expressed in terms of primary energy, this balance is in general considered an energy saving for the users. Obtained results are shown in the following figures.

Fig. 7. Total energy saving in case of electric heater and natural gas heater Fig. 7. Total energy saving in case of electric heater and natural gas heater

 By observing the graphs, it can be seen that primary energy savings are much more consistent in case of electric heater in comparison with natural gas one. Anyway, in both cases, by increasing the PVT collector surface the total energy saving is not increasing linearly, which leads to conclude that global system efficiency is slightly decreasing by increasing PVT area.
This  happens  because  the  largest  number  of  collectors  increases  the  heat  transfer  fluid  mean temperature in each loop, while progressively reducing both the PV and thermal efficiency.
However, to perform a complete assessment of the PVT energy performance, global system costs and
savings potentials must be taken in consideration, as reported hereafter.

Read more http://www.thermalplant.com/software/optimization-of-solar-thermal-fraction-in-pvt-systems/

IBM Sunflower (Welcome to the Thunder Dome II (part two)

IBM and Airlight team up to develop the Sunflower. HCPVT collector. (High Concentration Photovoltaic Thermal.)

Everything is better with a Swiss scientist to show you around, no?

I found this embedded here at Gizmag. A much better story than the others, thank goodness. The collector dish is more creative than the rest of their scheme, I think. They use a fibrous concrete for the dish. Vacuum shaped sheer sheets of metalized foils or the like for the compound primary (40 square meters!) There would need to be dynamic control of that vacuum as the atmospheric pressure changes you do not want a new focal length imposed as the weather and temperature changes....

This just in: a friend tracked down this EDN story. It is not too interested in the offboard bits (low temp implementations and balance of system stuff) but a nice juicy account of a voltage management scheme comes up late in the story, spoiler alert: something called a "Δ-converter" is important. As is putting this important voltage management gear pretty darn close to the cells. Or so it seems.

All of this is worrisome as these are the same cells that are sitting at a 2,000 suns focal point. I'm going to call this "putting all your eggs in one frying pan." Shows a whole lot of faith in the tracking and the cooling apparatus.

I also wonder which disconnections are requiring Flyback Diodes (freewheeling?) Dear readers, what do you see when you read that report. (The images on the EDN story seem to have been pulled. But the PDF still has them (download link here)

Japan rethinking distributed power

Like Hawaii before it, Japan is facing down "too much of a good thing" problem.

"Half of Japan's electric utilities move to restrict additional solar power"

 http://www.eenews.net/stories/1060006761

It will get worked out, but look for more of this kind of trouble before it settles down.

Cool tool to explore current energy use by buildings in the USofA

Take a look! they have about a million buildings (I wish it were not by state but by latitude) still lots and lots of cool data to play with.



www.buildingenergy.com

IBM - Welcome to the Thunder Dome II

I've been meaning to discuss and size up the IBM hybrid attempt. I saw their cell/module cooling device for large high concentration dishes awhile back. take a look:

 

Illustration from a Whitepaper on the IBM Sunflower (hybrid CPVT)

What do you see? you see water inlets and outlets for a mission critical back side cooling array. That is the left/bottom side plumbing bits. We cannot see the very smart way they put a high flow highly conductive network for flowing very close to the back of the cells (the 9 dark squares) For size you can see the thermocouple plugs (grey with two different sized and colored blades) they are about a half inch wide (just checked, .66 inches or 17 mm which means those cells are 10mm/10mm.


This needs to be really heat hardy as the cells are supposed to be exposed to some 2000 suns. The paper (or some-other source, they are starting to run-together, sorry) says they are backside conductor cells. Those black faces, unlined by traditional front-side conductors, are confirmation of that.

The two thermocouples are there to monitor the coolant temperature before and after to regulate the flow of coolant. This of course means they have the traditional tradeoff issues that I am trying to avoid with frequency splitting. If the temp goes up the voltage goes down and the electric yield drops. So they are stuck with a lot of very warm water as a product. The good news is they have a vision of this as a very large device and some ideas about what to do with the warm water. More on that in the next post.

I saw some confused notions about using this for boiling water for desalination. The description in that story is pretty vague and has a real units of measure problem. Maybe a deadline pressure meets domain knowledge weakness caused it. Anyhow, further looking shows they have a reverse osmosis scheme (in separate equipment) that uses pressure rather than brute force boiling (which is why reverse osmosis and the related technologies are being explored in general: less energy intensive.) The cooling circuit needs to be closed to keep the high purity and reliability going behind the cells.

We'll look at the collector's reflector array next time.

You get more of what you measure...

I had not noticed SolarThermalWorld until today. Looks like PVT is in a ghetto there too. Still some good coverage of PVT with a thermal emphasis. Fair enough. This story got my attention and maybe it should get yours.

Story here 

here is what jumped out for me:

• So far, PVT collectors have not been included in the standard. But there is already a so-called extended scope, which means that they may be included later in a second part of the standard.
• Fluid-based collectors will see some changes in their testing procedures compared to EN 12975-2. The new standard regards the collector gross area as the relevant reference for all area-specific data, e.g., the yield per area. Until now, the reference used in Germany has been the aperture area, which has presented some difficulties in comparing collector data on an international basis.

PVT with its interaction between the energy streams is going to be tough to pin down. My design has low interaction between the "sides" which is great for me but all of the hybrids are going to need to represent the various modes of operation and the variety of operating temperatures is vexing.